Rock pore wall surface complex mixed wettability characterization method

Abstract

The invention discloses a rock pore wall surface complex mixed wettability characterization method which comprises the following steps: acquiring pore structure parameters, and constructing a two-dimensional complex pore structure matrix model based on the pore structure parameters; based on the two-dimensional complex pore structure matrix model, obtaining a pore wall surface, and endowing the pore wall surface with a first contact angle to obtain single-phase wettability characterization; grouping and sampling the pore wall surfaces according to a first proportion, and endowing each group of sampled pore wall surfaces with a second contact angle to obtain mixed wettability characterization, the first proportion being equal proportion; grouping and sampling the pore wall surfaces according to a second proportion, and endowing each group of sampled pore wall surfaces with a third contact angle to obtain complex mixed wettability characterization, the second proportion being a non-equal proportion; based on the single-phase wettability characterization, the mixed wettability characterization, and the complex mixed wettability characterization, comprehensive wettability characterization is obtained. According to the method, the complex mixing wettability of the reservoir rock pore structure can be accurately represented.

Description

Technical Field

[0001] The invention belongs to the technical field of CO2 geological storage and safe and efficient development of low-permeability oil reservoirs, and in particular relates to a method for characterizing the complex mixed wettability of rock pore walls. Background Art

[0002] As one of the important basic characteristic parameters of reservoir rocks, wettability is a key factor controlling the microscopic distribution and flow characteristics of multiphase fluids in porous media. The wettability of the pore structure wall of reservoir rocks is extremely complex, which is of great significance to the distribution of fluids and the improvement of the imbibition recovery rate. Therefore, studying new methods for characterizing the wettability of rock pore walls can provide a basis for visualizing and accurately describing and quantitatively analyzing the complex wettability behavior under complex pore structures.

[0003] The wettability of rocks plays a decisive role in imbibition. The stronger the water-wetness of the core, the better the imbibition effect. The wettability of rocks can be mainly divided into three types: water-wet, oil-wet and mixed-wet. Unlike artificial cores, the wettability of natural cores is relatively complex, mainly mixed-wet. However, most of the existing studies have characterized and studied single-phase wettability, and the research on mixed wettability is still in the initial exploration stage, while there is still a large gap in the characterization and research of complex mixed wettability. In addition, traditional experimental measurements of wettability cannot accurately characterize wettability at the pore scale, which inevitably leads to certain limitations. New methods for characterizing reservoir rock wettability have become a key basic scientific issue for exploring complex wettability behavior, revealing the microscopic imbibition mechanism of multiphase fluid flow, and improving the imbibition recovery rate of oil and gas development. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a method for characterizing the complex mixed wettability of rock pore walls, which can accurately characterize the complex mixed wettability of the pore structure of reservoir rocks. It has important theoretical and engineering significance for revealing the microscopic flow mechanism of fluids under complex mixed wettability in the fields of CO2 geological storage and oil and gas development, and improving the imbibition recovery rate of oil reservoirs.

[0005] To achieve the above purpose, a method for characterizing complex mixed wettability of rock pore walls is provided, comprising:

[0006] Acquiring pore structure parameters, and constructing a two-dimensional complex pore structure matrix model based on the pore structure parameters;

[0007] Based on the two-dimensional complex pore structure matrix model, the pore wall surface is obtained, and a first contact angle is assigned to obtain a single-phase wettability characterization;

[0008] The pore walls are grouped and sampled according to a first ratio, and a second contact angle is assigned to each group of the sampled pore walls to obtain mixed wettability characterization, wherein the first ratio is an equal ratio;

[0009] The pore walls are grouped and sampled according to a second ratio, and a third contact angle is assigned to each group of the sampled pore walls to obtain a complex mixed wettability characterization, wherein the second ratio is a non-equal ratio;

[0010] Based on the single-phase wettability characterization, mixed wettability characterization and complex mixed wettability characterization, a comprehensive wettability characterization is obtained.

[0011] Optionally, the pore structure parameters include: porosity, permeability, capillary tortuosity and pore fractal dimension.

