A laboratory experimental method for determining the degree of anisotropy of rock mechanics in formations

Abstract

The present invention belongs to the technical field of rock fracture mechanics in petroleum engineering, and provides an indoor experimental method for determining the degree of mechanical anisotropy of formation rock, including step S01: drilling a full-diameter core from the research target formation or selecting a full-diameter core at a corresponding formation position from a core library, and preparing three mutually perpendicular standard rock samples on each full-diameter core; step S02: conducting longitudinal and transverse wave velocity tests on the prepared standard rock samples, and calculating the dynamic elastic parameters of the rock; step S03: conducting a uniaxial compression test on the prepared standard rock samples, and calculating the compressive strength and static elastic parameters of the rock; step S04: using a discrete coefficient calculation model to calculate the degree of mechanical anisotropy of formation rock. The present invention can study the difference in the degree of mechanical anisotropy of rocks at different formation depths, provide a test and calculation method for determining the degree of mechanical anisotropy of formation rock, and further provide a reference for hydraulic fracturing design and drilling design of formations, which has important theoretical and engineering research significance.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum engineering, in particular to the technical field of rock fracture mechanics in petroleum engineering, and specifically relates to an indoor experimental method for determining the degree of anisotropy of formation rock mechanics. Background Art

[0002] With the increasing demand for energy, the demand for oil extraction is also increasing. In particular, with the widespread application of hydraulic fracturing technology, oil and gas production has been greatly improved. When carrying out hydraulic fracturing, clarifying the mechanical properties of formation rocks is a key issue. Anisotropy is one of the important properties of rock mechanics. Understanding the degree of anisotropy of reservoir rocks is of great reference significance for judging whether complex fractures are generated and the degree of tortuosity of hydraulic fractures. In addition, during the fracturing drilling process, phenomena such as casing damage and wellbore deformation are closely related to the anisotropic properties of the mechanical rock around the well. Therefore, understanding the degree of anisotropy of formation rocks has a good guiding role in fracturing design and drilling design.

[0003] However, there are currently few methods for evaluating the anisotropy of rocks in real reservoirs, and there is a lack of fixed testing and calculation methods for studying the degree of anisotropy of formation rocks.

[0004] The existing patent document CN103115820A discloses a method for determining the anisotropy of a jointed rock mass, and the technical solution adopted is: first, a multi-scale jointed rock mass is constructed that can fully reflect the mechanical properties of rocks and joints and the spatial distribution characteristics of joints. The jointed rock masses of different scales include three groups of specimens, and their major axis directions are respectively along the X, Y, and Z directions; then, virtual uniaxial compression loading is performed along the major axis directions of various types of jointed rock masses to obtain stress-strain curves, and mechanical parameters such as uniaxial compressive strength and elastic modulus of the jointed rock mass along the X, Y, and Z axes are extracted; finally, an anisotropy index ξ is established to determine the anisotropy of mechanical parameters such as uniaxial compressive strength and elastic modulus of the jointed rock mass in different axial directions at different scales, thereby quantitatively studying the anisotropic characteristics of the jointed rock mass. The scheme is simple in principle and easy to operate, but it uses particle flow numerical simulation calculations, and the simulation is affected by the artificial parameter settings. The virtual loading method used has low credibility in the simulation results, which will make the calculation results not objective; the scheme does not consider dynamic parameters, and the calculated anisotropy degree is not objective, comprehensive, and accurate enough; the scheme calculates the anisotropy index of each parameter, and cannot macroscopically characterize the rock mechanics anisotropy of the formation position as a whole; and the scheme is mainly aimed at jointed rock masses, and the research object is limited. In real strata, in addition to the development of joints, there are still irregular natural cracks, bedding, solution pores, etc. Summary of the invention

[0005] The present invention aims to address the technical problems existing in the prior art and provide an indoor experimental method for determining the degree of mechanical anisotropy of formation rocks. The method can study the differences in the degree of anisotropy of rocks in different formations, provide a test and calculation method for determining the degree of anisotropy of formation rocks, and further provide a reference for hydraulic fracturing design and drilling design of formations, which has important theoretical and engineering research significance.

