A method for testing underground reservoir capacity based on dual pore structure

Abstract

The present invention relates to the technical field of reservoir capacity testing, and specifically discloses a method for testing underground reservoir capacity based on a dual-pore structure, comprising the following steps: (1) obtaining a void water storage coefficient K1 through a preloaded static specimen impact disturbance test and a saturated rock mass confined compaction test. (2) obtaining a pore water storage coefficient K2 through a crushing expansion-water storage characteristic test in a full stress-strain process under triaxial conditions. (3) calculating and obtaining the underground reservoir capacity V by using the void water storage coefficient K1 and the pore water storage coefficient K2. c The above method of the present invention regards the rock mass in the goaf as a dual-pore structure, thereby dividing the main water storage space into two parts: voids and pores. It takes into account key factors such as the stress state of the rock mass, rock properties, original cracks in the rock mass, mining energy, overburden pressure, water content, initial pores, etc., and truly restores the formation process of the underground reservoir water storage space, ensures the consistency of the water storage space with the site, and realizes the accurate test of the underground reservoir capacity.

Description

Technical Field

[0001] The invention relates to the technical field of reservoir capacity testing, and in particular to a method for testing underground reservoir capacity based on a dual pore structure. Background Art

[0002] The water storage coefficient and storage capacity of underground reservoirs represent the water storage capacity of underground reservoirs. They are the core parameters for designing and planning underground reservoirs in coal mine underground reservoir construction projects and are of great significance. The water storage coefficient and storage capacity of underground reservoirs are directly related to the composition of water storage space and are greatly affected by field parameters such as rock mass stress state, rock mass lithology, original rock mass cracks, mining energy, overburden pressure, water content, initial porosity, etc. This brings great difficulties to the determination of underground reservoir capacity. It is difficult to comprehensively consider the above influencing factors through simple methods to accurately and reliably predict the storage capacity of coal mine underground reservoirs. To this end, scholars at home and abroad have invented a variety of underground reservoir water storage coefficient and storage capacity testing methods.

[0003] For example, the Chinese patent application number 201711222824.3 discloses a method for calculating the water storage coefficient of underground water reservoirs in coal mines. However, this method mainly considers the influence of rock mass lithology and overburden pressure on the water storage coefficient and reservoir capacity, does not consider the influence of key factors such as mining energy, and ignores key water storage spaces such as voids formed by the rotation of collapsed rock mass and delamination voids of fractured rock layers. The Chinese patent application number 201810154644.4 discloses a method, storage medium and device for calculating the water storage capacity of underground water reservoirs. However, the technology does not provide a specific method for calculating the water storage coefficient of the top rock layers of different layers after the collapse of the top rock layers of different layers according to the surface equation of the reservoir bottom and the surface equation of the accumulation morphology after the collapse of the top rock layers of different layers. The Chinese patent application number 201711222863.3 discloses a method for determining the water storage coefficient of underground water reservoirs in coal mines and electronic equipment. However, the method for obtaining the key parameter of the expansion coefficient used to calculate the water storage coefficient in this technology is not given, which is not conducive to practical operation. Chinese patent application number 201710976512.5 discloses a method for accurately measuring the storage capacity of underground water reservoirs in coal mines. However, the method does not provide a method for obtaining key parameters such as the water storage coefficient and the expansion coefficient used to calculate the storage capacity.

[0004] It can be seen that the current technologies of this type generally fail to fully consider the impact of key field parameters such as rock stress state, rock lithology, original rock cracks, mining energy, overburden pressure, water content, initial porosity, etc. on the void structure and pore structure water storage performance, resulting in inaccurate prediction results. In addition, some technologies do not explain the specific methods for obtaining key parameters such as water storage coefficient or crushing expansion coefficient based on key influencing factors on site, making the relevant technologies difficult to apply in practice. Summary of the invention

[0005] In view of the above problems, the present invention provides a method for testing the underground reservoir capacity based on a dual-pore structure, which truly restores the formation process of the underground reservoir water storage space, ensures the consistency of the water storage space with the site, and realizes accurate testing of the underground reservoir capacity. Specifically, the technical solution of the present invention is as follows.

[0006] A method for testing the storage capacity of underground reservoirs based on a dual porosity structure comprises the following steps:

[0007] (1) The void water storage coefficient K1 of the broken rock block is obtained through the impact disturbance test of preloaded static specimens and the lateral confined compaction test of saturated rock mass.

[0008] (2) The pore water storage coefficient K2 of the same broken rock block as in step (1) is obtained through the crushing swelling-water storage characteristic test in the full stress-strain process under triaxial conditions.