[0012] Optionally, based on the two-dimensional complex pore structure matrix model, obtaining the pore wall surface includes:

[0013] Based on the two-dimensional complex pore structure matrix model and combined with the fracture morphology, a fracture morphology rock matrix model is constructed;

[0014] Based on the fracture morphology rock matrix model, the pore wall surface is obtained.

[0015] Optionally, the crack morphology includes: Y-shaped crack and S-shaped crack.

[0016] Optionally, the pore walls are sampled in groups according to a first ratio, and a second contact angle is assigned to each group of the sampled pore walls to obtain the mixed wettability characterization, including:

[0017] The pore walls are sampled in groups according to a first ratio, and a control equation of the wettability wall is combined, and a second contact angle is assigned to each group of the sampled pore walls to obtain a mixed wettability characterization.

[0018] Optionally, the pore walls are sampled in groups according to a second ratio, and a third contact angle is assigned to each group of the sampled pore walls to obtain the complex mixed wettability characterization, including:

[0019] The pore walls are sampled in groups according to the second ratio, combined with the control equation of the wettability wall, and a third contact angle is assigned to each group of the sampled pore walls to obtain a complex mixed wettability characterization.

[0020] Optionally, the control equation is:

[0021] u=0

[0022]

[0023] Where u is the fluid velocity; n is the unit normal vector; ξ is the interface thickness parameter; is the phase field variable, which varies continuously from -1 to 1; θ is the contact angle; γ is the mobility; λ is the mixing energy; ψ is the dimensionless covariate of the phase field.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects:

[0025] The present invention makes up for the shortcomings of the existing complex pore structure wettability characterization method, realizes the refined upgrade of wettability from single phase to complex mixture, and makes the wettability characterization results more consistent with the real natural core. At the same time, the present invention also has the beneficial effects of simple experimental method, less operation process and accurate characterization results. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0027] Figure 1 This is a flow chart of a method for characterizing complex mixed wettability of rock pore walls according to an embodiment of the present invention;

[0028] Figure 2 1 is a diagram of a single-phase wettability rock matrix model established in an embodiment of the present invention, wherein (a) is an S-type single-phase wettability model with a contact angle of 30°, (b) is an S-type single-phase wettability model with a contact angle of 60°, (c) is an S-type single-phase wettability model with a contact angle of 90°, (d) is a Y-type single-phase wettability model with a contact angle of 30°, (e) is a Y-type single-phase wettability model with a contact angle of 60°, and (f) is a Y-type single-phase wettability model with a contact angle of 90°;

[0029] Figure 3 Schematic diagram of the mixed wettability rock matrix model established in an embodiment of the present invention, wherein (a) is an S-type mixed wettability model in which the contact angles of 30°, 60°, and 90° are randomly and non-repeatingly distributed at a ratio of 1:1:1, and (b) is a Y-type mixed wettability model in which the contact angles of 30°, 60°, and 90° are randomly and non-repeatingly distributed at a ratio of 1:1:1;

[0030] Figure 4The figure is a model diagram of complex mixed wettability rock matrix established in an embodiment of the present invention, wherein (a) is an S-type complex mixed wettability model in which the contact angles of 30°, 60°, and 90° are randomly and non-repeatingly distributed at 1:2:3, (b) is an S-type complex mixed wettability model in which the contact angles of 30°, 60°, and 90° are randomly and non-repeatingly distributed at 1:3:2, (c) is an S-type complex mixed wettability model in which the contact angles of 30°, 60°, and 90° are randomly and non-repeatingly distributed at 2:1:3, (d) is an S-type complex mixed wettability model in which the contact angles of 30°, 60°, and 90° are randomly and non-repeatingly distributed at 2:3:1, (e) is an S-type complex mixed wettability model in which the contact angles of 30°, 60°, and 90° are randomly and non-repeatingly distributed at 3:2:1, and (f) is an S-type complex mixed wettability model in which the contact angles of 30°, 60°, and 90° are randomly and non-repeatingly distributed at 3:1:2. DETAILED DESCRIPTION

[0031] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0032] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0033] The present invention proposes a method for characterizing the complex mixed wettability of rock pore walls. Figure 1 As shown, the specific steps include:

