Method and device for determining a diffusion coefficient of CO2 flooding

Abstract

The application provides a method and device for determining a CO2 flooding diffusion coefficient, and the method comprises the following steps: obtaining preset temperature conditions and pressure conditions; simulating CO2 displacement of a target oil sample according to the preset temperature conditions and pressure conditions; obtaining an initial position of a liquid column and a position of an expanded liquid column interface after CO2 displacement for a preset time; obtaining a specific volume of CO2 under the preset temperature conditions and pressure conditions, and a saturated concentration of CO2 diffusion in the target oil sample; and determining a diffusion coefficient of CO2 flooding in the target oil sample according to the initial position of the liquid column, the position of the expanded liquid column interface, the specific volume and the saturated concentration. The above scheme solves the technical problem that the existing determination process of the diffusion coefficient of CO2 flooding in unconventional reservoirs is too complicated and takes too long, and achieves the technical effect of quickly and accurately determining the diffusion coefficient of CO2 flooding.

Description

Technical Field

[0001] This application belongs to the field of oil and gas exploration technology, and in particular relates to a method and apparatus for determining the CO2 flooding diffusion coefficient. Background Technology

[0002] With the continuous development of oil and gas exploration and development, conventional oil and gas reservoir development has entered its later stages, and low-permeability and unconventional oil and gas development has gradually become an important source of fossil fuels. Following low-permeability reservoirs, unconventional reservoirs, represented by tight oil and shale oil, are the focus of unconventional oil and gas exploration and development. To address the difficulties in injection and high seepage resistance in low-permeability and unconventional reservoirs, current methods primarily utilize gas injection flooding and gas injection huff and puff to improve oil recovery. Because CO2 has a relatively low critical temperature and pressure, it can form a supercritical state under formation conditions; therefore, CO2 is considered a medium with good miscibility with crude oil. Furthermore, as a common greenhouse gas, CO2 can effectively occupy pore space in the formation and remain in the reservoir during oil and gas field development, playing a positive role in low-carbon and carbon reduction.

[0003] Diffusion and crude oil expansion are important mechanisms of CO2 enhanced oil recovery (EOR), and the mutual diffusion between crude oil and CO2 can weaken the convection effect caused by concentration gradients. After CO2 injection, crude oil expands. As the pressure of the CO2-oil system increases, significant interdiffusion and mass transfer effects occur between crude oil and CO2, allowing more light components to be extracted by CO2 and form a miscible phase, thereby improving EOR efficiency. The recovery rate under diffusion mechanisms is 5%-10% higher than that without diffusion mechanisms. Low pressure gradients can limit the convection of individual components, and the component differences between fractures and the matrix make oil and gas diffusion the main driving mechanism. The diffusion coefficient of CO2 in oil products is an important variable in the CO2 huff and puff process, affected not only by temperature, pressure, and composition, but also by changes in pore throats and pore phase states. Fluid diffusion in nanoscale confined spaces differs significantly from that in large spaces, mainly in terms of surface effects, fluid layer thickness, molecular collision frequency, diffusion rate, and diffusion mode. These differences have a significant impact on fluid diffusion behavior at the nanoscale. Existing methods for determining diffusion coefficients suffer from drawbacks such as long processing times (several days), high sample consumption, lack of visual information, and significant susceptibility to subjective experience. These methods fail to achieve the goal of simultaneously observing the oil and gas diffusion process in real time while simultaneously detecting the diffusion coefficient with high precision and speed. Furthermore, the diffusion properties of CO2 in the pores of unconventional reservoirs differ from those in the bulk phase, and existing methods cannot meet the requirements for nanoscale measurements.

[0004] There is currently no effective solution for how to quickly, accurately, and continuously measure the diffusion coefficient of CO2 flooding in unconventional reservoirs. Summary of the Invention

[0005] The purpose of this application is to provide a method and apparatus for determining the diffusion coefficient of CO2 flooding, which can achieve the technical effect of quickly and accurately determining the diffusion coefficient of CO2 flooding.

[0006] This application provides a method and apparatus for determining the CO2 diffusion coefficient, which is implemented as follows:

[0007] A method for determining the CO2 diffusion coefficient, the method comprising:

[0008] Obtain the preset temperature and pressure conditions;

[0009] Simulate CO2 displacement of the target oil sample according to preset temperature and pressure conditions;

[0010] Obtain the position of the expanded liquid column interface after a preset CO2 displacement time;

[0011] The specific volume of CO2 under the preset temperature and pressure conditions, and the saturation concentration of CO2 diffused in the target oil sample are obtained.

[0012] The diffusion coefficient of CO2 in the target oil sample is determined based on the initial position of the liquid column, the position of the liquid column interface after expansion, the specific volume, and the saturation concentration.

[0013] In one embodiment, determining the CO2 diffusion coefficient in the target oil sample based on the initial position of the liquid column, the interface position of the expanded liquid column, the specific volume, and the saturation concentration includes:

[0014] The diffusion coefficient of CO2 in the target oil sample is calculated using the following formula:

[0015]

[0016] Where D represents the CO2 diffusion coefficient in the target oil sample. The average CO2 concentration is represented by t, the diffusion time is represented by x0, and the initial position of the liquid column is represented by x. t ν represents the position of the liquid column interface after expansion at time t. A C represents the specific volume of CO2 under preset temperature and pressure conditions. Ai This indicates the saturation concentration of CO2 diffusion in the oil phase.

[0017] In one embodiment, simulating CO2 displacement of a target oil sample according to preset temperature and pressure conditions includes:

[0018] A micro-nano fluid control device was constructed, and the vacuum pump valve was opened to evacuate the experimental pipeline and conduct system pressure resistance and sealing tests.

[0019] After passing the pressure resistance test and the sealing test, the experimental temperature was adjusted to the preset temperature conditions using a constant temperature water bath.

