Experimental apparatus and method for enhancing oil recovery by high-frequency pulsed CO2 injection

Abstract

This invention discloses an experimental apparatus and method for enhancing oil recovery through high-frequency pulsed CO2 injection, relating to the field of oil and gas extraction technology. The apparatus includes a high-frequency pulsed injection module, a pulse waveform adjustment module, and a nuclear magnetic resonance (NMR) module. The high-frequency pulsed injection module comprises a first pneumatic valve, a second pneumatic valve, and a pneumatic valve controller. The first pneumatic valve is connected to a high-pressure CO2 source, and the second pneumatic valve is connected to a low-pressure CO2 source. The pneumatic valve controller controls the first and second pneumatic valves to interlock and instantaneously switch according to pulse parameters, generating high-frequency pressure pulses. The pulse waveform adjustment module adjusts the waveform of the high-frequency pressure pulses. The NMR module, based on the adjusted high-frequency pressure pulses, alternately injects high-pressure and low-pressure CO2 into the experimental core, collects NMR data of the experimental core before and after pulsed injection, and generates an adjustment signal to adjust the pulse parameters. This invention can achieve instantaneous pressure changes and enhance the pulse effect.

Description

Technical Field

[0001] This invention relates to the field of oil and gas extraction technology, and in particular to an experimental apparatus and method for enhancing oil recovery by high-frequency pulsed CO2 injection. Background Technology

[0002] CO2 huff and puff is one of the important means to improve the recovery rate of unconventional oil reservoirs. CO2 huff and puff can include three stages: CO2 injection, well shut-in, and depressurization production. Traditional CO2 huff and puff mainly relies on diffusion mass transfer, and the effective CO2 reception distance is short, resulting in limited improvement in recovery rate. How to further enhance the diffusion mass transfer effect and further increase the effective CO2 reception distance is the key to improving the recovery rate of unconventional oil reservoirs.

[0003] Existing pulse injection methods achieve pressure changes by altering the displacement pump flow rate, aiming to enhance CO2 mass transfer through periodic pressure fluctuations. However, this method relies on pump flow rate adjustment, resulting in slow pressure changes and difficulty in achieving instantaneous pressure variations. Furthermore, the pulse waveform and pulse parameters of existing pulse injection methods cannot be independently adjusted, making it impossible to conduct optimization experiments on unconventional reservoir cores with different pore structures. The pulse effect is limited, thus failing to fundamentally solve the problems of short effective distance and low recovery rate in CO2 huff and puff technology for unconventional oil reservoirs.

[0004] There is currently no effective solution to the above problems. Summary of the Invention

[0005] This specification provides an experimental apparatus and method for enhancing oil recovery by high-frequency pulsed CO2 injection, in order to solve the technical problems in the prior art where the pulsed injection pressure changes slowly and the pulse waveform and pulse parameters cannot be adjusted independently.

[0006] In one aspect, the embodiments of this specification provide an experimental device for enhancing oil recovery by high-frequency pulse injection of CO2, including: a high-frequency pulse injection module, a pulse waveform adjustment module, and a nuclear magnetic resonance module; The high-frequency pulse injection module includes a first pneumatic valve, a second pneumatic valve, and a pneumatic valve controller. The inlet of the first pneumatic valve is connected to a high-pressure CO2 source, and the inlet of the second pneumatic valve is connected to a low-pressure CO2 source. The outlets of the first and second pneumatic valves are connected in parallel to form a common output terminal. The pneumatic valve controller is electrically connected to the control terminals of the first and second pneumatic valves and is used to control the first and second pneumatic valves to interlock and switch instantaneously according to the set pulse parameters, so that high-pressure CO2 and low-pressure CO2 are output alternately to generate high-frequency pressure pulses. The pressure value of the high-pressure CO2 is a first set value, and the pressure value of the low-pressure CO2 is a second set value. The first set value is greater than the second set value. The pulse waveform adjustment module is connected in series between the common output terminal and the input terminal of the nuclear magnetic resonance module, and is used to adjust the waveform shape of the high-frequency pressure pulse. The nuclear magnetic resonance module is used to inject high-pressure CO2 and low-pressure CO2 alternately into the experimental core based on the adjusted high-frequency pressure pulse, and to collect nuclear magnetic resonance data of the experimental core before and after pulse injection, and generate an adjustment signal to adjust the pulse parameters.

[0007] In some embodiments, the experimental apparatus further includes a dual-voltage stabilization module, which includes a high-voltage stabilization module and a low-voltage stabilization module; The high-pressure stabilization module includes a plunger pump connected to a high-pressure CO2 source. The plunger pump operates continuously in a constant-pressure mode to maintain the pressure of the high-pressure CO2 source at a first set value. The pressure compensation response cycle of the plunger pump is no greater than one-tenth of the switching cycle of the first pneumatic valve and the second pneumatic valve. The low-pressure stabilization module includes a second back pressure valve and a second hand-cranked pump connected to a low-pressure CO2 source, used to maintain the pressure of the low-pressure CO2 source at a second set value.

[0008] In some embodiments, the pneumatic valve controller is further configured with an interlock logic circuit, which ensures that at most one of the first and second pneumatic valves is open at any given time, and that the dead time when both pneumatic valves are closed is less than the pulse period.

[0009] In some embodiments, the pulse waveform adjustment module includes a buffer chamber and / or a throttle valve. The buffer chamber is used to attenuate the steepness of the rising and / or falling edges of the high-frequency pressure pulse, and the throttle valve is used to limit the instantaneous flow rate of CO2. The pulse waveform adjustment module is used to adjust the waveform shape of the high-frequency pressure pulse by changing the buffer chamber of different volumes and / or adjusting the opening of the throttle valve.

[0010] In some embodiments, the nuclear magnetic resonance module includes a core holder and a nuclear magnetic resonance analyzer. The input end of the core holder is connected to the output end of the pulse waveform adjustment module, and is used to hold the experimental core and receive the adjusted high-frequency pressure pulse. The detection chamber of the nuclear magnetic resonance analyzer accommodates the core holder and is used to collect the T2 spectrum and one-dimensional frequency encoded data of the experimental core before and after pulse injection. The nuclear magnetic resonance module also includes a feedback control unit, which is electrically connected to the nuclear magnetic resonance analyzer and the pneumatic valve controller, respectively, and is used to generate the adjustment signal based on the T2 spectrum and one-dimensional frequency encoding data.

[0011] Secondly, embodiments of this specification also provide an experimental method for enhancing oil recovery by high-frequency pulsed CO2 injection, using the aforementioned experimental apparatus. The method includes: Nuclear magnetic resonance data of the experimental core were collected before pulse injection, and the pressure of the high-pressure CO2 source was maintained at a first set value, and the pressure of the low-pressure CO2 source was maintained at a second set value, wherein the first set value was greater than the second set value. By setting pulse parameters through the pneumatic valve controller, the first pneumatic valve and the second pneumatic valve are controlled to switch interlocked instantaneously according to the set pulse parameters, so that high-pressure CO2 and low-pressure CO2 are output alternately, generating high-frequency pressure pulses; By changing the buffer chamber of different volumes and / or adjusting the opening of the throttle valve, the waveform of the high-frequency pressure pulse is adjusted, and based on the adjusted high-frequency pressure pulse, high-pressure CO2 and low-pressure CO2 are alternately injected into the experimental core, and nuclear magnetic resonance data of the experimental core are collected after pulse injection. Based on the nuclear magnetic resonance data of the experimental cores before and after pulse injection, an adjustment signal is generated to adjust the pulse parameters set by the pneumatic valve controller.

[0012] In some embodiments, adjusting the waveform shape of the high-frequency pressure pulse by changing the buffer chamber of different volumes and / or adjusting the opening of the throttle valve includes: When the experimental core is a fractured core, no buffer chamber is installed or a buffer chamber with a volume smaller than the first volume threshold is used, so that the high-frequency pressure pulse forms a square wave pulse with steep rising and falling edges. When the experimental core is a mixed core, a buffer cavity with a volume greater than or equal to the first volume threshold and less than or equal to the second volume threshold is used to make the high-frequency pressure pulse form a trapezoidal wave pulse with a smooth rising and falling edge. When the experimental core is a dense core, a buffer cavity with a volume greater than the second volume threshold is used to make the high-frequency pressure pulse form an exponential wave pulse with slowly changing pressure. The rise and fall speeds of the high-frequency pressure pulses can be adjusted by regulating the opening of the throttle valve.

[0013] In some embodiments, the nuclear magnetic resonance data includes T2 spectra and one-dimensional frequency-coded data; correspondingly, generating an adjustment signal for adjusting the pulse parameters set by the pneumatic valve controller based on the nuclear magnetic resonance data of the experimental core before and after pulse injection includes: The effective CO2 reception distance is calculated based on the one-dimensional frequency encoding data before and after pulse injection. Based on the T2 spectrum before and after pulse injection, the recovery rates of small pores, medium and small pores, and large pores are calculated according to the relaxation time partition. The effective CO2 recovery distance, micropore recovery rate, medium-small pore recovery rate and macropore recovery rate are compared with their respective preset thresholds. When any of the indicators is lower than its corresponding preset threshold, an adjustment signal corresponding to the indicator is generated. Based on the generated adjustment signal, adjust at least one of the pulse parameters set by the pneumatic valve controller.

[0014] In some embodiments, the pulse parameters include pulse frequency, pulse duty cycle, and pulse pressure difference. The pulse frequency is the alternation switching frequency of the first pneumatic valve and the second pneumatic valve. The pulse duty cycle is the ratio of the duration of the high-pressure CO2 injection phase to the pulse period within one pulse cycle. The pulse pressure difference is the difference between the pressure of the high-pressure CO2 source and the pressure of the low-pressure CO2 source. Accordingly, adjusting at least one of the pulse parameters set by the pneumatic valve controller according to the generated adjustment signal includes: Upon receiving the first adjustment signal corresponding to the effective CO2 receiving distance, increase the pulse frequency or increase the pulse voltage difference; Upon receiving the second adjustment signal corresponding to the micropore recovery rate, decrease the pulse duty cycle or increase the pulse differential pressure. Upon receiving the third adjustment signal corresponding to the recovery rate of small and medium pores, the pulse frequency is increased; Upon receiving the fourth adjustment signal corresponding to the large porosity recovery rate, increase the pulse pressure difference; When the first adjustment signal, the second adjustment signal, the third adjustment signal, and the fourth adjustment signal are received simultaneously, injection is first performed with a symmetrical pulse with a pulse frequency higher than the first frequency threshold and a high-voltage injection duration equal to the low-voltage injection duration. Then, injection is performed with an asymmetrical pulse with a pulse frequency lower than the second frequency threshold and a high-voltage injection duration shorter than the low-voltage injection duration. The first frequency threshold is greater than the second frequency threshold.

[0015] In some embodiments, the method further includes: Determine whether the difference between the nuclear magnetic resonance data acquired this time and the nuclear magnetic resonance data acquired last time is less than a preset change threshold; When the difference is less than a preset change threshold, it is determined that the pulse injection effect has reached a stable state, the pulse injection is stopped and the well is shut down for production. When the difference is greater than or equal to a preset change threshold, it is determined that the pulse injection effect has not yet stabilized, and the steps of interlocking instantaneous switching and adjusting the high-frequency pressure pulse waveform shape are continued, or the pulse parameters are adjusted according to the current nuclear magnetic resonance data and then the steps of interlocking instantaneous switching and adjusting the high-frequency pressure pulse waveform shape are continued.

