Carbon dioxide diffusion coefficient characterization method for carbon dioxide-water alternating gas drive in tight oil reservoirs

Abstract

The embodiment of the specification provides a carbon dioxide diffusion coefficient characterization method for carbon dioxide-water alternating flooding of tight oil reservoirs, which comprises the following steps: treating a first core and a second core with water saturation and oil saturation, performing water flooding on the first core so that the first core is affected by a water slug, performing carbon dioxide diffusion experiments on the first core and the second core, and locating the second core on the side of the first core away from the first intermediate container; constructing a first diffusion model of carbon dioxide at the first core affected by the water slug; constructing a second diffusion model of carbon dioxide at the second core not affected by the water slug; solving the first diffusion model and the second diffusion model to obtain a first diffusion coefficient of carbon dioxide at the first core and a second diffusion coefficient of carbon dioxide at the second core; and evaluating the diffusion mass transfer capacity of carbon dioxide into crude oil by using the first diffusion coefficient and the second diffusion coefficient. The method 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 a method for characterizing the carbon dioxide diffusion coefficient in tight oil reservoirs using alternating carbon dioxide-water vapor flooding. Background Technology

[0002] Due to the poor reservoir properties, complex pore structure, small pore size, and poor crude oil mobility of tight oil reservoirs, the carbon dioxide-water vapor alternating flooding technique is often employed. In this technique, the injected temperature and pressure exceed the critical temperature and pressure of carbon dioxide, placing it in a supercritical state. In this state, carbon dioxide has extremely strong diffusion capabilities, dissolving into the crude oil through diffusion, increasing its volume and reducing its density and viscosity. Furthermore, carbon dioxide does not undergo mass transfer with the crude oil, extracting lighter components and reducing the carbon dioxide-to-crude oil mobility ratio and interfacial tension, thus improving crude oil production and recovery. Therefore, the carbon dioxide diffusion mass transfer effect plays a crucial role in enhancing the recovery rate of carbon dioxide-water vapor alternating flooding in tight oil reservoirs.

[0003] Quantitatively characterizing the diffusion patterns during carbon dioxide-water-gas alternating flooding in tight oil reservoirs is of significant practical importance for revealing the carbon dioxide diffusion mechanism in such reservoirs. Constructing mathematical models is the most common method for quantitatively characterizing carbon dioxide diffusion capacity and patterns. However, existing mathematical models for carbon dioxide diffusion in tight oil reservoirs fail to consider the impact of alternating water-gas slug injection on carbon dioxide diffusion.

[0004] In view of this, the embodiments of this specification aim to provide a method and apparatus for characterizing the carbon dioxide diffusion coefficient in tight oil reservoirs using carbon dioxide-water vapor alternating flooding. 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 a method for characterizing the carbon dioxide diffusion coefficient in tight oil reservoirs using a carbon dioxide-water-gas alternating flooding approach, thereby solving the problem that the prior art does not consider the influence of the water slug formed by water flooding 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 a method for characterizing the carbon dioxide diffusion coefficient in tight oil reservoirs using a carbon dioxide-water vapor alternating flooding system, including:

[0008] The first and second cores are treated with saturated water and saturated oil. The first core is subjected to water drive to make it subject to water slugging. The first and second cores are placed in a core holder and supercritical carbon dioxide in the first intermediate container is pumped into the core holder to conduct a carbon dioxide diffusion experiment on the first and second cores. The second core is located on the side of the first core away from the first intermediate container.

[0009] Construct a first diffusion model of carbon dioxide at the first core sample affected by the water sluice.

[0010] Construct a second diffusion model for carbon dioxide in the second core sample that is not affected by the water slug;

[0011] Solving the first diffusion model yields the first diffusion coefficient of carbon dioxide at the first core affected by the water slug, and solving the second diffusion model yields the second diffusion coefficient of carbon dioxide at the second core unaffected by the water slug.

[0012] The diffusion mass transfer capacity of carbon dioxide into crude oil is evaluated using the first diffusion coefficient and the second diffusion coefficient.

[0013] Specifically, the first diffusion model is:

[0014]

[0015] Where C(x1,t) is the carbon dioxide concentration at time t on the first core sample at coordinate x1; D e1 τ1 is the first diffusion coefficient of carbon dioxide in the saturated fluid porous medium of the first core under the influence of the water slug; φ1 is the tortuosity of the first core; φ1 is the porosity of the first core.

