Test method for factors affecting porosity

Abstract

The present invention provides a method for testing factors affecting porosity, which comprises the following steps: constructing a skeleton particle deformation model, and placing the skeleton particle deformation model in a rigid constraint body that does not undergo displacement and deformation; filling the pores of the skeleton particle deformation model with a rigid fluid, and applying an overburden pressure to the upper surface of the rigid constraint body; changing the number of spheres, Young's modulus, and Poisson's ratio of the skeleton particle deformation model, gradually reducing the pore filling pressure of the rigid fluid, calculating the deformation of the spheres and the porosity change of the skeleton particle deformation model, and analyzing the influence of the skin effect on the porosity change and the influence of the constrained deformation on the porosity change. The method for testing factors affecting porosity provided by the present invention adopts a finite element numerical simulation method to study the deformation of skeleton particles and the change of porosity during the deformation of the porous medium body, and tests the influence of the skin effect and the constrained particle deformation on the porosity.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas reservoir exploitation, and in particular to a method for testing factors affecting porosity. Background Art

[0002] Most oil and gas reservoir rocks have been compacted and cemented and are dense porous media. During the oil reservoir exploitation process, the pore pressure decreases, the rock is compressed, and mainly elastic deformation occurs, and the porosity changes less with stress.

[0003] In the prior art, the degree of change of reservoir porosity with stress is usually studied by experimental methods. Experiments show that under the confining pressure of 10-30MPa, the porosity of reservoir rocks varies by 5-40%. In reserve evaluation research, the porosity is also usually corrected by the experimental test method of loading confining pressure. According to the dual effective stress theory of porous media, the body deformation of rock follows the principle of unchanged porosity. The assumption of body deformation is that the shape of the skeleton particles remains unchanged during compression, and the deformation of the skeleton and pores is proportional. After the rock is compressed, the arrangement form and particle size distribution of the skeleton particles do not change, so the porosity of the rock will not change during the body deformation.

[0004] However, under real conditions, the rock skeleton particles are in contact with each other, and the deformation of the particles is constrained by the adjacent particles. The shape of the skeleton particles will change during the compression process, and the assumption of proportional deformation is not strictly followed.

[0005] At present, it is difficult to avoid the influence of skin effect in conventional porosity testing, and the analysis of conventional porosity change is limited to the premise of unconstrained deformation of particles. However, the skin effect of the test will exaggerate the stress sensitivity of porosity, and at the same time, the particles are constrained to deform during the change of porosity.

[0006] Therefore, the present invention provides a method for testing factors affecting porosity. Summary of the invention

[0007] In order to solve the above problems, the present invention provides a method for testing factors affecting porosity, which comprises the following steps:

[0008] Constructing a skeleton particle deformation model, and placing the skeleton particle deformation model in a rigid constraint body without displacement and deformation;

[0009] Filling the pores of the skeleton particle deformation model with a rigid fluid and applying an overlying pressure to the upper surface of the rigid constraint body;

[0010] By changing the number of spheres, Young's modulus and Poisson's ratio of the skeleton particle deformation model, the pore filling pressure of the rigid fluid is gradually reduced, the sphere deformation and the porosity change of the skeleton particle deformation model are calculated, and the influence of the skin effect on the porosity change and the influence of constrained deformation on the porosity change are analyzed.

[0011] According to one embodiment of the present invention, the skeleton particle deformation model is a cubic stack of multiple spheres arranged closely together, and the six surface contact walls of the skeleton particle deformation model are constant stress boundaries, allowing displacement, and the walls are rigid, non-deformable walls.

[0012] According to one embodiment of the present invention, the method further comprises the following steps:

[0013] Multiple groups of skeleton particle deformation models with different numbers of spheres are set, and the Young's modulus and Poisson's ratio of each group of skeleton particle deformation models are the same. The pore filling pressure of the rigid fluid is gradually reduced, the sphere deformation and the porosity change of the skeleton particle deformation model are calculated, and the influence of the skin effect on the porosity change is analyzed.

[0014] According to one embodiment of the present invention, the method further comprises the following steps:

[0015] Experiments were conducted based on the skeleton particle deformation model with multiple groups of different numbers of spheres to determine the relationship between the number of spheres, the skin effect and the porosity change, wherein the number of spheres is negatively correlated with the skin effect, and the skin effect is positively correlated with the porosity change.