[0020] Simulate CO2 displacement of the target oil sample under preset pressure conditions;

[0021] Accordingly, the initial position of the liquid column and the position of the expanded liquid column interface after the preset CO2 displacement time are obtained, including:

[0022] The oil volume change was imaged after each pressure increment by gradually increasing the pressure at a low constant flow rate to form an image sequence.

[0023] The image sequence was processed for grayscale and scale to obtain the position of the liquid column interface at multiple time points after CO2 displacement.

[0024] In one embodiment, the micro / nano fluid control device is provided with a micro / nano fluid control chip. The channels in the micro / nano fluid control chip include: a flow-aiding channel and a blind-end channel, wherein the flow-aiding channel and the blind-end channel are arranged perpendicular to each other, and the end of the blind-end channel connected to the flow-aiding channel is open, while the end away from the flow-aiding channel is sealed.

[0025] During the simulation of CO2 displacement of the target oil sample under preset temperature and pressure conditions, the oil in the flow aid channel is replaced by low-pressure CO2, and the continuous flow in the flow aid channel removes the oil in the blind end channel, leaving a separate oil plug in the blind end channel, wherein the length of the oil plug accounts for 2 / 3 of the length of the blind end channel.

[0026] In one embodiment, determining the CO2 diffusion coefficient in the target oil sample based on the initial position of the liquid column, the interface position of the expanded liquid column, the specific volume, and the saturation concentration includes:

[0027] After simulating CO2 displacement of the target oil sample, the positions of the expanded liquid column interface at multiple displacement time points were obtained.

[0028] The diffusion coefficient at multiple displacement time points is determined based on the position of the liquid column interface after expansion at multiple displacement time points.

[0029] Based on the diffusion coefficients at the multiple displacement time points, plot the diffusion coefficient variation curve over time.

[0030] The diffusion coefficient corresponding to the maximum expansion distance is determined as the CO2 flooding diffusion coefficient in the target oil sample.

[0031] In one embodiment, obtaining the saturation concentration of CO2 diffusion in the target oil sample includes:

[0032] After the diffusion process is completed, obtain the maximum average concentration of CO2 in the target oil sample;

[0033] The maximum average concentration of CO2 in the target oil sample is taken as the saturation concentration of CO2 diffusion in the target oil sample.

[0034] An apparatus for determining the CO2 diffusion coefficient, comprising:

[0035] The first acquisition module is used to acquire preset temperature and pressure conditions;

[0036] The simulation module is used to simulate CO2 displacement of the target oil sample according to preset temperature and pressure conditions;

[0037] The second acquisition module is used to acquire the initial position of the liquid column and the position of the expanded liquid column interface after a preset CO2 displacement time.

[0038] The third acquisition module is used to acquire the specific volume of CO2 under the preset temperature and pressure conditions, as well as the saturation concentration of CO2 diffused in the target oil sample.

[0039] The determination module is used to determine the diffusion coefficient of CO2 in the target oil sample based on the initial position of the liquid column, the interface position of the expanded liquid column, the specific volume, and the saturation concentration.

[0040] An electronic device includes a processor and a memory for storing processor-executable instructions, wherein the processor, when executing the instructions, implements the steps of the method described above.

[0041] A computer-readable storage medium having a computer program / instructions stored thereon, which, when executed by a processor, implement the steps of the above-described method.

[0042] A computer program product includes a computer program / instructions that, when executed by a processor, implement the steps of the above-described method.

[0043] The method for determining the CO2 flooding diffusion coefficient provided in this application simulates CO2 displacement of a target oil sample under preset temperature and pressure conditions to obtain the initial position of the liquid column and the position of the expanded liquid column interface after a preset CO2 displacement time. Then, by using the specific volume of CO2 under the preset temperature and pressure conditions, as well as the saturation concentration of CO2 diffusion in the target oil sample, the initial position of the liquid column, and the position of the expanded liquid column interface, the CO2 flooding diffusion coefficient in the target oil sample is determined. This method solves the technical problem that the existing process for determining the CO2 flooding diffusion coefficient in unconventional reservoirs is too cumbersome and time-consuming, achieving the technical effect of quickly and accurately determining the CO2 flooding diffusion coefficient. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of this application 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 recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This is a flowchart of one embodiment of the method for determining the CO2 diffusion coefficient provided in this application;

[0046] Figure 2 This is a schematic diagram of the device provided in this application for measuring the CO2 flooding diffusion coefficient in unconventional reservoirs;

[0047] Figure 3 This is a schematic diagram of the flow-aiding channel and blind-end channel provided in this application;

[0048] Figure 4 This is a schematic diagram of the diffusion coefficient versus time provided in this application;

[0049] Figure 5 This is a hardware structure block diagram of an electronic device for determining the CO2 diffusion coefficient provided in this application;

[0050] Figure 6 This is a schematic diagram of the module structure of one embodiment of the CO2 diffusion coefficient determination device provided in this application. Detailed Implementation

[0051] To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this application.

[0052] Figure 1This is a flowchart of one embodiment of the method for determining the CO2 diffusion coefficient provided in this application. Although this application provides method operation steps or apparatus structures as shown in the following embodiments or figures, more or fewer operation steps or module units may be included in the method or apparatus based on conventional or non-inventive effort. In steps or structures where there is no logically necessary causal relationship, the execution order of these steps or the module structure of the apparatus is not limited to the execution order or module structure described in the embodiments and figures of this application. When the method or module structure is applied in actual devices or terminal products, it can be executed sequentially or in parallel according to the method or module structure shown in the embodiments or figures (e.g., in a parallel processor or multi-threaded processing environment, or even a distributed processing environment).