[0006] In order to achieve the above technical objectives, the present invention adopts the following technical solutions:

[0007] An indoor experimental method for determining the degree of mechanical anisotropy of formation rock, the method comprising the following steps:

[0008] Step S01: Drill a full-diameter core from the target formation or select a full-diameter core from a core library at a corresponding formation position, and prepare three mutually perpendicular standard rock samples from each full-diameter core;

[0009] Step S02: Conduct longitudinal and transverse wave velocity tests on the prepared standard rock sample, and calculate the dynamic elastic parameters of the rock;

[0010] Step S03: carrying out a uniaxial compression test on the prepared standard rock sample, and calculating the compressive strength and static elastic parameters of the rock;

[0011] Step S04: Calculate the degree of formation rock mechanical anisotropy using a discrete coefficient calculation model.

[0012] Furthermore, in step S01, the diameter of the full-diameter core is 8-10 cm and the length is not less than 6 cm; and three mutually perpendicular standard rock samples are prepared on the full-diameter core, wherein one standard rock sample is prepared in the vertical direction and two standard rock samples are prepared in the horizontal direction; the vertical rock sample is prepared along the length direction parallel to the full-diameter core, and the horizontal rock sample is prepared along the plane where the full-diameter core diameter is located, and the two horizontal rock samples are perpendicular to each other.

[0013] Furthermore, in step S01, when preparing horizontal rock samples, in order to ensure that the horizontal samples are perpendicular to each other, a marking line a is first drawn at any coring position, and the direction of the marking line is parallel to the axis direction of the full-diameter core; a tape measure is used to measure the distance s along the circumferential direction of the full-diameter core with the marking line a as the starting position, and a marking line b is drawn. A marking point is selected on each marking line, and the length direction of the horizontal core is parallel to the line connecting the centers of the full-diameter circles where the marking points are located, wherein the distance R is the diameter of the full diameter core.

[0014] Furthermore, in step S01, a standard rock sample is prepared by wire cutting using anhydrous diamond wire; the prepared standard rock sample is a cylindrical sample with a diameter of 25 mm and a length of 50 mm.

[0015] Furthermore, in step S02, the prepared standard rock sample is subjected to an acoustic wave test, and an acoustic wave transmitting probe and an acoustic wave receiving probe are respectively placed on the upper and lower end surfaces of the standard rock sample, and a coupling agent is applied between the probe and the end surface of the standard rock sample; a longitudinal wave and a transverse wave are simultaneously emitted by an acoustic wave device, and the longitudinal wave velocity V of the measured standard rock sample is recorded. p and shear wave velocity V s .

[0016] Furthermore, in step S02, the rock density ρ of the standard sample is measured, and combined with the longitudinal wave velocity V of the standard rock sample p and shear wave velocity V s Calculate the dynamic elastic modulus E of rock d and the dynamic Poisson's ratio μ d , the calculation method is:

[0017]

[0018]

[0019] Furthermore, in the step S03, the standard rock sample after the acoustic wave test in step S02 is taken out and placed in a rock mechanics parameter testing machine to carry out a uniaxial compression test; loading is stopped after the rock is damaged, and the loaded stress-strain curve is checked; the compressive strength C, static elastic modulus E and static Poisson's ratio μ of the rock are calculated from the stress-strain curve.

[0020] Furthermore, in step S04, three standard rock samples of the same full-diameter core are subjected to acoustic wave testing and uniaxial compression testing, and the calculated results are set to be: E d1 、E d2 、E d3 ;μ d1 , μ d2 , μ d3 ;C1, C2, C3; E1, E2, E3; μ1, μ2, μ3.

[0021] Furthermore, in step S04, the discrete coefficient model is used to calculate the anisotropy degree of the rock, and the calculation process is: the dynamic elastic modulus, dynamic Poisson's ratio, compressive strength, static elastic modulus and static Poisson's ratio of the standard rock sample of the same full-diameter core in three directions are calculated respectively. The discrete coefficient V s The calculation formula is:

[0022]

[0023] In the above formula, V s is the coefficient of dispersion, σ is the variance of each variable, and M is the arithmetic mean of each variable.