[0016] According to one embodiment of the present invention, the method further comprises the following steps:

[0017] Multiple groups of skeleton particle deformation models with different Poisson's ratios are set, and the Young's modulus and the number of spheres in each group of skeleton particle deformation models are the same. The pore filling pressure of the rigid fluid is gradually reduced, the deformation of the spheres and the porosity change of the skeleton particle deformation model are calculated, and the influence of constrained deformation on the porosity change is analyzed.

[0018] According to one embodiment of the present invention, the method further comprises the following steps:

[0019] Experiments were conducted based on the skeleton particle deformation model with multiple groups of different Poisson's ratios to determine the relationship between Poisson's ratio, constrained deformation and porosity change, wherein the Poisson's ratio is positively correlated with the porosity change.

[0020] According to one embodiment of the present invention, the method further comprises the following steps:

[0021] A graph showing the change of porosity with pore filling pressure is drawn, and the effects of skin effect and constrained deformation on porosity change are analyzed based on the porosity change.

[0022] According to one embodiment of the present invention, the overburden pressure is greater than the pore filling pressure.

[0023] According to one embodiment of the present invention, the method further comprises the following steps:

[0024] By changing the material, number of spheres, Young's modulus and Poisson's ratio of the skeleton particle deformation model, the pore filling pressure of the rigid fluid is gradually reduced, the sphere deformation and the porosity change of the skeleton particle deformation model are calculated, and the influence of the skin effect on the porosity change and the influence of constrained deformation on the porosity change are analyzed.

[0025] According to an embodiment of the present invention, the spherical material of the skeleton particle deformation model is a rubber sphere, a clay sphere and a quartz sphere.

[0026] The porosity influencing factor testing method provided by the present invention adopts the finite element numerical simulation method to study the deformation of skeleton particles and the change of porosity during the deformation of the porous medium body, and tests the influence of the skin effect and constrained particle deformation on the porosity; conventional porosity testing is difficult to avoid the influence of the skin effect, and the analysis of conventional porosity changes is limited to the premise of unconstrained deformation of particles. The tested skin effect will exaggerate the stress sensitivity of the porosity, and at the same time, the particles are constrained to deform during the change of porosity. The present invention avoids the above defects of the prior art and reveals the relationship between constrained deformation and skin effect and porosity change through a variety of combined tests.

[0027] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0029] Figure 1 Deformation pattern diagram showing the bulk deformation of the rock;

[0030] Figure 2 A volume change diagram showing the bulk deformation of the rock;

[0031] Figure 3Deformation pattern diagram showing structural deformation of rock;

[0032] Figure 4 A diagram showing the volume changes of the rock’s structural deformation;

[0033] Figure 5 A schematic diagram of the shape changes of the skeleton particles is shown;

[0034] Figure 6 A flow chart of a method for testing factors affecting porosity according to an embodiment of the present invention is shown;

[0035] Figure 7 A schematic diagram of a skeleton particle deformation model according to an embodiment of the present invention is shown;

[0036] Figure 8 A graph showing the variation of porosity with pore filling pressure under the condition of quartz sphere particles arranged in 10×10×10 according to an embodiment of the present invention is shown;

[0037] Fig. 9 A graph showing the variation of porosity with pore filling pressure under the condition of quartz sphere particles arranged at 30×30×30 according to an embodiment of the present invention is shown;

[0038] Fig.10 A graph showing the change of porosity with pore filling pressure when the Poisson's ratio μ is 0 under the condition that the quartz sphere particles are arranged in 30×30×30 according to one embodiment of the present invention;

[0039] Fig.11 A graph showing the variation of porosity with pore filling pressure under the condition of clay sphere particles arranged in 10×10×10 according to an embodiment of the present invention is shown;

[0040] Fig.12 A graph showing the variation of porosity with pore filling pressure under the condition of clay sphere particles arranged at 30×30×30 according to an embodiment of the present invention; and

[0041] Fig.13 The graph shows the change of porosity with pore filling pressure when the clay sphere particles are arranged in 30×30×30 according to an embodiment of the present invention and the Poisson's ratio μ is 0. DETAILED DESCRIPTION

[0042] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0043] like Figure 1 and Figure 2As shown in Figure 1, reservoir rocks are usually subject to the combined effects of overburden pressure (external stress, σ) and pore pressure (internal stress, p, including p1 and p2). During the production of oil reservoirs, the pore pressure decreases, the effective stress of the rock increases, and the skeleton particles of the rock deform, causing the rock to be compressed.

