Method for carbon dioxide diffusion experiment of carbon dioxide-water alternating flooding in tight oil reservoir

Abstract

The embodiment of the present specification provides a carbon dioxide diffusion experiment method for carbon dioxide-water alternating flooding of compact oil reservoirs, which comprises: performing water saturation and oil saturation treatment on a first core and a second core, and calculating oil saturation of the first core and oil saturation of the second core; performing water flooding on the first core to make the first core affected by a water slug and calculate water saturation of the first core; performing carbon dioxide diffusion experiment on the first core and the second core and recording a curve of pressure change of the first intermediate container with time; according to the oil saturation of the first core, the oil saturation of the second core, the water saturation and the curve of pressure change with time, the diffusion coefficients of carbon dioxide at the first core and at the second core are calculated; and the diffusion mass transfer capacity of carbon dioxide to crude oil is evaluated by using the diffusion coefficients of carbon dioxide. The embodiment of the present specification can improve the accuracy of carbon dioxide diffusion coefficient calculation and provide a reliable basis for evaluating the diffusion mass transfer capacity.

Description

Technical Field

[0001] The embodiments in this specification relate to the field of oil and gas development technology, and in particular to an experimental method for carbon dioxide diffusion in tight oil reservoirs using alternating carbon dioxide-water vapor displacement. Background Technology

[0002] Tight oil reservoirs are characterized by small pore throats, dense pores, complex pore structures, and poor crude oil flow. One commonly used development method is the carbon dioxide-water-gas alternating flooding method. In this process, the injected carbon dioxide is in a supercritical state and exhibits strong diffusivity. Under the influence of carbon dioxide diffusion, it dissolves into the crude oil, causing volume expansion, reduced density and viscosity, and lightening of the crude oil. It also continuously transfers mass with the crude oil and extracts light hydrocarbon components, enriching it with carbon dioxide and ultimately achieving a miscible displacement state. This significantly reduces the oil-gas ratio and oil-gas interfacial tension, thereby improving oil recovery. Therefore, carbon dioxide diffusion is a crucial mechanism for enhancing oil recovery in tight oil reservoirs using the carbon dioxide-water-gas alternating flooding method, and experimental physical simulation of carbon dioxide diffusion is an important method for studying it.

[0003] However, existing physical simulation methods for carbon dioxide diffusion experiments in tight oil reservoirs only consider the effects of parameters such as permeability, porosity, and water saturation on carbon dioxide diffusion. There is little research on the impact of alternating water-gas slug injection during carbon dioxide-water-gas alternating drive in tight oil reservoirs on carbon dioxide diffusion, resulting in inaccurate carbon dioxide diffusion coefficients.

[0004] In view of this, the embodiments in this specification aim to provide an experimental method for carbon dioxide diffusion in tight oil reservoirs using alternating carbon dioxide-water vapor displacement. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, the purpose of the embodiments in this specification is to provide an experimental method for carbon dioxide diffusion in tight oil reservoirs using alternating carbon dioxide-water-gas flooding, thereby solving the problem that the prior art does not consider the impact of water flooding operations on carbon dioxide diffusion, resulting in inaccurate calculation of the carbon dioxide diffusion coefficient.

[0006] To solve the above-mentioned technical problems, the specific technical solutions of the embodiments in this specification are as follows:

[0007] Firstly, embodiments of this specification provide an experimental method for carbon dioxide diffusion in tight oil reservoirs via alternating carbon dioxide-water vapor displacement, including:

[0008] The first and second core samples were treated with saturated water and saturated oil, and the oil saturation of the first and second core samples at the end of the saturated oil treatment was calculated.

[0009] The first core was subjected to water flooding to make the first core subject to the influence of water slugs, and the water saturation of the first core was calculated at the end of the water flooding.

[0010] Carbon dioxide in the first intermediate container is pumped into the core holder to conduct a carbon dioxide diffusion experiment on the first core and the second core placed in the core holder, and the pressure change curve of the first intermediate container over time during the diffusion experiment is recorded. The second core is located on the side of the first core away from the first intermediate container.

[0011] Based on the curves showing the changes in oil saturation of the first core, oil saturation of the second core, water saturation, and pressure over time, the diffusion coefficients of carbon dioxide at the first core and the second core were calculated.

[0012] The diffusion coefficients of carbon dioxide at the first and second core samples were used to evaluate the diffusion mass transfer capacity of carbon dioxide into crude oil.

[0013] Specifically, the first and second core samples were treated with saturated water and saturated oil, including:

[0014] Vacuum the first core and the second core.

[0015] The formation water in the second intermediate container is pumped into the core holder to saturate the first and second cores after vacuuming.

[0016] Adjust the temperature of the incubator to the set temperature;

[0017] The crude oil in the third intermediate container is pumped into the core holder to saturate the first and second cores. The confining pressure of the confining pressure pump connected to the core holder is set to be 2 MPa greater than the injection pressure of the crude oil. The first intermediate container, the second intermediate container, the third intermediate container and the core holder are located in the constant temperature chamber.