[0053] Specifically, such as Figure 1 As shown, the method for determining the CO2 diffusion coefficient described above may include the following steps:

[0054] Step 101: Obtain the preset temperature and pressure conditions;

[0055] Step 102: Simulate CO2 displacement of the target oil sample according to the preset temperature and pressure conditions;

[0056] Step 103: Obtain the initial position of the liquid column and the position of the expanded liquid column interface after the preset CO2 displacement time;

[0057] Specifically, assuming the initial position of the liquid column is x0, and the position of the liquid column interface after expansion following a preset CO2 displacement time is x0, t .

[0058] Step 104: Obtain the specific volume of CO2 under the preset temperature and pressure conditions, and the saturation concentration of CO2 diffused in the target oil sample;

[0059] The specific volume of CO2 under the preset temperature and pressure conditions can be obtained by looking up a table. Specifically, a table of the specific volume of CO2 under different temperature and pressure conditions can be pre-set, and the specific volume of CO2 under the preset temperature and pressure conditions can be obtained by looking up the table.

[0060] In implementation, the saturation concentration of CO2 diffusion in the target oil sample can be obtained as follows: The maximum average concentration of CO2 in the target oil sample after the diffusion process is completed is obtained; this maximum average concentration of CO2 in the target oil sample is used as the saturation concentration of CO2 diffusion in the target oil sample. That is, the maximum average concentration of CO2 after the diffusion process is used instead of the saturation concentration of CO2 diffusion in the target oil sample.

[0061] Step 105: Determine the diffusion coefficient of CO2 in the target oil sample based on the initial position of the liquid column, the position of the expanded liquid column interface, the specific volume, and the saturation concentration.

[0062] In practical implementation, based on the initial position of the liquid column, the position of the expanded liquid column interface, the specific volume, and the saturation concentration, the diffusion coefficient of CO2 in the target oil sample can be calculated using the following formula:

[0063]

[0064] Where D represents the CO2 diffusion coefficient in the target oil sample. The average CO2 concentration is represented by t, the diffusion time is represented by x0, and the initial position of the liquid column is represented by x. t ν represents the position of the liquid column interface after expansion at time t. A C represents the specific volume of CO2 under preset temperature and pressure conditions. Ai This indicates the saturation concentration of CO2 diffusion in the oil phase.

[0065] Specifically, simulating CO2 displacement of target oil samples according to preset temperature and pressure conditions can include:

[0066] S1: Set up a micro-nano fluid control device, open the vacuum pump valve to evacuate the experimental pipeline and conduct system pressure resistance test and sealing test;

[0067] S2: After the pressure resistance test and sealing test are passed, the experimental temperature is adjusted to the preset temperature conditions through a constant temperature water bath.

[0068] S3: Simulate CO2 displacement of the target oil sample under preset pressure conditions;

[0069] Accordingly, obtaining the initial position of the liquid column and the position of the liquid column after a preset CO2 displacement time can include:

[0070] S1: Gradually increase the pressure at a constant flow rate, and image the change in oil volume after each pressure increment to form an image sequence;

[0071] S2: Perform grayscale and scale processing on the image sequence to obtain the dilation distance at multiple time points after CO2 displacement.

[0072] The aforementioned micro / nanofluidic device may incorporate a micro / nanofluidic chip. The channels within this chip may include a flow-aiding channel and a blind-end channel. The flow-aiding channel and the blind-end channel are arranged perpendicularly to each other. The end of the blind-end channel connected to the flow-aiding channel is open, while the end away from the flow-aiding channel is sealed. During the simulation of CO2 displacement of the target oil sample under preset temperature and pressure conditions, the oil in the flow-aiding channel is replaced by low-pressure CO2. The continuous flow in the flow-aiding channel removes the oil from the blind-end channel, leaving a separate oil plug within the blind-end channel. The blind-end channel design ensures system sealing during the step-by-step pressurization process. Therefore, the influence of oil expansion convection is minimal within the blind-end channel.

[0073] Furthermore, determining the diffusion coefficient of CO2 in the target oil sample based on the initial position of the liquid column, the interface position of the expanded liquid column, the specific volume, and the saturation concentration may include:

[0074] S1: After simulating CO2 displacement of the target oil sample, obtain the position of the expanded liquid column interface at multiple displacement time points;

[0075] S2: Determine the diffusion coefficient at multiple displacement time points based on the interface position of the expanded liquid column at multiple displacement time points;

[0076] S3: Based on the diffusion coefficients at the multiple displacement time points, plot the diffusion coefficient variation curve over time;

[0077] S4: Determine the diffusion coefficient corresponding to the maximum expansion distance as the CO2-driven diffusion coefficient in the target oil sample.

[0078] That is, by plotting the diffusion coefficient change curve over time, the diffusion coefficient when the diffusion length no longer changes can be determined, thereby determining the expansion distance. The diffusion coefficient corresponding to the diffusion length no longer changes is used as the diffusion coefficient of CO2 in the target oil sample.

[0079] The above method will be described below with reference to a specific embodiment. However, it is worth noting that this specific embodiment is only for better illustration of this application and does not constitute an improper limitation of this application.

[0080] This example provides an apparatus and method for measuring the CO2 flooding diffusion coefficient of unconventional reservoirs, in order to solve the technical problems of long testing cycles, large sample consumption, and large testing scale in existing methods.

[0081] Specifically, the device for measuring the CO2 flooding diffusion coefficient of unconventional reservoirs can be as follows: Figure 2As shown, it includes: two fluid medium injection containers (CO2 high-pressure piston intermediate container 1 and high-pressure piston intermediate container 12), a fluid injection system (dual-cylinder constant pressure and constant speed injection pump 3 and single-cylinder constant pressure and constant speed injection pump 18), an image acquisition system 8, an image processing system 13, a temperature control system, fluid pressure relief and venting valves 6 and 17, a vacuum system 7, and a chip holder 9. The micro-nano fluid control chip 10 is located inside the chip holder 9 and is directly connected to the temperature sensor 11.