[0009] (3) The underground reservoir capacity V is calculated by using the void water storage coefficient K1 and the pore water storage coefficient K2 c , the calculation formula is shown in formula (1):

[0010] (1).

[0011] In the formula (1), V i is the volume of a certain lithology layer in the underground reservoir, K 1i is the water storage coefficient of the void part of a certain rock mass in the underground reservoir, K 2i It is the water storage coefficient of the pore part of a certain rock mass in the underground reservoir.

[0012] Furthermore, in step (1), the method for obtaining the broken rock blocks is as follows: sampling the rock layers of each lithology in the rock mass of the caving zone and processing them into standard specimens. Then, the impact energy Q required for the test is determined according to the collapse height h of the goaf. Then, the pre-loaded static stress σ1 required for the test is determined according to the ground stress conditions. Then, the broken rock blocks are obtained through the impact disturbance test of the pre-loaded static specimen.

[0013] Furthermore, the impact energy Q required for the test is obtained by formula (2):

[0014] (2).

[0015] In formula (2), ρ is the rock mass density, V' is the volume of the standard specimen, h is the collapse height of the goaf, and g is the gravitational acceleration.

[0016] Furthermore, after obtaining the broken rock blocks, the compaction load σ2 required for the test is determined according to the overburden pressure of the goaf. Then, the saturated rock mass confined compaction test is performed to obtain the void water storage coefficient K1 of the broken rock blocks.

[0017] Furthermore, in step (2), samples of each lithology in the rock mass of the caving zone are taken, the original cracks are retained, and the samples are processed into standard specimens. Then, the confining pressure σ3 required for the test is determined according to the ground stress conditions, and then the crushing expansion-water storage characteristic test in the full stress-strain process under triaxial conditions is carried out to obtain the pore water storage coefficient K2 under different stress conditions, and the corresponding pore water storage coefficient K2 is found in the test results according to the overburden pressure of the goaf.

[0018] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0019] The underground reservoir capacity test method proposed in the present invention regards the rock mass in the goaf as a dual pore structure, thereby dividing the main water storage space of the rock mass in the goaf into two parts: voids and pores according to the size of the space. This lays the foundation for comprehensively considering the influence of key field parameters such as the stress state of the rock mass, the lithology of the rock mass, the original cracks of the rock mass, the mining energy, the overburden pressure, the water content state, the initial pores, etc. on the water storage performance of the void structure and the pore structure, so that the present invention can truly restore the formation process of the underground reservoir water storage space through basic tests, ensure the consistency of the water storage space with the site, and realize the accurate test of the underground reservoir capacity. This is because the evolution process and influencing factors of voids and pores are different. If the voids and pores are not distinguished in the goaf rock mass, but the two are mixed, when testing the overall water storage coefficient of voids and pores, the real evolution process of different water storage spaces cannot be fully reflected, and the influencing factors of the voids and pores can only be mixed together for consideration. The present invention regards the rock mass in the goaf area as a dual-pore structure, distinguishes the voids and pores of the rock mass in the goaf area, thereby restoring its different formation processes through different tests, and considers the important influencing factors in the void water storage coefficient, namely, overburden pressure, rock mass lithology, mining energy, and water content state, and considers the important influencing factors in the pore water storage coefficient, namely, rock mass stress state, rock mass lithology, original cracks in the rock mass, water content state, initial pores, etc., so that these influencing factors and their mutual coupling can be comprehensively considered in the calculation process of the water storage capacity of the rock mass in the goaf area, thereby making the calculation of the water storage capacity of the rock mass in the goaf area more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0021] Figure 1 It is a schematic diagram of the structure of an underground water reservoir in a goaf of a mine in Shenhua Mining Area in the following embodiments.

[0022] Figure 2 The following is a test diagram of the coarse sandstone specimen subjected to a pre-loaded static specimen impact disturbance test in the following example.

[0023] Figure 3 The following is a test diagram of the mudstone specimen subjected to a pre-loaded static specimen impact disturbance test in the following example.

[0024] Figure 4 These are the coarse sandstone broken blocks obtained by the impact disturbance test of the pre-loaded static specimen in the following examples.

[0025] Figure 5 The broken mudstone blocks are obtained by the impact disturbance test of the pre-loaded static specimen in the following examples.

[0026] Figure 6 The following is a graph showing the test results of the pore water storage coefficient of coarse sandstone under different stress conditions in the following examples.

