An online nuclear magnetic physical simulation experiment system and method for reservoir large liquid volume energy supplement

Abstract

The application discloses an oil reservoir large-liquid-volume energy supplementing on-line nuclear magnetic physical simulation experiment system and method, which comprises a displacement pump, an intermediate container, a nuclear magnetic resonance test module and a manual pump which are connected in sequence, the intermediate container is used for storing injection medium, and the nuclear magnetic resonance test module is used for placing a processed target core; the displacement pump is used for controlling the inlet pressure of the inlet end of the nuclear magnetic resonance test module, and driving the injection medium to be injected into the target core under different injection liquid volume conditions; the manual pump is used for controlling the back pressure of the outlet end of the nuclear magnetic resonance test module; and the nuclear magnetic resonance test module is used for testing the nuclear magnetic resonance T2 spectrum and layered T2 spectrum of the target core under different injection liquid volume conditions. The application can realize real-time, efficient and nondestructive nuclear magnetic resonance test on the target core in the displacement process, and can intuitively and quantitatively study the dynamic change characteristics of the micro-pore structure and the permeability under different injection liquid volume conditions based on the system.

Description

Technical Field

[0001] This invention relates to the field of petroleum development technology, and in particular to an online nuclear magnetic resonance physics simulation experimental system and method for large-volume energy replenishment in oil reservoirs. Background Technology

[0002] Tight / shale oil reservoirs refer to oil reservoirs with extremely low permeability, mainly existing in tight sandstone or shale. Their post-fracture depletion development is characterized by high initial production and rapid decay rates. Conventional methods of water and gas injection to replenish energy are insufficient to establish an effective pressure displacement system, limiting the production enhancement effect. Large-scale fluid injection can effectively replenish and maintain formation energy, and is a key technology for improving oil recovery.

[0003] Current technologies often employ indoor physical simulation experiments to model large-volume fluid replenishment. However, existing techniques combine conventional displacement physical simulation experiments with offline low-field nuclear magnetic resonance (NMR) technology to simulate the fluid injection process. This method requires frequent core sampling for NMR testing, which is susceptible to unpredictable factors such as changes in pore structure and oil saturation caused by core stress release, affecting the experimental results. Furthermore, this method only observes two states: before and after the experiment, failing to achieve continuous, real-time dynamic monitoring throughout the entire process. This can lead to discrepancies between the experimental results and the actual dynamic process of the injected fluid. In short, existing physical simulation experiments cannot perform real-time, efficient, and non-destructive NMR testing of cores, nor can they provide a direct and quantitative study of the dynamic changes in micropore structure and permeability under different injection volumes. Consequently, they cannot provide a reference for developing reasonable development strategies and formulating production work procedures on-site.

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

[0005] This specification provides an online nuclear magnetic resonance (NMR) physical simulation experimental system and method for large-volume fluid replenishment in oil reservoirs. This system addresses the problem that existing technologies cannot perform real-time, efficient, and non-destructive NMR testing on core samples, and cannot intuitively and quantitatively study the dynamic changes in micropore structure and permeability under different fluid injection conditions.

[0006] Firstly, this specification provides an online nuclear magnetic resonance physics simulation experimental system for large-volume energy replenishment in oil reservoirs, comprising:

[0007] The system consists of a displacement pump, an intermediate container, a nuclear magnetic resonance (NMR) testing module, and a manual pump connected in sequence. The intermediate container stores the injection medium, and the NMR testing module holds the processed target core.

[0008] The displacement pump is used to control the inlet pressure at the inlet end of the nuclear magnetic resonance testing module and drive the injection medium to inject into the target core according to different injection volume conditions. The manual pump is used to control the back pressure at the outlet end of the nuclear magnetic resonance testing module. The nuclear magnetic resonance testing module is used to test the nuclear magnetic resonance T2 spectrum and layered T2 spectrum of the target core under different injection volume conditions.

[0009] In some embodiments, the nuclear magnetic resonance testing module is further connected to a nuclear magnetic resonance data acquisition module, which is used to acquire the nuclear magnetic resonance T2 spectrum and layered T2 spectrum of the target core under different injection volume conditions, as well as the volume change of the displacement pump.

[0010] In some embodiments, the displacement pump is sequentially connected via pipeline to a first pressure sensor, a first valve, an intermediate container, a second valve, a second pressure sensor, and a nuclear magnetic resonance testing module. The first pressure sensor is used to monitor whether the pressure in the pipeline is equal to the inlet pressure set in the displacement pump. The second pressure sensor is used to monitor whether the injection pressure of the injected medium is equal to the inlet pressure set in the displacement pump. The first valve is used to control the displacement pump to drive, and the second valve is used to control the injection of the injected medium into the target core.

[0011] In some embodiments, the nuclear magnetic resonance testing module is also connected to a third valve and a confining pressure providing module. The confining pressure providing module is used to provide a confining pressure greater than the inlet pressure to the target core, and the third valve is used to control the confining pressure providing module to provide the confining pressure.

[0012] In some embodiments, the nuclear magnetic resonance testing module is further connected in sequence to a fourth valve, a third pressure sensor, a back pressure valve, a fourth pressure sensor, and a manual pump via pipelines. The manual pump is also used to set the back pressure of the back pressure valve. The back pressure valve is used to control whether the injected medium flows out. The third pressure sensor is used to monitor whether the pressure in the pipeline at the outlet end of the nuclear magnetic resonance testing module is greater than the back pressure of the back pressure valve. The fourth pressure sensor is used to monitor whether the back pressure of the back pressure valve is equal to the back pressure set by the manual pump. The fourth valve is used to control the back pressure valve to control the flow of the injected medium.