[0016] The initial conditions for the first diffusion model are:

[0017]

[0018] Where L is the sum of the lengths of the first core and the second core, and the lengths of the first core and the second core are equal;

[0019] The boundary conditions for the first diffusion model are:

[0020] C(x1,t)=C i1 (x1 = 0, 0 < t < t1)

[0021] Among them, C i1t1 represents the initial concentration of carbon dioxide in the saturated fluid porous medium of the first core affected by the water slug; t1 represents the time it takes for carbon dioxide to diffuse to the interface between the first core affected by the water slug and the second core not affected by the water slug.

[0022] Furthermore, the first diffusion coefficient of carbon dioxide at the first core sample affected by the water sluice is obtained by solving the first diffusion model, including:

[0023] The first diffusion model is optimized by introducing a carbon dioxide deviation factor correction function, resulting in the optimized first diffusion model, the initial conditions of the optimized first diffusion model, and the boundary conditions of the optimized first diffusion model.

[0024] Based on the optimized first diffusion model, the initial conditions of the optimized first diffusion model, and the boundary conditions of the optimized first diffusion model, the first diffusion equation of carbon dioxide at the first core affected by the water sluice is obtained.

[0025] Solve the first diffusion equation to obtain the first diffusion coefficient.

[0026] Furthermore, solving the first diffusion equation yields the first diffusion coefficient, including:

[0027] Integrate the first diffusion equation;

[0028] The first diffusion coefficient is calculated based on the integrated first diffusion equation;

[0029] The first diffusion equation is:

[0030]

[0031] The first diffusion equation after integration is:

[0032]

[0033] Where, ΔM I D represents the first diffusion molar amount of carbon dioxide in the first core sample affected by the water sluice. e1 is the first diffusion coefficient.

[0034] Specifically, the second diffusion model is:

[0035]

[0036] Where C(x2,t) is the carbon dioxide concentration at coordinate x2 on the second core at time t, and D e2τ2 is the second diffusion coefficient of carbon dioxide in the saturated fluid porous medium of the second core that is not affected by the water slug, φ2 is the tortuosity of the second core, φ2 is the porosity of the second core, L is the sum of the lengths of the first core and the second core, the lengths of the first core and the second core are equal, and t2 is the time when the diffusion of carbon dioxide in the second core that is not affected by the water slug ends.

[0037] The initial conditions for the second diffusion model are:

[0038]

[0039] The boundary conditions for the second diffusion model are:

[0040] C(x2,t)=C i2 (x2=0,t>0)

[0041]

[0042] Among them, C i2 The concentration of carbon dioxide at the initial moment of diffusion in the saturated fluid porous medium of the second core, which is unaffected by the water slug.

[0043] Furthermore, solving the second diffusion model yields the diffusion coefficient of carbon dioxide at the second core sample unaffected by the water sluice, including:

[0044] The second diffusion model is optimized by introducing a carbon dioxide deviation factor correction function, resulting in the optimized second diffusion model, the initial conditions of the optimized second diffusion model, and the boundary conditions of the optimized second diffusion model.

[0045] Based on the optimized second diffusion model, its initial conditions, and its boundary conditions, the second diffusion equation for carbon dioxide at the second core unaffected by the water sluice is obtained.

[0046] Solve the second diffusion equation to obtain the second diffusion coefficient.

[0047] Furthermore, by solving the second diffusion equation, the second diffusion coefficient is obtained, including:

[0048] Integrate the second diffusion equation;

[0049] The second diffusion coefficient is calculated based on the integrated second diffusion equation;

[0050] The second diffusion equation is:

[0051]

[0052] The second diffusion equation after integration is:

[0053]

[0054] Where, ΔM II D represents the second diffusion molar amount of carbon dioxide in the second core sample unaffected by the water slug. e2 is the second diffusion coefficient.

[0055] Preferably, the method further includes:

[0056] The first diffusion molar amount and / or the second diffusion molar amount are corrected using the modified BWR equation, which is as follows:

[0057]

[0058] Where ε = 1 / Z, Z is the deviation factor; A', B', C', a', b', and c' are all characteristic parameters, and the value of A' is 2.53 × 10⁻⁶. 5 B' has a value of 43.29; C' has a value of 1.43 × 10⁻⁶. 10 R is the radius of the first core sample; T is the temperature; P is the pressure; the value of a' is 1.31 × 10⁻⁶. 7 The value of b' is 4.19 × 10. 3 The value of c' is 1.33 × 10⁻⁶. 12 The value of α' is 6.48 × 10 4 The value of γ is 4.48 × 10⁻⁶. 3 .