[0027] Figure 7 The following is a graph showing the test results of the pore water storage coefficient of mudstone under different stress conditions in the following examples. DETAILED DESCRIPTION

[0028] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0029] For the convenience of description, if the words "up", "down", "left" and "right" appear in the present invention, they only indicate that they are consistent with the up, down, left and right directions of the drawings themselves, and do not limit the structure. They are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or component needs to have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0030] The underground reservoir capacity testing method based on the dual porosity structure of the present invention is now further described in conjunction with the accompanying drawings and specific embodiments of the specification.

[0031] A method for testing the storage capacity of underground reservoirs based on a dual porosity structure comprises the following steps:

[0032] 1. Obtain the void water storage coefficient K1 of the broken rock block through the impact disturbance test of the preloaded static specimen and the lateral confined compaction test of the saturated rock mass. Specifically, it includes the following steps:

[0033] (1) Obtaining broken rock blocks: Sample the rock layers of each lithology in the rock mass of the caving zone, and then process the samples into standard specimens. Determine the impact energy Q required for the test according to the collapse height h of the goaf, which is obtained by formula (1):

[0034] (1).

[0035] In the above formula (1), ρ is the rock mass density, V' is the volume of the standard specimen, h is the collapse height of the goaf, and g is the gravitational acceleration.

[0036] (2) Determine the pre-loaded static stress σ1 required for the test according to the axial ground stress conditions obtained from the on-site survey. Then obtain the broken rock blocks through the impact disturbance test of the pre-loaded static specimen. The steps of the impact disturbance test of the pre-loaded static specimen are: use the full strain rate dynamic and static combined loading multifunctional rock mechanics test system disclosed in the patent document with application number 202011467117.2 and patent name "Full strain rate dynamic and static combined loading multifunctional rock mechanics test system and method". During the test, first place the standard specimen in the above step (1) on the height adjustment bolt of the dynamic and static loading mechanism of the full strain rate dynamic and static combined loading multifunctional rock mechanics test system, and then use the multifunctional loading cylinder of the dynamic and static loading mechanism to apply the σ1. After the stress is stable, the impact weight and the through impact rod of the dynamic and static loading mechanism are used to apply the impact energy Q calculated according to the above formula (1) to the standard specimen for impact crushing, and after completion, the broken rock blocks are obtained.

[0037] (3) After obtaining the broken rock block, determine the compaction load σ2 required for the test according to the overburden pressure of the goaf obtained from the on-site survey. Then, use the compaction device that can realize visualization and intelligence of the compaction process disclosed in the patent document of application number 202022932713.5 to carry out the lateral confinement compaction test of the saturated rock mass. Specifically: first, place the broken rock block in the transparent compaction cylinder of the compaction device that can realize visualization and intelligence of the compaction process, then use the loading module to apply the σ2 to the broken rock block, and then use the constant speed and constant pressure pump connected to the compaction cylinder to obtain the broken rock block pore water storage coefficient K1 in real time for standby.

[0038] 2. Obtain the pore water storage coefficient K2 of the same broken rock block as in step (1) through a crushing expansion-water storage characteristic test in the full stress-strain process under triaxial conditions. Specifically, the method includes the following steps:

[0039] (i) Sampling of each lithology in the rock mass of the caving zone is carried out, with the original fractures retained in the samples, and then the samples are processed into standard specimens.

[0040] (ii) Determine the confining pressure σ3 required for the test according to the horizontal ground stress conditions obtained from the on-site survey, and then conduct a crushing swelling-water storage characteristic test in the full stress-strain process under triaxial conditions according to a self-balancing coal rock triaxial loading seepage and displacement test instrument and method disclosed in application number 201910729553.3 to obtain the pore water storage coefficient K2 under different stress conditions. Specifically: place the standard specimen in the triaxial chamber of the triaxial test module. Then use the electric booster pump of the pressure loading module to apply the confining pressure σ3 required for the test, use the universal testing machine of the pressure loading module to apply axial pressure, use the fluid injection module to obtain the pore water storage coefficient under different stress conditions in real time, and find the corresponding pore water storage coefficient K2 according to the overburden pressure of the goaf in the test results.

[0041] 3. Use the above method to calculate the void water storage coefficient K1 and pore water storage coefficient K2 of each lithology sample prepared, and then calculate the underground reservoir capacity V according to formula (2): c :

[0042] (2).

[0043] In the formula (2), V i is the volume of a certain lithology layer in the underground reservoir, K 1i is the water storage coefficient of the void part of a certain rock mass in the underground reservoir, K 2i It is the water storage coefficient of the pore part of a certain rock mass in the underground reservoir.