[0082] Furthermore, the fluid medium injection system may include: a dual-cylinder constant pressure and constant speed injection pump 3, a single-cylinder constant pressure and constant speed injection pump 18, fluid medium injection containers (CO2 high-pressure piston intermediate container 1 and high-pressure piston intermediate container 12), and inlet pressure sensors 4 and 5; the image acquisition system 8 may include: an optical microscope, a camera, and an image processing system 13; the temperature control system may include: an oven 2, a chip holder 9, a constant temperature water bath 14, an insulating rubber tube 16, and a temperature sensor 11. The outlet of the dual-cylinder constant pressure and constant speed pump 3 is connected to the inlet end of the CO2 high-pressure intermediate container 1 placed in the oven. The outlet end of the CO2 high-pressure intermediate container 1 is connected to the inlet end of the chip holder 9. The outlet of the CO2 high-pressure intermediate container 1 is connected to the inlet pressure sensors 4 and 5 and connected to the computer 13. A pinhole is reserved at the bottom of the chip holder 9 for external connection of the temperature sensor 11. The insulating rubber tube 16 passes through the chip holder 9.

[0083] Furthermore, vent valves 6 and 17 are connected to the pipeline inlet and outlet, respectively, and vacuum system 7 is connected to the inlet pipeline. The micro / nano fluid control chip 10 is made of silicon, which is resistant to temperature, pressure, and chemical corrosion. The channel of the micro / nano fluid control chip 10 consists of a flow-aiding channel and a blind-end experimental channel. The blind-end channel of the micro / nano fluid control chip needs to ensure the system's sealing during the step-by-step pressurization process. Therefore, the influence of oil expansion convection can be observed to be relatively small in the blind-end channel.

[0084] The image acquisition system 8 described above may include: an LED light source, a high-powered microscope, a high-speed camera, and a computer. The LED light source is used to provide an excitation light source. The microscope is coupled to the high-speed camera and connected to the computer 13 to record image sequences in real time. The image acquisition system 8 is positioned above the chip holder and its position is adjusted by a three-axis slide for focusing.

[0085] The injection speed of the dual-cylinder constant pressure and constant speed injection pump 1 is 0.0001-15.0000 ml / min, and the pressure is 0.01-72.41 MPa. The injection speed of the single-cylinder constant pressure and constant speed injection pump 2 is 0.001-10.000 ml / min, and the pressure is 0.001-75.000 MPa. The detection accuracy of the inlet high pressure sensor 4 is 0.01 MPa, and the detection pressure range is 0.01-50.00 MPa. The detection accuracy of the inlet low pressure sensor 5 is 0.01 MPa, and the detection pressure range is 0.01-12.00 MPa. The working pressure range of the CO2 high pressure piston intermediate container 1 is 0-20 MPa, the working temperature is ≤150℃, and the capacity is 100 ml. The working pressure range of the piston intermediate container 12 is 0-50 MPa, the working temperature is ≤120℃, and the capacity is 50 ml.

[0086] In one embodiment, the temperature control range of the above-mentioned constant temperature water bath 14 is 0.00-100.00℃, the temperature control accuracy is ±0.01℃, the detection accuracy of the temperature sensor 11 is 0.1℃, and the detection temperature range is -50.0℃-200.0℃.

[0087] In this example, based on the above-described apparatus for measuring the CO2 flooding diffusion coefficient of unconventional reservoirs, a method for measuring the CO2 flooding diffusion coefficient of unconventional reservoirs is also provided, which may include the following steps:

[0088] S1: Build as follows Figure 2 The micro / nano fluid control device is shown. Then, the vacuum pump valve is opened to evacuate the experimental pipeline and the system pressure resistance test and sealing test are performed.

[0089] S2: Set the experimental temperature using a constant temperature water bath 14;

[0090] S3: Using the high-pressure injection pump 1 to push the piston 1 of the CO2 intermediate container at constant pressure or speed, low-pressure CO2 (P<5bar) is injected into the chip to replace the air.

[0091] S4: Open the valve of the piston-type intermediate container 12, and use the single-cylinder injection pump 18 to pump in an oil sample to saturate the micro-nano fluid control chip, and wait for the equilibrium state.

[0092] S5: As Figure 3 As shown, the wide channel on the right is the flow aid channel, and the channel on the left, perpendicular to the flow aid channel, is the blind end channel. The oil in the flow aid channel is replaced by low-pressure CO2. The continuous flow in the flow aid channel removes the oil in the blind end channel through angular flow, leaving a separate oil plug in the blind end channel. The initial oil plug length for each test is adjusted to 1 / 3-2 / 3 of the blind end channel length, thus providing sufficient space for oil expansion during the test.

[0093] S6: Close the chip's outlet valve and begin testing. The experiment is conducted in constant pressure mode. The CO2 intermediate container 1 is heated at a constant temperature in an oven, and the pressure is gradually increased, causing the CO2 to change from the gas phase to the liquid phase (supercritical state); after each pressure increase step, the oil volume change is imaged under constant pressure.

[0094] S7: Import the corresponding image sequence into image processing software, perform grayscale and scale adjustments on the image sequence, and obtain the dilation distance x. t Then, the diffusion coefficient of CO2 in the experimental oil sample was calculated using a diffusion model.

[0095] Specifically, the diffusion coefficient can be calculated using the following formula:

[0096]

[0097] Where t is the diffusion time, x0 is the initial position of the liquid column, and x t Let be the position of the liquid column at time t. ν represents the average CO2 concentration. A C represents the specific volume of CO2 under the corresponding temperature and pressure conditions. Ai Where is the saturation concentration of CO2 diffusion in the oil phase, and D is the diffusion coefficient, in m³ / s. 2 / s. Where, C Ai The maximum average CO2 concentration after the diffusion process is completed can be used instead.