[0034] Obtain pore structure parameters, and construct a two-dimensional complex pore structure matrix model based on the pore structure parameters;

[0035] Based on the two-dimensional complex pore structure matrix model, the pore wall is obtained and the first contact angle is assigned to obtain the single-phase wettability characterization;

[0036] Specifically, the two-dimensional complex pore structure rock matrix numerical model was imported into the physical field based on the phase field method in COMSOL Multiphysics software. Under the "wetting wall" boundary command, all pore walls in the model were extracted, and then the same contact angle (30°, 60°, 90°) was given in the settings to establish 6 single-phase wettability rock matrix models. The single-phase wettability rock matrix model is shown in the figure. Figure 2 As shown in (a)-(f).

[0037] The pore walls are grouped and sampled according to a first ratio, and a second contact angle is assigned to each group of pore walls after sampling to obtain mixed wettability characterization, wherein the first ratio is an equal ratio;

[0038] The pore walls are grouped and sampled according to the second ratio, and a third contact angle is assigned to each group of pore walls after sampling to obtain a complex mixed wettability characterization, wherein the second ratio is non-equal ratio;

[0039] Obtain comprehensive wettability characterization based on single-phase wettability characterization, mixed wettability characterization, and complex mixed wettability characterization.

[0040] Specifically, based on the established two-dimensional complex pore structure matrix numerical model with different crack morphologies, the present invention imports the model into COMSOL Multiphysics software, assigns the same contact angle to all pore walls, and establishes a single-phase wettability rock matrix model; counts and numbers all pore walls, uses Excel to adopt a non-repeating random sampling function to sample all numbers in three groups at a ratio of 1:1:1, imports each group of numbers into the software and assigns different contact angles to establish a mixed wettability rock matrix model; finally, the complexity of the mixed wettability is further upgraded, three groups of all pore walls are randomly selected according to different proportions, and different contact angles are assigned to establish a complex mixed wettability model, thereby realizing a refined upgrade of the wettability of the rock matrix model from single phase to mixed and then to complex mixed.

[0041] Furthermore, the pore structure parameters include: porosity, permeability, capillary tortuosity, pore fractal dimension, etc.

[0042] Furthermore, based on the two-dimensional complex pore structure matrix model, the pore wall surface is obtained including:

[0043] Based on the two-dimensional complex pore structure matrix model and combined with the fracture morphology, a fracture morphology rock matrix model is constructed;

[0044] Based on the rock matrix model of fracture morphology, the pore wall surface is obtained.

[0045] Furthermore, the crack morphology includes: Y-shaped crack and S-shaped crack.

[0046] Specifically, under the "Wall" boundary command in the COMSOL Multiphysics software, all boundaries were selected in the settings, and all pore walls of the model were counted and numbered. The S-type and Y-type crack models had 2944 and 2884 pore walls, respectively, and all pore wall numbers were output to Excel.

[0047] Further, a first proportion sampling is performed on the pore wall surface, and a second contact angle is assigned to the sampled pore wall surface, and the mixed wettability characterization is obtained, including:

[0048] The pore wall is sampled at a first ratio, and combined with the control equation of the wettability wall, a second contact angle is assigned to the sampled pore wall to obtain the mixed wettability characterization.

[0049] Specifically, the “Position & “,”” command (such as A1 & “,”) is used in Excel software to convert the number into the standard format of COMSOL Multiphysics software, and each group of numbers is integrated together by merging cells and retaining all contents; then each group of pore wall numbers is imported into the “wetting wall” boundary command in COMSOL Multiphysics software; finally, different contact angles (30°, 60°, 90°) are randomly assigned to each group of pore walls in an equal proportion of 1:1:1 without repetition, and two mixed wettability rock matrix models are established. The mixed wettability wall data are shown in Table 1. The mixed wettability rock matrix model diagram, as shown in Table 1 Figure 3 As shown in (a)-(b).

[0050] Table 1

[0051]

[0052]

[0053] Furthermore, the pore wall is sampled at a second ratio, and a third contact angle is assigned to the sampled pore wall to obtain complex mixed wettability characterization including:

[0054] The pore wall is sampled at a second ratio, and combined with the control equation of the wettability wall, a third contact angle is assigned to the sampled pore wall to obtain the mixed wettability characterization.

