A method for calculating error of full diameter core radial permeability test

Abstract

The application discloses a kind of full-diameter core radial permeability test error calculation methods, belong to oil and gas exploration technical field, it is characterized in that, include the following steps: a, preparation core;B, the true value k of permeability when the texture of core and the end surface of core are parallel is calculated / / ; the true value of permeability when the texture of core and the end surface of core are vertical is calculated to simulate the permeability value c that passes through the left and right sides of cuboid;D, the radial permeability test error value ε of core is calculated by formula 5.The application can carry out error analysis to core radial permeability test, effectively estimate the accuracy of core radial permeability test, carry out reliability evaluation to core radial permeability test.

Description

Technical Field

[0001] This invention relates to the field of oil and gas exploration technology, and in particular to a method for calculating the error of radial permeability testing of full-diameter core samples. Background Technology

[0002] Permeability is a key parameter for evaluating oil and gas reservoirs and geothermal resources. GB / T29172-2012, "Methods for Core Analysis," describes a method for testing the transverse permeability of full-diameter cores on pages 131-132. This method was first proposed by Collins, and the detailed process is documented in "Determination of the Transverse Permeability of Large Core Samples from Petroleum Reservoirs," published in the 1952 issue of *J. of App. Physics*, Vol. 6, pp. 681-683. The most significant advantage of this method is its ability to measure the radial permeability of cores, a common feature in the oil and gas industry, using relatively simple experimental equipment. However, some scholars, both domestically and internationally, argue that this method relies on the assumption of core isotropy based on complex variable functions. However, the calculated results are used to characterize anisotropy. Therefore, the radial permeability obtained using this method is inaccurate and cannot address the systematic error evaluation problem of full-diameter permeability testing.

[0003] Chinese patent document CN110441204A, published on November 12, 2019, discloses a digital evaluation method for fracturing fluid damage in tight reservoirs based on digital core simulation, characterized by the following steps:

[0004] Step 1: Sample preparation and scanning; Obtain a 1mm side length cubic core sample from the rock core, and use a CT scanning device to perform rotational scanning at resolutions of 1μm and 0.5μm respectively to construct two three-dimensional grayscale data volumes. The three-dimensional structure of pores and skeleton is characterized by grayscale threshold segmentation, i.e., watershed algorithm.

[0005] Step 2: Optimize scanning resolution through mercury intrusion curve simulation; Based on the Yang-Laplace equation and pore morphology method, simulate the mercury intrusion process of the two data volumes in Step 1, search for the mercury intrusion area, mark the pore throat size, and obtain the pore throat distribution map. If the main pore throat is greater than 1 resolution, it means that the selected scanning resolution can better characterize the lowest level pore throat of the measured sample. This resolution is the optimal resolution for modeling.

[0006] Step 3: Optimize the grid side length through porosity; Select the data volume determined in Step 2, and select one grid point (pixel) at the center to construct a cube (volume element) with a side length of 50 grids and calculate the porosity. Then, increase the side length of the cube (volume element) by 50 grids and calculate the porosity. Obtain the relationship curve between the porosity and side length of the cube (volume element). When the relative change rate of porosity is less than 5%, it is the optimal grid side length. Calculate the permeability of the cube (volume element) representing this value.

[0007] Step 4: Core damage simulation experiment; Take a 1mm side length cubic core sample from Step 1, place it in a high-pressure container with different fracturing fluids, heat and pressurize it to formation conditions, remove it at different time points, and construct a three-dimensional digital core model with the resolution and grid side length obtained in Step 2 and Step 3.

[0008] Step 5: Simulate and calculate the porosity and permeability parameters of the three-dimensional digital core constructed at different time points, and use the reduction in porosity and permeability as the evaluation criteria for the damage of different fracturing fluids to tight reservoirs.

[0009] The patent document discloses a digital evaluation method for fracturing fluid damage in tight reservoirs based on digital core simulation. This method utilizes digital core technology and is less expensive than traditional techniques. However, it cannot perform error analysis on the radial permeability test of the core, cannot estimate the accuracy of the radial permeability test, and cannot assess the reliability of the radial permeability test. Summary of the Invention

[0010] In order to overcome the shortcomings of the prior art, this invention provides a method for calculating the error of radial permeability testing of full-diameter core samples. This invention can perform error analysis on radial permeability testing of core samples, effectively estimate the accuracy of radial permeability testing of core samples, and conduct reliability assessment of radial permeability testing of core samples.