[0098] The aforementioned device can realistically simulate the temperature and pressure conditions of unconventional reservoirs. By using a dual-cylinder constant-pressure, constant-speed injection pump 3 and a single-cylinder constant-pressure, constant-speed injection pump 18, precise control of trace fluids can be achieved, allowing for injection into the micro / nanofluidic chip. Furthermore, a temperature control system can be integrated to control the required temperature and pressure during the experiment; and an image acquisition system enables visual detection and image analysis of CO2 diffusion phenomena. The method presented in this example is simple to operate and establishes a rapid and accurate measurement method for the CO2 diffusion coefficient in micro / nanopores using micro / nanofluidic experimental technology, thus solving several problems in existing technologies, such as long testing cycles, large sample consumption, and large testing scales.

[0099] The following is a specific example to illustrate this:

[0100] This example provides an apparatus and method for measuring the CO2 displacement diffusion coefficient, such as... Figure 2As shown, the device includes: two fluid medium injection containers (a high-pressure reciprocating intermediate container 1 and a high-pressure reciprocating intermediate container 12 for CO2), a fluid injection system (a dual-cylinder constant-pressure and constant-speed injection pump 3 and a single-cylinder constant-pressure and constant-speed injection pump 18), an image acquisition system 8, an image processing system 13, a temperature control system, fluid pressure relief and venting valves 6 and 17, a vacuum system 7, and a chip holder 9. The micro / nanofluidic chip 10 is housed inside the chip holder 9 and directly connected to a temperature sensor 11. It can withstand high-temperature and high-pressure experimental conditions (P≤20MPa, T≤150℃, resistant to corrosion from various chemical reagents). The chip channel provides sufficient observation area under a light source. Microchannel holes on both sides of the chip are connected to the outlets of the two intermediate containers via needle valves. The micro / nanofluidic chip, along with O-rings and other pipe and valve fittings, is connected to integrate and seal the entire nanofluidic system.

[0101] Specifically, the fluid injection system may include: a dual-cylinder constant pressure and constant speed injection pump 3, a single-cylinder constant pressure and constant speed injection pump 18, a CO2 high-pressure piston intermediate container 1, a high-pressure piston intermediate container 12, and inlet pressure sensors 4 and 5. The dual-cylinder constant pressure and constant speed injection pump 3 has an injection speed of 0.0001 ml / min-15.0000 ml / min and a pressure of 0.01 MPa-72.41 MPa. The single-cylinder constant pressure and constant speed injection pump 18 has an injection speed of 0.001 ml / min-10.000 ml / min and a pressure of 0.001 MPa-75.000 MPa. The inlet high pressure sensor 4 has a detection accuracy of 0.01 MPa and a detection pressure range of 0.01 MPa-50.00 MPa. The inlet low pressure sensor 5 has a detection accuracy of 0.01 MPa and a detection pressure range of 0.01 MPa-12.00 MPa. The outlet of the CO2 high-pressure piston intermediate container 1 is connected to pressure sensors 4 and 5 and connected to computer 13 to record the flow rate data of the pressure pump online, monitor the fluid in real time, and promptly feed back to the computer to regulate the CO2 injection pressure.

[0102] The image acquisition system 8 may include an optical microscope, a camera, and a computer 13. The temperature control system may include a chip holder 9, a constant temperature water bath 14, an insulating rubber tube 16, a temperature control medium, and a temperature sensor 11. The temperature sensor has a detection accuracy of 0.1℃ and a detection temperature range of -50.0℃ to 200.0℃. The temperature sensor 11 is externally connected to the bottom of the chip holder 9, and the insulating rubber tube 16 is externally connected to the heating holes 15 on both sides. The two vent valves are connected to the inlet and outlet pipes, and the vacuum pump is connected to the inlet pipe.

[0103] The outlet of the dual-cylinder constant-pressure and constant-speed injection pump 3 is connected to the inlet of the high-pressure reciprocating intermediate container 1 for CO2. A needle valve is installed at the connection point, and deionized water is placed at the bottom of the container. The intermediate container is embedded in an oven to ensure that the injected CO2 is at the critical temperature (31°C). The outlet is connected to a pressure sensor and a vacuum pump via a four-way valve, and the pipeline connecting the four-way valve is connected to the chip inlet via a needle valve. The chip holder 9 has a pinhole for an external temperature sensor at the bottom; inserting the probe allows for real-time monitoring of the chip surface temperature. The chip holder 9 has four heating holes on both sides, with embedded insulating rubber tubing to maintain the entire micro / nanofluidic chip at the temperature required for the target experiment.

[0104] Based on the aforementioned apparatus for measuring the CO2 diffusion coefficient, measuring the diffusion coefficient of CO2 in n-hexane at a pore size of 1000 nm at 75°C can include the following steps:

[0105] S1: Construct the micro / nano fluid control device described above, open the vacuum pump valve to evacuate the experimental pipeline, and conduct system pressure resistance and sealing tests.

[0106] S2: Set the experimental temperature to 75℃ using a constant temperature water bath 14 and wait for the temperature to stabilize;

[0107] S3: Using a high-pressure injection pump to push the piston of the CO2 high-pressure piston intermediate container 1 at constant pressure or constant speed, low-pressure CO2 (P<5bar) is injected into the chip to replace the air;

[0108] S4: Open the valve of the high-pressure piston intermediate container 12, and use the single-cylinder constant pressure and constant speed injection pump 18 to pump in oil sample to saturate the 1000nm chip, and wait for the equilibrium state.

[0109] S5: As Figure 3 As shown, the wide channel on the right is the flow aid channel, and the channel on the left, perpendicular to the flow aid channel, is the blind end channel. The oil in the flow aid channel is replaced by low-pressure CO2. The continuous flow in the main channel removes the oil in the blind end channel through angular flow, leaving a separate oil plug in the blind end channel. The initial oil plug length for each test is adjusted to 1 / 3-2 / 3 of the blind end channel length to provide sufficient space for oil expansion during the test.