[0013] Secondly, the embodiments of this specification also provide a method for online nuclear magnetic resonance physics simulation of large-volume oil reservoir energy replenishment. Based on the above-mentioned system, the method includes:

[0014] The core samples after oil and salt washing were processed to obtain the target core samples;

[0015] Increase the inlet pressure at the inlet of the nuclear magnetic resonance test module in the displacement pump, and simultaneously increase the back pressure at the outlet of the nuclear magnetic resonance test module in the manual pump. Use the nuclear magnetic resonance test module to test the nuclear magnetic resonance T2 spectrum and layered T2 spectrum of the target core without pressure difference, and use the nuclear magnetic resonance data acquisition module to acquire the nuclear magnetic resonance T2 spectrum and layered T2 spectrum of the target core without pressure difference.

[0016] Continue to increase the inlet pressure at the inlet of the nuclear magnetic resonance (NMR) test module in the displacement pump, and then increase the back pressure at the outlet of the NMR test module in the manual pump according to the preset pressure difference. Use the NMR test module to test the NMR T2 spectrum and layered T2 spectrum of the target core under different injection times at different inlet pressures, and record the volume change of the displacement pump under different injection times at different inlet pressures. At the same time, use the NMR data acquisition module to collect the NMR T2 spectrum and layered T2 spectrum of the target core under different injection times at different inlet pressures.

[0017] In some embodiments, the process of treating the core after oil and salt washing to obtain the target core includes:

[0018] The core samples were dried after being washed with oil and salt to obtain dry core samples.

[0019] A vacuum pump is used to evacuate the dry core sample, and then simulated formation water is injected to saturate it, resulting in a core saturated with water.

[0020] Simulated oil was injected into the core saturated water sample until no more water was produced from the outlet of the core saturated water sample, thus obtaining a core saturated oil sample, which was used as the target core.

[0021] In some embodiments, the method further includes:

[0022] A predetermined number of injection volume test points are designed on the target core, and a confining pressure supply module is used to provide a confining pressure to the target core that is greater than the inlet pressure.

[0023] In some embodiments, the method further includes:

[0024] Based on the nuclear magnetic resonance T2 spectra of the liquid injection at different inlet pressures or injection times without differential pressure, different pore sizes are classified.

[0025] Determine the area of ​​the first spectral line corresponding to the target pore size under different pore sizes without differential pressure, and the area of ​​the second spectral line corresponding to the target pore size under liquid injection at the target injection time;

[0026] Based on the difference between the area of ​​the first spectral line and the area of ​​the second spectral line, the spectral line change values ​​under different injection times at each inlet pressure are determined.

[0027] The total spectral area corresponding to the nuclear magnetic resonance T2 spectrum without pressure difference is determined. Based on the ratio of the spectral line change value to the total spectral line area, the dynamic change characteristics of the micropore structure under the target aperture at the target injection time are determined.

[0028] In some embodiments, the method further includes:

[0029] Based on the change in displacement pump volume at different injection times under various inlet pressures, the dynamic characteristics of permeability change at different injection times under various inlet pressures are determined.

[0030] This specification provides an online nuclear magnetic resonance (NMR) simulation system for large-volume reservoir recharge, comprising: a displacement pump, an intermediate container, an NMR testing module, and a manual pump connected in sequence. The intermediate container stores the injection medium, and the NMR testing module holds the processed target core. The displacement pump controls the inlet pressure at the inlet of the NMR testing module and drives the injection medium to inject into the target core according to different injection volume conditions. The manual pump controls the back pressure at the outlet of the NMR testing module. The NMR testing module is used to test the NMR T2 spectrum and layered T2 spectrum of the target core under different injection volume conditions. This online NMR simulation system eliminates the need for frequent core removal for NMR testing, avoiding the impact of frequent core removal on experimental results due to stress release, changes in pore structure, and variations in oil saturation. The nuclear magnetic resonance (NMR) testing module can continuously and dynamically monitor the energy replenishment process of simulated oil injection under different injection volume conditions. The NMR data acquisition module can also collect the NMR T2 spectrum and layered T2 spectrum of the target core under different injection volume conditions in a timely manner, thus providing a data basis for subsequent quantitative analysis of the dynamic changes in micropore structure and permeability during the injection process.

[0031] This specification provides an online nuclear magnetic resonance (NMR) physical simulation experiment method for large-volume energy replenishment in oil reservoirs, comprising: processing the core after oil and salt washing to obtain the target core; increasing the inlet pressure at the inlet end of the NMR testing module in the displacement pump, and simultaneously increasing the back pressure at the outlet end of the NMR testing module in the manual pump; using the NMR testing module to test the NMR T2 spectrum and layered T2 spectrum of the target core without pressure difference; and simultaneously using the NMR data acquisition module to acquire the NMR T2 spectrum and layered T2 spectrum of the target core without pressure difference. The inlet pressure of the nuclear magnetic resonance (NMR) testing module in the displacement pump is continuously increased, and the back pressure of the NMR testing module in the manual pump is increased according to the preset pressure difference. The NMR testing module is used to test the NMR T2 spectrum and layered T2 spectrum of the target core at different injection times under various inlet pressures. The volume change of the displacement pump at different injection times under various inlet pressures is recorded. Simultaneously, the NMR data acquisition module is used to collect the NMR T2 spectrum and layered T2 spectrum of the target core at different injection times under various inlet pressures. Through the above-described online NMR physical simulation experiment method for large-volume reservoir injection, the dynamic changes in micropore structure and permeability during large-volume fluid injection can be accurately characterized. This provides a reference for designing reasonable injection volumes and development strategies in oilfields, aiming to achieve effective utilization of tight / shale reservoirs. Attached Figure Description

[0032] 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:

[0033] Figure 1 This is a schematic diagram of the structure of an online nuclear magnetic resonance physics simulation experimental system for large-volume energy replenishment in oil reservoirs, provided in the embodiments of this specification.