[0016] This specification provides an experimental apparatus and method for enhancing oil recovery by high-frequency pulsed CO2 injection. By connecting the outlets of a first pneumatic valve and a second pneumatic valve in parallel to form a common output terminal, and controlling the two pneumatic valves to interlock and instantaneously switch, high-pressure CO2 and low-pressure CO2 are output alternately. This generates high-frequency pressure pulses without relying on slow pump flow rate changes, solving the problems of slow pressure changes and inability to generate high-frequency pressure pulses in traditional pulsed injection methods. By connecting a pulse waveform adjustment module in series between the common output terminal and the input terminal of the nuclear magnetic resonance (NMR) module, the waveform of the high-frequency pressure pulses can be adjusted according to experimental requirements, providing matching pulse waveform conditions for cores with different pore structures. The NMR module, based on the adjusted high-frequency pressure pulses, alternately injects high-pressure and low-pressure CO2 into the experimental core, collects NMR data before and after pulsed injection, and generates adjustment signals to adjust pulse parameters, achieving integrated closed-loop control of "injection-acquisition-feedback". The aforementioned device solves the problems of slow pressure change and inability to independently adjust pulse waveform and pulse parameters in existing pulse injection methods, providing reliable technical support for indoor experimental research on CO2 huff and puff to enhance oil recovery in unconventional reservoirs. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a schematic diagram of the structural composition of an experimental device for enhancing oil recovery by high-frequency pulsed CO2 injection, as provided in the embodiments of this specification. Figure 2 This is a schematic flowchart of an experimental method for enhancing oil recovery by high-frequency pulsed CO2 injection, as provided in the embodiments of this specification. Figure 3 This is a schematic diagram of the square wave pulse pressure changing over time provided in the embodiments of this specification; Figure 4 This is a schematic diagram of the curve of trapezoidal wave pulse pressure changing over time provided in the embodiments of this specification; Figure 5 This is a schematic diagram of the exponential wave pulse pressure changing over time, as provided in the embodiments of this specification. Figure 6 This is a schematic diagram of the core T2 spectrum and crude oil distribution in each region provided in the embodiments of this specification; Figure 7This is a schematic diagram of the comparison curves of core T2 spectra under different injection conditions provided in the embodiments of this specification; Figure 8 This is a schematic diagram of the effective distance under different CO2 injection modes provided in the embodiments of this specification.

[0018] Explanation of reference numerals in the attached figures: 1. Plunger pump; 2. First six-way valve; 3. High-pressure CO2 source; 4. Low-pressure CO2 source; 5. Second six-way valve; 6. First back pressure valve; 7. Three-way valve; 8. First hand-cranked pump; 9. Nuclear magnetic resonance module; 10. Core holder; 11. Non-magnetic plug; 12. Experimental core; 13. First waste liquid collection container; 14. First pneumatic valve; 15. Second pneumatic valve; 16. Pneumatic valve controller; 17. Second back pressure valve; 18. Second hand-cranked pump; 19. Second waste liquid collection container; 20. First circulation pump; 21. Second circulation pump; 22. First constant temperature water bath; 23. Second constant temperature water bath; 24. First two-way valve; 25. Second two-way valve; 26. Buffer chamber; 27. Throttling valve. Detailed Implementation

[0019] To enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this specification, and not all embodiments. Based on the embodiments in this specification, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this specification.

[0020] Unconventional oil and gas resources such as tight oil and shale oil are abundant, but their development mainly relies on horizontal well drilling and hydraulic fracturing technology, resulting in extremely low primary recovery rates. CO2 huff and puff, as a potential means of enhancing oil recovery, has been validated in laboratories and pilot oilfields.

[0021] CO2 huff and puff can be divided into three stages: CO2 injection, well shut-in, and depressurization production. During the huff and puff process, the mass transfer between CO2 and the oil phase is mainly diffusion-based, resulting in a short effective CO2 reception distance and limited recovery improvement. Therefore, further enhancing diffusion mass transfer and increasing the effective CO2 reception distance are key to improving the recovery rate of unconventional reservoirs. Traditional pulsed CO2 injection achieves pressure changes by adjusting the displacement pump flow rate. However, this method results in slow pressure changes, making it difficult to achieve instantaneous pressure changes. Furthermore, the pulse waveform of existing pulsed injection methods is uncontrollable, and the pulse parameters cannot be independently adjusted. This prevents optimization experiments on unconventional reservoir cores with different pore structures, limiting the pulse effect and failing to fundamentally solve the problems of short effective distance and low recovery rate in CO2 huff and puff technology for unconventional reservoirs.

[0022] To address the aforementioned issues, this specification provides an experimental apparatus and method for enhancing oil recovery through high-frequency pulsed CO2 injection. A pneumatic valve controller precisely controls a first pneumatic valve and a second pneumatic valve to switch instantaneously according to set pulse parameters. This allows for switching between different pressure CO2 gas sources to achieve high-frequency pulsed CO2 injection, enabling instantaneous pressure changes and enhancing CO2 uptake, diffusion, and mass transfer. This, in turn, increases the effective CO2 receiving distance and improves the recovery rate of unconventional reservoirs. Furthermore, a pulse waveform adjustment module adjusts the waveform of the high-frequency pressure pulse, providing matching pulse waveform conditions for core samples with different pore structures. A nuclear magnetic resonance (NMR) module collects NMR data before and after pulse injection and generates adjustment signals, achieving closed-loop feedback adjustment of the pulse parameters.

[0023] It should be noted that the embodiments in this specification provide an experimental device and method for enhancing oil recovery by high-frequency pulsed CO2 injection, which can be applied to CO2 huff and puff in unconventional reservoirs and can fundamentally solve the problems of short effective distance and low recovery rate of CO2 huff and puff technology in unconventional reservoirs.

[0024] It should also be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. The acquisition, transmission, storage, use, and processing of data in the technical solution of this application all comply with the relevant provisions of national laws and regulations.

[0025] The following description, in conjunction with the accompanying drawings, introduces an experimental apparatus and method for enhancing oil recovery by high-frequency pulsed CO2 injection, as provided in the embodiments of this specification.

[0026] Figure 1 This is a schematic diagram of the structure of an experimental device for enhancing oil recovery by high-frequency pulse injection of CO2, as provided in the embodiments of this specification. The experimental device may include: a high-frequency pulse injection module, a pulse waveform adjustment module, and a nuclear magnetic resonance module 9. The high-frequency pulse injection module may include a first pneumatic valve 14, a second pneumatic valve 15, and a pneumatic valve controller 16. The inlet of the first pneumatic valve 14 is connected to a high-pressure CO2 source 3, and the inlet of the second pneumatic valve 15 is connected to a low-pressure CO2 source 4. The outlets of the first pneumatic valve 14 and the second pneumatic valve 15 are connected in parallel to form a common output terminal. The pneumatic valve controller 16 is electrically connected to the control terminals of the first pneumatic valve 14 and the second pneumatic valve 15, and is used to control the first pneumatic valve 14 and the second pneumatic valve 15 to interlock and switch instantaneously according to the set pulse parameters, so that high-pressure CO2 and low-pressure CO2 are output alternately to generate high-frequency pressure pulses. The pressure value of the high-pressure CO2 is a first set value, and the pressure value of the low-pressure CO2 is a second set value. The first set value is greater than the second set value. The pulse waveform adjustment module is connected in series between the common output terminal and the input terminal of the nuclear magnetic resonance module 9, and can be used to adjust the waveform shape of the high-frequency pressure pulse. The nuclear magnetic resonance module 9 can be used to alternately inject high-pressure CO2 and low-pressure CO2 into the experimental core 12 based on the adjusted high-frequency pressure pulse, and to collect nuclear magnetic resonance data of the experimental core 12 before and after pulse injection, and generate an adjustment signal to adjust the pulse parameters.

[0027] Specifically, the experimental setup may include a high-frequency pulse injection module, a pulse waveform adjustment module, and a nuclear magnetic resonance (NMR) module 9. The pulse waveform adjustment module can be connected in series between the output of the high-frequency pulse injection module and the input of the NMR module 9. The high-frequency pulse injection module can be used to generate high-frequency pressure pulses by alternating the output of high-pressure CO2 and low-pressure CO2 when two pneumatic valves (such as the first pneumatic valve 14 and the second pneumatic valve 15) are interlocked and momentarily switched according to the pulse parameters set by the pneumatic valve controller 16. The pulse waveform adjustment module can be used to adjust the pulse waveform shape of the high-frequency pressure pulses. The NMR module 9 can be used to receive the adjusted high-frequency pressure pulses and collect NMR data from the experimental core 12 before and after pulse injection to generate an adjustment signal for adjusting the pulse parameters.

[0028] Interlocking instantaneous switching refers to the control signals of two pneumatic valves being mutually locked, ensuring that at any given time only one pneumatic valve is open. When one pneumatic valve closes, the other immediately opens, with the switching time between the two actions on the order of milliseconds. High-frequency pulse injection refers to the process of alternating injection of high-pressure CO2 and low-pressure CO2 at millisecond-level speeds. High-frequency pressure pulse refers to the pressure generated by the alternating injection of high-pressure CO2 and low-pressure CO2 at a first set value (P). high (i.e., the pressure maintained by the high-pressure CO2 source) and the second set value (P) low The pressure wave that alternates between the pressure maintained by the low-pressure CO2 source and the pressure value of the high-pressure CO2 can be a first set value, and the pressure value of the low-pressure CO2 can be a second set value. The first set value can be much larger than the second set value.

[0029] The aforementioned high-frequency pulse injection module may include a first pneumatic valve 14, a second pneumatic valve 15, and a pneumatic valve controller 16. The inlet of the first pneumatic valve 14 is connected to a high-pressure CO2 source 3, which can also be referred to as a high-pressure CO2 intermediate container. The inlet of the second pneumatic valve 15 is connected to a low-pressure CO2 source 4, which can also be referred to as a low-pressure CO2 intermediate container. The pneumatic valve controller 16 can output control signals according to set pulse parameters to control the two pneumatic valves to alternately open and close, thereby achieving high-frequency CO2 injection. The high-frequency pulse injection module thus has two operating modes: Operating Mode 1: When the first pneumatic valve 14 is open and the second pneumatic valve 15 is closed, the high-pressure CO2 source 3 is connected to the nuclear magnetic resonance module 9 through the pulse waveform adjustment module. The high-pressure CO2 flows through the first pneumatic valve 14 to the common output end of both, enabling the injection of high-pressure CO2 into the experimental core 12 in the nuclear magnetic resonance module 9 for a duration of up to a first duration T. high .

[0030] Operating Mode 2: When the first pneumatic valve 14 is closed and the second pneumatic valve 15 is open, the low-pressure CO2 source 4 is connected to the nuclear magnetic resonance module 9 through the pulse waveform adjustment module. The low-pressure CO2 flows to the common output end of both via the second pneumatic valve 15, enabling the injection of low-pressure CO2 into the experimental core 12 in the nuclear magnetic resonance module 9 for a duration that can be a second duration T. low =TT high T represents the pulse injection cycle, also known as the switching cycle between the first and second pneumatic valves. The aforementioned operating modes one and two can be alternately switched at a high frequency (millisecond-level alternation) by the pneumatic valve controller 16 according to the set pulse parameters. Due to the fast response speed of the pneumatic valves, the switching between the two valves can be completed instantaneously, thereby generating a high-frequency pressure pulse with steep rising and falling edges at the common output terminal. When this high-frequency pressure pulse acts on the experimental core 12, it can increase the internal pressure of the core to P. high and P low The rapid, alternating pressure fluctuations create periodic pressure waves. These periodic pressure waves disrupt the traditional diffusion-based mass transfer mode in CO2 injection, adding pressure wave-driven forced convection and disturbance mass transfer to the crude oil in core 12, in addition to diffusion mass transfer. This initially enhances the mass transfer effect of CO2 within the core.

[0031] The aforementioned pulse waveform adjustment module is connected in series between the common output terminal of the first pneumatic valve 14 and the second pneumatic valve 15 and the input terminal of the nuclear magnetic resonance module 9. It can receive high-frequency pressure pulses and adjust their waveform. By adjusting the waveform, different pressure impact intensities and pressure change rates can be matched to cores with different pore structures, enabling the high-frequency pressure pulses to more effectively act on pores of different scales within the core. It should be noted that the pore structure of unconventional oil reservoirs (such as shale oil and tight oil) cores exhibits typical multi-scale characteristics, meaning that pores of different scales exist simultaneously within the core, ranging from nanometer-scale to micrometer-scale to millimeter-scale fractures, forming a complex pore network. Through the adjusted high-frequency pressure pulses, appropriate pressure fluctuations can be applied to pores of different scales, thereby achieving effective utilization across the entire scale from macroscopic fractures to nanopores, ultimately effectively improving the CO2 recovery rate of unconventional oil reservoirs.