[0018] Furthermore, water-drive the first core sample to subject it to the influence of a water slug, including:

[0019] The formation water in the second intermediate container is pumped into the core holder to drive the first core placed in the core holder. The confining pressure of the confining pressure pump connected to the core holder is gradually increased and made to be 2 MPa greater than the injection pressure of the formation water.

[0020] Furthermore, carbon dioxide from the first intermediate container is pumped into the core holder to conduct a carbon dioxide diffusion experiment on the first and second cores placed in the core holder, including:

[0021] The confining pressure of the confining pump connected to the core holder is set to be 2 MPa greater than the pressure of the first intermediate container. The valve between the first intermediate container and the core holder is opened to allow the carbon dioxide to be pumped into the core holder to conduct a carbon dioxide diffusion experiment on the first core and the second core.

[0022] Specifically, based on the curves showing the changes in oil saturation of the first core, oil saturation of the second core, water saturation, and pressure over time, the diffusion coefficients of carbon dioxide at the first core and the second core are calculated, including:

[0023] Calculate the rate of pressure decrease at each time point on the pressure-time curve.

[0024] Based on the pressure drop rate at each time point, the pressure-time curve is divided into a first stage of carbon dioxide diffusion at the first core affected by the water slug and a second stage of carbon dioxide diffusion at the second core unaffected by the water slug.

[0025] The diffusion coefficient of carbon dioxide at the first core is obtained based on the first stage of the curves showing the oil saturation, water saturation, and pressure changes over time in the first core.

[0026] The diffusion coefficient of carbon dioxide at the second core was obtained based on the oil saturation of the second core and the second stage of the pressure-time curve.

[0027] Preferably, before treating the first and second core samples with saturated water and saturated oil, the method further includes:

[0028] A preset amount of nitrogen gas is pumped into the core holder, and the first pressure value of the core holder is recorded.

[0029] After closing the air inlet valve of the core holder, closing the confining pressure valve and back pressure valve connected to the core holder, and maintaining this for a preset time, the second pressure value of the core holder is obtained.

[0030] Determine whether the difference between the second pressure value and the first pressure value is within a preset difference range;

[0031] If so, the sealing performance of the core holder is deemed to meet the requirements.

[0032] Preferably, the length and diameter of the first core are equal to the length and diameter of the second core;

[0033] The permeability and porosity of the first core and the second core are respectively within the preset permeability difference and porosity difference ranges.

[0034] Secondly, the embodiments of this specification also provide an experimental apparatus for carbon dioxide diffusion in tight oil reservoirs using alternating carbon dioxide-water vapor displacement, comprising:

[0035] The first processing module is used to treat the first core and the second core with saturated water and saturated oil, and to calculate the oil saturation of the first core and the oil saturation of the second core at the end of the saturated oil treatment.

[0036] The second processing module is used to perform water flooding on the first core so that the first core is affected by the water slug, and to calculate the water saturation of the first core at the end of the water flooding.

[0037] The third processing module is used to pump carbon dioxide from the first intermediate container into the core holder to conduct a carbon dioxide diffusion experiment on the first core and the second core placed in the core holder, and to record the pressure change curve of the first intermediate container over time during the diffusion experiment. The second core is located on the side of the first core away from the first intermediate container.

[0038] The calculation module is used to calculate the diffusion coefficient of carbon dioxide at the first core and the second core based on the oil saturation of the first core, the oil saturation of the second core, the water saturation, and the pressure changing over time.

[0039] The evaluation module is used to evaluate the diffusion mass transfer capacity of carbon dioxide into crude oil by utilizing the diffusion coefficients of carbon dioxide at the first core and the second core.

[0040] Thirdly, the embodiments of this specification also provide a carbon dioxide-water vapor alternating flooding carbon dioxide diffusion experimental system for tight oil reservoirs, comprising:

[0041] An intermediate container is connected to one end of the core holder. The intermediate container includes a first intermediate container filled with carbon dioxide, a second intermediate container filled with formation water, and a third intermediate container filled with crude oil.

[0042] Core holder for holding the first core and / or the second core;

[0043] A constant temperature chamber is used to regulate the temperature of the core holder and the intermediate container placed inside it;

[0044] A displacement pump, connected to the intermediate container, is used to pump one or more of carbon dioxide, formation water, and / or crude oil into the core holder;

[0045] A back pressure pump is connected to the end of the core holder furthest from the intermediate container;

[0046] A confining pressure pump, connected to the core holder, is used to apply confining pressure to the core holder;

[0047] The controller is connected to the displacement pump and the constant temperature chamber. The pressure detection system is connected to the core holder, the confining pressure pump, the back pressure pump and the intermediate container; it is used to execute the method described in the above technical solution.

[0048] Fourthly, embodiments of this specification provide a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the method provided by the above-described technical solution.