[0034] Figure 2 This is a schematic flowchart of an online nuclear magnetic resonance physics simulation experiment method for large-volume energy replenishment in oil reservoirs, provided in the embodiments of this specification.

[0035] Figure 3 This is the nuclear magnetic resonance T2 spectrum of the dynamic change in injection volume provided in the embodiments of this specification;

[0036] Figure 4 This is a quantitative analysis diagram of the dynamic changes in the micropore structure provided in the embodiments of this specification;

[0037] Figure 5These are the pseudo-permeability curves corresponding to each injection volume provided in the embodiments of this specification;

[0038] Figure 6 This is a T2 spectrum imaging of fluid transport in a large volume of injected fluid, as provided in the embodiments of this specification.

[0039] [Explanation of Labels in the Attached Image]

[0040] 0. Pipeline; 01. First pressure sensor; 02. First valve; 03. Second valve; 04. Second pressure sensor; 05. Third valve; 06. Fourth valve; 07. Third pressure sensor; 08. Fourth pressure sensor; 1. Displacement pump; 2. Intermediate container; 21. Injection medium; 3. Nuclear magnetic resonance testing module; 31. Target core; 4. Manual pump; 5. Nuclear magnetic resonance data acquisition module; 6. Confining pressure supply module; 61. Confining pressure control; 62. Fluorine oil; 7. Back pressure valve; 8. Liquid collection device. Detailed Implementation

[0041] 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.

[0042] As mentioned above, tight / shale oil reservoirs have poor physical properties, narrow pore throats, and extremely low permeability. Generally, production wells have no natural production capacity or their natural production capacity is below the lower limit of industrial oil flow. Currently, the development method combining horizontal wells and volumetric fracturing has achieved initial activation of tight / shale oil reservoirs. However, post-fracturing depletion-type development is characterized by high initial production and rapid decay rates. Conventional water and gas injection methods are insufficient to establish an effective pressure displacement system, limiting the production enhancement effect. Large-scale fluid injection can effectively replenish and maintain formation energy, and is a key enhanced oil recovery technology. Current research on large-volume fluid replenishment focuses on establishing a qualitative relationship between injection volume and oil displacement efficiency, a qualitative description of the oil displacement mechanism, and the establishment of analytical models. However, the impact of large-scale fluid injection on the reservoir's microstructure and permeability remains unclear, and relevant reference data are lacking. Therefore, accurately simulating large-volume fluid replenishment using indoor physical simulation experiments and studying the changes in microstructure and permeability during this process is of great significance for revealing the fluid seepage mechanism and evaluating the recovery effect.

[0043] For physical simulation experiments, the most common approach is to combine conventional displacement physics simulation experiments with offline low-field nuclear magnetic resonance (NMR) technology to simulate the injected fluid process. However, this method requires frequent core sampling for NMR testing, which can be affected by uncertainties such as changes in pore structure and oil saturation caused by core stress release. Furthermore, this method can only observe two states: before and after the experiment, and cannot achieve continuous, real-time dynamic monitoring of the entire experimental process. This may lead to discrepancies between the experimental results and the dynamic process of the injected fluid.

[0044] Currently, there is no online nuclear magnetic resonance physics simulation experimental method for the large-volume fluid replenishment process in tight / shale reservoirs, and there is a lack of theoretical understanding of the dynamic evolution of reservoir parameters after large-scale fluid injection.

[0045] To address the aforementioned issues, this specification provides an online nuclear magnetic resonance (NMR) physical simulation experimental system and method for large-volume fluid replenishment in oil reservoirs. This system can perform NMR testing on core samples in real time, efficiently, and non-destructively, allowing for intuitive and quantitative study of the dynamic changes in micropore structure and permeability under different fluid injection conditions. This provides a reference for developing reasonable development strategies and formulating production work procedures on-site.

[0046] It should be noted that the embodiments in this specification provide an online nuclear magnetic resonance physics simulation experimental system and method for large-volume energy replenishment in oil reservoirs, and the oil reservoirs involved specifically refer to tight / shale oil reservoirs.

[0047] See Figure 1 As shown in the embodiments of this specification, an online nuclear magnetic resonance physics simulation experimental system for large-volume fluid replenishment in oil reservoirs is provided. This system may include:

[0048] The displacement pump 1, intermediate container 2, nuclear magnetic resonance testing module 3, and manual pump 4 are connected in sequence. The intermediate container 2 stores the injection medium 21, and the nuclear magnetic resonance testing module 3 holds the processed target core 31.

[0049] The displacement pump 1 can be used to control the inlet pressure at the inlet end of the nuclear magnetic resonance test module 3 and drive the injection medium 21 to inject into the target core 31 according to different injection volume conditions. The manual pump 4 can be used to control the back pressure at the outlet end of the nuclear magnetic resonance test module 3. The nuclear magnetic resonance test module 3 can be used to test the nuclear magnetic resonance T2 spectrum and layered T2 spectrum of the target core 31 under different injection volume conditions.

[0050] In some embodiments, the displacement pump 1 and the manual pump 4 can work together to generate different flow pressure gradient conditions, and the nuclear magnetic resonance testing module 3 can also be used to test the nuclear magnetic resonance T2 spectrum and layered T2 spectrum of the target core 31 under different flow pressure gradient conditions.

[0051] In some embodiments, the above-mentioned nuclear magnetic resonance testing module 3 can also be connected to the nuclear magnetic resonance data acquisition module 5, which can be used to acquire the nuclear magnetic resonance T2 spectrum and layered T2 spectrum of the target core 31 under different injection volume conditions.