[0032] The aforementioned nuclear magnetic resonance module 9 can receive regulated high-frequency pressure pulses, enabling alternating injection of high-pressure and low-pressure CO2 into the experimental core 12. Specifically, the high-pressure injection phase (high-pressure CO2 injection phase) generates pressure shocks, while the low-pressure injection phase (low-pressure CO2 injection phase) promotes CO2 diffusion and dissolved gas release. The alternation of high and low pressure transforms the mass transfer between CO2 and the experimental core 12 from a single diffusion mass transfer to a combination of diffusion mass transfer and pressure wave disturbance mass transfer, thereby significantly increasing the CO2 mass transfer effect of the experimental core 12, effectively extending the effective CO2 huff and puff distance, and improving the recovery rate of unconventional oil reservoirs. The nuclear magnetic resonance module 9 can also collect nuclear magnetic resonance data of the experimental core 12 before and after pulse injection, generating adjustment signals to adjust the pulse parameters. Adjusting the pulse parameters based on these adjustment signals allows the pulse parameters to gradually approach the optimal combination, further extending the effective CO2 huff and puff distance, improving the utilization of crude oil in the pores of each size in the experimental core 12, and ultimately achieving a significant improvement in the CO2 huff and puff recovery rate of unconventional oil reservoirs.

[0033] Through the synergistic effect of the various modules in the above-mentioned experimental device, an integrated closed-loop control of "pulse generation-waveform adjustment-core injection-data acquisition-signal feedback" was achieved, providing reliable technical support for indoor experimental research on CO2 huff and puff to enhance oil recovery in unconventional reservoirs.

[0034] In some embodiments, the above-described experimental apparatus may further include a dual-voltage stabilization module, which may include a high-voltage stabilization module and a low-voltage stabilization module; The high-pressure stabilization module may include a plunger pump 1 connected to the high-pressure CO2 source 3. The plunger pump 1 operates continuously in a constant-pressure mode to maintain the pressure of the high-pressure CO2 source 3 at a first set value P. high Furthermore, the pressure compensation response cycle of the plunger pump 1 is not greater than one-tenth of the switching cycle of the first pneumatic valve 14 and the second pneumatic valve 15. The low-pressure stabilization module may include a second back pressure valve 17 and a second hand-cranked pump 18 connected to the low-pressure CO2 source 4, for maintaining the pressure of the low-pressure CO2 source 4 at a second set value P. low .

[0035] Specifically, the output of the aforementioned dual-pressure stabilization module can be connected to the input of the aforementioned high-frequency pulse injection module. It may include a high-pressure stabilization module and a low-pressure stabilization module, which are independent of each other and can be used to maintain the pressure stability of the high-pressure CO2 source 3 and the low-pressure CO2 source 4 in the high-frequency pulse injection module, respectively.

[0036] The high-pressure stabilization module may include a plunger pump 1 (or a high-precision plunger pump), which can be connected to the high-pressure CO2 source 3 (high-pressure CO2 intermediate container) through the first six-way valve 2, and continuously operate in constant pressure mode to maintain the pressure of the high-pressure CO2 source 3, and monitor the pressure of the high-pressure CO2 source in real time through the pressure sensor P of the high-pressure CO2 source 3.

[0037] When the pressure of the high-pressure CO2 source 3 is detected to be lower than the first set value P high At that time, plunger pump 1 immediately starts to perform pressure compensation, restoring the pressure to the first set value P. high The pressure compensation response period of the plunger pump 1 is configured to be no greater than one-tenth of the switching period (i.e., pulse period) of the first pneumatic valve 14 and the second pneumatic valve 15. For example, when the pulse frequency is 10Hz and the switching period or pulse period is 0.1 seconds, the pressure compensation response period of the plunger pump 1 must be no greater than 0.01 seconds.

[0038] The low-pressure stabilization module may include a second hand-cranked pump 18 and a second back pressure valve 17. The second hand-cranked pump 18 can be connected to the low-pressure CO2 source 4 (low-pressure CO2 intermediate container) through the second back pressure valve 17, that is, the second back pressure valve 17 is connected in series at the output end of the low-pressure CO2 source 4, and the control end of the second hand-cranked pump 18 is connected to the second back pressure valve 17. The second hand-cranked pump 18 can apply a stable back pressure to the low-pressure CO2 source 4 through the second back pressure valve 17. The unidirectional conduction characteristic of the second back pressure valve 17 can prevent pressure from flowing to the low-pressure side during high-pressure injection. The second hand-cranked pump 18 and the second back pressure valve 17 together form an independent low-pressure stabilization loop, maintaining the pressure of the low-pressure CO2 source 4 at a second set value P. low The first set value is greater than the second set value, and the difference between the two constitutes the pulse pressure difference. The pulse pressure difference determines the intensity of each pulse injection. The larger the pulse pressure difference, the stronger the impact stripping capability during high-pressure injection and the more obvious the expansion effect during low-pressure injection.

[0039] The set pressure of the second back pressure valve 17 is equal to the target pressure of the low-pressure CO2 source 4 (i.e., by adjusting the set pressure of the second back pressure valve 17, the pressure at the outlet of the low-pressure CO2 source 4 can be precisely controlled at the required target value, i.e., the second set value). When the pressure inside the low-pressure CO2 source 4 is lower than the set pressure of the second back pressure valve 17, the second back pressure valve 17 closes, preventing fluid from flowing out. When the pressure inside the low-pressure CO2 source 4 is higher than the set pressure of the second back pressure valve 17, the second back pressure valve 17 opens, allowing excess pressure to be released, thereby stabilizing the pressure of the low-pressure CO2 source 4 at the target value. This setting does not require continuous operation of the plunger pump 1 to maintain stable low-pressure side pressure, simplifying system control. At the same time, the one-way characteristic of the second back pressure valve 17 can automatically prevent high pressure from flowing to the low-pressure side during high-pressure injection, eliminating the need for additional control logic and improving the reliability and response speed of the device.

[0040] Through the aforementioned dual-pressure stabilization module, the rapid pressure compensation response of the high-pressure side plunger pump ensures that the pressure recovers to the first set value before the next high-pressure injection begins after each high-pressure injection, guaranteeing the amplitude consistency of each pulse during continuous high-frequency pulse injection. The independent low-pressure side stabilization loop effectively prevents flow from the high-pressure side to the low-pressure side during high-pressure injection, ensuring that the pulse pressure difference remains constant throughout the experiment. The two modules work together to guarantee the stability of the pulse amplitude and the accuracy of the pulse pressure difference during high-frequency pulse injection, thereby ensuring the effective injection of high-frequency pulses.

[0041] In some embodiments, the pneumatic valve controller 16 may also be configured with an interlock logic circuit, which ensures that at most one of the first pneumatic valve 14 and the second pneumatic valve 15 is open at any given time, and that the dead time when both pneumatic valves are closed is less than the pulse period.

[0042] Specifically, the interlock logic circuit can be implemented by logic gate circuits or programmable logic devices. The interlock logic circuit has two input terminals (first input terminal and second input terminal) and two output terminals (first output terminal and second output terminal): the two input terminals receive the first control signal and the second control signal issued by the pneumatic valve controller, respectively, and the two output terminals are connected to the control terminal of the first pneumatic valve 14 and the control terminal of the second pneumatic valve 15, respectively.

[0043] The core function of the interlock logic circuit is to achieve "interlock" control of the two pneumatic valves. Its logic is as follows: When the first control signal is an open command, the interlock logic circuit sets the first output to an open signal and simultaneously forces the second output to a closed signal, ensuring that the second pneumatic valve 15 cannot open when the first pneumatic valve 14 is open. When the second control signal is an open command, the interlock logic circuit sets the second output to an open signal and simultaneously forces the first output to a closed signal, ensuring that the first pneumatic valve 14 cannot open when the second pneumatic valve 15 is open. When both control signals are open commands simultaneously (e.g., due to program errors or interference), the interlock logic circuit forces both outputs to a closed signal according to a preset priority (e.g., prioritizing the closing of the first pneumatic valve 14), preventing both pneumatic valves from opening simultaneously. Through this logic, the interlock logic circuit ensures that at any given time, at most one of the first pneumatic valve 14 and the second pneumatic valve 15 is in the open state. This allows for instantaneous switching between high-pressure and low-pressure CO2, generating high-frequency pressure pulses with steep rising and falling edges, thus enhancing the mass transfer effect of CO2.

[0044] The interlock logic circuit also controls the switching sequence between the two pneumatic valves, implementing a "close first, open later" switching order. Specifically, when switching from the open state of the first pneumatic valve 14 to the open state of the second pneumatic valve 15, the interlock logic circuit first sends a closing signal to the first pneumatic valve 14. After the first pneumatic valve 14 is fully closed, it then sends an opening signal to the second pneumatic valve 15. During this switching process, there is a time interval during which both pneumatic valves are closed; this time interval is called the dead time. The interlock logic circuit is configured to set this dead time to be less than the pulse period. For example, when the pulse frequency is 5Hz, the pulse period is 0.2 seconds, and the dead time can be set to 0.005 seconds (5 milliseconds), which is much smaller than the pulse period. The specific value of the dead time can be optimized according to the response characteristics of the pneumatic valves and experimental requirements, as long as it is less than the pulse period.

[0045] The interlocking logic circuit effectively prevents the direct connection between high-pressure CO2 and low-pressure CO2 in the pipeline caused by the simultaneous opening of two pneumatic valves, avoiding pressure crosstalk and pulse differential pressure failure. Simultaneously, the setting of a dead time shorter than the pulse period ensures the continuity of the pressure pulse, preventing pulse interruption due to excessively long dead time and thus ensuring the integrity and stability of the high-frequency pressure pulse.

[0046] In some embodiments, the pulse parameters may include pulse frequency, pulse duty cycle, and pulse differential pressure. The pneumatic valve controller 16 can independently set these three pulse parameters.

[0047] The pulse frequency is the alternating switching frequency of the first pneumatic valve 14 and the second pneumatic valve 15, and its range can be 0.1Hz to 10Hz. The pulse pressure difference is the difference between the pressure of the high-pressure CO2 source 3 and the pressure of the low-pressure CO2 source 4, ΔP = P high -P low The pulse duty cycle can be independently set by the plunger pump 1 and the second back pressure valve 17. high The ratio of the first duration to the pulse period T, D=T high / T. The pneumatic valve controller 16 can independently set the opening duration of the first pneumatic valve 14 and the second pneumatic valve 15. The opening durations of the two pneumatic valves do not need to be equal, so that the pulse duty cycle D is continuously adjustable in the range of 0% to 100%.

[0048] The pneumatic valve controller 16 can control the first pneumatic valve 14 and the second pneumatic valve 15 to switch instantaneously and interlock according to the set initial pulse parameters. Subsequently, it can also adjust the initial pulse parameters according to the adjustment signal generated by the feedback control unit until the pulse parameters reach the optimal, so that the effective CO2 receiving distance and the recovery rate of each aperture zone can reach the optimal.

[0049] By setting three independent parameters—pulse frequency, pulse duty cycle, and pulse pressure difference—the mass transfer effect of CO2 can be optimized from different dimensions: adjusting the pulse frequency controls the period of the pressure wave and the conditions for standing wave formation; high-frequency pulses (≥5Hz) can form standing waves inside the core, expanding the CO2 sweep range. Adjusting the pulse duty cycle controls the ratio of high-pressure injection to low-pressure injection duration; when D < 50%, the low-pressure injection duration (i.e., the second duration T) is... low The duration of high-pressure injection (i.e., the first duration T) is greater than the high-pressure injection duration. high This facilitates dissolved gas release and crude oil reflux, promoting CO2 diffusion into micropores. Adjusting the pulse pressure difference can control the intensity of the high-pressure impact and the driving force of low-pressure diffusion; a larger ΔP can enhance oil film stripping ability and the expansion effect of CO2. Independent adjustment and synergistic optimization of these three parameters can comprehensively improve the mass transfer efficiency between CO2 and crude oil from three dimensions: macroscopic sweep, microscopic diffusion, and impact stripping, ultimately extending the effective CO2 receiving distance and significantly improving the recovery rate of unconventional reservoirs.

[0050] In some embodiments, the pulse waveform adjustment module may include a buffer chamber 26 and / or a throttle valve 27. The buffer chamber 26 is used to attenuate the steepness of the rising and / or falling edges of the high-frequency pressure pulse, and the throttle valve 27 is used to limit the instantaneous flow rate of CO2. The pulse waveform adjustment module is used to adjust the waveform shape of the high-frequency pressure pulse by changing the buffer chamber 26 of different volumes and / or adjusting the opening of the throttle valve 27.