[0044] There are two basic deformation mechanisms of rocks: structural deformation and bulk deformation. Bulk deformation refers to the overall deformation of the rock caused by the deformation of the skeleton particles themselves (such as Figure 1 During the deformation of the main body, the shape and arrangement of the skeleton particles do not change, but the volume of the skeleton particles themselves changes (e.g. Figure 1 ). The porosity of rock has nothing to do with the size of the skeleton particles, but is related to the arrangement of the skeleton particles and the particle size distribution. Pores are the existence form of porous media, not a substance. Changes in stress state cannot directly act on the pores of rock, but instead cause deformation of the pores through the deformation of the rock skeleton particles. During the deformation of the body, only the volume of the skeleton particles changes, and the shape and arrangement of the particles do not change. Therefore, the skeleton volume and pore volume of the rock change in proportion, and the porosity of the rock does not change (such as Figure 2 ).

[0045] like Figure 3 and Figure 4 As shown in Figure 2, during the structural deformation of the rock, the volume of the skeleton particles themselves does not change, but the arrangement of the particles changes (e.g. Figure 3 At this time, the pore volume of the rock decreases, but the skeleton volume does not change, so the porosity will change significantly (such as Figure 4 ). Structural deformation is actually the compaction or microscopic destruction of rock, which usually occurs in loose porous media (uncemented rock). Dense media are mainly characterized by bulk deformation, while loose media are mainly characterized by structural deformation.

[0046] In the prior art, an assumption for the deformation of the rock body is that the shape of the skeleton particles remains unchanged, that is, each skeleton particle is compressed independently. However, in reality, the skeleton particles in the porous medium are in contact with each other, and the stress change is transmitted through the contact of the skeleton particles. This contact has certain constraints on the deformation of the skeleton particles. Therefore, the deformation of the skeleton particles in the porous medium is essentially a constrained deformation, such as Figure 5 Since the rock has been cemented, the arrangement of the skeleton particles is generally difficult to change, but during the compression process, the shape of the particles will change to a certain extent, such as Figure 5 (a) with Figure 5 (b).

[0047] The skeleton particles are constrained by the neighboring particles at the contact position, while the pore position is uniformly constrained by the fluid pressure. During the loading process, the skeleton stress σ sThe elastic deformation of the skeleton particles will decrease at the constrained position (contact position), while the elastic deformation will increase at the unconstrained position (pore).

[0048] Therefore, constrained elastic deformation changes the shape of the skeleton particles to a certain extent, thus destroying the assumption of proportional deformation (the skeleton volume and pore volume of the rock change proportionally, and the porosity of the rock does not change). Under the condition of constrained deformation, the deformation of the skeleton particles depends on the elastic model E of the skeleton particles. s and Poisson's ratio μ. The elastic modulus determines the degree of elastic deformation of the particles, while the Poisson's ratio determines the degree of deformation of the skeleton particles in the "pore" direction. This constrained deformation changes the shape of the skeleton particles to a certain extent and has a certain impact on the porosity.

[0049] In the prior art, it is difficult to avoid the influence of the skin effect when testing porosity, and the analysis of porosity changes is limited to the premise of unconstrained deformation of particles. In practice, the tested skin effect will exaggerate the stress sensitivity of porosity. At the same time, particles are constrained to deform during the change of porosity. Therefore, in order to overcome the above defects of the prior art, this application studies the influence of the skin effect and constrained deformation on porosity changes and provides a method for testing factors affecting porosity.

[0050] Figure 6 A flow chart of a method for testing factors affecting porosity according to an embodiment of the present invention is shown.

[0051] like Figure 6 In step S601, a skeleton particle deformation model is constructed, and the skeleton particle deformation model is placed in a rigid constraint body that does not undergo displacement and deformation.