[0024] Furthermore, in step S04, the calculated discrete coefficient V s The anisotropy degree V of the formation rock is obtained by averaging. The calculation model of the anisotropy degree V of the formation rock is:

[0025]

[0026] in, are the arithmetic means of the dynamic elastic modulus, dynamic Poisson's ratio, compressive strength, static elastic modulus and static Poisson's ratio of the rock samples in three different directions on the same full-diameter core; j represents the number of variables, i.e. i represents rock samples from three different coring directions of each full-diameter core.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] (1) The present invention provides an indoor experimental method for determining the degree of mechanical anisotropy of formation rock. The dynamic elastic parameters of the rock are obtained through acoustic wave testing, and the compressive strength and static elastic parameters of the rock are calculated through uniaxial compression testing; finally, the degree of mechanical anisotropy of the formation rock is calculated based on the obtained dynamic elastic parameters, compressive strength and static elastic parameters using a discrete coefficient calculation model. The larger the value of the anisotropy degree V of the formation rock, the stronger the degree of mechanical anisotropy of the rock; the above method of the present application is simple in principle, easy to operate, low in cost, and has good use effect. It can study the differences in the degree of anisotropy of rocks in different formations, provide testing and calculation methods for determining the degree of anisotropy of formation rocks, and further provide a reference for hydraulic fracturing design and drilling design of formations, which has important theoretical and engineering research significance;

[0029] (2) Compared with patent document CN103115820A: Patent document CN103115820A uses particle flow numerical simulation calculation, the simulation is interfered by artificial parameter settings, and the virtual loading method used makes the result not objective, while the present application uses experimental methods to calculate mechanical anisotropy, which can reflect the objective laws of rock mechanics; Patent document CN103115820A does not consider the influence of dynamic parameters, resulting in incomplete anisotropy evaluation, while the present application fully considers the influence of dynamic mechanical properties of rock on anisotropy, introduces acoustic wave testing and dynamic elastic constant processing methods, and can more comprehensively evaluate rock mechanics anisotropy; Patent document CN103115820A only Calculating the anisotropy of different parameters does not provide a method for overall evaluation of rock mechanics anisotropy, and the present application defines a new method for rock mechanics anisotropy, which can comprehensively consider the combined effects of compressive strength, dynamic elastic constant and static elastic constant, and can comprehensively reflect the degree of rock mechanics anisotropy; Patent document CN103115820A is mainly aimed at jointed rock masses, and its research object has limitations. In real strata, in addition to the development of joints and bedding, there are still irregular natural cracks, solution pores, etc., and there are also relatively homogeneous rocks. The method proposed in the present application can comprehensively measure various rock mechanics anisotropies, not only jointed rocks, but also can evaluate bedding, natural crack development, solution pore development and homogeneous lithology rocks. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A flow chart of an indoor experimental method for determining the degree of mechanical anisotropy of formation rock according to an embodiment of the present invention;

[0031] Figure 2 A schematic diagram of a rock sampling structure according to an embodiment of the present invention;

[0032] Figure 3 A schematic diagram of the acoustic wave test structure of an embodiment of the present invention;

[0033] Description of the markings in the figure:

[0034] 1. Full diameter core; 2. Vertical rock sample; 3. Horizontal 0 degree rock sample; 4. Horizontal 90 degree rock sample; 5. Standard rock sample; 6. Acoustic wave transmitting probe; 7. Acoustic wave receiving probe; 8. Acoustic wave testing system. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] Combination Figure 1-3 As shown, an embodiment of the present invention provides an indoor experimental method for determining the degree of mechanical anisotropy of formation rock; the method comprises the following steps:

[0037] Step S01: Drill a full-diameter core from the target formation or select a full-diameter core from a core library at a corresponding formation position, and prepare three mutually perpendicular standard rock samples from each full-diameter core;

[0038] In step S01, a full-diameter core is drilled from the target formation for research, or a full-diameter core 1 with a core diameter of 10 cm and a length of not less than 6 cm is selected from the core library, and three mutually perpendicular standard rock samples are prepared on the full-diameter core 1, wherein one standard rock sample is prepared in the vertical direction, and two standard rock samples are prepared in the horizontal direction; the vertical rock sample is prepared along the length direction parallel to the full-diameter core, and the horizontal rock sample is prepared along the plane where the diameter of the full-diameter core is located, and the two horizontal rock samples are perpendicular to each other; to ensure that the horizontal samples are mutually perpendicular, a marking line a is first drawn at any of the coring positions, and the direction of the marking line is parallel to the axis direction of the full-diameter core; a tape measure is used to measure the distance s along the circumferential direction of the full-diameter core with the marking line a as the starting position, and a marking line b is drawn, and a marking point is selected on each marking line, so that the length direction of the horizontal core is parallel to the line connecting the centers of the full-diameter circles where the marking points are located, wherein the distance R is the diameter of the full-diameter core 1.