[0110] S6: Close the chip's outlet valve and begin testing. The experiment was conducted in constant-rate mode, with the CO2 intermediate container heated to 45°C in an oven; the pressure was gradually increased at a constant flow rate of 0.1 ml / min, and the oil volume change was imaged after each pressure increment.

[0111] S7: Import the corresponding image sequence into image processing software, perform grayscale and scale adjustments, and obtain the position x of the expanded liquid column interface. t The diffusion coefficient of CO2 in the experimental oil sample at a specific time was calculated using the following one-dimensional diffusion model:

[0112]

[0113] in, The average CO2 concentration is represented by t, the diffusion time is represented by x0, and the initial position of the liquid column is represented by x. t ν represents the position of the liquid column at time t. A C represents the specific volume of CO2 under the corresponding temperature and pressure conditions. Ai The saturation concentration of CO2 diffused in the oil phase can be represented by the maximum average concentration of CO2 after the diffusion process is complete. D represents the diffusion coefficient, with units of m³. 2 / s.

[0114] S8: Draw as shown Figure 4 The diffusion coefficient curve shown is a time curve. The diffusion coefficient calculated using the expansion distance recorded when the diffusion length no longer changes is taken as the target diffusion coefficient.

[0115] In the example above, an apparatus and method for measuring the CO2 diffusion coefficient in unconventional reservoirs are provided, including: a micro / nano fluid control chip, a fluid injection system, an image acquisition system, an image processing system, and a temperature control system. This apparatus can realistically simulate the temperature and pressure conditions of unconventional reservoirs. The fluid injection system uses a dual-cylinder constant-pressure, constant-speed pump, capable of injecting trace amounts of fluid into the micro / nano fluid control chip at constant pressure or constant speed. Simultaneously, the temperature control system can control the required temperature and pressure during the experiment. The bright-field imaging mode of the image acquisition system can capture the phase interface, enabling visual detection and capture of CO2 diffusion phenomena. The image processing system can analyze image sequences. This invention achieves rapid measurement of the CO2 diffusion coefficient in reservoir fluids through micro / nano fluid control technology, solving the technical problems of long experimental cycles, complex experimental procedures, and high sample consumption in existing experimental methods.

[0116] The methods and embodiments provided in the above-described embodiments of this application can be executed in a mobile terminal, computer terminal, or similar computing device. Taking operation on an electronic device as an example... Figure 5 This is a hardware block diagram of an electronic device for determining the CO2 diffusion coefficient provided in this application. Figure 5 As shown, the electronic device 510 may include one or more (only one is shown in the figure) processors 502 (processors 502 may include, but are not limited to, processing devices such as microprocessors MCUs or programmable logic devices FPGAs), a memory 504 for storing data, and a transmission module 506 for communication functions. Those skilled in the art will understand that... Figure 5 The structure shown is for illustrative purposes only and does not limit the structure of the electronic device described above. For example, electronic device 510 may also include... Figure 5The more or fewer components shown, or having the same Figure 5 The different configurations shown.

[0117] The memory 504 can be used to store software programs and modules of application software, such as the program instructions / modules corresponding to the method for determining the CO2 diffusion coefficient in this embodiment. The processor 502 executes various functional applications and data processing by running the software programs and modules stored in the memory 504, thereby implementing the method for determining the CO2 diffusion coefficient of the aforementioned application. The memory 504 may include high-speed random access memory, and may also include non-volatile memory, such as one or more magnetic storage devices, flash memory, or other non-volatile solid-state memory. In some instances, the memory 504 may further include memory remotely located relative to the processor 502, and these remote memories can be connected to the electronic device 10 via a network. Examples of such networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof.

[0118] The transmission module 506 is used to receive or send data via a network. Specific examples of the network described above may include a wireless network provided by the communication provider of the electronic device 10. In one example, the transmission module 506 includes a Network Interface Controller (NIC), which can connect to other network devices via a base station to communicate with the Internet. In another example, the transmission module 506 may be a Radio Frequency (RF) module, used for wireless communication with the Internet.

[0119] At the software level, the aforementioned device for determining the CO2 diffusion coefficient can be as follows: Figure 6 As shown, it includes:

[0120] The first acquisition module 601 is used to acquire preset temperature and pressure conditions;

[0121] Simulation module 602 is used to simulate CO2 displacement of the target oil sample according to preset temperature and pressure conditions;

[0122] The second acquisition module 603 is used to acquire the initial position of the liquid column and the position of the expanded liquid column interface after a preset CO2 displacement time.

[0123] The third acquisition module 604 is used to acquire the specific volume of CO2 under the preset temperature and pressure conditions, and the saturation concentration of CO2 diffused in the target oil sample.

[0124] The determination module 605 is used to determine the diffusion coefficient of CO2 in the target oil sample based on the initial position of the liquid column, the interface position of the expanded liquid column, the specific volume, and the saturation concentration.

[0125] In one implementation, the determining module 605 can specifically calculate the diffusion coefficient of CO2 in the target oil sample according to the following formula:

[0126]

[0127] Where D represents the CO2 diffusion coefficient in the target oil sample. The average CO2 concentration is represented by t, the diffusion time is represented by x0, and the initial position of the liquid column is represented by x. t ν represents the position of the liquid column interface after expansion at time t. A C represents the specific volume of CO2 under preset temperature and pressure conditions. Ai The value represents the saturation concentration of CO2 diffusion in the oil phase, and D represents the diffusion coefficient.

[0128] In one implementation, the simulation module 602 can specifically build a micro-nano fluid control device, open the vacuum pump valve to evacuate the experimental pipeline and conduct system pressure resistance test and sealing test; after the pressure resistance test and sealing test are passed, the experimental temperature is adjusted to the preset temperature conditions through a constant temperature water bath; and CO2 is used to displace the target oil sample under preset pressure conditions.