[0044] The above-mentioned underground water reservoir capacity test method regards the rock mass in the goaf as a dual-pore structure, thereby dividing the main water storage space of the rock mass in the goaf into two parts: voids and pores according to the size of the space. This lays the foundation for comprehensively considering the impact of key field parameters such as rock mass stress state, rock mass lithology, original rock mass cracks, mining energy, overburden pressure, water content, initial porosity, etc. on the water storage performance of void structure and pore structure. Through basic tests, the formation process of underground water reservoir storage space can be truly restored, ensuring the consistency of water storage space with the site, and realizing accurate testing of underground water reservoir capacity. Below, based on the above-mentioned underground water reservoir capacity test method, the underground water reservoir in the goaf of a mine in Shenhua Mining Area (such as Figure 1 The storage capacity V c Perform the calculation:

[0045] Working conditions: The rock mass of the collapsed roof within the water storage range is coarse sandstone and mudstone. The rock mass volume of coarse sandstone within the water storage range is measured to be V1=2.8×10 7 m 3 , the rock mass volume of coarse sandstone is V2=1.9×10 7 m 3The density of coarse sandstone is ρ=2.01 g / cm³, the density of mudstone is ρ=2.45 g / cm³, and the collapse height of the goaf is 4.9m. The on-site survey shows that the axial stress at the goaf is 12.5MPa, the horizontal stress is 7MPa, and the overburden pressure in the goaf after the rock collapse is 12MPa.

[0046] 1. Obtain the void water storage coefficient K of coarse sandstone and mudstone broken rock blocks through the impact disturbance test of preloaded static specimens and the lateral confined compaction test of saturated rock mass 11 , K 12 Specifically, the following steps are included:

[0047] (1) Obtaining broken rock blocks: Sample the coarse sandstone and mudstone layers in the rock mass of the caving zone, and then process the samples into standard specimens (diameter 50 mm, height 100 mm). Determine the impact energy Q1 and Q2 required for the test based on the collapse height h (4.9 m) of the goaf and the density of the coarse sandstone rock mass (ρ = 2.01 g / cm³) and the density of the mudstone rock mass (ρ = 2.45 g / cm³):

[0048]

[0049]

[0050] (2) According to the axial ground stress (12.5 MPa), the required pre-load static stress σ1 for the test is determined to be 12.5 MPa. Then, by pre-loading the static specimen ( Figure 2 For coarse sandstone specimens, Figure 3 The impact disturbance test was used to obtain the coarse sandstone broken rock blocks ( Figure 4 shown), mudstone broken blocks ( Figure 5 As shown in the figure, the impact energies for coarse sandstone and mudstone in the test are Q1=19.33J and Q2=23.56J respectively.

[0051] (3) After obtaining the coarse sandstone broken rock blocks and mudstone broken rock blocks, the compaction load σ2 required for the test is determined to be 12 MPa according to the overburden pressure of the goaf (12 MPa). Then, the above-mentioned compaction device that can realize visualization and intelligence of the compaction process and the constant speed and constant pressure pump connected to its compaction cylinder are used to carry out the lateral confined compaction test of the saturated rock mass to obtain the void water storage coefficient K of the coarse sandstone broken rock blocks. 11 =7.2%, pore water storage coefficient of mudstone broken rock block K 12 =3.9%, reserve.

[0052] 2. Obtain the pore water storage coefficient K of coarse sandstone and mudstone broken blocks through the crushing expansion-water storage characteristic test under full stress-strain process under triaxial conditions 21 , K 22 Specifically, the following steps are included:

[0053] (i) Sampling of each lithology in the rock mass of the caving zone (the coarse sandstone and mudstone mentioned above) is performed, the original cracks are retained in the samples, and then the samples are processed into standard specimens (diameter 50 mm, height 100 mm).

[0054] (ii) According to the horizontal ground stress (7 MPa), the confining pressure σ3 required for the test is determined to be 7 MPa, and then the crushing expansion-water storage characteristic test in the full stress-strain process under triaxial conditions is carried out according to the above-mentioned "A self-balancing coal rock triaxial loading seepage and displacement test instrument and method" to obtain the pore water storage coefficient of the coarse sandstone broken rock block and the mudstone broken rock block under different stress conditions: Figure 6 , Figure 7 The pore water storage coefficient test results of coarse sandstone and mudstone under different stress conditions are shown in Figure 1. Then, according to the overburden pressure of 12MPa, the corresponding pore water storage coefficient K is found in the test results. 21 =2.7%, K 22 =1.5%.