[0051] Specifically, a removable and replaceable pulse waveform adjustment module may also be installed on the pipeline between the first pneumatic valve 14 and / or the second pneumatic valve 15 and the nuclear magnetic resonance module. The pulse waveform adjustment module may include a buffer chamber 26 and / or a throttle valve 27.

[0052] The buffer chamber 26 is a pressure-resistant chamber with a certain volume. Its inlet is connected to the common output terminal of the first pneumatic valve 14 and the second pneumatic valve 15, and its outlet is connected to the inlet of the throttle valve 27. The buffer chamber 26 is used to attenuate the steepness of the rising and / or falling edges of the pulse pressure waveform. When the pneumatic valve is opened, high-pressure CO2 or low-pressure CO2 first enters the buffer chamber 26. Because the buffer chamber 26 has a certain volume, the pressure inside the chamber will not be built up instantaneously, but will gradually rise before being output, thus making the originally steep rising edge of the pressure pulse smoother.

[0053] This device provides multiple buffer chambers 26 of different volumes for experimental selection. By changing the buffer chambers 26 with different volumes, the rise and fall steepness of the pressure pulse can be independently adjusted without changing the pulse frequency and pulse duty cycle, thereby controlling the pressure impact intensity. (1) When no buffer chamber is installed or a small-volume buffer chamber with a volume less than the first volume threshold is used: the instantaneous switching of the pneumatic valve generates an approximately square wave pressure pulse at the front end of the core sample, with steep rising and falling edges, and the pressure is at P high and P low The instantaneous jump between these waveforms generates the strongest instantaneous impact effect. This waveform is suitable for fractured cores (mainly millimeter-scale fractures), and can use steep pressure impacts to quickly peel off the oil film on the fracture surface, solving the problem of strong oil film adhesion in fractured cores and the difficulty in peeling it off with conventional injection.

[0054] (2) When using a medium-volume buffer chamber with a volume greater than or equal to the first volume threshold and less than or equal to the second volume threshold: the rising and falling edges of the pressure pulse are partially attenuated, generating an approximately trapezoidal pressure pulse. Compared to a square wave pulse, the rising and falling edges of the trapezoidal pulse have a certain slope, resulting in a moderate impact effect while still maintaining a high pressure amplitude. This waveform is suitable for mixed cores (where fractures and matrix coexist). The moderate impact intensity can strip the oil film from the fracture surface without causing CO2 to flow along the fracture and fail to enter the matrix pores due to excessive impact, thus balancing the displacement needs of both fractures and matrix.

[0055] (3) When using a large-volume buffer chamber with a volume greater than the second volume threshold: the rising and falling edges of the pressure pulse are significantly attenuated, producing a pressure pulse with an approximately exponentially decaying waveform. The pressure rises and falls slowly, the impact effect is weak, but the pressure change is gradual, which is conducive to the slow diffusion of CO2 into the micropores. This waveform is suitable for dense cores (mainly composed of nanoscale micropores), which can avoid the problem that CO2 cannot enter the micropores due to excessively rapid pressure impact, allowing CO2 sufficient time to slowly permeate into the nanoscale pores.

[0056] An adjustable throttle valve 27 is connected in series between the outlet of the buffer chamber 26 and the input of the nuclear magnetic resonance module to limit the instantaneous flow rate of CO2 through the pipeline, further regulating the pressure change rate of the pulse waveform. The throttle valve 27 limits the instantaneous flow rate of CO2 by changing the flow cross-sectional area: the larger the opening of the throttle valve 27, the larger the instantaneous flow rate, the faster the pressure change rate, and the stronger the impact effect; the smaller the opening of the throttle valve 27, the smaller the instantaneous flow rate, the slower the pressure change rate, and the weaker the impact effect. By adjusting the opening of the throttle valve 27, the rise and fall rates of the pressure pulse can be further fine-tuned based on the impact intensity determined by the buffer chamber 26, achieving precise control of the pressure change rate.

[0057] It should be noted that the waveform shape is determined by three parameters: the steepness of the rising edge, the steepness of the falling edge, and the rate of pressure change (i.e., a comprehensive reflection of the buffer chamber volume and the throttle valve opening adjustment). The buffer chamber volume determines the steepness of the rising / falling edge (small volume → steep → square wave; medium volume → moderate → trapezoidal wave; large volume → gentle → exponential wave), and the throttle valve opening determines the rate of pressure change (large opening → fast speed; small opening → slow speed). Square wave, trapezoidal wave, and exponential wave are three typical waveform shapes, differing in the steepness of the rising / falling edge and the rate of pressure change.

[0058] The pulse waveform adjustment module described above enables continuous adjustment of the pulse waveform. It can match the optimal pulse waveform to the core with different pore structures, thereby giving full play to the physical effects of various pulse waveforms and maximizing the oil displacement effect.

[0059] In some embodiments, the above-mentioned nuclear magnetic resonance module 9 may include a core holder 10 and a nuclear magnetic resonance analyzer. The input end of the core holder 10 is connected to the output end of the pulse waveform adjustment module, and is used to hold the experimental core 12 and receive the adjusted high-frequency pressure pulse. The detection chamber of the nuclear magnetic resonance analyzer accommodates the core holder 10 and is used to collect the T2 spectrum and one-dimensional frequency encoded data of the experimental core 12 before and after pulse injection. The nuclear magnetic resonance module may further include a feedback control unit, which is electrically connected to the nuclear magnetic resonance analyzer and the pneumatic valve controller 16, respectively, and is used to generate the adjustment signal based on the T2 spectrum and one-dimensional frequency encoding data.

[0060] Specifically, the core holder 10 can be made of non-magnetic material to avoid interfering with the magnetic field of the nuclear magnetic resonance analyzer. One end of the core holder 10 can be equipped with a non-magnetic plug 11 (or a sealing plug) to seal and fix the experimental core 12 inside the core holder 10. The input end of the core holder 10 is connected to the output end of the pulse waveform adjustment module via a pipeline to receive high-frequency pressure pulses after waveform adjustment. The experimental core 12 can be a tight core, shale core, or fractured core from an unconventional oil reservoir, with a permeability range from 0.01 mD to 10 mD, covering tight cores, low-permeability cores, and medium-to-high permeability cores. Shale permeability can be even lower, such as 0.0001 mD. Specific values ​​can be adjusted according to actual conditions, and this specification does not impose specific limitations on this.

[0061] The nuclear magnetic resonance (NMR) analyzer employs low-field NMR technology, and its detection chamber has a sufficient inner diameter to accommodate the core holder 10. Before pulse injection, the NMR analyzer performs a first scan of the experimental core 12 within the core holder 10, acquiring the initial T2 spectrum and one-dimensional frequency-coded data (i.e., initial NMR data) of the experimental core 12. After pulse injection, the NMR analyzer performs a second scan, acquiring the T2 spectrum and one-dimensional frequency-coded data of the experimental core 12. The T2 spectrum reflects the fluid distribution in pores of different sizes within the core, and the one-dimensional frequency-coded data reflects the spatial distribution of the fluid along its length within the core.

[0062] The feedback control unit is electrically connected to both the nuclear magnetic resonance (NMR) analyzer and the pneumatic valve controller 16. The feedback control unit receives the T2 spectrum and one-dimensional frequency-coded data acquired by the NMR analyzer and processes the data from both datasets. Based on the one-dimensional frequency-coded data, the feedback control unit calculates the effective CO2 recovery distance. Based on the T2 spectrum data, it calculates the recovery rates for small pores, medium-small pores, and large pores according to relaxation time partitions. These four indicators are compared to their respective preset thresholds. When any indicator falls below its preset threshold, the feedback control unit generates an adjustment signal corresponding to that indicator and sends this signal to the pneumatic valve controller 16 to adjust pulse parameters, such as pulse frequency, pulse duty cycle, and pulse differential pressure.

[0063] Under pulse parameter conditions, when the duty cycle D > 50%, the high-pressure injection duration is longer than the low-pressure injection duration, and the core as a whole experiences a higher average pressure, which is conducive to the continuous penetration of CO2 into the deeper parts of the core. When the duty cycle D < 50%, the low-pressure injection duration is longer than the high-pressure injection duration, and the core as a whole experiences a lower average pressure, which is conducive to the release of dissolved gas in the core pores and the reflux of crude oil. Therefore, upon receiving the second adjustment signal corresponding to the micropore recovery rate, the feedback control unit can reduce the pulse duty cycle D (making it less than 50%) to prolong the low-pressure maintenance duration, promote the release of dissolved gas and the reflux of crude oil, thereby improving the micropore recovery rate.

[0064] The aforementioned nuclear magnetic resonance module enables quantitative assessment of the effective CO2 receiving distance and the recovery rate of each pore size zone, providing a data foundation for closed-loop optimization of pulse parameters. The feedback control unit converts the detection results into adjustment signals and sends them to the pneumatic valve controller, allowing the pulse parameters to be dynamically adjusted based on the actual response of the core, thus forming a complete closed-loop control link.

[0065] In some embodiments, the experimental apparatus may further include a first hand-cranked pump 8 and a three-way valve 7. The first hand-cranked pump 8 is connected to the confining pressure port of the core holder 10 via the three-way valve 7, and is used to apply confining pressure to the core holder 10 to simulate the pressure of the overlying rock strata. The pressure value of the confining pressure is set according to experimental requirements, and is usually higher than the fluid pressure inside the core to prevent fluid from flowing out from the gap between the core and the inner wall of the holder.

[0066] Among them, a pressure sensor P can also be installed on the pipeline of the first hand-cranked pump 8 and the three-way valve 7 to monitor the pressure value of the confining pressure in real time and ensure that the confining pressure is stable within the set range.

[0067] In some embodiments, the above-described experimental apparatus may further include a waste liquid collection module, which may include a first waste liquid collection container 13 and a second waste liquid collection container 19. The first waste liquid collection container 13 is connected to the output end of the core holder 10 via a first backpressure valve 6 and a three-way valve 7, for collecting the oil-water mixture produced from the output end of the core holder 10 during pulse injection and production stages. Specifically, the output end of the core holder 10 is connected to one port of the three-way valve 7 via a pipeline, the other port of the three-way valve 7 is connected to the inlet of the first backpressure valve 6 via a pipeline, and the outlet of the first backpressure valve 6 is connected to the first waste liquid collection container 13 via a pipeline. The first backpressure valve 6 is used to maintain the back pressure at the output end of the core holder 10, simulating formation backpressure conditions and preventing excessive vaporization of the produced fluid under low pressure. The three-way valve 7 is used to switch the flow direction of the produced fluid, directing it to the first waste liquid collection container 13 during normal production and directing it to other pipelines during venting or cleaning.

[0068] The second waste liquid collection container 19 can be connected to the low-pressure CO2 source 4 via the second backpressure valve 17 and the second double-way valve 25, and is used to collect CO2 and residual liquid released during the depressurization or venting of the low-pressure CO2 source 4. When the experiment ends or when it is necessary to replace the CO2 in the low-pressure CO2 source 4, the second double-way valve 25 is opened, and the pressure relief rate is controlled by the second backpressure valve 17 to discharge the residual CO2 and liquid in the low-pressure CO2 source 4 into the second waste liquid collection container 19.

[0069] A pressure sensor P can also be installed on the second six-way valve 5 to monitor the pressure at the common output terminal and the inlet of the pulse waveform adjustment module. This pressure sensor can record the pressure change curve at the core tip in real time during pulse injection, verifying whether the pneumatic valve switching is normal and whether the pulse waveform meets the set requirements.

[0070] In some embodiments, the above-mentioned experimental apparatus may further include a first circulating pump 20, a second circulating pump 21, a first constant temperature water bath 22, and a second constant temperature water bath 23.

[0071] The first circulating pump 20 and the first constant-temperature water bath 22 can be used to control the temperature of the low-pressure CO2 source 4 and the high-pressure CO2 source 3. The first constant-temperature water bath 22 heats the water and maintains it at the set temperature. The first circulating pump 20 drives the hot water to circulate between the insulation jacket of the intermediate container and the constant-temperature water bath, so that the CO2 temperature in the high-pressure CO2 source 3 and the low-pressure CO2 source 4 remains constant, avoiding pressure drift caused by temperature fluctuations and ensuring the accuracy of the pulse pressure difference ΔP.