[0039] In order to prevent the mudstone in the rock sample from being affected by water-sensitive reaction when it meets water, wire cutting is used to prepare vertical rock sample 2, horizontal 0 degree rock sample 3 and horizontal 90 degree rock sample 4 on the full diameter core 1 respectively. The three rock samples are made into standard rock sample 5 by wire cutting, which has a length of 50 mm and a diameter of 25 mm.

[0040] Step S02: Conduct longitudinal and transverse wave velocity tests on the prepared standard rock sample, and calculate the dynamic elastic parameters of the rock;

[0041] The three standard rock samples were tested by sonic wave. Coupling agent was applied to the upper and lower end faces of the standard rock sample 5 to prevent noise interference and sonic wave transmission attenuation. The sonic wave transmitting probe 6 and the sonic wave receiving probe 7 were placed on the upper and lower sides respectively. The sonic wave testing system 8 was started to record the longitudinal wave velocity V of the rock sample. p and shear wave velocity V s ; Measure the rock density ρ of the standard sample, and combine it with the longitudinal wave velocity V of the standard rock sample p and shear wave velocity V s Calculate the dynamic elastic modulus E of rock d and the dynamic Poisson's ratio μ d , the calculation method is:

[0042]

[0043]

[0044] Step S03: carrying out a uniaxial compression test on the prepared standard rock sample, and calculating the compressive strength and static elastic parameters of the rock;

[0045] The standard rock sample after the ultrasonic test is taken down and placed in a rock mechanics parameter testing machine for uniaxial compression test. When the rock is destroyed, the loading is stopped and the stress-strain curve of the loading is checked. The compressive strength C, static elastic modulus E and static Poisson's ratio μ of the rock are calculated from the stress-strain curve.

[0046] Step S04: using a discrete coefficient calculation model to calculate the degree of anisotropy of formation rock mechanics;

[0047] The acoustic wave test and uniaxial compression test were carried out on three standard rock samples of the same full-diameter core, and the calculated results were set as follows: d1 、E d2 、E d3 ;μ d1 , μ d2 , μ d3 ; C1, C2, C3; E1, E2, E3; μ1, μ2, μ3; The discrete coefficient model is used to calculate the anisotropy of the rock. The calculation process is: calculate the discrete coefficients of the dynamic elastic modulus, dynamic Poisson's ratio, compressive strength, static elastic modulus and static Poisson's ratio of the standard rock sample of the same full-diameter core in three directions respectively. The calculation formula of the discrete coefficient is:

[0048]

[0049] In the above formula, V s is the coefficient of dispersion, σ is the variance of each variable, and M is the arithmetic mean of each variable.

[0050] The average dispersion coefficient is used to describe the anisotropy degree V of the formation where the full-diameter core is located. s The anisotropy degree V of the formation rock is obtained by averaging. The calculation model of the anisotropy degree V of the formation rock is:

[0051]

[0052] in, are the arithmetic means of the dynamic elastic modulus, dynamic Poisson's ratio, compressive strength, static elastic modulus and static Poisson's ratio of the rock samples in three different directions on the same full-diameter core; j represents the number of variables, i.e. i represents rock samples from three different coring directions of each full-diameter core.

[0053] The larger the value of the anisotropy degree V of the formation rock calculated by the above method, the stronger the anisotropy degree of the rock. The above method of the present application is simple in principle, easy to operate, low in cost, and has good use effect. It can study the difference in the anisotropy degree of rocks in different formations, provide a test and calculation method for determining the anisotropy degree of formation rocks, and further provide a reference for hydraulic fracturing design and drilling design of formations, which has important theoretical and engineering research significance.

[0054] The above description is only an embodiment of the present application and is not intended to limit the present invention. Any modification, equivalent replacement and improvement made within the scope of the present invention shall be included in the protection scope of the present invention.