[0052] In one embodiment, a schematic diagram of a skeleton particle deformation model is shown in FIG. Figure 7 As shown, the skeleton particle deformation model is a cubic stack of multiple spheres arranged closely together. The six surface contact walls of the skeleton particle deformation model are constant stress boundaries, which allow displacement, and the walls are rigid and non-deformable walls.

[0053] like Figure 7, the skeleton particle deformation model includes n×n×m spheres, wherein the x direction includes n spheres, the y direction includes n spheres, and the z direction includes m spheres, and n and m are positive integers. Specifically, the skeleton particle deformation model can be constructed by the finite element analysis software ABAQUES. Theoretically, n and m have no value range, and can take as large a value as possible under the condition of the computer's computing power. In one embodiment, n takes a value range of 10 to 50, and m takes a value range of 10 to 50, and a value greater than or equal to 30 is a larger value.

[0054] Figure 7 In the model, the skeleton particles are located in a rigid constraint that does not displace or deform, and are closely arranged; the gray plane on the surface of the sphere is the moving surface, and the external stress (overburden pressure σ) is applied to the skeleton particles through the downward movement of the gray plane. The gray upper plane is a rigid contact surface, which is displaced but not deformed. In the model, there is a contact surface (skin) between the porous medium and the constraint.

[0055] The experimental results are a joint manifestation of the porous medium itself and the skin characteristics. The influence of the existence of the skin on the test results is called the skin effect. Inside the tightly packed porous medium, a skeleton particle is adjacent to 12 nearby particles, and there are 12 constraint positions. However, the number of constraint positions for the skeleton particles on the skin is significantly reduced (at least 6). Therefore, the deformation mode of the skeleton particles on the skin is different from that inside the porous medium. Since the constraint wall does not deform and displace, the skin in the numerical experiment is a rigid skin, and only the deformation mode of the particles changes.

[0056] like Figure 6 In step S602, the pores of the skeleton particle deformation model are filled with a rigid fluid, and an overlying pressure is applied to the upper surface of the rigid constraint body.

[0057] Specifically, the pore filling pressure of the rigid fluid in the skeleton particle deformation model is p, and the upper contact wall of the skeleton particle deformation model is a rigid contact surface, which moves downward and loads an overlying pressure σ on the skeleton particles, and the overlying pressure is greater than the pore filling pressure (σ is greater than p); in one embodiment, the pore filling pressure p is 0.65σ.

[0058] like Figure 6 In step S603, the number of spheres, Young's modulus and Poisson's ratio of the skeleton particle deformation model are changed, the pore filling pressure of the rigid fluid is gradually reduced, the sphere deformation and the porosity change of the skeleton particle deformation model are calculated, and the influence of the skin effect on the porosity change and the influence of constrained deformation on the porosity change are analyzed.

[0059] In one embodiment, multiple groups of skeleton particle deformation models with different numbers of spheres are set, and the Young's modulus and Poisson's ratio of each group of skeleton particle deformation models are the same. The pore filling pressure of the rigid fluid is gradually reduced, the sphere deformation and the porosity change of the skeleton particle deformation model are calculated, and the influence of the skin effect on the porosity change is analyzed.

[0060] Furthermore, experiments were conducted based on the skeleton particle deformation model with multiple groups of different numbers of spheres to determine the relationship between the number of spheres, skin effect and porosity change. Among them, the number of spheres is negatively correlated with the skin effect, and the skin effect is positively correlated with the porosity change.

[0061] In one embodiment, multiple groups of skeleton particle deformation models with different Poisson's ratios are set, and the Young's modulus and the number of spheres in each group of skeleton particle deformation models are the same. The pore filling pressure of the rigid fluid is gradually reduced, the deformation of the spheres and the porosity change of the skeleton particle deformation model are calculated, and the influence of constrained deformation on the porosity change is analyzed.

[0062] Furthermore, experiments were conducted based on multiple groups of skeleton particle deformation models with different Poisson's ratios to determine the relationship between Poisson's ratio, constrained deformation and porosity change, among which the Poisson's ratio was positively correlated with the porosity change.