[0059] Secondly, embodiments of this specification also provide a device for characterizing the carbon dioxide diffusion coefficient in tight oil reservoirs using alternating carbon dioxide-water vapor flooding, comprising:

[0060] The processing module is used to treat the first core and the second core with saturated water and saturated oil, to water drive the first core so that the first core is affected by the water slug, to place the first core and the second core in a core holder and to pump supercritical 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, wherein the second core is located on the side of the first core away from the first intermediate container;

[0061] The first construction module is used to construct a first diffusion model of carbon dioxide at the first core affected by the water slug.

[0062] The second building module is used to build a second diffusion model of carbon dioxide in the second core that is not affected by the water slug;

[0063] The solution module is used to solve the first diffusion model to obtain the first diffusion coefficient of carbon dioxide at the first core affected by the water slug, and to solve the second diffusion model to obtain the second diffusion coefficient of carbon dioxide at the second core unaffected by the water slug.

[0064] The evaluation module is used to evaluate the diffusion mass transfer capacity of carbon dioxide into crude oil using the first diffusion coefficient and the second diffusion coefficient.

[0065] Thirdly, embodiments of this specification also 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 solutions.

[0066] By adopting the above technical solution, the embodiment of this specification provides a method, apparatus, and computer equipment for characterizing the carbon dioxide diffusion coefficient in tight oil reservoirs using a carbon dioxide-water-gas alternating flooding method. Before conducting a supercritical carbon dioxide diffusion experiment, the first core is subjected to water flooding treatment, causing the first core to be affected by a water slug. By constructing a first diffusion model and a second diffusion model respectively, the first diffusion coefficient of carbon dioxide at the first core affected by the water slug and the second diffusion coefficient at the second core unaffected by the water slug are calculated. This fully considers the impact of water flooding treatment on carbon dioxide diffusion, greatly improves the accuracy of carbon dioxide diffusion coefficient calculation, and provides a more reliable basis for oil development and exploitation.

[0067] 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

[0068] 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.

[0069] Figure 1 This document illustrates a step-by-step diagram of a method for characterizing the carbon dioxide diffusion coefficient in a tight oil reservoir using a carbon dioxide-water vapor alternating flooding technique, as provided in an embodiment of this specification.

[0070] Figure 2 This diagram illustrates the steps involved in solving the first diffusion model to obtain the first diffusion coefficient of carbon dioxide at the first core sample affected by the water sluice in an embodiment of this specification.

[0071] Figure 3This diagram illustrates the steps involved in solving the second diffusion model to obtain the diffusion coefficient of carbon dioxide in a second core sample unaffected by the water sluice in an embodiment of this specification.

[0072] Figure 4 This document shows a schematic diagram of a carbon dioxide diffusion coefficient characterization device for tight oil reservoir carbon dioxide-water vapor alternating flooding, as provided in an embodiment of this specification.

[0073] Figure 5 A schematic diagram of the structure of a computer device provided in an embodiment of this specification is shown.

[0074] Explanation of symbols in the attached drawings:

[0075] 41. Processing module;

[0076] 42. First building block;

[0077] 43. Second building block;

[0078] 44. Solver module;

[0079] 45. Evaluation Module;

[0080] 502. Computer equipment;

[0081] 504, Processor;

[0082] 506. Memory;

[0083] 508. Drive mechanism;

[0084] 510. Input / Output Module;

[0085] 512. Input devices;

[0086] 514. Output devices;

[0087] 516. Presentation equipment;

[0088] 518. Graphical User Interface;

[0089] 520. Network interface;

[0090] 522. Communication link;

[0091] 524. Communication bus. Detailed Implementation

[0092] 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 this specification.

[0093] 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.

[0094] This specification provides an embodiment of a method for characterizing the carbon dioxide diffusion coefficient in tight oil reservoirs using a carbon dioxide-water vapor alternating flooding system. Figure 1 This diagram illustrates the steps of a method for characterizing the carbon dioxide diffusion coefficient in a tight oil reservoir using a carbon dioxide-water vapor alternating flooding system, as provided in the embodiments of this specification. While this specification provides the operational steps described in the embodiments or flowcharts, more or fewer operational steps may be included based on conventional or non-inventive methods. The order of steps listed in the embodiments is merely one possible execution order among many and does not represent the only possible order. In actual system or device products, the methods shown in the embodiments or accompanying drawings can be executed sequentially or in parallel. Specifically, as shown in the embodiments or accompanying drawings... Figure 1 As shown, the method may include:

[0095] S110: The first core and the second core are treated with saturated water and saturated oil. The first core is subjected to water drive so that it is affected by water slugging. The first core and the second core are placed in a core holder and supercritical 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. The second core is located on the side of the first core away from the first intermediate container.