[0049] Using the above technical solution, the carbon dioxide diffusion experiment method for carbon dioxide-water-gas alternating flooding in tight oil reservoirs provided in this specification takes into account the influence of water slugs formed during water flooding on carbon dioxide diffusion. By simulating a first core affected by a water slug and a second core unaffected by a water slug before conducting carbon dioxide diffusion experiments, the diffusion coefficient of carbon dioxide at the cores affected by and unaffected by the water slug can be obtained more accurately. This provides a basis for evaluating the diffusion and mass transfer capacity of carbon dioxide into crude oil and is of great significance for studying the seepage mechanism of carbon dioxide-water-gas alternating flooding in tight oil reservoirs.

[0050] To make the above and other objects, features and advantages of the embodiments of this specification more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0051] To more clearly illustrate the technical solutions in the embodiments or prior art of this specification, the drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this specification. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0052] Figure 1 This specification shows a schematic diagram of a carbon dioxide-water vapor alternating drive carbon dioxide diffusion experimental system for tight oil reservoirs, as provided in an embodiment of the present specification.

[0053] Figure 2This specification illustrates a step-by-step schematic diagram of an experimental method for carbon dioxide diffusion in tight oil reservoirs using alternating carbon dioxide-water vapor flooding, as provided in an embodiment of this specification.

[0054] Figure 3 This specification illustrates the steps of treating the first and second core samples with saturated water and saturated oil according to an embodiment of the present specification.

[0055] Figure 4 This specification illustrates the steps involved in calculating the diffusion coefficients of carbon dioxide at the first and second core samples, as described in the embodiments of this specification.

[0056] Figure 5 A schematic diagram showing the pressure change over time in the first intermediate container during the diffusion process is shown.

[0057] Figure 6 This specification illustrates the steps for performing a sealing check on a core holder according to an embodiment of the present invention.

[0058] Figure 7 This specification shows a schematic diagram of a carbon dioxide-water vapor alternating drive carbon dioxide diffusion experimental device for tight oil reservoirs, as provided in an embodiment of the present specification.

[0059] Figure 8 A schematic diagram of the structure of a computer device provided in an embodiment of this specification is shown.

[0060] Explanation of symbols in the attached drawings:

[0061] 10. Core holder;

[0062] 11. First pressure gauge;

[0063] 20. Intermediate container;

[0064] 21. First intermediate container;

[0065] 22. Second intermediate container;

[0066] 23. The third intermediate container;

[0067] 30. Incubator;

[0068] 40. Displacement pump;

[0069] 50. Back pressure pump;

[0070] 51. Second pressure gauge;

[0071] 60. Confining pressure pump;

[0072] 61. Third pressure gauge;

[0073] 70. Controller;

[0074] 81. First core sample;

[0075] 82. Second core sample;

[0076] 100. First processing module;

[0077] 200. Second processing module;

[0078] 300. Third processing module;

[0079] 400. Calculation module;

[0080] 500. Application Module;

[0081] 802. Computer equipment;

[0082] 804, Processor;

[0083] 806. Memory;

[0084] 808. Drive mechanism;

[0085] 810. Input / Output Module;

[0086] 812. Input devices;

[0087] 814. Output devices;

[0088] 816. Presentation equipment;

[0089] 818. Graphical User Interface;

[0090] 820. Network interface;

[0091] 822. Communication link;

[0092] 824. Communication bus. Detailed Implementation

[0093] 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 are within the scope of protection of the embodiments of this specification.

[0094] It should be noted that the terms "first," "second," etc., used in this specification, claims, and the foregoing drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, apparatus, product, or device that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0095] Carbon dioxide diffusion is a crucial mechanism for enhancing oil recovery in tight oil reservoirs through alternating carbon dioxide-water-gas flooding. Experimental physical simulation of carbon dioxide diffusion is an important method for studying it. However, existing methods for experimental physical simulation of carbon dioxide diffusion in tight oil reservoirs only consider the effects of parameters such as permeability, porosity, and water saturation on carbon dioxide diffusion. There is limited research on the impact of alternating water-gas slug injection during alternating carbon dioxide-water-gas flooding on carbon dioxide diffusion, resulting in inaccurate carbon dioxide diffusion coefficients. To address these issues, this specification provides an experimental method and system for carbon dioxide diffusion in alternating carbon dioxide-water-gas flooding of tight oil reservoirs.

[0096] like Figure 1 As shown in the illustration, a carbon dioxide-water vapor alternating flooding carbon dioxide diffusion experimental system for tight oil reservoirs is provided in an embodiment of this specification. The system includes:

[0097] The intermediate container 20 is connected to one end of the core holder 10. The intermediate container 20 includes a first intermediate container 21 filled with carbon dioxide, a second intermediate container 22 filled with formation water, and a third intermediate container 23 filled with crude oil.

[0098] The core holder 10 is used to hold the first core 81 and / or the second core 82; specifically, the core holder 10 is connected to the intermediate container 20 through a six-way valve, and the first intermediate container 21, the second intermediate container 22 and the third intermediate container 23 are respectively connected to different ports of the six-way valve.

[0099] The constant temperature chamber 30 is used to regulate the temperature of the core holder 10 and the intermediate container 20 placed therein; that is, to regulate the core temperature, as well as the temperature of the carbon dioxide, formation water and crude oil injected into the core holder 10, so as to accurately simulate the formation environment where the core is located.