[0011] This invention is achieved through the following technical solution:

[0012] A method for calculating the error of radial permeability testing of full-diameter core samples, characterized by comprising the following steps:

[0013] a. Prepare core samples, record the direction of the core texture and the core end face, and record the relationship between the direction of airflow through the core and the core texture;

[0014] b. When the core texture is parallel to the core end face, the core is divided into layers 1, 2, ..., and n according to the development of the lamellarity. The permeability of each layer corresponds to k1, k2, ..., and k, respectively. n The thicknesses of each layer are h1, h2, ... and h, respectively. n The true permeability k is calculated using Equation 1 when the core texture is parallel to the core end face. / / ;

[0015]

[0016] Where, k / / h represents the true permeability when the core texture is parallel to the core end face. i Let k be the thickness of the i-th layer of the core. i Let be the permeability of the i-th layer of the core.

[0017] When the core texture is perpendicular to the core end face, fluid flows in along the direction of lamination development. Based on the development of the laminations, the core is divided into layers 1, 2, ..., and n, with the permeabilities of each layer corresponding to k1, k2, ..., and k, respectively. n Draw a core section along the midline of the opposite end faces of the arc surface, and denote the heights of each layer on the section as h′1, h′2, ... and h′. n The true permeability value when the core texture is perpendicular to the core end face is calculated using Equation 2.

[0018]

[0019] in, h′ represents the true permeability when the core texture is perpendicular to the core end face, L is the core height, and h′ is the true permeability value. i To create a core section along the midline of the opposite end faces of the arc, the height of the i-th layer on the section is given.

[0020] When the core texture is perpendicular to the core end face, and fluid flows in perpendicular to the direction of lamination development, the core is divided into layers 1, 2, ..., and n according to the development of the laminations. The permeability of each layer corresponds to k1, k2, ..., and k, respectively. n The thicknesses of each layer are H1, H2, ... and H. n A cuboid was constructed, with the core end face a square with the core diameter as its side length. The height of the cuboid was the height of the core. The permeability of each layer was designed based on the core end face, and the thickness distribution ratio was kept consistent with the core end face. The cuboid was designed with an input pressure of 1 MPa on the left side and an output pressure of 0 on the right side, with no fluid flow on other faces. A finite element mesh was established, and the seepage field distribution of the cuboid was obtained according to Darcy's law. The cuboid core was divided into 2l+1 equal parts from top to bottom. The average seepage flow values ​​kc1, kc2, ..., kc of each section were read from the numerical simulation results. 2m+1 The permeability values ​​through the left and right sides of the cuboid were calculated using Equation 3.

[0021]

[0022] in, k is the simulated permeability value passing through the left and right sides of the cuboid.Ci Let be the average seepage flow rate at the i-th cross section;

[0023] c. Calculate the simulated values ​​of the core test results, and set up a three-dimensional cylindrical model. The permeability of each layer is determined according to k1, k2, ... and k n The fluid is set to flow in from end A and out from end B. A finite element mesh is established, and the seepage field distribution is obtained according to Darcy's law. The core sample is divided into 2m+1 equal parts from top to bottom. The average seepage flow values ​​q1, q2, ..., q of each section are read from the numerical simulation results of the seepage field. 2m+1 The simulated value k of the core test results is calculated using Equation 4. * ;

[0024]

[0025] Where, k * q represents the simulated value of the core test results. i Let be the average seepage flow rate at the i-th cross section;

[0026] d. Calculate the radial permeability test error value ε of the core using Equation 5;

[0027]

[0028] Where ε is the radial permeability test error value of the core, and k * These are simulated values ​​of the test results from the rock core.

[0029] In step a, core preparation specifically refers to re-preparing the core if the lamination development direction of the obtained core shows a broken line or a turn, until a core with a single lamination development direction is obtained.

[0030] In step a, recording the relationship between the direction of the airflow through the core and the core texture specifically refers to recording whether the core texture is perpendicular or parallel to the core end face after the airflow is added.

[0031] When the core end face is perpendicular to the core texture, the flow direction of the fluid is observed.

[0032] The observed flow direction of the fluid specifically refers to whether the fluid flows in along or perpendicular to the lamination development direction. If the flow direction of the fluid is at an angle to the lamination development direction, the position of the core is readjusted until the fluid flows in along or perpendicular to the lamination development direction.

[0033] In step b, the permeability values ​​of each layer are obtained by using a common permeability testing method based on core samples of the same type of material.

[0034] In step b, the thickness and area of ​​each layer are obtained through CT scans or MRI images.

[0035] In step c, the pressure at boundary A is set to 1 MPa, the pressure at boundary C is 0, and there is no flow at boundaries B and D.

[0036] In step d, k and k i Same, k i The true permeability k is the value when the core texture is parallel to the core end face. / / True permeability when core texture is perpendicular to the core end face Or the simulated permeability values ​​passing through the left and right sides of the cuboid.