[0096] In the embodiments described in this specification, one end of the core holder is connected to an intermediate container, which 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.

[0097] When saturating the first and second core samples with water, 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. 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, so that the formation water is injected along the axial direction of the first and second core samples.

[0098] When saturating the first and second cores with oil, crude oil in the third intermediate container is pumped into the core holder until no more water comes out of the outlet of the core holder. The back pressure pump is set to 9 MPa, the crude oil flow rate is set to 0.01 mL / min, and the confining pressure pump is set to a confining pressure that is 2 MPa greater than the crude oil injection pressure, so that the crude oil is injected along the axial direction of the first and second cores.

[0099] Treating the first and second core samples with saturated water and oil can simulate the formation conditions of the core samples, which is beneficial to improving the accuracy of subsequent calculations of the carbon dioxide diffusion coefficient. Furthermore, the saturated water and oil treatment of the first and second core samples can be performed simultaneously in the same core holder or separately.

[0100] Furthermore, in the embodiments of this specification, only the first core is subjected to water flooding to make it subject to the influence of the water slug, so as to simulate the oil displacement zone formed by the alternating water and carbon dioxide flooding in the actual mining scenario, and provide conditions for studying the influence of the water slug on carbon dioxide diffusion.

[0101] Finally, in the supercritical carbon dioxide diffusion experiment, the pressure in the first intermediate container was increased to 17 MPa, and the confining pressure of the confining pump was set to be 2 MPa greater than the pressure in the first intermediate container. Carbon dioxide from the first intermediate container was pumped into the core holder until the pressure in the first intermediate container no longer changed. The first and second cores were placed in the same core holder, ensuring close contact, with the second core located on the side of the first core furthest from the intermediate container. Thus, during carbon dioxide diffusion, carbon dioxide diffused along the core axis from the first core affected by the water slug to the second core unaffected by the water slug, allowing for the calculation of the water slug's influence on carbon dioxide diffusion.

[0102] S120: Construct a first diffusion model of carbon dioxide at the first core sample affected by the water slug.

[0103] S130: Construct a second diffusion model for carbon dioxide in the second core that is not affected by the water slug.

[0104] S140: Solve the first diffusion model to obtain the first diffusion coefficient of carbon dioxide at the first core affected by the water slug, and solve the second diffusion model to obtain the second diffusion coefficient of carbon dioxide at the second core unaffected by the water slug.

[0105] S150: Using the first diffusion coefficient and the second diffusion coefficient, evaluate the mass transfer capacity of carbon dioxide into crude oil.

[0106] This specification provides a method for characterizing the carbon dioxide diffusion coefficient in tight oil reservoirs using a carbon dioxide-water-gas alternating flooding system. Before conducting supercritical carbon dioxide diffusion experiments, the first core sample is subjected to water flooding, thus influencing the carbon dioxide diffusion due to the presence of a water slug. This fully considers the impact of water flooding on carbon dioxide diffusion. Furthermore, by constructing a first diffusion model and a second diffusion model, the first diffusion coefficient of carbon dioxide at the water-slug-affected first core sample and the second diffusion coefficient at the unaffected second core sample are calculated. This significantly improves the accuracy of carbon dioxide diffusion coefficient calculations and provides a more reliable basis for oil development and extraction.

[0107] Furthermore, in the embodiments of this specification, the first diffusion model is:

[0108]

[0109] Where C(x1,t) is the carbon dioxide concentration at time t on the first core sample at coordinate x1; D e1 τ1 is the first diffusion coefficient of carbon dioxide in the saturated fluid porous medium of the first core under the influence of the water slug; φ1 is the tortuosity of the first core; φ1 is the porosity of the first core.

[0110] The initial conditions for the first diffusion model are:

[0111]

[0112] Where L is the sum of the lengths of the first core and the second core, and the lengths of the first core and the second core are equal;

[0113] The boundary conditions for the first diffusion model are:

[0114]

[0115] Among them, C i1 t1 represents the initial concentration of carbon dioxide in the saturated fluid porous medium of the first core affected by the water slug; t1 represents the time it takes for carbon dioxide to diffuse to the interface between the first core affected by the water slug and the second core not affected by the water slug.