[0072] The second circulation pump 21 and the second constant temperature water bath 23 are used to control the temperature of the core holder 10. The second constant temperature water bath 23 heats the water and maintains it at the set temperature. The second circulation pump 21 drives the hot water to circulate between the insulation jacket of the core holder 10 and the constant temperature water bath, so that the temperature of the core holder 10 and the experimental core 12 inside it remains constant, ensuring that the mass transfer behavior of CO2 in the core is not affected by temperature fluctuations.

[0073] The aforementioned dual-loop constant temperature system allows for independent temperature control of the CO2 source and core, meeting the experimental requirements for simulating the temperature differences between different injection temperatures and formation temperatures.

[0074] In some embodiments, the components are connected by high-pressure resistant stainless steel pipelines, and valves are provided at key nodes to control the opening and closing of the pipelines and the flow direction of the fluid.

[0075] In some embodiments, the high-pressure CO2 source 3 and the low-pressure CO2 source 4 can also be replaced with other gas sources according to changes in the actual scenario, such as alternating CO2 / N2, alternating CO2 / CH4, alternating miscible and immiscible phases, etc.

[0076] The working principle of the above experimental setup is explained below: First, the saturated oil core 12 is loaded into the core holder 10, and both ends are sealed and fixed with non-magnetic plugs 11. Confining pressure is applied to the core holder 10 via a first hand-operated pump 8 and a three-way valve 7 to simulate the pressure of the overlying strata. The second circulation pump 21 and the second constant-temperature water bath 23 are then started to heat the core holder 10 and the experimental core 12 inside, maintaining it at the set experimental temperature. The experimental core 12 is then scanned for the first time using a nuclear magnetic resonance (NMR) analyzer to obtain the initial T2 spectrum and one-dimensional frequency encoding data of the experimental core 12, which will serve as a benchmark for subsequent comparisons.

[0077] The plunger pump 1 is connected to the high-pressure CO2 source 3 via the first six-way valve 2, and the plunger pump 1 is started to operate in constant pressure mode to maintain the pressure of the high-pressure CO2 source 3 at the first set value P. high The plunger pump 1 is connected to the low-pressure CO2 source 4 via the first six-way valve 2, and is initially pressurized to approximately the second set value P. lowDisconnect afterward. A stable back pressure is applied to the low-pressure CO2 source 4 via the second hand-cranked pump 18 and the second back pressure valve 17, maintaining its pressure at the second set value P. low And P high >P low .

[0078] The pneumatic valve controller 16 outputs a control signal according to the set pulse parameters (such as pulse frequency f and pulse duty cycle D). An interlocking logic circuit ensures that at most one of the first pneumatic valve 14 and the second pneumatic valve 15 is open at any given time. When the first pneumatic valve 14 is open and the second pneumatic valve 15 is closed, high-pressure CO2 flows from the high-pressure CO2 source 3 through the first pneumatic valve 14 to the common output terminal; when the first pneumatic valve 14 is closed and the second pneumatic valve 15 is open, low-pressure CO2 flows from the low-pressure CO2 source 4 through the second pneumatic valve 15 to the common output terminal. Due to the fast response speed of the pneumatic valves, the switching between the two pneumatic valves is completed within milliseconds, and the pressure at the common output terminal is within P... high and P low The instantaneous transition between these states generates a high-frequency pressure pulse with steep rising and falling edges.

[0079] The high-frequency pressure pulse enters the pulse waveform adjustment module. Based on the pore structure type of the experimental core 12, a buffer chamber of appropriate volume is selected and / or the opening of the throttle valve is adjusted. For fractured cores, no buffer chamber is installed or a small-volume buffer chamber is used to form a square wave pulse; for mixed-type cores, a medium-volume buffer chamber is used to form a trapezoidal wave pulse; for dense cores, a large-volume buffer chamber is used to form an exponential wave pulse. The pressure change rate is fine-tuned using the throttle valve. The adjusted high-frequency pressure pulse enters the nuclear magnetic resonance module 9.

[0080] The adjusted high-frequency pressure pulse is applied to the experimental core 12 within the core holder 10, causing alternating injection of high-pressure and low-pressure CO2 into the core. The high-pressure injection phase generates pressure shocks, stripping the oil film and expanding pore throats. The low-pressure injection phase promotes CO2 diffusion and dissolved gas release. The alternation of high and low pressure transforms the mass transfer between CO2 and crude oil from a single diffusion mass transfer to a combination of diffusion mass transfer and pressure wave disturbance mass transfer.

[0081] After the pulse injection was completed, the nuclear magnetic resonance analyzer performed a second scan of the core to obtain the T2 spectrum and one-dimensional frequency-coded data of experimental core 12. The feedback control unit received the data from the two scans, calculated the effective CO2 recovery distance and the recovery rate of each zone, and generated an adjustment signal after comparing it with the preset threshold.

[0082] The feedback control unit sends an adjustment signal to the pneumatic valve controller. The pneumatic valve controller adjusts the pulse frequency f, pulse duty cycle D, or pulse pressure difference ΔP based on the adjustment signal. This injection-detection-adjustment process is repeated until all indicators reach the preset target values. When the effective CO2 recovery distance and the recovery rate of each zone reach the target values, pulse injection is stopped, the two-way valve is opened, and the produced fluid enters the waste fluid collection system, initiating the well-shutting production stage.

[0083] Based on the above working principle, this device realizes the complete process of high-frequency pressure pulse generation, waveform adjustment, core injection, data acquisition and closed-loop feedback adjustment, providing reliable technical support for indoor experimental research on CO2 huff and puff to enhance oil recovery in unconventional reservoirs.

[0084] The entire experimental procedure is explained below: Step 1) After saturating the experimental core 12 with oil, place it into the core holder 10 and scan the core with a nuclear magnetic resonance spectrometer to determine the T2 spectrum and one-dimensional frequency coding of the saturated oil core. Step 2) Control the first hand-cranked pump 8 and the three-way valve 7 to apply confining pressure to the core holder 10 to a certain pressure; Step 3) Control the valves of the first six-way valve 2 and the second six-way valve 5 to connect the pipelines between the high-pressure CO2 source 3, the low-pressure CO2 source 4 and the plunger pump 1. At the same time, adjust the first pneumatic valve 14 and the second pneumatic valve 15 to be in the closed state through the pneumatic valve controller 16. Step 4) Set the plunger pump 1 to constant pressure mode to construct the initial pressure of high pressure CO2 source 3 and low pressure CO2 source 4. After reaching the initial pressure, control the valve of the first six-way valve 2 to disconnect the plunger pump 1 from the low pressure CO2 source 4. Step 5) Control the second hand pump 18 to apply back pressure to the second back pressure valve 17 and open the second double-way valve 25 to maintain the low-pressure CO2 source 4 at the set pressure; Step 6) Control the valve of the second six-way valve 5 to connect the pipeline between the first pneumatic valve 14, the second pneumatic valve 15 and the core holder 10; Step 7) The pneumatic valve controller 16, the first pneumatic valve 14, the second pneumatic valve 15, the high-pressure CO2 source 3, and the low-pressure CO2 source 4 constitute a high-frequency pulse CO2 injection system. The pneumatic valve controller 16 adjusts the opening and closing of the first pneumatic valve 14 and the second pneumatic valve 15 at high frequency to achieve high-frequency pulse CO2 injection. During the injection process, the pressure sensor P on the second six-way valve 5 monitors the CO2 injection pressure at the front end of the core. Step 8) After the pulse injection is completed, the first pneumatic valve 14 and the second pneumatic valve 15 are controlled to the closed state by the pneumatic valve controller 16, and the first double-way valve 24 is opened to enter the production stage; Step 9) Scan the experimental core 12 using a nuclear magnetic resonance spectrometer, calculate the T2 spectrum and one-dimensional frequency code of the experimental core 12, calculate the CO2 effective distance and recovery rate, and evaluate the improvement of CO2 throughput performance by pulsed CO2 injection.

[0085] Figure 2 This is a schematic flowchart of an experimental method for enhancing oil recovery by high-frequency pulsed CO2 injection, as provided in the embodiments of this specification. Using the above-described experimental apparatus, the method may include: S201: Collect nuclear magnetic resonance data of the experimental core before pulse injection, and maintain the pressure of the high-pressure CO2 source at a first set value and the pressure of the low-pressure CO2 source at a second set value, wherein the first set value is greater than the second set value. S202: The pulse parameters are set by the pneumatic valve controller, and the first pneumatic valve and the second pneumatic valve are interlocked and switched instantaneously according to the set pulse parameters, so that high pressure CO2 and low pressure CO2 are output alternately, generating high frequency pressure pulses; S203: By changing the buffer chamber of different volumes and / or adjusting the opening of the throttle valve, the waveform of the high-frequency pressure pulse is adjusted, and based on the adjusted high-frequency pressure pulse, high-pressure CO2 and low-pressure CO2 are alternately injected into the clamped experimental core, and nuclear magnetic resonance data of the experimental core after pulse injection are collected. S204: Based on the nuclear magnetic resonance data of the experimental core before and after pulse injection, generate an adjustment signal to adjust the pulse parameters set by the pneumatic valve controller.

[0086] Specifically, the entire processing flow of the above experimental method can be as follows: First, initial T2 spectra and one-dimensional frequency-coded data of the experimental core were acquired using a nuclear magnetic resonance analyzer before pulse injection, serving as a benchmark for subsequent comparisons. Simultaneously, a high-pressure CO2 source and a low-pressure CO2 source were established using a dual-pressure stabilization module, maintaining the pressure at a first set value P. high Second setting value P low And P high >P low This creates a pulse pressure difference ΔP.

[0087] Then, by setting pulse parameters such as pulse frequency f and pulse duty cycle D through the pneumatic valve controller, the first pneumatic valve and the second pneumatic valve are controlled to interlock and switch instantaneously according to the set pulse parameters, so that high pressure CO2 and low pressure CO2 are output alternately, generating high-frequency pressure pulses with steep rising and falling edges.

[0088] Next, by changing the buffer chambers of different volumes and / or adjusting the opening of the throttle valve, the waveform of the high-frequency pressure pulse was adjusted to match the pulse waveform with the pore structure of the experimental core. Then, based on the adjusted high-frequency pressure pulse, high-pressure CO2 and low-pressure CO2 were alternately injected into the clamped experimental core, and nuclear magnetic resonance data after pulse injection were collected.

[0089] Finally, based on the nuclear magnetic resonance data of the experimental cores before and after pulse injection, an adjustment signal is generated to adjust the pulse parameters set by the pneumatic valve controller, thereby achieving closed-loop optimization of the pulse parameters.

[0090] By employing a complete closed-loop control process of "acquisition-injection-detection-feedback," pulse parameters can be dynamically optimized based on the actual response of the core, gradually approaching the optimal pulse combination. This significantly extends the effective CO2 recovery distance, improves the utilization of crude oil in pores of various sizes, and ultimately achieves a significant increase in CO2 huff and puff recovery in unconventional reservoirs. Furthermore, this method can match appropriate pulse waveforms and parameters to cores with different pore structures (fractured, mixed, and tight), demonstrating strong adaptability and versatility.

[0091] In some embodiments, adjusting the waveform of the high-frequency pressure pulse by changing the buffer chamber of different volumes and / or adjusting the opening of the throttle valve in S203 above may, in specific implementation, include: When the experimental core is a fractured core, no buffer chamber is installed or a buffer chamber with a volume smaller than the first volume threshold is used, so that the high-frequency pressure pulse forms a square wave pulse with steep rising and falling edges. When the experimental core is a mixed core, a buffer cavity with a volume greater than or equal to the first volume threshold and less than or equal to the second volume threshold is used to make the high-frequency pressure pulse form a trapezoidal wave pulse with a smooth rising and falling edge. When the experimental core is a dense core, a buffer cavity with a volume greater than the second volume threshold is used to make the high-frequency pressure pulse form an exponential wave pulse with slowly changing pressure. The rise and fall speeds of the high-frequency pressure pulses can be adjusted by regulating the opening of the throttle valve.

[0092] Specifically, when the experimental core is a fractured core, no buffer chamber is installed or a volume smaller than the first volume threshold (e.g., V) is used. th1 A buffer chamber (approximately 1 mL) is used to generate square wave pulses with steep rising and falling edges for the high-frequency pressure pulses. The principle behind this is: without the buffer chamber, after the pneumatic valve opens, high-pressure or low-pressure CO2 directly enters the core holder through the pipeline. Due to the very small pipeline volume, the pressure increases rapidly from P in an extremely short time (milliseconds). low Jump to P high Or from P high Jump to Plow This forms an approximately ideal square wave pulse. Fractured cores are characterized by well-developed fractures and a dense matrix, with crude oil primarily located on the fracture surface. The square wave pulse has steep rising and falling edges, generating instantaneous pressure shocks that rapidly strip away the oil film from the fracture surface, causing the crude oil to detach and flow with CO2.