[0100] Displacement pump 40, connected to intermediate container 20, is used to pump one or more of carbon dioxide, formation water and / or crude oil into core holder 10 to perform saturated water treatment, saturated oil treatment, water flooding treatment or carbon dioxide diffusion treatment on the core placed in core holder 10. Preferably, displacement pump 40 is an ISCO pump.

[0101] The back pressure pump 50 is connected to the end of the core holder 10 that is furthest from the intermediate container 20.

[0102] A confining pressure pump 60 is connected to the core holder 10 and is used to apply pressure to the core holder 10.

[0103] The controller 70 is connected to the displacement pump 40 and the constant temperature chamber 30, and is used to perform a carbon dioxide-water vapor alternating displacement carbon dioxide diffusion experimental method for tight oil reservoirs as provided in the embodiments of this specification below.

[0104] Furthermore, the carbon dioxide-water vapor alternating flooding carbon dioxide diffusion experimental system for tight oil reservoirs provided in the embodiments of this specification also includes:

[0105] The first pressure gauge 11 is connected to the core holder 10, the second pressure gauge 51 is connected to the back pressure pump 50, the third pressure gauge 61 is connected to the confining pressure pump 60, and the fourth pressure gauge (not shown in the figure) is connected to the first intermediate container 21.

[0106] The first pressure gauge 11, the second pressure gauge 51, the third pressure gauge 61, and the fourth pressure gauge are all connected to the controller 70 so that the controller 70 can monitor the injection pressure when carbon dioxide, formation water, or crude oil is injected into the core holder 10, the back pressure of the back pressure pump, the magnitude of the confining pressure applied to the core holder 10, and the pressure change of the first intermediate container 21 when carbon dioxide is injected into the core holder 10.

[0107] like Figure 2 This diagram illustrates the steps of a carbon dioxide-water vapor alternating displacement carbon dioxide diffusion experiment method for tight oil reservoirs, as provided in the embodiments of this specification. This specification provides the operational steps of the method described in the embodiments or flowcharts, but based on conventional or non-inventive labor, more or fewer operational steps may be included. The order of steps listed in the embodiments is merely one possible execution order among many and does not represent the only possible execution order. In actual system or device products, the methods shown in the embodiments or drawings can be executed sequentially or in parallel. Specifically, as shown in the diagrams... Figure 2 As shown, the method may include the following steps:

[0108] S210: Treat the first core and the second core with saturated water and saturated oil, and calculate the oil saturation of the first core and the oil saturation of the second core at the end of the saturated oil treatment.

[0109] Treating the first and second core samples with saturated water and saturated oil to simulate the formation environment in which the cores are located helps improve the accuracy of carbon dioxide diffusion coefficient calculations. In the embodiments of this specification, the length and diameter of the first core are equal to those of the second core; the permeability and porosity of the first core are equal to those of the second core, or the permeability and porosity of the first core and the second core are respectively within preset permeability difference and porosity difference ranges.

[0110] S220: Water drive the first core to subject it to the influence of a water slug, and calculate the water saturation of the first core at the end of the water drive.

[0111] In the embodiments of this specification, only the first core is subjected to water flooding to make it subject to the influence of water slugs, so as to simulate the oil displacement zone formed by the alternating flooding of water and carbon dioxide in the actual mining scenario, and to provide conditions for studying the influence of water slugs on carbon dioxide diffusion.

[0112] S230: The carbon dioxide in the first intermediate container is pumped into the core holder to conduct a carbon dioxide diffusion experiment on the first core and the second core placed in the core holder, and the pressure change curve of the first intermediate container over time during the diffusion experiment is recorded. The second core is located on the side of the first core away from the first intermediate container.

[0113] In the embodiments described in this specification, during the carbon dioxide diffusion experiment, the first core and the second core are placed in close contact, and the sizes of the first core and the second core are adapted to the cavity of the core holder. The second core is located on the side of the first core away from the intermediate container, so that during the carbon dioxide diffusion process, carbon dioxide diffuses along the axis of the core from the first core affected by the water slug to the second core unaffected by the water slug.

[0114] S240: Based on the curves showing the changes in oil saturation of the first core, oil saturation of the second core, water saturation, and pressure over time, the diffusion coefficients of carbon dioxide at the first core and the second core are calculated.

[0115] S250: The diffusion coefficients of carbon dioxide at the first and second cores are used to evaluate the diffusion mass transfer capacity of carbon dioxide into crude oil.

[0116] The carbon dioxide diffusion experimental method provided in the embodiments of this specification involves water-drive treatment of the first core sample before conducting the carbon dioxide diffusion experiment, which causes the first core sample to be affected by the water slug. This fills the gap in the existing simulation experiments regarding the impact of water-drive treatment on the carbon dioxide diffusion coefficient. By taking into account the impact of water-drive treatment, the calculation results of the carbon dioxide diffusion coefficient are more accurate, providing a more reliable basis for oil development and extraction.