[0052] Specifically, the nuclear magnetic resonance (NMR) testing module 3 can perform real-time, online testing of the T2 spectrum and layered T2 spectrum of the target core during the displacement process, featuring high efficiency, speed, and non-destructive operation. The NMR testing module 3 can be connected to the NMR data acquisition module 5, which can accurately and rapidly acquire the NMR T2 spectrum and layered T2 spectrum of the target core 31 under different injection volumes. It can also directly acquire and record the volume change of the displacement pump 1 under different injection volumes. This provides a basis for subsequent intuitive and quantitative research on the dynamic changes in micropore structure and permeability under different injection volumes, and offers a reference for developing reasonable development strategies and formulating production work procedures on-site.

[0053] In some embodiments, the displacement pump 1 can be sequentially connected to a first pressure sensor 01, a first valve 02, an intermediate container 2, a second valve 03, a second pressure sensor 04, and a nuclear magnetic resonance testing module 3 via a pipeline 0. The first pressure sensor 01 can be used to monitor whether the pressure in the pipeline 0 is equal to the inlet pressure set in the displacement pump 1. The second pressure sensor 04 can be used to monitor whether the injection pressure of the injection medium 21 is equal to the inlet pressure set in the displacement pump 1. The first valve 02 can be used to control the displacement pump 1 to drive. The second valve 03 can be used to control the injection medium 21 to be injected into the target core 31.

[0054] Specifically, the inlet pressure at the inlet of the nuclear magnetic resonance (NMR) testing module 3 can be flexibly set in the displacement pump 1, thereby controlling the inlet pressure at the inlet of the NMR testing module 3. The displacement pump 1 and the NMR testing module 3 can be sequentially connected via pipeline 0 to a first pressure sensor 01, a first valve 02, an intermediate container 2, a second valve 03, and a second pressure sensor 04. The first pressure sensor 01 monitors whether the pressure in the pipeline 0 is equal to the inlet pressure set in the displacement pump 1, and the second pressure sensor 04 monitors whether the injection pressure of the injection medium 21 is equal to the inlet pressure set in the displacement pump 1, thus ensuring that the pressure of the displacement pump 1 can be correctly transmitted. The first valve 02 controls the displacement pump 1 to drive it; for example, when the first valve 02 is opened, the displacement pump 1 can drive the injection medium 21 in the intermediate container 2. The second valve 03 controls the injection of the injection medium 21 into the target core 31; for example, when the second valve 03 is opened, the injection medium 21 can be driven to inject into the target core 31. This allows for a more flexible experimental system, better meeting the actual needs of users. The injection medium 21 can be any liquid with nuclear magnetic resonance signals, including simulated oil. This invention can inject simulated oil into the target core 31. The target core 31 can be a processed core saturated with oil.

[0055] In some embodiments, the above-mentioned nuclear magnetic resonance testing module 3 can also be connected to a third valve 05 and a confining pressure providing module 6. The confining pressure providing module 6 can be used to provide a confining pressure greater than the inlet pressure to the target core 31, and the third valve 05 can be used to control the confining pressure providing module 6 to provide confining pressure.

[0056] Specifically, the confining pressure providing module 6 may include a confining pressure control 61 and fluorinated oil 62. The fluorinated oil 62 is circulated through the confining pressure control 61 to provide confining pressure. To clamp the target core and simulate real formation pressure conditions, the confining pressure can be designed to be higher than the inlet pressure or injection pressure. The third valve 05 can be used to control the confining pressure provided by the confining pressure providing module 6. For example, when the third valve 05 is opened, the confining pressure providing module 6 can provide confining pressure to the target core 31. This increases the flexibility of the experimental system.

[0057] In some embodiments, the above-mentioned nuclear magnetic resonance testing module 3 may also be connected in sequence to a fourth valve 06, a third pressure sensor 07, a back pressure valve 7, a fourth pressure sensor 08, and a manual pump 4 via a pipeline 0. The manual pump 4 may also be used to set the back pressure of the back pressure valve 7. The back pressure valve 7 may be used to control whether the injected medium 21 flows out. The third pressure sensor 07 may be used to monitor whether the pressure in the pipeline at the outlet end of the nuclear magnetic resonance testing module 3 is greater than the back pressure of the back pressure valve 7. The fourth pressure sensor 08 may be used to monitor whether the back pressure of the back pressure valve 7 is equal to the back pressure set by the manual pump 4. The fourth valve 06 may be used to control the back pressure valve 7 to control the flow of the injected medium 21.

[0058] Specifically, the manual pump 4 can be configured to control the back pressure of the back pressure valve 7 at the outlet of the NMR test module 3, thereby controlling whether the injected medium 21 flows out. A third pressure sensor 07 between the NMR test module 3 and the back pressure valve 7 can monitor whether the pressure of the injected medium 21 in the pipeline at the outlet of the NMR test module 3 is greater than the back pressure of the back pressure valve 7. If it is greater, the injected medium 21 can flow out smoothly; if it is less than the back pressure, it cannot flow out. A fourth pressure sensor 08 between the back pressure valve 7 and the manual pump 4 can monitor whether the back pressure of the back pressure valve 7 is equal to the back pressure set by the manual pump 4, ensuring correct pressure transmission. A fourth valve 06 can control the back pressure valve 7 to control the flow of the injected medium 21. For example, when the fourth valve 06 is opened, the back pressure valve 7 can be controlled to control the injected medium 21 to flow out from the outlet of the NMR test module 3.