[0116] Theoretically, the boundary conditions are only satisfied at the end boundary of the second core sample, which is far from the intermediate container. The first diffusion model corresponds to only the diffusion stage of carbon dioxide in a saturated fluid porous medium affected by water drive. Therefore, the boundary conditions for this diffusion stage need to be optimized. Specifically, in the embodiments of this specification, such as... Figure 2 As shown, step S140, solving the first diffusion model to obtain the first diffusion coefficient of carbon dioxide at the first core affected by the water sluice, may further include:

[0117] S210: Introduce a carbon dioxide deviation factor correction function to optimize the first diffusion model, and obtain the optimized first diffusion model, the initial conditions of the optimized first diffusion model, and the boundary conditions of the optimized first diffusion model.

[0118] Let the carbon dioxide deviation factor correction function be f(x,t), then the optimized first diffusion model is:

[0119] C(x1,t)=C i1 +f(x1,t) (4)

[0120]

[0121] The initial conditions for the optimized first diffusion model are:

[0122] f(x1,t)=-C i1 (t=0,0<x1<L) (6)

[0123] The optimized boundary conditions for the first diffusion model are:

[0124] f(x1,t)=0(x1=0,0<t<t1) (7)

[0125]

[0126] S220: Based on the optimized first diffusion model, the initial conditions of the optimized first diffusion model, and the boundary conditions of the optimized first diffusion model, the first diffusion equation of carbon dioxide at the first core affected by the water sluice is obtained.

[0127] S230: Solve the first diffusion equation to obtain the first diffusion coefficient.

[0128] Specifically, the process of solving the first diffusion equation is as follows:

[0129] Assuming the variables in the carbon dioxide deviation factor correction function f(x,t) are separable, then:

[0130] f(x,t)=X(x)T(t) (9)

[0131] Where X(x) is a function of coordinate x, and T(t) is a function of time t.

[0132] Substituting equation (9) into equation (5), we get:

[0133]

[0134] Equation (10) can be transformed into:

[0135]

[0136] make:

[0137]

[0138]

[0139] Where a is a constant. Integrating equations (12) and (13) respectively, we get:

[0140]

[0141] X = A cosx + B sin x (15)

[0142] Substituting equations (14) and (15) into equation (9), we get:

[0143]

[0144] Where parameters A and B are integration constants. Equation (9) is a linear equation, and its general solution is the sum of all solutions to equation (16), that is:

[0145]

[0146] Substituting equations (4) and (5) into equation (17), we get:

[0147] A n =0 (18)

[0148]

[0149] Substituting equations (18) and (19) into equation (17), the initial condition, i.e., equation (16), can be transformed into:

[0150]

[0151] Integrating equation (20) over the range [0, L], we have:

[0152]

[0153] Substituting equations (18), (19), and (20) into equation (17), we get:

[0154]

[0155] Substituting equation (22) into equation (4) yields the first diffusion equation:

[0156]

[0157] Solving the first diffusion equation yields the first diffusion coefficient, which is obtained by integrating equation (23):

[0158]

[0159] Where, ΔM I D represents the first diffusion molar amount of carbon dioxide in the first core sample affected by the water sluice. e1 This is the first diffusion coefficient, ΔM. I This can be obtained by observing the change in the carbon dioxide content in the first intermediate container.

[0160] Furthermore, in the embodiments of this specification, the second diffusion model is:

[0161]

[0162] Where C(x2,t) is the carbon dioxide concentration at coordinate x2 on the second core at time t, and D e2 τ2 is the diffusion coefficient of carbon dioxide in the saturated fluid porous medium of the second core that is not affected by the water slug, φ2 is the tortuosity of the second core, φ2 is the porosity of the second core, L is the sum of the lengths of the first core and the second core, the lengths of the first core and the second core are equal, and t2 is the time when the diffusion of carbon dioxide in the second core that is not affected by the water slug ends.

[0163] The initial conditions for the second diffusion model are:

[0164]

[0165] The boundary conditions for the second diffusion model are:

[0166] C(x2,t)=C i2 (x2=0,t>0) (27)

[0167]

[0168] Among them, C i2 The concentration of carbon dioxide at the initial moment of diffusion in the saturated fluid porous medium of the second core, which is unaffected by the water slug.

[0169] like Figure 3 As shown, step S140, solving the second diffusion model to obtain the diffusion coefficient of carbon dioxide at the second core unaffected by the water sluice, further includes:

[0170] S310: Introduce a carbon dioxide deviation factor correction function to optimize the second diffusion model, and obtain the optimized second diffusion model, the initial conditions of the optimized second diffusion model, and the boundary conditions of the optimized second diffusion model.

[0171] The carbon dioxide deviation factor correction function introduced for optimizing the second diffusion model is the same as the carbon dioxide deviation factor correction function introduced for optimizing the first diffusion model, which is Equation (9). The optimization process for the second diffusion model is similar to that for the first diffusion model, and will not be repeated here.