[0093] When the experimental core is a mixed-type core, a volume greater than or equal to the first volume threshold and less than or equal to the second volume threshold (e.g., V) is used. th2 A buffer chamber (approximately 10 mL) is used to create a trapezoidal wave pulse with gentle rising and falling edges for the high-frequency pressure pulse. The principle is as follows: After installing a medium-volume buffer chamber, when the pneumatic valve opens, CO2 first enters the buffer chamber. Due to the buffer chamber's volume, the pressure inside does not build up instantaneously but gradually increases before being output, making the originally steep rising edge gentler, forming a trapezoidal wave. Mixed core samples are characterized by the coexistence of fractures and matrix, requiring both the stripping of oil films from the fracture surface and the driving of CO2 into the matrix pores. The trapezoidal wave pulse has a certain slope on both the rising and falling edges, resulting in a moderate impact effect. This provides sufficient impact stripping to the fracture surface without causing excessive impact that would prevent CO2 from flowing along the fractures and entering the matrix.

[0094] When the experimental core is a dense core, a buffer chamber with a volume greater than the second volume threshold is used to generate exponential wave pulses with slowly changing pressure from the high-frequency pressure pulses. The principle behind this is that after installing a large-volume buffer chamber, the filling time constant is very large, resulting in a very slow pressure rise that exhibits an exponential growth trend, forming an exponential wave. Dense cores are characterized by well-developed micropores and narrow pore throats, making it difficult for CO2 to enter. The exponential wave pulses experience a slow pressure rise and fall, resulting in a weaker impact effect, but the pressure change is gradual, which facilitates the slow diffusion of CO2 into the micropores and avoids the problem of CO2 being unable to enter the micropores due to excessively rapid pressure impact.

[0095] By adjusting the opening of the throttle valve, the rise and fall rates of the high-frequency pressure pulse can be fine-tuned. The throttle valve limits the instantaneous flow rate of CO2 by changing the flow cross-sectional area: the larger the throttle valve opening, the larger the instantaneous flow rate and the faster the pressure change rate; the smaller the throttle valve opening, the smaller the instantaneous flow rate and the slower the pressure change rate. Adjusting the throttle valve allows for further fine control of the pressure change rate based on the waveform determined by the buffer chamber, to adapt to the specific needs of different core samples.

[0096] By selecting different waveforms for cores with different pore structures, the impact intensity and pressure change rate of the pulse waveform can be matched with the pore characteristics of the core, thereby giving full play to the physical effects of various pulse waveforms and maximizing the oil displacement effect.

[0097] In some embodiments, the nuclear magnetic resonance data in S204 above may include T2 spectrum and one-dimensional frequency encoded data; correspondingly, the generation of the adjustment signal for adjusting the pulse parameters set by the pneumatic valve controller based on the nuclear magnetic resonance data of the experimental core before and after pulse injection in S204 may, in specific implementation, include: The effective CO2 reception distance is calculated based on the one-dimensional frequency encoding data before and after pulse injection. Based on the T2 spectrum before and after pulse injection, the recovery rates of small pores, medium and small pores, and large pores are calculated according to the relaxation time partition. The effective CO2 recovery distance, micropore recovery rate, medium-small pore recovery rate and macropore recovery rate are compared with their respective preset thresholds. When any of the indicators is lower than its corresponding preset threshold, an adjustment signal corresponding to the indicator is generated. Based on the generated adjustment signal, adjust at least one of the pulse parameters set by the pneumatic valve controller.

[0098] Specifically, the effective CO2 reception distance is calculated based on the one-dimensional frequency encoded data before and after pulse injection. More specifically, the peak point at the end of the inclined transition zone is determined as the crack surface location L based on the one-dimensional frequency encoded data before pulse injection. fracture Based on the one-dimensional frequency-encoded data after pulse injection, the location where the oil saturation first exceeds the preset saturation threshold (98%) from the fracture surface into the core was determined as the CO2 front location L. frontier CO2 effective effective distance L front That is, the position L of the CO2 leading edge. frontier Location L of the crack surface fracture The difference is calculated using the formula: L front =L frontier -L fracture , where L front L represents the effective CO2 penetration distance, reflecting the effective propagation depth of CO2 within the core. frontier This is the CO2 front position, i.e., the position where the oil saturation first exceeds the preset saturation threshold; L fracture This represents the location of the fracture surface, specifically the peak point at the end of the over-dipping zone. The formula for calculating the oil saturation at a point in the core after a single production run is: (S1-S...) ３ ) / (S １ -S2)×100%, where S1 is the signal amplitude at this point in the saturated oil core, S2 is the signal amplitude at this point in the dry core, and S3 is the signal amplitude at this point after one production.

[0099] Based on the T2 spectra before and after pulse injection, the recovery rates for micropores, small-to-medium pores, and large pores were calculated according to relaxation time zones. Specifically, regions with relaxation times less than 10 ms in the T2 spectrum were defined as micropore regions (corresponding to nanoscale pores), regions with relaxation times between 10 ms and 100 ms were defined as small-to-medium pore regions (corresponding to micrometer-scale pores), and regions with relaxation times greater than 100 ms were defined as large pore regions (corresponding to fractures and ultra-large pores). The formulas for calculating the recovery rate of each region are as follows: R1=(Q produced,1 / Q total,1 )×100% R2=( Q produced,2 / Q total,2 )×100% R3=( Q produced,3 / Q total,3 )×100% Wherein, R1 is the recovery rate of small pores (%); R2 is the recovery rate of medium and small pores (%); R3 is the recovery rate of large pores (%); Q total,i Q represents the total area under the T2 peak in region i before the experiment, indicating the initial oil content in that region; remaining,i Q represents the total area under the T2 peak in region i after the experiment, indicating the remaining oil content in that region; produced,i The Q value of the oil extracted from this area produced,i =Q total,i -Q remaining,i , which is the difference between the total area under the T2 spectral peak in region i before the experiment and the total area under the T2 spectral peak in region i after the experiment.

[0100] The effective effective distance of CO2 L front Compared with a preset distance threshold, when the effective effective distance L of CO2 is... front When the distance is less than a preset threshold, a first adjustment signal is generated. The micropore recovery rate R1 is compared with a preset micropore recovery rate threshold; when R1 is less than the preset micropore recovery rate threshold, a second adjustment signal is generated. The medium-small pore recovery rate R2 is compared with a preset medium-small pore recovery rate threshold; when R2 is less than the preset medium-small pore recovery rate threshold, a third adjustment signal is generated. The large pore recovery rate R3 is compared with a preset large pore recovery rate threshold; when R3 is less than the preset large pore recovery rate threshold, a fourth adjustment signal is generated.

[0101] Through the above steps, a quantitative evaluation of the pulse injection effect was achieved, and the effective CO2 receiving distance and the utilization of pores of different sizes were quantified separately. This provides a precise quantitative basis for targeted adjustment of pulse parameters and avoids the deficiency that relying solely on total recovery rate cannot distinguish the utilization of different pores.

[0102] In some embodiments, the pulse parameters include pulse frequency, pulse duty cycle, and pulse pressure difference. The pulse frequency is the alternation switching frequency of the first pneumatic valve and the second pneumatic valve. The pulse duty cycle is the ratio of the duration of the high-pressure CO2 injection phase to the pulse period within one pulse cycle. The pulse pressure difference is the difference between the pressure of the high-pressure CO2 source and the pressure of the low-pressure CO2 source. Accordingly, adjusting at least one of the pulse parameters set by the pneumatic valve controller according to the generated adjustment signal includes: Upon receiving the first adjustment signal corresponding to the effective CO2 receiving distance, increase the pulse frequency or increase the pulse voltage difference; Upon receiving the second adjustment signal corresponding to the micropore recovery rate, decrease the pulse duty cycle or increase the pulse differential pressure. Upon receiving the third adjustment signal corresponding to the recovery rate of small and medium pores, the pulse frequency is increased; Upon receiving the fourth adjustment signal corresponding to the large porosity recovery rate, increase the pulse pressure difference; When the first adjustment signal, the second adjustment signal, the third adjustment signal, and the fourth adjustment signal are received simultaneously, injection is first performed with a symmetrical pulse with a pulse frequency higher than the first frequency threshold and a high-voltage injection duration equal to the low-voltage injection duration. Then, injection is performed with an asymmetrical pulse with a pulse frequency lower than the second frequency threshold and a high-voltage injection duration shorter than the low-voltage injection duration. The first frequency threshold is greater than the second frequency threshold.

[0103] Specifically, the pulse frequency f mentioned above is the alternating switching frequency of the first and second pneumatic valves, which can range from 0.1Hz to 10Hz, or even smaller, such as from 0.01Hz to 10Hz. The specific value can be adjusted according to the actual situation, and this manual does not impose a specific limitation on it. The pulse duty cycle D is the duration T of the high-pressure CO2 injection phase within one pulse period T. high The ratio of the pulse period to the pulse period T, i.e., D=T high / T. The pulse pressure difference ΔP is the pressure P of the high-pressure CO2 source. high Pressure P of the low-pressure CO2 source low The difference, i.e., ΔP = P high -P low .

[0104] Based on the generated adjustment signal, at least one of the pulse parameters set by the pneumatic valve controller is adjusted, specifically including: Upon receiving the first adjustment signal corresponding to the effective CO2 reception distance, the pulse frequency f or the pulse pressure difference ΔP is increased. Increasing the pulse frequency f can cause the preceding and following pressure waves to superimpose inside the core to form a standing wave (when f ≥ 5Hz), thus expanding the CO2's reach. Increasing the pulse pressure difference ΔP can enhance the driving force of high-pressure injection, allowing CO2 to penetrate deeper.

[0105] Upon receiving the second adjustment signal corresponding to the recovery rate through micropores, either decrease the pulse duty cycle D or increase the pulse pressure difference ΔP. Decreasing the pulse duty cycle D (even if D < 50%) prolongs the low-pressure injection duration, making the low-pressure injection phase longer than the high-pressure injection phase. This facilitates the release of dissolved gas from the core pores and the reflux of crude oil, thereby promoting CO2 diffusion into the micropores. Increasing the pulse pressure difference ΔP enhances the throat expansion effect during high-pressure injection, helping CO2 enter the micropores.

[0106] Upon receiving the third adjustment signal corresponding to the recovery rate in small and medium-sized pores, the pulse frequency f is increased. Increasing the pulse frequency f can create a stronger standing wave effect, generating repeated pressure fluctuations that displace small and medium-sized pores, thereby increasing the utilization rate of crude oil in these pores.

[0107] Upon receiving the fourth adjustment signal corresponding to the large porosity recovery rate, the pulse pressure differential ΔP is increased. Large pores are the main channels for CO2 flow; increasing the pulse pressure differential ΔP can directly enhance the displacement velocity within the large pores, thereby increasing the recovery rate of crude oil from them.

[0108] When the first adjustment signal, the second adjustment signal, the third adjustment signal, and the fourth adjustment signal are received simultaneously, the frequency is first set to a value higher than the first frequency threshold f. th1 (For example, 1Hz; the specific value can be adjusted according to the actual situation, and this manual does not limit it) a pulse frequency and a symmetrical pulse (D=50%) with the high-pressure injection duration equal to the low-pressure injection duration, and then injected at a frequency lower than the second frequency threshold f. th2 Injection is performed using asymmetric pulses (D < 50%) with a pulse frequency of 1 Hz (e.g., high-pressure injection duration shorter than low-pressure injection duration), where the first frequency threshold is greater than the second frequency threshold. This multi-segment pulse sequence first uses high-frequency symmetric pulses (f ≥ 5 Hz, D = 50%) to form a standing wave inside the core, expanding the CO2 sweep range. Then, low-frequency asymmetric pulses (f ≤ 1 Hz, D < 50%) form a waveform of short-duration high-pressure impact and long-duration low-pressure maintenance, promoting CO2 penetration into the deeper core and diffusion into micropores, thus synergistically addressing the issues of sweep range and microscopic movement.