[0059] In some embodiments, the system may further include a liquid collection device 8, which is connected to a back pressure valve 7 and can be used to collect the outflowing injection medium 21, such as collecting outflowing simulated oil, thereby achieving the purpose of resource recycling.

[0060] The aforementioned online nuclear magnetic resonance (NMR) simulation system for large-volume reservoir energy replenishment eliminates the need for frequent core extraction for NMR testing. This avoids the uncertainties caused by stress release in the core, which can alter pore structure and oil saturation, thus affecting the experimental results. The NMR testing module 3 continuously and dynamically monitors the energy replenishment process of the simulated oil injection under different injection volumes. The NMR data acquisition module 5 promptly acquires the NMR T2 spectra and layered T2 spectra of the target core under different injection volumes, recording the volume change of the displacement pump. This provides a data foundation for subsequent quantitative analysis of the dynamic changes in micropore structure and permeability during the injection process.

[0061] See Figure 2As shown in the embodiments of this specification, an online nuclear magnetic resonance (NMR) simulation experiment method for large-volume replenishment in oil reservoirs is also provided. This method is based on the above-described online NMR simulation experiment system for large-volume replenishment in oil reservoirs, and may include:

[0062] S201: Process the core after oil and salt washing to obtain the target core;

[0063] S202: Increase the inlet pressure at the inlet of the nuclear magnetic resonance test module in the displacement pump, and at the same time increase the back pressure at the outlet of the nuclear magnetic resonance test module in the manual pump. Use the nuclear magnetic resonance test module to test the nuclear magnetic resonance T2 spectrum and layered T2 spectrum of the target core without pressure difference, and at the same time use the nuclear magnetic resonance data acquisition module to acquire the nuclear magnetic resonance T2 spectrum and layered T2 spectrum of the target core without pressure difference.

[0064] S203: Continue to increase the inlet pressure at the inlet of the nuclear magnetic resonance test module in the displacement pump, and then increase the back pressure at the outlet of the nuclear magnetic resonance test module in the manual pump according to the preset pressure difference. Use the nuclear magnetic resonance test module to test the nuclear magnetic resonance T2 spectrum and layered T2 spectrum of the target core under different injection times at different inlet pressures, and record the volume change of the displacement pump under different injection times at different inlet pressures. At the same time, use the nuclear magnetic resonance data acquisition module to collect the nuclear magnetic resonance T2 spectrum and layered T2 spectrum of the target core under different injection times at different inlet pressures.

[0065] In some embodiments, the displacement pump 1 in the above system can generate different injection volume conditions, which may include: an initial state without pressure differential, and injection conditions at different injection times with various inlet pressures. Specifically, the inlet pressure set in the displacement pump 1 and the back pressure set in the manual pump 4 can be increased simultaneously (e.g., simultaneously increasing the inlet pressure and setting the back pressure to 12 MPa) to form an initial state without pressure differential. Alternatively, the inlet pressure set in the displacement pump 1 can be increased, and the back pressure set in the manual pump 4 can be increased according to a preset pressure differential (e.g., 4 MPa). For example, the inlet pressure can be increased to 16 MPa while maintaining the back pressure at 12 MPa, or the inlet pressure can be increased to 19 MPa while maintaining the back pressure at 15 MPa, etc., thus maintaining a flow pressure differential of 4 MPa to simulate the process of large-volume fluid injection to replenish energy. Different injection pressures or inlet pressures represent different injection volumes.

[0066] In some embodiments, the process of treating the core after oil and salt washing in step S201 above to obtain the target core may include:

[0067] The core samples were dried after being washed with oil and salt to obtain dry core samples.

[0068] A vacuum pump is used to evacuate the dry core sample, and then simulated formation water is injected to saturate it, resulting in a core saturated with water.

[0069] Simulated oil was injected into the core saturated water sample until no more water was produced from the outlet of the core saturated water sample, thus obtaining a core saturated oil sample, which was used as the target core.

[0070] Specifically, before conducting a large-volume liquid replenishment physical simulation experiment, core preparation and saturation work can be carried out first:

[0071] The core samples can be dried after washing away oil and salt to obtain dry core samples. After drying, basic physical information such as porosity, permeability, length, and diameter can be measured. The nuclear magnetic resonance T2 spectrum of the dry core sample can be tested as a base signal to eliminate the interference of residual signals in the dry sample on the saturated fluid signal.

[0072] The dried core sample is then placed in a vacuum container. After checking the seal, a vacuum pump is used to evacuate the container for at least 24 hours. Simulated formation water is then injected to saturate the core, resulting in a saturated water sample. The simulated formation water can be prepared using heavy water based on actual formation water data. After saturation, the nuclear magnetic resonance T2 spectrum of the saturated water sample can be tested to establish bound water.

[0073] Finally, the water-saturated core sample was loaded into the core holder, maintaining a confining pressure 3.0 MPa to 5.0 MPa higher than the injection pressure. Simulated oil at a rate of 3 PV or more was injected into the water-saturated core sample until no more water flowed from the outlet, resulting in a water-saturated core sample. After saturation, the nuclear magnetic resonance T2 spectrum of the water-saturated core sample was measured to determine the state of bound water-saturated oil. This water-saturated core sample can be used as the target core for further processing.

[0074] By processing the core samples, changes in oil signals can be observed during formal experiments.

[0075] In some embodiments, after S202 or before S203, the following may also be included in the specific implementation:

[0076] A predetermined number of injection volume test points are designed on the target core, and a confining pressure supply module is used to provide a confining pressure to the target core that is greater than the inlet pressure.