[0129] Accordingly, the initial position of the liquid column and the position of the liquid column after a preset time of CO2 displacement are obtained, including: gradually increasing the pressure at a constant flow rate, and imaging the change in oil volume after each pressure increase operation to form an image sequence; performing grayscale processing and scale bar processing on the image sequence to obtain the position of the expanded liquid column interface at multiple time points after CO2 displacement.

[0130] In one embodiment, the micro / nanofluidic device includes a micro / nanofluidic chip. The channels in the micro / nanofluidic chip include a flow-aiding channel and a blind-end channel. The flow-aiding channel and the blind-end channel are arranged perpendicularly to each other. One end of the blind-end channel connected to the flow-aiding channel is open, and the other end away from the flow-aiding channel is sealed. During the process of simulating CO2 displacement of the target oil sample according to preset temperature and pressure conditions, the oil in the flow-aiding channel is replaced by low-pressure CO2. The continuous flow in the flow-aiding channel removes the oil in the blind-end channel through angular flow, leaving a separate oil plug in the blind-end channel.

[0131] In one embodiment, the determining module 605 can specifically obtain the expanded liquid column interface position at multiple displacement time points after simulating CO2 displacement of the target oil sample; determine the diffusion coefficient at multiple displacement time points based on the expanded liquid column interface position at multiple displacement time points; plot the diffusion coefficient change curve with time based on the diffusion coefficient at the multiple displacement time points; and determine the diffusion coefficient corresponding to the maximum expansion distance as the CO2 displacement diffusion coefficient in the target oil sample.

[0132] In one embodiment, the third acquisition module 604 can specifically acquire the maximum average concentration of CO2 in the target oil sample after the diffusion process is completed; and take the maximum average concentration of CO2 in the target oil sample as the saturation concentration of CO2 diffusion in the target oil sample.

[0133] The embodiments of this application also provide a specific implementation of an electronic device capable of implementing all steps in the method for determining the CO2 diffusion coefficient in the above embodiments. The electronic device specifically includes: a processor, a memory, a communication interface, and a bus; wherein the processor, memory, and communication interface communicate with each other via the bus; the processor is used to call a computer program in the memory, and when the processor executes the computer program, it implements all steps in the method for determining the CO2 diffusion coefficient in the above embodiments. For example, when the processor executes the computer program, it implements the following steps:

[0134] Step 1: Obtain the preset temperature and pressure conditions;

[0135] Step 2: Simulate CO2 displacement of the target oil sample according to the preset temperature and pressure conditions;

[0136] Step 3: Obtain the initial position of the liquid column and the position of the expanded liquid column interface after the preset CO2 displacement time;

[0137] Step 4: Obtain the specific volume of CO2 under the preset temperature and pressure conditions, and the saturation concentration of CO2 diffused in the target oil sample;

[0138] Step 5: Determine the diffusion coefficient of CO2 in the target oil sample based on the initial position of the liquid column, the position of the expanded liquid column interface, the specific volume, and the saturation concentration.

[0139] Embodiments of this application also provide a computer-readable storage medium capable of implementing all steps of the method for determining the CO2 diffusion coefficient in the above embodiments. The computer-readable storage medium stores a computer program that, when executed by a processor, implements all steps of the method for determining the CO2 diffusion coefficient in the above embodiments. For example, when the processor executes the computer program, it implements the following steps:

[0140] Step 1: Obtain the preset temperature and pressure conditions;

[0141] Step 2: Simulate CO2 displacement of the target oil sample according to the preset temperature and pressure conditions;

[0142] Step 3: Obtain the initial position of the liquid column and the position of the expanded liquid column interface after the preset CO2 displacement time;

[0143] Step 4: Obtain the specific volume of CO2 under the preset temperature and pressure conditions, and the saturation concentration of CO2 diffused in the target oil sample;

[0144] Step 5: Determine the diffusion coefficient of CO2 in the target oil sample based on the initial position of the liquid column, the position of the expanded liquid column interface, the specific volume, and the saturation concentration.

[0145] As described above, this embodiment of the application simulates CO2 displacement of a target oil sample under preset temperature and pressure conditions to obtain the initial position of the liquid column and the position of the liquid column after a preset CO2 displacement time, thereby determining the expansion distance. Furthermore, by using the specific volume of CO2 under the preset temperature and pressure conditions, as well as the saturation concentration of CO2 diffusion in the target oil sample, the initial position of the liquid column, and the position of the liquid column interface after expansion, the diffusion coefficient of CO2 in the target oil sample is determined. This solution solves the technical problem that the determination process for the diffusion coefficient of CO2 in unconventional reservoirs is too cumbersome and time-consuming, achieving the technical effect of quickly and accurately determining the diffusion coefficient of CO2.

[0146] 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. In particular, hardware + program embodiments are relatively simple in description because they are fundamentally similar to method embodiments; relevant parts can be referred to the descriptions in the method embodiments.

[0147] The foregoing has described specific embodiments of this specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims may be performed in a different order than that shown in the embodiments and may still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require the specific or sequential order shown to achieve the desired result. In some embodiments, multitasking and parallel processing are possible or may be advantageous.

[0148] While this application provides the method operation steps as described in the embodiments or flowcharts, more or fewer operation steps may be included based on conventional or non-inventive labor. The order of steps listed in the embodiments is merely one possible execution order among many and does not represent the only execution order. In actual device or client product execution, the methods shown in the embodiments or drawings can be executed sequentially or in parallel (e.g., in a parallel processor or multi-threaded processing environment).

[0149] While this specification provides method operation steps as described in the embodiments or flowcharts, more or fewer operation steps may be included based on conventional or non-inventive means. The order of steps listed in the embodiments is merely one possible execution order among many and does not represent the only execution order. In actual device or end 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 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 the process, method, product, or apparatus that includes said elements is not excluded.