[0063] Specifically, in the first experiment, smaller n and m values ​​are set, both n and m are ≤10, and the Young's modulus E and Poisson's ratio μ of the sphere are set. The Young's modulus and Poisson's ratio are determined according to the material of the sphere. The Young's modulus E and Poisson's ratio μ of three different materials are shown in Table 1 below. The fluid pressure p is gradually reduced within the elastic deformation range of the sphere, and each calculation point is reduced by 5-8MPa. Numerical experiments are carried out, and the deformation of each sphere can be calculated by ABAQUES software to calculate the porosity change of the sphere stack.

[0064] Specifically, in the second experiment, larger values ​​of n and m were set, both n and m ≥ 30, and the Young's modulus E and Poisson's ratio μ of the sphere were set. The Young's modulus and Poisson's ratio were determined according to the material of the sphere. The fluid pressure p was gradually reduced within the elastic deformation range of the sphere, and each calculation point was reduced by 5-8 MPa. Numerical experiments were carried out, and the deformation of each sphere and the porosity change of the sphere stack can be calculated by ABAQUES software.

[0065] Specifically, in the third experiment, larger values ​​of n and m are set, both n and m ≥ 30, and the Young's modulus E of the sphere is set, which is determined according to the material of the sphere. The Poisson's ratio μ is set to 0, and the fluid pressure p is gradually reduced within the elastic deformation range of the sphere, with each calculation point reduced by 5-8MPa. Numerical experiments are carried out, and the deformation of each sphere can be calculated by ABAQUES software, and the porosity change of the sphere stack can be calculated.

[0066] Furthermore, in the first experiment, the second experiment and the third experiment, the material of the spheres is the same, and any one of rubber spheres, clay spheres and quartz spheres is selected, and the particle size of the spheres is 1 mm.

[0067] In the first experiment, n=10, m=10, Young's modulus was 50000 MPa, Poisson's ratio was 0.24, and the initial given value of p was 40 MPa, which was reduced by 5 MPa at each calculation point until it reached 20 MPa.

[0068] In the second experiment, n=30, m=30, Young's modulus was 50000 MPa, Poisson's ratio was 0.24, and the initial given value of p was 40 MPa, which was reduced by 5 MPa at each calculation point until it reached 20 MPa.

[0069] In the third experiment, n=30, m=30, Young's modulus was 50000 MPa, Poisson's ratio was 0, and the initial given value of p was 40 MPa, which was reduced by 5 MPa at each calculation point until it reached 20 MPa.

[0070] Specifically, by comparing the numerical change results of the porosity between the first experiment and the second experiment, the influence of the skin effect on the porosity change is analyzed; by comparing the numerical change results of the porosity between the second experiment and the third experiment, the influence of constrained deformation on the porosity change is analyzed.

[0071] Table 1 Mechanical parameters of three materials

[0072] Material Young's modulus, MPa Poisson's ratio, decimal Gripper cover (rubber) 100 0.47 Soft minerals (clay) 5000 0.35 Hard minerals (quartz) 50000 0.24

[0073] In one embodiment, a graph showing changes in porosity versus pore filling pressure is plotted, and the effects of skin effect and constrained deformation on the porosity change are analyzed based on the porosity change.

[0074] In one embodiment, the material, number of spheres, Young's modulus and Poisson's ratio of the skeleton particle deformation model are changed, the pore filling pressure of the rigid fluid is gradually reduced, the sphere deformation and the porosity change of the skeleton particle deformation model are calculated, and the influence of the skin effect on the porosity change and the influence of constrained deformation on the porosity change are analyzed.

[0075] In one embodiment, the spherical material of the skeleton particle deformation model is a rubber sphere, a clay sphere, and a quartz sphere.

[0076] Embodiment 1:

[0077] S11. Construct a cubic stacking model of n×n×m spheres tightly arranged, which is the skeleton particle deformation model, such as Figure 7The skeleton particles are located in a rigid constraint body that does not undergo displacement or deformation, where n and m are positive integers. Theoretically, n and m have no value range. They can be taken as large as possible under the computing power of the computer. Generally speaking, n ranges from 10 to 50, and m ranges from 10 to 50. A value greater than or equal to 30 is considered a large value.

[0078] S12. The six surface contact walls of the skeleton particle deformation model are set as constant stress boundaries. The boundaries can be displaced, and the walls are rigid and non-deformable walls. The pore filling pressure in the cubic pile is a rigid fluid with a pressure of p. The upper surface contact wall of the cubic pile is a rigid contact surface, and its downward movement loads an overlying pressure σ on the skeleton particles, where σ is greater than p. Preferably, p takes a value of 0.65σ.