[0109] By using different adjustment signals corresponding to different parameter adjustment strategies, pulse parameters can be specifically optimized based on the actual response of the core sample. Multi-segment pulse sequences can collaboratively address displacement problems at different scales, achieving comprehensive optimization from macroscopic impact to microscopic dynamism.

[0110] In some embodiments, after S204 above, in a specific implementation, a (stable state determination step) may also be included: Determine whether the difference between the nuclear magnetic resonance data acquired this time and the nuclear magnetic resonance data acquired last time is less than a preset change threshold; When the difference is less than the preset change threshold, it is determined that the pulse injection effect has reached a stable state, the pulse injection is stopped and the well-closing production step is entered. When the difference is greater than or equal to a preset change threshold, it is determined that the pulse injection effect has not yet stabilized, and the steps of interlocking instantaneous switching and adjusting the high-frequency pressure pulse waveform shape are continued, or the pulse parameters are adjusted according to the current nuclear magnetic resonance data and then the steps of interlocking instantaneous switching and adjusting the high-frequency pressure pulse waveform shape are continued.

[0111] Specifically, it is determined whether the difference between the currently acquired NMR data and the previously acquired NMR data is less than a preset change threshold. Specifically, the rate of change ΔS of the total area under the T2 spectral peak between the two acquisitions can be calculated using the following formula:

[0112] Where ΔS is the rate of change (%) of the total area under the T2 spectral peak between the two acquisitions; S before S represents the total area under the T2 peak from the previous acquisition; after This represents the total area beneath the T2 peak in this spectral analysis. Alternatively, the change in the position of the CO2 leading edge in the one-dimensional frequency coding, ΔL, can be calculated using the following formula:

[0113] Among them, L before Location of the CO2 front from the last collection (unit: cm); L after ΔL represents the position of the CO2 leading edge during this sampling (unit: cm); ΔL represents the change in the position of the CO2 leading edge between the two samplings (unit: cm).

[0114] When the difference is less than a preset change threshold (i.e., ΔS < ε or ΔL < ε), it is determined that the pulse injection effect has reached a stable state, and pulse injection is stopped, entering the well-closing production step. This means that continuing injection can no longer further improve the oil displacement effect, and injection should be terminated in time to save time and experimental costs.

[0115] When the difference is greater than or equal to a preset change threshold (i.e., ΔS ≥ ε or ΔL ≥ ε), it is determined that the pulse injection effect has not yet stabilized. The steps of interlocking instantaneous switching and adjusting the high-frequency pressure pulse waveform morphology continue, or the pulse parameters are adjusted based on the current NMR data before continuing the steps of interlocking instantaneous switching and adjusting the high-frequency pressure pulse waveform morphology. This means that the injection is still producing an effect, and continued injection is needed to further propel CO2 or utilize more crude oil.

[0116] The above steps enable automatic termination of the pulse injection process, avoiding ineffective injections and improving experimental efficiency. Simultaneously, it automatically resumes injection or adjusts parameters before continuing injection if the effect is unstable, ensuring the experiment achieves optimal oil displacement.

[0117] In some embodiments, the above experimental method may further include an initialization setting step for pulse parameters.

[0118] Specifically, after acquiring nuclear magnetic resonance data from the experimental core before pulse injection, and before setting the pulse parameters through the pneumatic valve controller, the pulse frequency f, pulse duty cycle D, and pulse pressure difference ΔP can be initialized based on the basic physical properties of the experimental core.

[0119] The initial setting of the pulse frequency f can be determined based on the permeability of the experimental core. For high-permeability cores (permeability greater than or equal to 1 mD), the pulse frequency f is set in the range of 5 Hz to 10 Hz, utilizing the high-frequency pulse to create a standing wave effect inside the core and expand the reach of CO2. For medium-to-low permeability cores (permeability greater than or equal to 0.1 mD, but less than 1 mD), the pulse frequency f is set in the range of 1 Hz to 5 Hz, achieving a balance between the standing wave effect and pulse residence time. For dense cores (permeability less than 0.1 mD), the pulse frequency f is set in the range of 0.1 Hz to 1 Hz, prioritizing sufficient residence time for each pulse to allow CO2 to fully penetrate into the deeper parts of the core.

[0120] The initial setting of the pulse duty cycle D can be determined based on the pore structure of the experimental core. For cores dominated by large pores (fracture type), the pulse duty cycle D is set to 50%, making the high-pressure injection duration equal to the low-pressure injection duration, thus generating a symmetrical pulse. For cores dominated by small pores (dense type), the pulse duty cycle D is set within the range of 20% to 40%, making the high-pressure injection duration shorter than the low-pressure injection duration, forming an asymmetrical waveform of "short-term high-pressure impact and long-term low-pressure maintenance," which is beneficial for CO2 diffusion into the small pores.

[0121] The initial setting of the pulse pressure difference ΔP can be determined based on the compactness of the experimental core. For compact cores, the pulse pressure difference ΔP is set within the range of 20 MPa to 45 MPa to enhance the throat expansion effect during high-pressure injection by utilizing a larger pulse pressure difference. For non-compact cores, the pulse pressure difference ΔP is set within the range of 10 MPa to 20 MPa to avoid core sand production or unexpected fractures due to excessive pulse pressure difference.

[0122] The technical effect of the above initialization setting steps is that: by reasonably setting the initial pulse parameters according to the basic physical properties of the rock core, the number of subsequent feedback adjustments can be reduced, the experimental process can be accelerated, and the experimental efficiency can be improved.

[0123] In some embodiments, after calculating the micropore recovery rate, small-medium pore recovery rate and large pore recovery rate, the step of calculating the total recovery rate may be included.

[0124] Specifically, total recovery rate R total The calculation is based on the weighted average of the recovery rate of each zone and its corresponding T2 spectral signal quantity. The calculation formula is as follows: R total =(R1×Q total,1 +R2×Q total,2 +R3×Q total,3 ) / (Q total,1 +Q total,2 +Q total,3 ) Total recovery rate R total It is one of the core indicators for evaluating the effect of pulse injection. When R total When R is ≥8%, the pulse injection effect is considered excellent; total When the rate is between 5% and 8%, the pulse injection is considered to have a good effect; when R total If the result is less than 5%, the pulse injection effect is considered poor, and the pulse parameters need to be adjusted and the experiment repeated.

[0125] By using a weighted average method to comprehensively evaluate the recovery of pores with different diameters, a quantitative basis is provided for the overall evaluation of pulse injection effect, while avoiding the deficiency that the recovery rate of a single zone cannot reflect the overall effect.

[0126] In some embodiments, the above method may further include the step of outputting an optimal combination of pulse parameters.

[0127] Specifically, when the effective effective distance of CO2 is L frontWhen the recovery rates R1, R2, and R3 of each zone all reach the preset target values, the current pulse parameter combination set by the pneumatic valve controller is recorded, including the pulse frequency f, pulse duty cycle D, and pulse pressure difference ΔP, as the optimal pulse parameter combination for the current experimental core. The optimal pulse parameter combination is output to a display device or storage device. This optimal pulse parameter combination is then associated with and stored with the physical properties of the experimental core (including core type, permeability, and porosity) to form an experimental database. When conducting subsequent experiments on different cores, the database can be searched for matching historical optimal pulse parameter combinations based on the physical properties of the new core, serving as a reference for the initial settings.

[0128] This invention addresses the technical problems of short effective distance and low recovery rate in CO2 huff and puff technology for unconventional oil reservoirs, as well as the shortcomings of existing pulse injection methods such as uncontrollable pulse waveforms and inability to independently adjust injection parameters. It proposes an experimental device and method for high-frequency pulsed CO2 injection to enhance oil recovery. This device precisely controls three independent parameters—pulse frequency, pulse differential pressure, and pulse duty cycle—using a pneumatic valve controller to achieve asymmetric, controllable pulse waveform CO2 injection. This enhances the CO2 huff and puff diffusion mechanism, effectively increases the effective distance of CO2 huff and puff, and improves the recovery rate of unconventional oil reservoirs.

[0129] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on describing the differences from other embodiments. For details, please refer to the foregoing descriptions of the relevant processing embodiments; they will not be repeated here.

[0130] The foregoing description of this method is for illustrative purposes only and describes specific embodiments. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps described in the claims may be performed in a different order than those shown in the embodiments and still achieve the desired results. Furthermore, the processes depicted in the drawings do not necessarily require the specific or sequential order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are possible or may be advantageous.

[0131] In a specific implementation scenario, see Figure 3 As shown, Figure 3 This is a schematic diagram of the square wave pulse pressure changing over time. Figure 3 As can be seen, the pressure switches instantaneously between 9 MPa and 13 MPa, with an extremely short transition time between the rising and falling edges, exhibiting typical square wave characteristics. This waveform is achieved by not installing a buffer chamber or using a small-volume buffer chamber. By utilizing steep pressure changes to generate strong mechanical disturbances, it can effectively strip crude oil from the fracture walls, making it suitable for displacement experiments on fractured cores.

[0132] See Figure 4 As shown, Figure 4 This is a schematic diagram of the trapezoidal wave pulse pressure changing over time. Figure 4 As can be seen, the pressure changes periodically in an approximately trapezoidal wave shape: the pressure rise and fall phases have a certain linear transition slope, the rise time and fall time are basically symmetrical, and the pressure in the plateau section is stable at two set values ​​of 13 MPa and 9 MPa. This waveform is achieved by using a medium-volume buffer chamber in conjunction with an adjustable flow valve. The pressure change maintains a sufficient gradient to drive CO2 infiltration into the core matrix, while avoiding the damage caused by the instantaneous impact of square wave pulses to fractured cores. It is suitable for displacement experiments of mixed cores.

[0133] See Figure 5 As shown, Figure 5 This is a schematic diagram of the pressure change over time in an exponential wave pulse. Figure 5 As can be seen, the pressure rises exponentially and falls exponentially, with no obvious linear transition. The pressure plateaus stabilize at two set values: 13 MPa and 9 MPa. This waveform is achieved through a large-volume buffer chamber and an adjustable flow valve, resulting in smooth pressure changes. This prevents CO2 from channeling through dense cores and promotes the slow permeation of CO2 into the micropores, making it suitable for displacement experiments on dense cores.

[0134] See Figure 6 As shown, Figure 6 This is a schematic diagram of the T2 spectrum of the core and the distribution of crude oil in each region. Figure 6 The horizontal axis represents relaxation time T2 (unit: ms), and the vertical axis represents the nuclear magnetic resonance signal amplitude. The curves include the T2 spectra of saturated oil cores, post-production cores, and dry cores. The shaded areas visually distinguish the produced oil signal, the remaining oil signal, and the background signal of the dry core.

[0135] Based on the relaxation time distribution, the T2 spectrum can be divided into three regions: a short relaxation region (T2 < 10 ms, corresponding to the micropore region), a medium relaxation region (10 ms ≤ T2 ≤ 100 ms, corresponding to the small to medium pore region), and a long relaxation region (T2 > 100 ms, corresponding to the large pore region). This invention, by comparing the signal amplitude changes in each region before and after the experiment, can calculate the recovery rate of different pore regions, providing a quantitative basis for evaluating the mobilization effect of pulse injection on pores of different sizes.

[0136] See Figure 7 As shown, Figure 7 This is a schematic diagram showing the comparison of T2 spectra of core samples under different injection conditions. Figure 7The horizontal axis represents relaxation time T2 (unit: ms), and the vertical axis represents the nuclear magnetic resonance signal amplitude. The curves correspond to the T2 spectrum distributions of saturated oil cores, 9MPa static injection, 13MPa static injection, 13-9MPa / 1 / 60Hz pulse injection, and dry cores, respectively. Figure 7 It is evident that under static injection conditions, the signal amplitude decrease in each region of the T2 spectrum is limited, especially in the short relaxation region (T2 < 10 ms), where the signal change is weak, indicating a low utilization rate of crude oil in micropores. However, after adopting the pulse injection method described in this invention, the signal amplitude in the entire T2 spectrum decreases significantly, with the decrease in the short relaxation region being significantly greater than that under static injection conditions. This demonstrates that high-frequency pulse injection can effectively drive crude oil in micropores and significantly improve the overall recovery rate of unconventional reservoirs.