[0150] For ease of description, the above devices are described in terms of function, divided into various modules. Of course, in implementing the embodiments of this specification, the functions of each module can be implemented in one or more software and / or hardware components, or a module that performs the same function can be implemented by a combination of multiple sub-modules or sub-units. The device embodiments described above are merely illustrative. For example, the division of units is only a logical functional division; in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces, or indirect coupling or communication connection between devices or units, and may be electrical, mechanical, or other forms.

[0151] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0152] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0153] The embodiments described in this specification can be described in the general context of computer-executable instructions, such as program modules, that are executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, etc., that perform a specific task or implement a specific abstract data type. The embodiments of 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.

[0154] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, system embodiments are basically similar to method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments. In the description of this specification, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the embodiments in this specification. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0155] The above description is merely an embodiment of the present specification and is not intended to limit the embodiments of the present specification. For those skilled in the art, various modifications and variations can be made to the embodiments of the present specification. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the embodiments of the present specification should be included within the scope of the claims of the embodiments of the present specification.

Claims

1. A method for determining the CO2 diffusion coefficient, characterized in that, The method includes: Obtain the preset temperature and pressure conditions; Simulate CO2 displacement of the target oil sample according to preset temperature and pressure conditions; Obtain the initial position of the liquid column and the position of the expanded liquid column interface after a preset CO2 displacement time; The specific volume of CO2 under the preset temperature and pressure conditions, and the saturation concentration of CO2 diffused in the target oil sample are obtained. The diffusion coefficient of CO2 in the target oil sample is determined based on the initial position of the liquid column, the position of the liquid column interface after expansion, the specific volume, and the saturation concentration.

2. The method according to claim 1, characterized in that, The diffusion coefficient of CO2 in the target oil sample is determined based on the initial position of the liquid column, the interface position of the expanded liquid column, the specific volume, and the saturation concentration, including: The diffusion coefficient of CO2 in the target oil sample is calculated using the following formula: Where D represents the CO2 diffusion coefficient in the target oil sample. The average CO2 concentration is represented by t, the diffusion time is represented by x0, and the initial position of the liquid column is represented by x. t ν represents the position of the liquid column interface after expansion at time t. A C represents the specific volume of CO2 under preset temperature and pressure conditions. Ai This indicates the saturation concentration of CO2 diffusion in the oil phase.

3. The method according to claim 1, characterized in that, Simulate CO2 displacement of the target oil sample under preset temperature and pressure conditions, including: A micro-nano fluid control device was constructed, and the vacuum pump valve was opened to evacuate the experimental pipeline and conduct system pressure resistance and sealing tests. After passing the pressure resistance test and the sealing test, the experimental temperature was adjusted to the preset temperature conditions using a constant temperature water bath. Simulate CO2 displacement of the target oil sample under preset pressure conditions; Accordingly, the initial position of the liquid column and the position of the expanded liquid column interface after the preset CO2 displacement time are obtained, including: The oil volume change was imaged after each pressure increment by gradually increasing the pressure at a low constant flow rate to form an image sequence. The image sequence was processed for grayscale and scale to obtain the position of the liquid column interface at multiple time points after CO2 displacement.

4. The method according to claim 3, characterized in that, The micro / nano fluid control device is equipped with a micro / nano fluid control chip. The channels in the micro / nano fluid control chip include a flow-aiding channel and a blind-end channel. The flow-aiding channel and the blind-end channel are arranged perpendicular to each other. The end of the blind-end channel connected to the flow-aiding channel is open, and the end away from the flow-aiding channel is sealed. During the simulation of CO2 displacement of the target oil sample under preset temperature and pressure conditions, the oil in the flow aid channel is replaced by low-pressure CO2, and the continuous flow in the flow aid channel removes the oil in the blind end channel, leaving a separate oil plug in the blind end channel, wherein the length of the oil plug accounts for 2 / 3 of the length of the blind end channel.

5. The method according to claim 1, characterized in that, The diffusion coefficient of CO2 in the target oil sample is determined based on the initial position of the liquid column, the interface position of the expanded liquid column, the specific volume, and the saturation concentration, including: After simulating CO2 displacement of the target oil sample, the positions of the expanded liquid column interface at multiple displacement time points were obtained. The diffusion coefficient at multiple displacement time points is determined based on the position of the liquid column interface after expansion at multiple displacement time points. Based on the diffusion coefficients at the multiple displacement time points, plot the diffusion coefficient variation curve over time. The diffusion coefficient corresponding to the maximum expansion distance is determined as the CO2 flooding diffusion coefficient in the target oil sample.

6. The method according to claim 1, characterized in that, Obtaining the saturation concentration of CO2 diffusion in the target oil sample includes: After the diffusion process is completed, obtain the maximum average concentration of CO2 in the target oil sample; The maximum average concentration of CO2 in the target oil sample is taken as the saturation concentration of CO2 diffusion in the target oil sample.

7. A device for determining the CO2 diffusion coefficient, characterized in that, include: The first acquisition module is used to acquire preset temperature and pressure conditions; The simulation module is used to simulate CO2 displacement of the target oil sample according to preset temperature and pressure conditions; The second acquisition module is used to acquire the initial position of the liquid column and the position of the expanded liquid column interface after a preset CO2 displacement time. The third acquisition module is used to acquire the specific volume of CO2 under the preset temperature and pressure conditions, as well as the saturation concentration of CO2 diffused in the target oil sample. The determination module is used to determine the diffusion coefficient of CO2 in the target oil sample based on the initial position of the liquid column, the interface position of the expanded liquid column, the specific volume, and the saturation concentration.

8. An electronic device comprising a processor and a memory for storing processor-executable instructions, characterized in that, When the processor executes the instructions, it implements the steps of the method according to any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program / instructions stored thereon, characterized in that, When the computer program / instructions are executed by the processor, they implement the steps of the method described in any one of claims 1 to 6.

10. A computer program product comprising a computer program / instructions, characterized in that, When the computer program / instructions are executed by the processor, they implement the steps of the method described in any one of claims 1 to 6.

Images