[0117] like Figure 3 As shown, step S210, which involves treating the first and second core samples with saturated water and saturated oil, may further include:

[0118] S310: Vacuum the first core and the second core.

[0119] S320: Pump formation water from the second intermediate container into the core holder to saturate the first and second cores after vacuum treatment.

[0120] S330: Adjust the temperature of the constant temperature chamber to the set temperature.

[0121] Specifically, in the embodiments of this specification, the set temperature can be 73°C.

[0122] S340: The crude oil in the third intermediate container is pumped into the core holder to saturate the first core and the second core. The confining pressure of the confining pressure pump connected to the core holder is set to be 2 MPa greater than the injection pressure of the crude oil. The first intermediate container, the second intermediate container, the third intermediate container and the core holder are located in the constant temperature chamber.

[0123] Specifically, the saturated oil treatment of the first and second core samples must continue until no more water flows out of the outlet of the core holder. During the saturated oil treatment process, the backpressure pump connected to the core holder is set to a pressure of 9 MPa, and the confining pressure of the confining pressure pump connected to the core holder is set to a confining pressure 2 MPa higher than the injection pressure of the crude oil, so that the crude oil diffuses along the axial direction of the core. Preferably, the crude oil is pumped into the core holder at a constant flow rate of 0.01 mL / min.

[0124] It should be noted that when treating the first and second cores with saturated water and saturated oil, both cores can be placed in a core holder to treat them with saturated water simultaneously. After the water treatment is completed, the cores can be treated with saturated oil to speed up the experimental process.

[0125] Since the second core is located on the side of the first core furthest from the intermediate container, there is a possibility that the injected formation water or crude oil may not completely displace the second core. Therefore, in some preferred embodiments, the first core may be placed separately in a core holder and subjected to saturated water and saturated oil treatment; and the second core may be placed separately in a core holder (which could be another core holder, or the first core could be removed and then the second core placed in after the saturated water and saturated oil treatments are completed) and subjected to saturated water and saturated oil treatments. This improves the completeness of the saturated water and saturated oil treatments on the first and second cores, thereby improving the accuracy of the subsequent carbon dioxide diffusion coefficient.

[0126] Furthermore, in the embodiments of this specification, step S220, which involves water-driving the first core to subject it to the influence of a water slug, can be:

[0127] The formation water in the second intermediate container is pumped into the core holder until water is seen at the outlet of the core holder to drive the first core placed in the core holder. The pressure of the back pressure pump connected to the core holder is set to 9 MPa, and the flow rate of the formation water is set to 0.01 mL / min. The confining pressure of the confining pressure pump connected to the core holder is gradually increased and made to be 2 MPa greater than the injection pressure of the formation water, that is, so that the formation water is displaced along the axial direction of the core.

[0128] It should be noted that when the first and second cores are placed in a core holder to simultaneously treat both cores with saturated water and saturated oil, the second core should be removed from the core holder before water flooding the first core. In other words, during water flooding, the core holder contains only the first core, so the water flooding will not affect the second core.

[0129] If the first core is treated with saturated water and saturated oil separately, and the second core is treated with saturated water and saturated oil separately, then the water flooding treatment of the first core can be carried out after the saturated oil treatment. The treatment of the first core (saturated water, saturated oil, and water flooding) and the treatment of the second core (saturated water and saturated oil) can be performed in parallel or sequentially, that is, the second core is treated accordingly after the first core has been treated.

[0130] In the embodiments of this specification, step S230, which involves pumping carbon dioxide from the first intermediate container into the core holder to conduct a carbon dioxide diffusion experiment on the first and second cores placed in the core holder, can be:

[0131] Increase the pressure of the first intermediate container to 17 MPa, set the confining pressure of the confining pressure pump connected to the core holder to be 2 MPa greater than the pressure of the first intermediate container, and open the valve between the first intermediate container and the core holder to allow the carbon dioxide to be pumped into the core holder until the pressure of the first intermediate container no longer changes.

[0132] like Figure 4 As shown, based on the curves showing the changes in oil saturation of the first core, oil saturation of the second core, water saturation, and pressure over time, the diffusion coefficients of carbon dioxide at the first core and the second core are calculated, including:

[0133] S410: Calculate the rate of pressure decrease at each time point on the curve of pressure changing over time.

[0134] like Figure 5 As shown, this is a curve depicting the pressure change of the first intermediate container during the monitored carbon dioxide diffusion process.

[0135] S420: Based on the pressure drop rate at each time point, the pressure-time curve is divided into a first stage of carbon dioxide diffusion at the first core affected by the water slug, and a second stage of carbon dioxide diffusion at the second core unaffected by the water slug.