[0037] The beneficial effects of this invention are mainly reflected in the following aspects:

[0038] 1. This invention includes: a) preparing a core sample, recording the direction of the core texture and the core end face, and recording the relationship between the direction of airflow through the core and the core texture; b) when the core texture is parallel to the core end face, dividing the core into layers 1, 2, ..., and n according to the development of the lamellar structure, with the permeability of each layer corresponding to k1, k2, ..., and k... n The thicknesses of each layer are h1, h2, ... and h, respectively. n The true permeability k is calculated using Equation 1 when the core texture is parallel to the core end face. / / When the core texture is perpendicular to the core end face, fluid flows in along the direction of lamination development. Based on the development of the laminations, the core is divided into layers 1, 2, ..., and n, with the permeabilities of each layer corresponding to k1, k2, ..., and k, respectively. n Draw a core section along the midline of the opposite end faces of the arc surface, and denote the heights of each layer on the section as h′1, h′2, ... and h′. n The true permeability value when the core texture is perpendicular to the core end face is calculated using Equation 2. When the core texture is perpendicular to the core end face, and fluid flows in perpendicular to the direction of lamination development, the core is divided into layers 1, 2, ..., and n according to the development of the laminations. The permeability of each layer corresponds to k1, k2, ..., and k, respectively. n The thicknesses of each layer are H1, H2, ... and H. nA cuboid was constructed, with the core end face a square with the core diameter as its side length. The height of the cuboid was the height of the core. The permeability of each layer was designed based on the core end face, and the thickness distribution ratio was kept consistent with the core end face. The cuboid was designed with an input pressure of 1 MPa on the left side and an output pressure of 0 on the right side, with no fluid flow on other faces. A finite element mesh was established, and the seepage field distribution of the cuboid was obtained according to Darcy's law. The cuboid core was divided into 2l+1 equal parts from top to bottom. The average seepage flow values ​​kc1, kc2, ..., kc of each section were read from the numerical simulation results. 2m+1 The permeability values ​​through the left and right sides of the cuboid were calculated using Equation 3. c. Calculate the simulated values ​​of the core test results, and set up a three-dimensional cylindrical model. The permeability of each layer is determined according to k1, k2, ... and k n The fluid is set to flow in from end A and out from end B. A finite element mesh is established, and the seepage field distribution is obtained according to Darcy's law. The core sample is divided into 2m+1 equal parts from top to bottom. The average seepage flow values ​​q1, q2, ..., q of each section are read from the numerical simulation results of the seepage field. 2m+1 The simulated value k of the core test results is calculated using Equation 4. * d. Calculate the radial permeability test error value ε of the core using Equation 5. As a complete technical solution, compared with the existing technology, it can perform error analysis on the radial permeability test of the core, effectively estimate the accuracy of the radial permeability test of the core, and conduct a reliability assessment of the radial permeability test of the core.

[0039] 2. This invention can objectively evaluate the accuracy or systematic error of core radial permeability test results, solving the problem that there were no other effective methods to evaluate the accuracy of core radial permeability test results.

[0040] 3. This invention uses different calculation methods to numerically simulate the true permeability value for different internal structures of the rock core, effectively ensuring the objectivity of the true permeability value calculation and improving the accuracy of systematic error evaluation.

[0041] 4. This invention can simulate the impact of a system composed of materials with different properties on the overall permeability, and can be used to study the degree of influence of the degree of difference in the properties of the components on the system error.

[0042] 5. In calculating the true value of permeability, this invention fully considers the usual habits when measuring permeability, making it convenient for operators to compare with axial permeability testing methods.

[0043] 6. This invention provides a feasible algorithm that can effectively evaluate the impact of conformal transformation using complex functions on the test results of the radial permeability test when the assumption of isotropy is assumed.

[0044] 7. In calculating the true value of permeability, this invention fully considers the usual habits when measuring permeability, making it convenient for operators to compare with the axial permeability test method. Attached Figure Description

[0045] The present invention will now be further described in detail with reference to the accompanying drawings and specific embodiments, wherein:

[0046] Figure 1 This is a schematic diagram of the core sample from which the fluid of the present invention flows in from end A and out from end B. Detailed Implementation

[0047] Example 1

[0048] See Figure 1 A method for calculating the error of radial permeability testing of full-diameter core samples includes the following steps:

[0049] a. Prepare core samples, record the direction of the core texture and the core end face, and record the relationship between the direction of airflow through the core and the core texture;

[0050] b. When the core texture is parallel to the core end face, the core is divided into layers 1, 2, ..., and n according to the development of the lamellarity. The permeability of each layer corresponds to k1, k2, ..., and k, respectively. n The thicknesses of each layer are h1, h2, ... and h, respectively. n The true permeability k is calculated using Equation 1 when the core texture is parallel to the core end face. / / ;

[0051]

[0052] Where, k / / h represents the true permeability when the core texture is parallel to the core end face. i Let k be the thickness of the i-th layer of the core. i Let be the permeability of the i-th layer of the core.