[0077] Specifically, during the formal large-volume energy replenishment physical simulation experiment on the processed target core, the target core can be placed in the nuclear magnetic resonance (NMR) testing module 3. Fluorinated oil 62 is circulated via confining pressure control 61 to provide confining pressure. Simulated oil is used as the injection medium 21 at the inlet of the NMR testing module 3. The inlet pressure and back pressure are increased to 12 MPa using displacement pump 1 and manual pump 3, respectively. The NMR testing module 3 is used to test the NMR T2 spectrum and layered T2 spectrum of the target core without pressure differential, using this as the initial state.

[0078] At least five injection volume test points can be designed based on actual formation pressure conditions and pressure holding levels. The confining pressure supply module 6 provides a confining pressure to the target core greater than the inlet pressure, such as at least 10 MPa higher than the designed minimum injection pressure, simulating actual formation and injection conditions. A 4 MPa pressure differential is then maintained to synchronously increase the back pressure, simulating the energy replenishment process of a large-volume injection. Each injection volume is stabilized for at least 2 hours until the flow rate of displacement pump 1 and the changes in the NMR T2 spectrum and stratified T2 spectrum measured at different times under each injection pressure are minimal. This indicates the injection endpoint at that injection pressure has been reached. The volume change of displacement pump 1 must be recorded during the injection process. Simultaneously, the NMR data acquisition module 5 can be used to collect in real-time the NMR T2 spectrum and stratified T2 spectrum of the target core without pressure differential, the NMR T2 spectrum and stratified T2 spectrum of the target core under different injection times at various inlet pressures, and the volume change of the displacement pump. Different injection times can include 1 hour, 2 hours, etc. Layered T2 spectral pseudocolor imaging can more intuitively and clearly show the fluid transport characteristics during the displacement process, and continuously and quantitatively characterize the fluid changes in different cross sections and pore sizes of the core.

[0079] In some embodiments, after S204 above, in specific implementation, it may further include:

[0080] Based on the nuclear magnetic resonance T2 spectra of the liquid injection at different inlet pressures or injection times without differential pressure, different pore sizes are classified.

[0081] Determine the area of ​​the first spectral line corresponding to the target pore size under different pore sizes without differential pressure, and the area of ​​the second spectral line corresponding to the target pore size under liquid injection at the target injection time;

[0082] Based on the difference between the area of ​​the first spectral line and the area of ​​the second spectral line, the spectral line change values ​​under different injection times at each inlet pressure are determined.

[0083] The total spectral area corresponding to the nuclear magnetic resonance T2 spectrum without pressure difference is determined. Based on the ratio of the spectral line change value to the total spectral line area, the dynamic change characteristics of the micropore structure under the target aperture at the target injection time are determined.

[0084] In some embodiments, after S204 above, in specific implementation, it may further include:

[0085] Based on the change in displacement pump volume at different injection times under various inlet pressures, the dynamic characteristics of permeability change at different injection times under various inlet pressures are determined.

[0086] Specifically, due to the anisotropic distribution of fluids within different core blocks, different pore sizes or diameters can be classified based on the peak distribution characteristics of the nuclear magnetic resonance T2 spectrum obtained during the experiment and the pore size classification criteria (e.g., 0.01–1 ms is considered small pore, 1–10 ms is considered medium pore, >10 ms is considered large pore, or <10 ms is considered small pore, >10 ms is considered small pore, etc.). Among these, the transverse relaxation time of the nuclear magnetic resonance T2 spectrum is positively correlated with the pore size, as shown in formula (1):

[0087]

[0088] Wherein, T2 is the H content in the porous medium. 1 Transverse relaxation time of nuclear fluid, ms; ρ2 is the surface relaxation rate of porous medium, μm / ms; It is the specific surface area of ​​pores in a porous medium, 1 / μm; F S is the shape factor; r is the aperture.

[0089] Then, determine the area M of the first spectral line corresponding to the target aperture i in different apertures without pressure differential. i The area of ​​the second spectral line corresponding to the target pore size i at the target injection time j at different injection times. Among them, the area of ​​the first spectral line M i The area enclosed by the NMR T2 spectrum corresponding to the target aperture i in the initial state and the x-axis is the area of ​​the second spectral line. Let the area enclosed by the NMR T2 spectrum of the target aperture i at injection time j and the x-axis be the area of ​​the NMR spectrum. Then, based on the area M of the first spectral line... i Area of ​​the second spectral line The difference Determine the spectral changes at different injection times under various inlet pressures. The target pore size can be any pore size within the defined pore size range, and the target injection time can be any injection time among different injection times. The NMR T2 spectra measured at different injection times under each injection pressure can be compared with the initial state NMR T2 spectra. The difference between the area enclosed by the NMR T2 spectra of different pore sizes and the x-axis and the area enclosed by the corresponding NMR T2 spectra of the initial state pore size and the x-axis is calculated to obtain the spectral changes for different pore sizes under different injection pressures.

[0090] Finally, the total spectral area M corresponding to the T2 NMR spectrum without pressure difference can be determined. o Based on the ratio of the spectral line change value to the total spectral line area, the dynamic change characteristics of the micropore structure at the target injection time j and target aperture i are determined according to the following formula (2).

[0091]

[0092] Among them, the total spectral area M o The total area enclosed by the initial T2 NMR spectrum and the x-axis is denoted as .

[0093] Simultaneously, layered T2 spectral imaging technology can be used to visually observe the changes in oil content at different sections of the target core, thereby qualitatively analyzing the main cross-sections where fluid migration and pore structure changes occur. Specifically, it can also determine the first layered spectrum corresponding to the target pore size under different pore sizes without differential pressure, and the second layered spectrum corresponding to the target pore size under injected fluid at the target injection time. Based on the changes in the first and second layered spectra, the spatial characteristics of fluid migration and micropore structure changes can be determined, such as the main cross-sections where micropore structure changes occur.