[0136] like Figure 5 As shown, the pressure drop rate exhibits two significant changes, approximately at 1000 min and 2250 min. During carbon dioxide diffusion, carbon dioxide first diffuses into the gap between the core holder and the first and second cores. Once the gap is filled, carbon dioxide, under the influence of confining pressure, axial pressure, and injection pressure, begins to diffuse from the first core, thus diffusing into it. Therefore, the first change in the pressure drop rate occurs at approximately 1000 min. After diffusion in the first core is complete, carbon dioxide further diffuses into the second core. Therefore, the second change in the pressure drop rate occurs at the boundary between the diffusion of carbon dioxide into the first and second cores. In the embodiments of this specification, the moment of the second change in the pressure drop rate is used as the basis for dividing the first and second stages.

[0137] S430: Based on the first stage of the curves showing the oil saturation, water saturation, and pressure changes over time in the first core, the diffusion coefficient of carbon dioxide at the first core is obtained.

[0138] The first stage is the diffusion stage of carbon dioxide in the first core affected by the water slug. Affected by the water slug, the water injected into the core displaces some of the crude oil and occupies the pores occupied by the displaced crude oil, which reduces the oil saturation and increases the water saturation of the first core, causing the carbon dioxide pressure drop curve to slow down, the carbon dioxide diffusion rate to decrease, and the diffusion of carbon dioxide in crude oil to be inhibited.

[0139] S440: Based on the oil saturation of the second core and the second stage of the pressure-time curve, the diffusion coefficient of carbon dioxide at the second core is obtained.

[0140] The second stage is the diffusion stage of carbon dioxide in the second core, which is not affected by the water slug. The second core is not affected by the water slug and has a high oil saturation, which increases the diffusion rate of carbon dioxide compared to the first stage and increases the pressure drop curve.

[0141] Combining the pressure-time curves of the first and second stages, it can be seen that the water slug inhibited the diffusion of carbon dioxide. Therefore, alternating water-gas drive can effectively suppress the diffusion rate of carbon dioxide towards the front edge, thereby reducing the degree of gas channeling and the gas breakthrough time.

[0142] Before treating the first and second core samples with saturated water and saturated oil, the method further includes:

[0143] The core holder was subjected to a sealing test.

[0144] Specifically, such as Figure 6 As shown, performing a sealing check on the core holder may include the following steps:

[0145] S610: Pump a preset amount of nitrogen into the core holder and record the first pressure value of the core holder.

[0146] For example, nitrogen gas at a pressure of 30 MPa or higher can be pumped into the core holder.

[0147] S620: After closing the air inlet valve of the core holder, closing the confining pressure valve and back pressure valve connected to the core holder, and maintaining this for a preset time, obtain the second pressure value of the core holder.

[0148] The preset duration can be 48 hours.

[0149] S630: Determine whether the difference between the second pressure value and the first pressure value is within a preset difference range.

[0150] The preset difference range can be less than 1 kPa.

[0151] S640: If so, the sealing performance of the core holder is deemed to meet the requirements.

[0152] Only when the core holder meets the sealing requirements can saturated water, saturated oil, water drive, and carbon dioxide diffusion experiments be carried out, which helps to ensure the accuracy of carbon dioxide diffusion coefficient calculation.

[0153] The carbon dioxide diffusion experimental method for carbon dioxide-water-gas alternating flooding in tight oil reservoirs provided in this specification creatively addresses the problem in existing technologies that do not consider the influence of water slugs on carbon dioxide diffusion. By simulating a first core sample affected by a water slug and a second core sample unaffected by a water slug before conducting carbon dioxide diffusion experiments, the diffusion coefficients of carbon dioxide at the first core sample affected by the water slug and the second core sample unaffected by the water slug are obtained. This provides a basis for evaluating the diffusion and mass transfer capacity of carbon dioxide into crude oil and is of great significance for studying the seepage mechanism of carbon dioxide-water-gas alternating flooding in tight oil reservoirs.

[0154] like Figure 7 As shown in the embodiments of this specification, an experimental apparatus for carbon dioxide diffusion in tight oil reservoirs via alternating carbon dioxide-water vapor flooding is also provided, comprising:

[0155] The first processing module 100 is used to treat the first core and the second core with saturated water and saturated oil, and to calculate the oil saturation of the first core and the oil saturation of the second core at the end of the saturated oil treatment.

[0156] The second processing module 200 is used to perform water flooding on the first core so that the first core is affected by the water slug, and to calculate the water saturation of the first core at the end of the water flooding.

[0157] The third processing module 300 is used to pump carbon dioxide from the first intermediate container into the core holder to conduct a carbon dioxide diffusion experiment on the first core and the second core placed in the core holder, and to record the pressure change curve of the first intermediate container over time during the diffusion experiment. The second core is located on the side of the first core away from the first intermediate container.

[0158] The calculation module 400 is used to calculate the diffusion coefficient of carbon dioxide at the first core and the second core based on the oil saturation of the first core, the oil saturation of the second core, the water saturation, and the pressure changing over time.

[0159] Evaluation module 500 is used to evaluate the diffusion mass transfer capacity of carbon dioxide into crude oil using the diffusion coefficients of carbon dioxide at the first core and the second core.

[0160] The beneficial effects obtained by the apparatus provided in the embodiments of this specification are consistent with the beneficial effects obtained by the methods described above, and will not be repeated here.