[0172] S320: Based on the optimized second diffusion model, the initial conditions of the optimized second diffusion model, and the boundary conditions of the optimized second diffusion model, the second diffusion equation of carbon dioxide in the second core unaffected by the water sluice is obtained.

[0173] S330: Solve to obtain the second diffusion equation and the second diffusion coefficient.

[0174] The process of solving the second diffusion equation is similar to that of solving the first diffusion equation, and will not be repeated here.

[0175] The final second diffusion equation is:

[0176]

[0177] Integrating the second diffusion equation, we get:

[0178]

[0179] Where, ΔM II D represents the second diffusion molar amount of carbon dioxide in the second core sample unaffected by the water slug. i2 is the second diffusion coefficient.

[0180] Since the carbon dioxide injected during the carbon dioxide diffusion experiment on the first and second core samples is in a supercritical state, in this embodiment of the specification, the method preferably further includes:

[0181] The first diffusion molar amount and / or the second diffusion molar amount are corrected using the modified BWR equation, which is as follows:

[0182]

[0183] Where ε = 1 / Z, Z is the deviation factor; A', B', C', a', b', and c' are all characteristic parameters, and the value of A' is 2.53 × 10⁻⁶. 5 B' has a value of 43.29; C' has a value of 1.43 × 10⁻⁶. 10 R is the radius of the first core sample; T is the temperature; P is the pressure; the value of a' is 1.31 × 10⁻⁶. 7 The value of b' is 4.19 × 10. 3 The value of c' is 1.33 × 10⁻⁶. 12 The value of α' is 6.48 × 10 4 The value of γ is 4.48 × 10⁻⁶. 3 .

[0184] After obtaining the deviation factor Z by solving equation (31), it is used to determine the first diffusion molar amount ΔM. I Second diffusion molar amount ΔM II Make corrections.

[0185] Finally, the corrected first diffusion molar amount ΔM I Second diffusion molar amount ΔM II Substituting these values ​​into equations (24) and (30), the accurate first and second diffusion coefficients can be calculated.

[0186] The carbon dioxide diffusion coefficient characterization method for tight oil reservoirs using alternating carbon dioxide-water-gas flooding provided in this specification takes into account the characteristics of slug injection in alternating carbon dioxide-water-gas flooding and, in conjunction with reservoir pore structure parameters (including tortuosity and porosity), constructs a first diffusion model for carbon dioxide in the first core sample affected by the water slug and a second diffusion model in the second core sample unaffected by the water slug. The method of separation of variables is used to solve both the first and second diffusion models, greatly improving the accuracy of the calculated carbon dioxide diffusion coefficient and providing more reliable technical support for oil development and exploitation.

[0187] like Figure 4 As shown, an embodiment of this specification provides a device for characterizing the carbon dioxide diffusion coefficient in a tight oil reservoir using a carbon dioxide-water vapor alternating flooding method, comprising:

[0188] Processing module 41 is used to treat the first core and the second core with saturated water and saturated oil, to water drive the first core so that the first core is affected by the water slug, to place the first core and the second core in a core holder and to pump supercritical carbon dioxide in the first intermediate container into the core holder to conduct a carbon dioxide diffusion experiment on the first core and the second core, wherein the second core is located on the side of the first core away from the first intermediate container;

[0189] The first construction module 42 is used to construct a first diffusion model of carbon dioxide at the first core affected by the water sluice.

[0190] The second building module 43 is used to build a second diffusion model of carbon dioxide in the second core that is not affected by the water slug;

[0191] The solver module 44 is used to solve the first diffusion coefficient of carbon dioxide at the first core affected by the water slug obtained by the first diffusion model, and to solve the second diffusion model to obtain the second diffusion coefficient of carbon dioxide at the second core unaffected by the water slug.

[0192] Evaluation module 45 is used to evaluate the diffusion mass transfer capacity of carbon dioxide into crude oil using the first diffusion coefficient and the second diffusion coefficient.

[0193] 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.

[0194] like Figure 5As shown, this specification provides a computer device according to an embodiment of the present specification. The carbon dioxide diffusion coefficient characterization device for tight oil reservoir carbon dioxide-water vapor alternating flooding 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 502 may include one or more processors 504, such as one or more central processing units (CPUs), each processing unit can implement one or more hardware threads. The computer device 502 may also include any memory 506 for storing any kind of information such as code, settings, data, etc. Non-limitingly, for example, the memory 506 may include any type of RAM, any type of ROM, flash memory device, 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 502. In one case, when the processor 504 executes associated instructions stored in any memory or combination of memories, the computer device 502 can perform any operation of the associated instructions. Computer device 502 also includes one or more drive mechanisms 508 for interacting with any memory, such as hard disk drive mechanism, optical disk drive mechanism, etc.