[0079] S13, set n and m values ​​to 10, set the Young's modulus of the quartz sphere (spherical particle size 1mm) to 50000MPa, Poisson's ratio to 0.24, p to an initial given value of 40MPa, reduce 5MPa at each calculation point until it reaches 20MPa, conduct numerical experiments, calculate the deformation of each sphere, calculate the porosity change of the sphere stack, and the test results are shown in Figure 8 The horizontal axis is the pore filling pressure p, the unit is MPA; the vertical axis is the porosity Φ, the unit is %.

[0080] S14, set n and m values ​​to 30, set the Young's modulus of the quartz sphere (spherical particle size 1mm) to 50000MPa, Poisson's ratio to 0.24, p to an initial given value of 40MPa, reduce 5MPa at each calculation point until it reaches 20MPa, conduct numerical experiments, calculate the deformation of each sphere, and calculate the porosity change of the sphere stack. Test results are shown in Fig. 9 The horizontal axis is the pore filling pressure p, the unit is MPA; the vertical axis is the porosity Φ, the unit is %.

[0081] S15, set n and m values ​​to 30, set the Young's modulus of the quartz sphere (spherical particle size 1mm) to 50000MPa, set the Poisson's ratio μ to 0, and the initial given value of p to 40MPa. Reduce 5MPa at each calculation point until it reaches 20MPa. Perform numerical experiments to calculate the deformation of each sphere and the porosity change of the sphere stack. The test results are shown in Fig.10 The horizontal axis is the pore filling pressure p, the unit is MPA; the vertical axis is the porosity Φ, the unit is %.

[0082] S16. Compare the results of the two numerical experiments of step S13 and step S14, and analyze the effect of the skin effect on the porosity change. It can be seen that the numerical experiment of step S13 has a large skin effect and a large porosity change, so the skin effect is an important factor affecting the porosity change. Compare the results of the two numerical experiments of step S14 and step S15, and analyze the effect of constrained deformation on porosity. It can be seen that the experimental results of Poisson's ratio of 0 show that the porosity remains basically unchanged, so it can be considered that the change in porosity mainly comes from the Poisson's ratio of the particles, that is, the lateral deformation effect.

[0083] Embodiment 2:

[0084] S21 and S22 are the same as S11 and S12 in the first embodiment, and are not described in detail here.

[0085] S23, set n and m values ​​to 10, set the Young's modulus of the clay sphere (spherical particle size 1mm) to 5000MPa, Poisson's ratio to 0.35, and the initial given value of p to 40MPa. Reduce 5MPa at each calculation point until it reaches 20MPa. Perform numerical experiments to calculate the deformation of each sphere and the porosity change of the sphere stack. The test results are shown in Fig.11 The horizontal axis is the pore filling pressure p, the unit is MPA; the vertical axis is the porosity Φ, the unit is %.

[0086] S24, set n and m values ​​to 30, set the Young's modulus of clay sphere (spherical particle size 1mm) to 5000MPa, Poisson's ratio to 0.35, p initial given value to 40MPa, reduce 5MPa at each calculation point until it reaches 20MPa, conduct numerical experiments, calculate the deformation of each sphere, and calculate the porosity change of the sphere stack. Test results are shown in Fig.12 The horizontal axis is the pore filling pressure p, the unit is MPA; the vertical axis is the porosity Φ, the unit is %.

[0087] S25, set n and m values ​​to 30, set the Young's modulus of the clay sphere (spherical particle size 1mm) to 5000MPa, set the Poisson's ratio μ to 0, and the initial given value of p to 40MPa. Reduce 5MPa at each calculation point until it reaches 20MPa. Perform numerical experiments to calculate the deformation of each sphere and the porosity change of the sphere stack. The test results are shown in Fig.13 The horizontal axis is the pore filling pressure p, the unit is MPA; the vertical axis is the porosity Φ, the unit is %.