[0137] Figure 8 A schematic diagram of the effective distance under different CO2 injection modes. Figure 8 The horizontal axis represents the distance along the core axis (unit: mm), and the vertical axis represents the nuclear magnetic resonance signal amplitude. The curves correspond to the signal distribution of saturated oil cores, 9MPa static injection for 4 hours, 13MPa static injection for 4 hours, 13-9MPa / 1 / 60Hz pulse injection, and dry cores, respectively. Figure 8 As can be seen, the signal amplitude of the dry core is extremely low, serving as a reference for an oil-free background. The signal amplitude of the saturated oil core is generally higher, representing the initial baseline state. Under static injection conditions, the effective CO2 reception distance increases slightly with increasing injection pressure. However, after using the 13-9 MPa / 1 / 60 Hz pulse injection of this invention, the signal amplitude at the core end decreases more significantly, and the effective CO2 reception distance is significantly longer than under static injection conditions. This demonstrates that high-frequency pulse injection can effectively promote CO2 penetration into the deep matrix of the core and significantly extend the effective reception distance. Figure 8 By comparing the signal attenuation positions at the ends of different curves, the technical advantages of the pulse injection method of this invention in enhancing CO2 mass transfer are intuitively demonstrated.

[0138] While this specification provides the steps of operation for the methods described in the embodiments or flowcharts, more or fewer steps may be included based on conventional or non-inventive means. The order of steps listed in the embodiments is merely one possible order of execution among many steps and does not represent the only possible order. In actual device or client product execution, the methods shown in the embodiments or drawings may be executed sequentially or in parallel (e.g., in a parallel processor or multi-threaded processing environment, or even a distributed data processing environment). The terms "comprising," "including," or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, product, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, product, or apparatus. Without further limitations, the presence of other identical or equivalent elements in a process, method, product, or apparatus that includes said elements is not excluded. The terms "first," "second," etc., are used to denote names and do not indicate any particular order.

[0139] Those skilled in the art will also know that, besides implementing the controller using purely computer-readable program code, the same functions can be achieved by logically programming the method steps, making the controller function as logic gates, switches, application-specific integrated circuits (ASICs), programmable logic controllers (PLCs), and embedded microcontrollers. Therefore, such a controller can be considered a hardware component, and the devices within it used to implement various functions can also be considered structures within that hardware component. Alternatively, the devices used to implement various functions can be considered as both software modules implementing the method and structures within a hardware component.

[0140] This specification can be described in the general context of computer-executable instructions that are executed by a computer, such as program modules. Generally, program modules include routines, programs, objects, components, data structures, classes, etc., that perform a specific task or implement a specific abstract data type. This specification can also be practiced in distributed computing environments, where tasks are performed by remote processing devices connected via a communication network. In distributed computing environments, program modules can reside in local and remote computer storage media, including storage devices.

[0141] As can be seen from the above description of the embodiments, those skilled in the art can clearly understand that this specification can be implemented by means of software plus necessary general-purpose hardware platforms. Based on this understanding, the technical solutions of this specification can essentially be embodied in the form of a software product. This computer software product can be stored in a storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, mobile terminal, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments of this specification.

[0142] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on its differences from other embodiments. This specification can be used in numerous general-purpose or special-purpose computer system environments or configurations. Examples include: personal computers, server computers, handheld or portable devices, tablet devices, multiprocessor systems, microprocessor-based systems, set-top boxes, programmable electronic devices, network PCs, minicomputers, mainframe computers, and distributed computing environments including any of the above systems or devices, etc.

[0143] Although this specification has been described by way of examples, those skilled in the art will recognize that many variations of this specification are possible without departing from its spirit, and it is intended that the appended claims cover such variations without departing from the spirit of this specification.

Claims

1. An experimental apparatus for enhancing oil recovery by high-frequency pulsed CO2 injection, characterized in that, include: High-frequency pulse injection module, pulse waveform adjustment module, and nuclear magnetic resonance module; The high-frequency pulse injection module includes a first pneumatic valve, a second pneumatic valve, and a pneumatic valve controller. The inlet of the first pneumatic valve is connected to a high-pressure CO2 source, and the inlet of the second pneumatic valve is connected to a low-pressure CO2 source. The outlets of the first and second pneumatic valves are connected in parallel to form a common output terminal. The pneumatic valve controller is electrically connected to the control terminals of the first and second pneumatic valves and is used to control the first and second pneumatic valves to interlock and switch instantaneously according to the set pulse parameters, so that high-pressure CO2 and low-pressure CO2 are output alternately to generate high-frequency pressure pulses. The pressure value of the high-pressure CO2 is a first set value, and the pressure value of the low-pressure CO2 is a second set value. The first set value is greater than the second set value. The pulse waveform adjustment module is connected in series between the common output terminal and the input terminal of the nuclear magnetic resonance module, and is used to adjust the waveform shape of the high-frequency pressure pulse. The nuclear magnetic resonance module is used to inject high-pressure CO2 and low-pressure CO2 alternately into the experimental core based on the adjusted high-frequency pressure pulse, and to collect nuclear magnetic resonance data of the experimental core before and after pulse injection, and generate an adjustment signal to adjust the pulse parameters.

2. The experimental apparatus according to claim 1, characterized in that, The experimental setup also includes a dual-voltage stabilization module, which comprises a high-voltage stabilization module and a low-voltage stabilization module. The high-pressure stabilization module includes a plunger pump connected to a high-pressure CO2 source. The plunger pump operates continuously in a constant-pressure mode to maintain the pressure of the high-pressure CO2 source at a first set value. The pressure compensation response cycle of the plunger pump is no greater than one-tenth of the switching cycle of the first pneumatic valve and the second pneumatic valve. The low-pressure stabilization module includes a second back pressure valve and a second hand-cranked pump connected to a low-pressure CO2 source, used to maintain the pressure of the low-pressure CO2 source at a second set value.

3. The experimental apparatus according to claim 1, characterized in that, The pneumatic valve controller is also equipped with an interlock logic circuit, which ensures that at most one of the first and second pneumatic valves is open at any given time, and that the dead time when both pneumatic valves are closed is less than the pulse period.

4. The experimental apparatus according to claim 1, characterized in that, The pulse waveform adjustment module includes a buffer chamber and / or a throttle valve. The buffer chamber is used to attenuate the steepness of the rising and / or falling edges of the high-frequency pressure pulse. The throttle valve is used to limit the instantaneous flow rate of CO2. The pulse waveform adjustment module is used to adjust the waveform shape of the high-frequency pressure pulse by changing the buffer chamber of different volumes and / or adjusting the opening of the throttle valve.

5. The experimental apparatus according to claim 1, characterized in that, The nuclear magnetic resonance module includes a core holder and a nuclear magnetic resonance analyzer. The input end of the core holder is connected to the output end of the pulse waveform adjustment module, which is used to hold the experimental core and receive the adjusted high-frequency pressure pulse. The detection chamber of the nuclear magnetic resonance analyzer accommodates the core holder and is used to collect the T2 spectrum and one-dimensional frequency encoded data of the experimental core before and after pulse injection. The nuclear magnetic resonance module also includes a feedback control unit, which is electrically connected to the nuclear magnetic resonance analyzer and the pneumatic valve controller, respectively, and is used to generate the adjustment signal based on the T2 spectrum and one-dimensional frequency encoding data.

6. An experimental method for enhancing oil recovery by high-frequency pulsed CO2 injection, characterized in that, The method, using the experimental apparatus according to any one of claims 1-5, comprises: Nuclear magnetic resonance data of the experimental core were collected before pulse injection, and the pressure of the high-pressure CO2 source was maintained at a first set value, and the pressure of the low-pressure CO2 source was maintained at a second set value, wherein the first set value was greater than the second set value. By setting pulse parameters through the pneumatic valve controller, the first pneumatic valve and the second pneumatic valve are controlled to switch interlocked instantaneously according to the set pulse parameters, so that high-pressure CO2 and low-pressure CO2 are output alternately, generating high-frequency pressure pulses; By changing the buffer chamber of different volumes and / or adjusting the opening of the throttle valve, the waveform of the high-frequency pressure pulse is adjusted, and based on the adjusted high-frequency pressure pulse, high-pressure CO2 and low-pressure CO2 are alternately injected into the experimental core, and nuclear magnetic resonance data of the experimental core are collected after pulse injection. Based on the nuclear magnetic resonance data of the experimental cores before and after pulse injection, an adjustment signal is generated to adjust the pulse parameters set by the pneumatic valve controller.

7. The experimental method according to claim 6, characterized in that, The method of adjusting the waveform of the high-frequency pressure pulse by changing the buffer chamber of different volumes and / or adjusting the opening of the throttle valve includes: When the experimental core is a fractured core, no buffer chamber is installed or a buffer chamber with a volume smaller than the first volume threshold is used, so that the high-frequency pressure pulse forms a square wave pulse with steep rising and falling edges. When the experimental core is a mixed core, a buffer cavity with a volume greater than or equal to the first volume threshold and less than or equal to the second volume threshold is used to make the high-frequency pressure pulse form a trapezoidal wave pulse with a smooth rising and falling edge. When the experimental core is a dense core, a buffer cavity with a volume greater than the second volume threshold is used to make the high-frequency pressure pulse form an exponential wave pulse with slowly changing pressure. The rise and fall speeds of the high-frequency pressure pulses can be adjusted by regulating the opening of the throttle valve.

8. The experimental method according to claim 6, characterized in that, The nuclear magnetic resonance data includes T2 spectra and one-dimensional frequency-coded data; correspondingly, the step of generating an adjustment signal to adjust the pulse parameters set by the pneumatic valve controller based on the nuclear magnetic resonance data of the experimental core before and after pulse injection includes: The effective CO2 reception distance is calculated based on the one-dimensional frequency encoding data before and after pulse injection. Based on the T2 spectrum before and after pulse injection, the recovery rates of small pores, medium and small pores, and large pores are calculated according to the relaxation time partition. The effective CO2 recovery distance, micropore recovery rate, medium-small pore recovery rate and macropore recovery rate are compared with their respective preset thresholds. When any of the indicators is lower than its corresponding preset threshold, an adjustment signal corresponding to the indicator is generated. Based on the generated adjustment signal, adjust at least one of the pulse parameters set by the pneumatic valve controller.

9. The experimental method according to claim 8, characterized in that, The pulse parameters include pulse frequency, pulse duty cycle, and pulse pressure difference. The pulse frequency is the alternation switching frequency of the first pneumatic valve and the second pneumatic valve. The pulse duty cycle is the ratio of the duration of the high-pressure CO2 injection phase to the pulse cycle within one pulse cycle. The pulse pressure difference is the difference between the pressure of the high-pressure CO2 source and the pressure of the low-pressure CO2 source. Accordingly, adjusting at least one of the pulse parameters set by the pneumatic valve controller according to the generated adjustment signal includes: Upon receiving the first adjustment signal corresponding to the effective CO2 receiving distance, increase the pulse frequency or increase the pulse voltage difference; Upon receiving the second adjustment signal corresponding to the micropore recovery rate, decrease the pulse duty cycle or increase the pulse differential pressure. Upon receiving the third adjustment signal corresponding to the recovery rate of small and medium pores, the pulse frequency is increased; Upon receiving the fourth adjustment signal corresponding to the large porosity recovery rate, increase the pulse pressure difference; When the first adjustment signal, the second adjustment signal, the third adjustment signal, and the fourth adjustment signal are received simultaneously, injection is first performed with a symmetrical pulse with a pulse frequency higher than the first frequency threshold and a high-voltage injection duration equal to the low-voltage injection duration. Then, injection is performed with an asymmetrical pulse with a pulse frequency lower than the second frequency threshold and a high-voltage injection duration shorter than the low-voltage injection duration. The first frequency threshold is greater than the second frequency threshold.

10. The experimental method according to claim 6, characterized in that, The method further includes: Determine whether the difference between the nuclear magnetic resonance data acquired this time and the nuclear magnetic resonance data acquired last time is less than a preset change threshold; When the difference is less than a preset change threshold, it is determined that the pulse injection effect has reached a stable state, the pulse injection is stopped and the well is shut down for production. When the difference is greater than or equal to a preset change threshold, it is determined that the pulse injection effect has not yet stabilized, and the steps of interlocking instantaneous switching and adjusting the high-frequency pressure pulse waveform shape are continued, or the pulse parameters are adjusted according to the current nuclear magnetic resonance data and then the steps of interlocking instantaneous switching and adjusting the high-frequency pressure pulse waveform shape are continued.

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