[0161] like Figure 8 The illustration shows a computer device provided in an embodiment of this specification. The tight oil reservoir carbon dioxide-water vapor alternating displacement carbon dioxide diffusion experimental apparatus in this specification can be the computer device in this embodiment, executing the methods described above in the embodiments of this specification. The computer device 802 may include one or more processors 804, such as one or more central processing units (CPUs), each processing unit capable of implementing one or more hardware threads. The computer device 802 may also include any memory 806 for storing information of any kind, such as code, settings, data, etc. Non-limitingly, for example, the memory 806 may include any type of RAM, any type of ROM, flash memory, hard disk, optical disk, etc. More generally, any memory can use any technology to store information. Further, any memory can provide volatile or non-volatile retention of information. Further, any memory can represent a fixed or removable component of the computer device 802. In one case, when the processor 804 executes associated instructions stored in any memory or combination of memories, the computer device 802 can perform any operation of the associated instructions. The computer device 802 also includes one or more drive mechanisms 808 for interacting with any memory, such as a hard disk drive mechanism, an optical disk drive mechanism, etc.

[0162] Computer device 802 may also include an input / output module 810 (I / O) for receiving various inputs (via input device 812) and providing various outputs (via output device 814). A specific output mechanism may include a presentation device 816 and an associated graphical user interface (GUI) 818. In other embodiments, the input / output module 810 (I / O), input device 812, and output device 814 may be omitted, and the device may function solely as a computer device within a network. Computer device 802 may also include one or more network interfaces 820 for exchanging data with other devices via one or more communication links 822. One or more communication buses 824 couple the components described above together.

[0163] Communication link 822 can be implemented in any way, such as via a local area network, a wide area network (e.g., the Internet), a point-to-point connection, or any combination thereof. Communication link 822 may include any combination of hardwired links, wireless links, routers, gateway functions, name servers, etc., governed by any protocol or combination of protocols.

[0164] Corresponding to Figures 2 to 4 and Figure 6 In addition to the methods described above, embodiments of this specification also provide a computer-readable storage medium storing a computer program that, when executed by a processor, performs the steps of the methods described above.

[0165] This specification also provides computer-readable instructions, wherein when a processor executes the instructions, the program therein causes the processor to perform the following... Figures 2 to 4 and Figure 6 The method shown.

[0166] This specification also provides a computer program product, including at least one instruction or at least one program segment, wherein the at least one instruction or the at least one program segment is loaded and executed by a processor to achieve the following: Figures 2 to 4 and Figure 6 The method.

[0167] It should be understood that in the various embodiments described herein, the sequence number of each process does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments in this specification.

[0168] It should also be understood that, in the embodiments of this specification, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this specification generally indicates that the preceding and following related objects have an "or" relationship.

[0169] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed in this specification can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of each example have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this specification.

[0170] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0171] In the embodiments provided in this specification, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and 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 couplings or direct couplings or communication connections shown or discussed may be indirect couplings or communication connections through some interfaces, devices, or units, or they may be electrical, mechanical, or other forms of connection.

[0172] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of the embodiments described in this specification, depending on actual needs.

[0173] Furthermore, the functional units in the various embodiments of this specification can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0174] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solutions of the embodiments of this specification, in essence, or the parts that contribute to the prior art, or all or part of the technical solutions, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this specification. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0175] This specification describes the principles and implementation methods of the embodiments using specific examples. The above descriptions of the embodiments are only for the purpose of helping to understand the methods and core ideas of the embodiments in this specification. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the embodiments in this specification. Therefore, the content of this specification should not be construed as a limitation on the embodiments in this specification.

Claims

1. A method for carbon dioxide diffusion in tight oil reservoirs using alternating carbon dioxide-water vapor displacement, characterized in that, include: The first and second core samples were treated with saturated water and saturated oil, and the oil saturation of the first and second core samples at the end of the saturated oil treatment was calculated. The first core was subjected to water flooding to make the first core subject to the influence of water slugs, and the water saturation of the first core was calculated at the end of the water flooding. Carbon dioxide in the first intermediate container is pumped into the core holder to conduct a carbon dioxide diffusion experiment on the first core and the second core placed in the core holder, and the pressure change curve of the first intermediate container over time during the diffusion experiment is recorded. The second core is located on the side of the first core away from the first intermediate container. Based on the time-varying curves of oil saturation of the first core, oil saturation of the second core, water saturation, and pressure, the diffusion coefficients of carbon dioxide at the first core and the second core are calculated. Specifically, the pressure decrease rate at each time point is calculated on the time-varying curve of pressure. Based on the pressure decrease rate at each time point, the time-varying curve of pressure is divided into a first stage of carbon dioxide diffusion at the first core affected by a water slug, and a second stage of carbon dioxide diffusion at the second core unaffected by a water slug. The diffusion coefficient of carbon dioxide at the first core is obtained based on the first stage of the time-varying curves of oil saturation, water saturation, and pressure. Similarly, the diffusion coefficient of carbon dioxide at the second core is obtained based on the second stage of the time-varying curves of oil saturation and pressure. The diffusion coefficients of carbon dioxide at the first and second core samples were used to evaluate the diffusion mass transfer capacity of carbon dioxide into crude oil.