[0088] S26. Compare the results of the two numerical experiments of step S23 and step S24, and analyze the effect of the skin effect on the porosity change. It can be seen that the numerical experiment of step S23 has a large skin effect and a large porosity change, so the skin effect is an important factor affecting the porosity change. Compare the results of the two numerical experiments of step S24 and step S25, and analyze the effect of constrained deformation on porosity. It can be seen that the experimental results of the Poisson's ratio of 0 show that the porosity change is very small and can be ignored. It is considered to be basically unchanged. Therefore, it can be considered that the change in porosity mainly comes from the Poisson's ratio of the particles, that is, the lateral deformation effect.

[0089] In summary, the porosity influencing factor testing method provided by the present invention adopts the finite element numerical simulation method to study the deformation of the skeleton particles and the change of porosity during the deformation of the porous medium body, and tests the influence of the skin effect and the constrained particle deformation on the porosity; conventional porosity testing is difficult to avoid the influence of the skin effect, and the analysis of conventional porosity changes is limited to the premise of unconstrained deformation of particles. The tested skin effect will exaggerate the stress sensitivity of the porosity, and at the same time, the particles are constrained to deform during the change of porosity. The present invention avoids the above defects of the prior art and reveals the relationship between constrained deformation and skin effect and porosity change through a variety of combined tests.

[0090] It should be understood that the embodiments disclosed in the present invention are not limited to the specific structures, processing steps or materials disclosed herein, but should be extended to equivalent substitutions of these features understood by ordinary technicians in the relevant field. It should also be understood that the terms used herein are only used for the purpose of describing specific embodiments and are not meant to be limiting.

[0091] The "one embodiment" or "embodiment" mentioned in the specification means that the specific features, structures or characteristics described in conjunction with the embodiment are included in at least one embodiment of the present invention. Therefore, the phrases "one embodiment" or "embodiment" appearing in various places throughout the specification do not necessarily refer to the same embodiment.

[0092] Although the embodiments disclosed in the present invention are as above, the contents described are only embodiments adopted for facilitating the understanding of the present invention and are not intended to limit the present invention. Any technician in the technical field to which the present invention belongs can make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in the present invention, but the patent protection scope of the present invention shall still be subject to the scope defined in the attached claims.

Claims

1. A method for testing factors affecting porosity, characterized in that: The method comprises the following steps: Constructing a skeleton particle deformation model, and placing the skeleton particle deformation model in a rigid constraint body without displacement and deformation; Filling the pores of the skeleton particle deformation model with a rigid fluid and applying an overlying pressure to the upper surface of the rigid constraint body; A plurality of groups of skeleton particle deformation models with different numbers of spheres are set, each group of skeleton particle deformation models has the same Young's modulus and Poisson's ratio, the pore filling pressure of the rigid fluid is gradually reduced, the sphere deformation and the porosity change of the skeleton particle deformation model are calculated, and the influence of the skin effect on the porosity change is analyzed; or, a plurality of groups of skeleton particle deformation models with different Poisson's ratios are set, each group of skeleton particle deformation models has the same Young's modulus and number of spheres, the pore filling pressure of the rigid fluid is gradually reduced, the sphere deformation and the porosity change of the skeleton particle deformation model are calculated, and the influence of constrained deformation on the porosity change is analyzed.

2. The method according to claim 1, characterized in that The skeleton particle deformation model is a cubic stack of multiple spheres arranged closely together. The six surface contact walls of the skeleton particle deformation model are constant stress boundaries, which allow displacement, and the walls are rigid non-deformable walls.

3. The method according to claim 1, characterized in that The method further comprises the following steps: Experiments were conducted based on the skeleton particle deformation model with multiple groups of different numbers of spheres to determine the relationship between the number of spheres, the skin effect and the porosity change, wherein the number of spheres is negatively correlated with the skin effect, and the skin effect is positively correlated with the porosity change.

4. The method according to claim 1, characterized in that The method further comprises the following steps: Experiments were conducted based on the skeleton particle deformation model with multiple groups of different Poisson's ratios to determine the relationship between Poisson's ratio, constrained deformation and porosity change, wherein the Poisson's ratio is positively correlated with the porosity change.

5. The method according to claim 1, characterized in that The method further comprises the following steps: A graph showing the change of porosity with pore filling pressure is drawn, and the effects of skin effect and constrained deformation on porosity change are analyzed based on the porosity change.

6. The method according to claim 1, characterized in that The overburden pressure is greater than the pore filling pressure.

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