[0094] Based on the volume change and flow pressure difference recorded at different injection times under different injection pressures during the experiment, the pseudo-permeability corresponding to each injection volume can be calculated, and the dynamic change characteristics of permeability under large-volume injection conditions can be quantitatively analyzed, as shown in formula (3):

[0095]

[0096] Where K is the pseudo-permeability of the target core, 10⁻³ μm²; μ is the fluid viscosity, mPa·s; L is the length of the target core, cm; Q is the fluid volume passing through the target core per unit time, cm³·s⁻¹, i.e., the ratio of the displacement pump volume difference to the corresponding injection time; Δp is the pressure difference between the two ends of the target core, MPa; and A is the cross-sectional area of ​​the target core, cm².

[0097] The above scheme enables physical simulation experiments of large-volume fluid replenishment energy on core models under actual formation conditions, accurately simulating the large-volume fluid replenishment energy process under actual formation pressure conditions. Simultaneously, it allows for real-time monitoring of fluid transport characteristics at different locations in the core using low-field nuclear magnetic resonance (NMR) technology during injection. By measuring NMR T2 spectra and layered T2 spectra at different injection volumes and times, the dynamic evolution of reservoir micropore structure and permeability under large-volume injection conditions can be quantitatively and qualitatively analyzed, providing a reference for developing reasonable production operating procedures in the oilfield later.

[0098] In a specific implementation scenario, using core samples from a tight sandstone reservoir in an oilfield and simulated oil compounded in the laboratory based on the physical properties of crude oil from the oilfield, a large-scale injection fluid replenishment energy physical simulation experiment was conducted according to the online nuclear magnetic resonance (NMR) physical simulation experimental system and method for large-volume reservoir energy replenishment established by this invention. The injection pressure was selected as 16 MPa, 19 MPa, 22 MPa, 25 MPa (overpressure), and 27 MPa (overpressure) based on actual formation conditions and different pressure holding levels. During the experiment, T2 spectrum and layered T2 spectrum tests were performed on the core samples. Combined with the changes in the displacement pump volume during the experiment, the dynamic changes in injection volume during the large-volume fluid injection process were obtained using NMR T2 spectra. The dynamic characteristics of changes in micropore structure, permeability, and fluid migration were quantitatively and qualitatively analyzed.

[0099] See Figure 3 As shown, Figure 3 The signal amplitude variations of the nuclear magnetic resonance T2 spectral lines are shown under the initial state and injection pressures of 16 MPa, 19 MPa, 22 MPa, 25 MPa, and 27 MPa. Based on the mathematical correlation between the nuclear magnetic resonance T2 spectral lines and pore size, pore sizes are classified into three categories: 0.01–1 ms for small pores, 1–100 ms for medium pores, and >100 ms for large pores and microcracks. Figure 3 It is clear that the impact of large-scale fluid injection on the microstructure is mainly reflected in small pores, large pores, and microcracks, while the mesopores remain basically unchanged.

[0100] See Figure 4 As shown, Figure 4 The relative changes in oil saturation are shown for >100 ms (large pores and microcracks), 1–100 ms (medium pores), and 0.01–1 ms (small pores). The oil saturation in small pores (0.01–1 ms) initially increases and then decreases, with a relative increase of -15.93%–14.76%. The oil saturation in microcracks (>100 ms) continues to increase from its initial state of no oil saturation, with a relative increase of 13.50%–25.41%, indicating that large-volume fluid injection can significantly open microcracks and promote oil seepage within small and medium pore throats.

[0101] See Figure 5 As shown, Figure 5 The initial permeability was shown to be 0.064 × 10⁻⁶. -3 μm 2 0.085×10 -3 μm 2 0.106×10 -3 μm 2The injection pressure changes with the calculated permeability. Large-scale fluid injection can significantly increase permeability and improve seepage capacity. The higher the initial permeability, the later the inflection point appears. The three core samples, ordered from lowest to highest permeability, show inflection points of 19 MPa, 22 MPa, and 27 MPa, respectively. Analysis suggests that higher permeability indicates a greater number of larger pore throats and better connectivity between them. The opening of microfractures has little effect on permeability improvement, requiring further increases in injection volume to achieve a substantial increase in permeability. Furthermore, the correlation between the permeability at each injection volume and the initial permeability is not significant.

[0102] See Figure 6 As shown, layered T2 spectra were acquired at different injection times (initial state, inlet pressure of 16 MPa, 19 MPa, 22 MPa, 25 MPa, and 27 MPa). From right to left, these represent the inlet and outlet ends. Brighter images indicate higher oil content. Layered T2 spectra imaging provides a more intuitive and continuous view of changes in the microstructure of the pores and accurately describes the energy replenishment location. Increasing the injection volume significantly opens the microcracks at the inlet end, and the number of smaller pores at the outlet end increases significantly. Overall, the image shifts towards areas with longer relaxation times, indicating that large-volume injection promotes the participation of all sizes of pores and throats in seepage, but the increase in seepage capacity varies at different locations.