[0055] 3. Based on the above test results, the underground reservoir capacity V is calculated according to the above formula (2): c :

[0056]

[0057] Finally, it should be noted that any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention. Although the above describes the specific implementation of the present invention in conjunction with the drawings, it is not a limitation of the protection scope of the present invention. Those skilled in the art should understand that on the basis of the technical solution of the present invention, various modifications or deformations that can be made by those skilled in the art without creative labor are still within the protection scope of the present invention.

Claims

1. A method for testing underground reservoir capacity based on dual pore structure, characterized in that: The steps include: (1) Obtaining the void water storage coefficient of the broken rock through the impact disturbance test of the preloaded static specimen and the lateral confined compaction test of the saturated rock mass K 1 ; (2) Obtain the pore water storage coefficient of the same broken rock block as in step (1) through the crushing expansion-water storage characteristic test under full stress-strain conditions under triaxial conditions K 2 ; (3) Through the void water storage coefficient K 1 and pore water storage coefficient K 2 Calculate the underground reservoir capacity V c , the calculation formula is shown in formula (1): (1); In the formula (1), V i is the volume of a certain lithology layer in the underground reservoir, K 1i is the water storage coefficient of the void part of a certain rock mass in the underground reservoir, K 2i is the water storage coefficient of the pore part of a certain lithology rock mass in the underground reservoir; In step (1), the method for obtaining the broken rock blocks is: sampling the rock layers of each lithology in the rock mass of the caving zone and processing them into standard test pieces; then, according to the collapse height of the goaf, h Determine the impact energy required for the test Q ; Then determine the required preload static stress for the test according to the ground stress conditions σ 1; then, the broken rock blocks are obtained through the impact disturbance test of the pre-loaded static specimen; In step (1), the saturated rock mass side confined compaction test is carried out using a compaction device that can realize visualization and intelligence of the compaction process. The specific steps are: firstly, the broken rock block is placed in a transparent compaction cylinder of the compaction device that can realize visualization and intelligence of the compaction process, and then the compaction load required for the test is applied to the broken rock block using a loading module. σ 2. Obtain the void water storage coefficient of the broken rock in real time through a constant speed and pressure pump connected to the compaction drum K 1 ; In step (2), samples of each lithology in the caving zone are taken, the original fractures are retained, and the samples are processed into standard specimens as test objects; then the confining pressure required for the test is determined according to the ground stress conditions. σ 3. Then, the expansion-water storage characteristic test under the full stress-strain process under triaxial conditions was carried out to obtain the pore water storage coefficient under different stress conditions. K 2 , and find the corresponding pore water storage coefficient according to the overburden pressure of the goaf in the test results K 2 ; In step (2), the steps of the crushing swelling-water storage characteristic test are: placing the standard specimen in the triaxial test module of the self-balanced coal rock triaxial loading seepage and displacement test instrument; then using the pressure loading module to apply the confining pressure required for the test σ 3. Use an external press to apply axial pressure, and use a fluid injection module to obtain the pore water storage coefficient under different stress conditions in real time K 2.

2. The underground reservoir capacity testing method based on dual porosity structure according to claim 1, characterized in that: The impact energy required for the test Q Through formula (2), we can obtain: (2); In formula (2), ρ is the rock mass density, V’ is the volume of the standard specimen, h is the collapse height of the goaf, g is the acceleration due to gravity.

3. The underground reservoir capacity testing method based on dual porosity structure according to claim 2 is characterized in that: The impact disturbance test of the pre-statically loaded specimen is carried out using a full strain rate dynamic and static combined loading multifunctional rock mechanics test system.

4. The underground reservoir capacity testing method based on dual porosity structure according to claim 3 is characterized in that: The steps of the impact disturbance test of the pre-static load specimen are as follows: placing the standard specimen in a full strain rate dynamic and static combined loading multifunctional rock mechanics test system, and then using the dynamic and static loading mechanism of the system to apply the pre-static load stress required for the test. σ 1; After the stress is stabilized, the dynamic and static loading mechanism is used to apply the stress calculated according to the formula (2) Q The standard specimen is impact crushed, and broken rock blocks are obtained after completion.

5. The underground reservoir capacity testing method based on dual porosity structure according to claim 1 is characterized in that: After obtaining the broken rock blocks, the compaction load required for the test is determined according to the overburden pressure of the goaf. σ 2. Then, the saturated rock mass confined compaction test is carried out to obtain the void water storage coefficient of the broken rock block. K 1 .

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