[0195] Computer device 502 may also include an input / output module 510 (I / O) for receiving various inputs (via input device 512) and providing various outputs (via output device 514). A specific output mechanism may include a presentation device 516 and an associated graphical user interface (GUI) 518. In other embodiments, the input / output module 510 (I / O), input device 512, and output device 514 may be omitted, and the device may function solely as a computer device within a network. Computer device 502 may also include one or more network interfaces 520 for exchanging data with other devices via one or more communication links 522. One or more communication buses 524 couple the components described above together.

[0196] Communication link 522 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 522 may include any combination of hardwired links, wireless links, routers, gateway functions, name servers, etc., governed by any protocol or combination of protocols.

[0197] Corresponding to, for example Figures 1 to 3 In addition to the method shown, 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 above-described method.

[0198] 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 1 to 3 The method shown.

[0199] 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 1 to 3 The method shown.

[0200] It should be understood that in the various embodiments of this specification, 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 of this specification.

[0201] 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. Furthermore, in the embodiments of this specification, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0202] 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 implementations should not be considered beyond the scope of the embodiments in this specification.

[0203] 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.

[0204] In the several 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.

[0205] 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.

[0206] 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.

[0207] 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.

[0208] This specification uses specific embodiments to illustrate the principles and implementation methods of this specification. The descriptions of the embodiments above are only for the purpose of helping to understand the methods and core ideas of 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 this specification. Therefore, the content of this specification should not be construed as a limitation on the embodiments of this specification.

Claims

1. A method for characterizing the carbon dioxide diffusion coefficient in tight oil reservoirs using a carbon dioxide-water vapor alternating flooding system, characterized in that... include: The first and second cores are treated with saturated water and saturated oil. The first core is subjected to water drive to make it subject to water slugging. The first and second cores are placed in a core holder and supercritical carbon dioxide in the first intermediate container is pumped into the core holder to conduct a carbon dioxide diffusion experiment on the first and second cores. The second core is located on the side of the first core away from the first intermediate container. Construct a first diffusion model of carbon dioxide at the first core sample affected by the water sluice. Construct a second diffusion model for carbon dioxide in the second core sample that is not affected by the water slug; Solving the first diffusion model yields the first diffusion coefficient of carbon dioxide at the first core affected by the water slug, and solving the second diffusion model yields the second diffusion coefficient of carbon dioxide at the second core unaffected by the water slug. The diffusion mass transfer capacity of carbon dioxide into crude oil is evaluated using the first diffusion coefficient and the second diffusion coefficient. The first diffusion model is: in, Coordinates on the first core exist The concentration of carbon dioxide at any given time; is the first diffusion coefficient of carbon dioxide in the first core saturated fluid porous medium affected by the water slug; The tortuosity of the first core sample; The porosity of the first core sample; The initial conditions for the first diffusion model are: in, The sum of the lengths of the first core and the second core is equal in length; The boundary conditions for the first diffusion model are: in, The concentration of carbon dioxide at the initial moment of diffusion in the saturated fluid porous medium of the first core sample affected by the water slug; The time it takes for carbon dioxide to diffuse to the interface between the first core sample affected by the water slug and the second core sample unaffected by the water slug; The second diffusion model is: in, Coordinates on the second core In The concentration of carbon dioxide at any given time. This is the second diffusion coefficient of carbon dioxide in the second core saturated fluid porous medium unaffected by the water slug. The second core tortuosity, The second core porosity, The sum of the lengths of the first and second core samples is equal in length. This is the time when carbon dioxide diffusion ends at the second core, which is not affected by water drive. The initial conditions for the second diffusion model are: The boundary conditions for the second diffusion model are: in, The concentration of carbon dioxide at the initial moment of diffusion in the saturated fluid porous medium of the second core, which is unaffected by the water slug.

2. The method according to claim 1, characterized in that, Solving the first diffusion model yields the first diffusion coefficient of carbon dioxide at the first core sample affected by the water sluice, further including; The first diffusion model is optimized by introducing a carbon dioxide deviation factor correction function, resulting in the optimized first diffusion model, the initial conditions of the optimized first diffusion model, and the boundary conditions of the optimized first diffusion model. Based on the optimized first diffusion model, the initial conditions of the optimized first diffusion model, and the boundary conditions of the optimized first diffusion model, the first diffusion equation of carbon dioxide at the first core affected by the water sluice is obtained. Solve the first diffusion equation to obtain the first diffusion coefficient.