[0055] Specifically, all pore wall numbers were randomly selected into three groups according to different proportions without duplication. After each group of pore wall numbers was re-imported into COMSOL Multiphysics, different contact angles (30°, 60°, 90°) were randomly and non-repeatedly assigned to each group of pore walls under the “wetting wall” boundary command. Six complex mixed wettability rock matrix models were established, and the contact angle distribution ratios were 1:2:3, 1:3:2, 2:1:3, 2:3:1, 3:2:1, and 3:1:2, respectively. The complex mixed wettability wall data are shown in Table 2. The complex mixed wettability rock matrix model diagram is shown in Table 2. Figure 4 As shown in (a)-(f).

[0056] Table 2

[0057]

[0058] Among them, the methods of obtaining and randomly assigning different contact angles of the pore wall for the S-type matrix and the Y-type matrix are the same.

[0059] Furthermore, the control equation is:

[0060] u=0

[0061]

[0062] Where u is the fluid velocity; n is the unit normal vector; ξ is the interface thickness parameter; is the phase field variable, which varies continuously from -1 to 1; θ is the contact angle; γ is the mobility; λ is the mixing energy; ψ is the dimensionless covariate of the phase field.

[0063] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for characterizing complex mixed wettability of rock pore walls, characterized in that: include: Acquiring pore structure parameters, and constructing a two-dimensional complex pore structure matrix model based on the pore structure parameters; Based on the two-dimensional complex pore structure matrix model, the pore wall surface is obtained, and a first contact angle is assigned to obtain a single-phase wettability characterization; The pore walls are grouped and sampled according to a first ratio, and a second contact angle is assigned to each group of the sampled pore walls to obtain mixed wettability characterization, wherein the first ratio is an equal ratio; The pore walls are grouped and sampled according to a second ratio, and a third contact angle is assigned to each group of the sampled pore walls to obtain a complex mixed wettability characterization, wherein the second ratio is a non-equal ratio; Based on the single-phase wettability characterization, mixed wettability characterization and complex mixed wettability characterization, a comprehensive wettability characterization is obtained.

2. A method for characterizing complex mixed wettability of rock pore walls according to claim 1, characterized in that: The pore structure parameters include porosity, permeability, capillary tortuosity and pore fractal dimension.

3. A method for characterizing complex mixed wettability of rock pore walls according to claim 1, characterized in that: Based on the two-dimensional complex pore structure matrix model, obtaining the pore wall surface includes: Based on the two-dimensional complex pore structure matrix model and combined with the fracture morphology, a fracture morphology rock matrix model is constructed; Based on the fracture morphology rock matrix model, the pore wall surface is obtained.

4. A method for characterizing complex mixed wettability of rock pore walls according to claim 3, characterized in that: The crack shapes include: Y-shaped cracks and S-shaped cracks.

5. A method for characterizing complex mixed wettability of rock pore walls according to claim 1, characterized in that: The pore walls are grouped and sampled according to a first ratio, and a second contact angle is assigned to each group of the sampled pore walls to obtain mixed wettability characterization, including: The pore walls are sampled in groups according to a first ratio, and a control equation of the wettability wall is combined, and a second contact angle is assigned to each group of the sampled pore walls to obtain a mixed wettability characterization.

6. A method for characterizing complex mixed wettability of rock pore walls according to claim 5, characterized in that: The pore walls are grouped and sampled according to the second ratio, and a third contact angle is assigned to each group of the sampled pore walls to obtain complex mixed wettability characterization, including: The pore walls are sampled in groups according to the second ratio, combined with the control equation of the wettability wall, and a third contact angle is assigned to each group of the sampled pore walls to obtain a complex mixed wettability characterization.

7. A method for characterizing complex mixed wettability of rock pore walls according to claim 6, characterized in that: The control equation is: u＝0 Where u is the fluid velocity; n is the unit normal vector; ξ is the interface thickness parameter; is the phase field variable, which varies continuously from -1 to 1; θ is the contact angle; γ is the mobility; λ is the mixing energy; ψ is the dimensionless covariate of the phase field.

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