2. The method according to claim 1, characterized in that, The first and second core samples were treated with saturated water and saturated oil, including: Vacuum the first core and the second core. The formation water in the second intermediate container is pumped into the core holder to saturate the first and second cores after vacuuming. Adjust the temperature of the incubator to the set temperature; The crude oil in the third intermediate container is pumped into the core holder to saturate the first and second cores. The confining pressure of the confining pressure pump connected to the core holder is set to be 2 MPa greater than the injection pressure of the crude oil. The first intermediate container, the second intermediate container, the third intermediate container and the core holder are located in the constant temperature chamber.

3. The method according to claim 1, characterized in that, Water-drive the first core sample to subject it to water slugging, including: The formation water in the second intermediate container is pumped into the core holder to drive the first core placed in the core holder. The confining pressure of the confining pressure pump connected to the core holder is gradually increased and made to be 2 MPa greater than the injection pressure of the formation water.

4. The method according to claim 1, characterized in that, Carbon dioxide from the first intermediate container is pumped into a core holder to conduct a carbon dioxide diffusion experiment on the first and second cores placed in the core holder, further comprising: The confining pressure of the confining pump connected to the core holder is set to be 2 MPa greater than the pressure of the first intermediate container. The valve between the first intermediate container and the core holder is opened to allow the carbon dioxide to be pumped into the core holder to conduct a carbon dioxide diffusion experiment on the first core and the second core.

5. The method according to claim 1, characterized in that, Before treating the first and second core samples with saturated water and saturated oil, the method further includes: A preset amount of nitrogen gas is pumped into the core holder, and the first pressure value of the core holder is recorded. After closing the air inlet valve of the core holder, closing the confining pressure valve and back pressure valve connected to the core holder, and maintaining this for a preset time, the second pressure value of the core holder is obtained. Determine whether the difference between the second pressure value and the first pressure value is within a preset difference range; If so, the sealing performance of the core holder is deemed to meet the requirements.

6. The method according to claim 1, characterized in that, The length and diameter of the first core are equal to the length and diameter of the second core; The permeability and porosity of the first core and the second core are respectively within the preset permeability difference and porosity difference ranges.

7. An experimental apparatus for carbon dioxide diffusion in tight oil reservoirs using alternating carbon dioxide-water vapor displacement, characterized in that, include: The first processing module is used to treat the first core and the second core with saturated water and saturated oil, and to calculate the oil saturation of the first core and the oil saturation of the second core at the end of the saturated oil treatment. The second processing module is used to perform water flooding on the first core so that the first core is affected by the water slug, and to calculate the water saturation of the first core at the end of the water flooding. The third processing module is used to pump carbon dioxide from the first intermediate container into the core holder to conduct a carbon dioxide diffusion experiment on the first core and the second core placed in the core holder, and to record the pressure change curve of the first intermediate container over time during the diffusion experiment. The second core is located on the side of the first core away from the first intermediate container. The calculation module is used to calculate the diffusion coefficients of carbon dioxide at the first core and the second core based on the oil saturation, water saturation, and pressure-time curves of the first core and the second core. Specifically, it calculates the pressure drop rate at each time point on the pressure-time curve; based on the pressure drop rate at each time point, it divides the pressure-time curve into a first stage of carbon dioxide diffusion at the first core affected by a water slug, and a second stage of carbon dioxide diffusion at the second core unaffected by a water slug; it obtains the diffusion coefficient of carbon dioxide at the first core based on the first stage of the pressure-time curve of the first core, the water saturation, and the first stage; and it obtains the diffusion coefficient of carbon dioxide at the second core based on the second stage of the pressure-time curve of the second core. The evaluation module is used to evaluate the diffusion mass transfer capacity of carbon dioxide into crude oil by utilizing the diffusion coefficients of carbon dioxide at the first core and the second core.

8. A carbon dioxide-water vapor alternating flooding carbon dioxide diffusion experimental system for tight oil reservoirs, characterized in that, include: An intermediate container is connected to one end of the core holder. The intermediate container includes a first intermediate container filled with carbon dioxide, a second intermediate container filled with formation water, and a third intermediate container filled with crude oil. Core holder for holding the first core and / or the second core; A constant temperature chamber is used to regulate the temperature of the core holder and the intermediate container placed inside it; A displacement pump, connected to the intermediate container, is used to pump one or more of carbon dioxide, formation water, and / or crude oil into the core holder; A back pressure pump is connected to the end of the core holder furthest from the intermediate container; A confining pressure pump, connected to the core holder, is used to apply confining pressure to the core holder; A controller, connected to the displacement pump and the constant temperature chamber; a pressure detection system, connected to the core holder, confining pressure pump, back pressure pump and the intermediate container; used to perform the method as described in any one of claims 1 to 6.

9. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the method as described in any one of claims 1 to 6.

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