3. The method according to claim 2, characterized in that, Solving the first diffusion equation to obtain the first diffusion coefficient further includes: Integrate the first diffusion equation; The first diffusion coefficient is calculated based on the integrated first diffusion equation; The first diffusion equation is: The first diffusion equation after integration is: in, This represents the first diffusion molar amount of carbon dioxide in the first core sample affected by the water sluice. is the first diffusion coefficient.

4. The method according to claim 1, characterized in that, Solving the second diffusion model yields the diffusion coefficient of carbon dioxide in the second core sample unaffected by the water sluice, further including: The second diffusion model is optimized by introducing a carbon dioxide deviation factor correction function, resulting in the optimized second diffusion model, the initial conditions of the optimized second diffusion model, and the boundary conditions of the optimized second diffusion model. Based on the optimized second diffusion model, its initial conditions, and its boundary conditions, the second diffusion equation for carbon dioxide at the second core unaffected by the water sluice is obtained. Solve the second diffusion equation to obtain the second diffusion coefficient.

5. The method according to claim 4, characterized in that, Solving the second diffusion equation yields the second diffusion coefficient, which further includes: Integrate the second diffusion equation; The second diffusion coefficient is calculated based on the integrated second diffusion equation; The second diffusion equation is: The second diffusion equation after integration is: in, This represents the second diffusion molar amount of carbon dioxide in the second core sample, which is unaffected by the water sluice. is the second diffusion coefficient.

6. The method according to claim 3 or 5, characterized in that, The method further includes: The first diffusion molar amount and / or the second diffusion molar amount are corrected using the modified BWR equation, which is as follows: in, , This is the deviation factor; , , , , , All are feature parameters. The value is 2.53 × 10 5 ; The value is 43.29; The value is 1.43 × 10 10 ; The radius of the first core sample; For temperature; For pressure; The value is 1.31 × 10 7 ; The value is 4.19 × 10 3 ; The value is 1.33 × 10 12 ; The value is 6.48 × 10 4 ; The value is 4.48 × 10 3 .

7. A device for characterizing the carbon dioxide diffusion coefficient in tight oil reservoirs using alternating carbon dioxide-water vapor flooding, characterized in that, include: The processing module is used to treat the first core and the second core with saturated water and saturated oil, to water drive the first core so that the first core is affected by the water slug, to place the first core and the second core in a core holder and to pump supercritical 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, wherein the second core is located on the side of the first core away from the first intermediate container; The first construction module is used to construct a first diffusion model of carbon dioxide at the first core sample affected by the water sluice; the first diffusion model is: in, Coordinates on the first core exist The concentration of carbon dioxide at any given time; is the first diffusion coefficient of carbon dioxide in the first core saturated fluid porous medium affected by the water slug; The tortuosity of the first core sample; The porosity of the first core sample; The initial conditions for the first diffusion model are: in, The sum of the lengths of the first core and the second core is equal in length; The boundary conditions for the first diffusion model are: in, The concentration of carbon dioxide at the initial moment of diffusion in the saturated fluid porous medium of the first core sample affected by the water slug; The time it takes for carbon dioxide to diffuse to the interface between the first core sample affected by the water slug and the second core sample unaffected by the water slug; The second construction module is used to construct a second diffusion model of carbon dioxide in the second core sample unaffected by the water sluice; the second diffusion model is: in, Coordinates on the second core In The concentration of carbon dioxide at any given time. This is the second diffusion coefficient of carbon dioxide in the second core saturated fluid porous medium unaffected by the water slug. The second core tortuosity, The second core porosity, The sum of the lengths of the first and second core samples is equal in length. This is the time when carbon dioxide diffusion ends at the second core, which is not affected by water drive. The initial conditions for the second diffusion model are: The boundary conditions for the second diffusion model are: in, The concentration of carbon dioxide at the initial moment of diffusion in the saturated fluid porous medium of the second core, which is not affected by the water slug; The solution module is used to solve the first diffusion model to obtain the first diffusion coefficient of carbon dioxide at the first core affected by the water slug, and to solve the second diffusion model to obtain the second diffusion coefficient of carbon dioxide at the second core unaffected by the water slug. The evaluation module is used to evaluate the diffusion mass transfer capacity of carbon dioxide into crude oil using the first diffusion coefficient and the second diffusion coefficient.

8. 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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