Claims

1. An indoor experimental method for determining the degree of anisotropy of formation rock mechanics, characterized in that: The method comprises the following steps: Step S01: Drill a full-diameter core from the target formation or select a full-diameter core from a core library at a corresponding formation position, and prepare three mutually perpendicular standard rock samples from each full-diameter core; Step S02: Conduct longitudinal and transverse wave velocity tests on the prepared standard rock sample, and calculate the dynamic elastic parameters of the rock; In step S02, the prepared standard rock sample is subjected to an acoustic wave test, and an acoustic wave transmitting probe and an acoustic wave receiving probe are respectively placed on the upper and lower end surfaces of the standard rock sample, and a coupling agent is applied between the probe and the end surface of the standard rock sample; a longitudinal wave and a transverse wave are simultaneously emitted by an acoustic wave device, and the longitudinal wave velocity V of the measured standard rock sample is recorded. p and shear wave velocity V s ; Measure the rock density ρ of the standard sample and combine it with the longitudinal wave velocity V of the standard rock sample p and shear wave velocity V s Calculate the dynamic elastic modulus E of rock d and the dynamic Poisson's ratio μ d , the calculation method is: Step S03: carrying out a uniaxial compression test on the prepared standard rock sample, and calculating the compressive strength and static elastic parameters of the rock; The standard rock sample after the acoustic wave test in step S02 is taken out and placed in a rock mechanics parameter testing machine to carry out a uniaxial compression test; when the rock is damaged, the loading is stopped and the loaded stress-strain curve is checked; the compressive strength C, static elastic modulus E and static Poisson's ratio μ of the rock are calculated from the stress-strain curve; Step S04: Calculate the degree of formation rock mechanical anisotropy using a discrete coefficient calculation model; The acoustic wave test and uniaxial compression test were carried out on three standard rock samples of the same full-diameter core, and the calculated results were set as follows: d1 、E d2 、E d3 ;μ d1 , μ d2 , μ d3 ;C1, C2, C3; E1, E2, E3; μ1, μ2, μ3; The discrete coefficient model is used to calculate the anisotropy of rock. The calculation process is as follows: the dynamic elastic modulus, dynamic Poisson's ratio, compressive strength, static elastic modulus and static Poisson's ratio of the standard rock sample with the same full-diameter core in three directions are calculated respectively. The discrete coefficient V s The calculation formula is: In the above formula, V s is the coefficient of dispersion, σ is the variance of each variable, and M is the arithmetic mean of each variable; The calculated dispersion coefficient V s The anisotropy degree V of the formation rock is obtained by averaging. The calculation model of the anisotropy degree V of the formation rock is: in, They are the arithmetic means of the dynamic elastic modulus, dynamic Poisson's ratio, compressive strength, static elastic modulus and static Poisson's ratio of the rock samples in three different directions on the same full-diameter core; j represents the number of variables, that is, i represents rock samples from three different coring directions of each full-diameter core.

2. The indoor experimental method for determining the degree of rock mechanical anisotropy of a formation according to claim 1, characterized in that: In step S01, the diameter of the full-diameter core is 8-10 cm and the length is not less than 6 cm; and three mutually perpendicular standard rock samples are prepared on the full-diameter core, wherein one standard rock sample is prepared in the vertical direction and two standard rock samples are prepared in the horizontal direction; the vertical direction rock sample is prepared along the length direction parallel to the full-diameter core, and the horizontal direction rock sample is prepared along the plane where the full-diameter core diameter is located, and the two horizontal direction rock samples are perpendicular to each other.

3. The indoor experimental method for determining the degree of rock mechanical anisotropy of a formation according to claim 2, characterized in that: In the step S01, when preparing horizontal rock samples, in order to ensure that the horizontal samples are perpendicular to each other, a marking line a is first drawn at any coring position, and the direction of the marking line is parallel to the axis direction of the full-diameter core; a tape measure is used to measure the distance s along the circumferential direction of the full-diameter core with the marking line a as the starting position, and a marking line b is drawn. A marking point is selected on each marking line, and the length direction of the horizontal core is parallel to the line connecting the centers of the full-diameter circles where the marking points are located, wherein the distance R is the diameter of the full diameter core.

4. The indoor experimental method for determining the degree of rock mechanical anisotropy of a formation according to claim 3, characterized in that: In the step S01, a standard rock sample is prepared by wire cutting using anhydrous diamond wire; the prepared standard rock sample is a cylindrical sample with a diameter of 25 mm and a length of 50 mm.

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