[0103] In summary, the aforementioned online nuclear magnetic resonance (NMR) simulation system and method for large-volume reservoir energy replenishment can accurately simulate the large-scale fluid injection energy replenishment process under actual formation pressure levels, revealing the dynamic evolution of reservoir parameters during this process. In practical applications, comprehensive analysis of NMR T2 spectra and stratified T2 spectra, along with the displacement fluid volume, at different injection volumes and stages allows for accurate quantitative and qualitative characterization of the dynamic changes in micropore structure and permeability during large-volume fluid injection. Furthermore, by comparing the differences in reservoir parameter evolution under different injection volumes, injection pressure differentials, injection times, and injection fluid media, suitable injection-production parameters for field practice can be obtained, providing a reference for the development of reasonable production operating procedures and the selection of enhanced oil recovery measures.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A large-volume, replenished-energy online nuclear magnetic resonance (NMR) physics simulation experimental system for oil reservoirs, characterized in that, include: The system consists of a displacement pump, an intermediate container, a nuclear magnetic resonance (NMR) testing module, and a manual pump connected in sequence. The intermediate container stores the injection medium, and the NMR testing module holds the processed target core. The displacement pump is used to control the inlet pressure at the inlet end of the nuclear magnetic resonance testing module and drive the injection medium to inject into the target core according to different injection volume conditions. The manual pump is used to control the back pressure at the outlet end of the nuclear magnetic resonance testing module. The nuclear magnetic resonance testing module is used to test the nuclear magnetic resonance T2 spectrum and layered T2 spectrum of the target core under different injection volume conditions.

2. The system according to claim 1, characterized in that, The nuclear magnetic resonance testing module is also connected to a nuclear magnetic resonance data acquisition module, which is used to acquire the nuclear magnetic resonance T2 spectrum and layered T2 spectrum of the target core under different injection volume conditions.

3. The system according to claim 1, characterized in that, The displacement pump is connected in sequence via pipeline to a first pressure sensor, a first valve, an intermediate container, a second valve, a second pressure sensor, and a nuclear magnetic resonance testing module. The first pressure sensor is used to monitor whether the pressure in the pipeline is equal to the inlet pressure set in the displacement pump. The second pressure sensor is used to monitor whether the injection pressure of the injected medium is equal to the inlet pressure set in the displacement pump. The first valve is used to control the displacement pump to drive, and the second valve is used to control the injection of the injected medium into the target core.

4. The system according to claim 1, characterized in that, The nuclear magnetic resonance testing module is also connected to a third valve and a confining pressure supply module. The confining pressure supply module is used to provide a confining pressure greater than the inlet pressure to the target core, and the third valve is used to control the confining pressure supply module to provide the confining pressure.

5. The system according to claim 1, characterized in that, The nuclear magnetic resonance testing module is also connected in sequence to a fourth valve, a third pressure sensor, a back pressure valve, a fourth pressure sensor, and a manual pump via pipelines. The manual pump is also used to set the back pressure of the back pressure valve. The back pressure valve is used to control whether the injected medium flows out. The third pressure sensor is used to monitor whether the pressure in the pipeline at the outlet end of the nuclear magnetic resonance testing module is greater than the back pressure of the back pressure valve. The fourth pressure sensor is used to monitor whether the back pressure of the back pressure valve is equal to the back pressure set by the manual pump. The fourth valve is used to control the back pressure valve to control the flow of the injected medium.

6. A method for online nuclear magnetic resonance physics simulation of large-volume fluid replenishment in oil reservoirs, characterized in that, Based on the system according to any one of claims 1-5, the method comprises: The core samples after oil and salt washing were processed to obtain the target core samples; Increase the inlet pressure at the inlet of the nuclear magnetic resonance test module in the displacement pump, and simultaneously increase the back pressure at the outlet of the nuclear magnetic resonance test module in the manual pump. Use the nuclear magnetic resonance test module to test the nuclear magnetic resonance T2 spectrum and layered T2 spectrum of the target core without pressure difference, and use the nuclear magnetic resonance data acquisition module to acquire the nuclear magnetic resonance T2 spectrum and layered T2 spectrum of the target core without pressure difference. Continue to increase the inlet pressure at the inlet of the nuclear magnetic resonance (NMR) test module in the displacement pump, and then increase the back pressure at the outlet of the NMR test module in the manual pump according to the preset pressure difference. Use the NMR test module to test the NMR T2 spectrum and layered T2 spectrum of the target core under different injection times at different inlet pressures, and record the volume change of the displacement pump under different injection times at different inlet pressures. At the same time, use the NMR data acquisition module to collect the NMR T2 spectrum and layered T2 spectrum of the target core under different injection times at different inlet pressures.

7. The method according to claim 6, characterized in that, The process of treating the core after oil and salt washing to obtain the target core includes: The core samples were dried after being washed with oil and salt to obtain dry core samples. A vacuum pump is used to evacuate the dry core sample, and then simulated formation water is injected to saturate it, resulting in a core saturated with water. Simulated oil was injected into the core saturated water sample until no more water was produced from the outlet of the core saturated water sample, thus obtaining a core saturated oil sample, which was used as the target core.

8. The method according to claim 6, characterized in that, The method further includes: A predetermined number of injection volume test points are designed on the target core, and a confining pressure supply module is used to provide a confining pressure to the target core that is greater than the inlet pressure.

9. The method according to claim 6, characterized in that, The method further includes: Based on the nuclear magnetic resonance T2 spectra of the liquid injection at different inlet pressures or injection times without differential pressure, different pore sizes are classified. Determine the area of ​​the first spectral line corresponding to the target pore size under different pore sizes without differential pressure, and the area of ​​the second spectral line corresponding to the target pore size under liquid injection at the target injection time; Based on the difference between the area of ​​the first spectral line and the area of ​​the second spectral line, the spectral line change values ​​under different injection times at each inlet pressure are determined. The total spectral area corresponding to the nuclear magnetic resonance T2 spectrum without pressure difference is determined. Based on the ratio of the spectral line change value to the total spectral line area, the dynamic change characteristics of the micropore structure under the target aperture at the target injection time are determined.

10. The method according to claim 6, characterized in that, The method further includes: Based on the change in displacement pump volume at different injection times under various inlet pressures, the dynamic characteristics of permeability change at different injection times under various inlet pressures are determined.

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