[0053] When the core texture is perpendicular to the core end face, fluid flows in along the direction of lamination development. Based on the development of the laminations, the core is divided into layers 1, 2, ..., and n, with the permeabilities of each layer corresponding to k1, k2, ..., and k, respectively. n Draw a core section along the midline of the opposite end faces of the arc surface, and denote the heights of each layer on the section as h′1, h′2, ... and h′. n The true permeability value when the core texture is perpendicular to the core end face is calculated using Equation 2.

[0054]

[0055] in, h′ represents the true permeability when the core texture is perpendicular to the core end face, L is the core height, and h′ is the true permeability value. i To create a core section along the midline of the opposite end faces of the arc, the height of the i-th layer on the section is given.

[0056] When the core texture is perpendicular to the core end face, and fluid flows in perpendicular to the direction of lamination development, the core is divided into layers 1, 2, ..., and n according to the development of the laminations. The permeability of each layer corresponds to k1, k2, ..., and k, respectively. n The thicknesses of each layer are H1, H2, ... and H. n A cuboid was constructed, with the core end face a square with the core diameter as its side length. The height of the cuboid was the height of the core. The permeability of each layer was designed based on the core end face, and the thickness distribution ratio was kept consistent with the core end face. The cuboid was designed with an input pressure of 1 MPa on the left side and an output pressure of 0 on the right side, with no fluid flow on other faces. A finite element mesh was established, and the seepage field distribution of the cuboid was obtained according to Darcy's law. The cuboid core was divided into 2l+1 equal parts from top to bottom. The average seepage flow values ​​kc1, kc2, ..., kc of each section were read from the numerical simulation results. 2m+1 The permeability values ​​through the left and right sides of the cuboid were calculated using Equation 3.

[0057]

[0058] in, k is the simulated permeability value passing through the left and right sides of the cuboid. Ci Let be the average seepage flow rate at the i-th cross section;

[0059] c. Calculate the simulated values ​​of the core test results, and set up a three-dimensional cylindrical model. The permeability of each layer is determined according to k1, k2, ... and k n The fluid is set to flow in from end A and out from end B. A finite element mesh is established, and the seepage field distribution is obtained according to Darcy's law. The core sample is divided into 2m+1 equal parts from top to bottom. The average seepage flow values ​​q1, q2, ..., q of each section are read from the numerical simulation results of the seepage field. 2m+1 The simulated value k of the core test results is calculated using Equation 4. * ;

[0060]

[0061] Where, k * q represents the simulated value of the core test results. i Let be the average seepage flow rate at the i-th cross section;

[0062] d. Calculate the radial permeability test error value ε of the core using Equation 5;

[0063]

[0064] Where ε is the radial permeability test error value of the core, and k * These are simulated values ​​of the test results from the rock core.

[0065] It can perform error analysis on core radial permeability testing, effectively estimate the accuracy of core radial permeability testing, and conduct reliability assessment of core radial permeability testing.

[0066] Example 2

[0067] See Figure 1 A method for calculating the error of radial permeability testing of full-diameter core samples includes the following steps:

[0068] a. Prepare core samples, record the direction of the core texture and the core end face, and record the relationship between the direction of airflow through the core and the core texture;

[0069] b. When the core texture is parallel to the core end face, the core is divided into layers 1, 2, ..., and n according to the development of the lamellarity. The permeability of each layer corresponds to k1, k2, ..., and k, respectively. n The thicknesses of each layer are h1, h2, ... and h, respectively. n The true permeability k is calculated using Equation 1 when the core texture is parallel to the core end face. / / ;

[0070]

[0071] Where, k / / h represents the true permeability when the core texture is parallel to the core end face. i Let k be the thickness of the i-th layer of the core. i Let be the permeability of the i-th layer of the core.

[0072] When the core texture is perpendicular to the core end face, fluid flows in along the direction of lamination development. Based on the development of the laminations, the core is divided into layers 1, 2, ..., and n, with the permeabilities of each layer corresponding to k1, k2, ..., and k, respectively. n Draw a core section along the midline of the opposite end faces of the arc surface, and denote the heights of each layer on the section as h′1, h′2, ... and h′. n The true permeability value when the core texture is perpendicular to the core end face is calculated using Equation 2.

[0073]

[0074] in, h′ represents the true permeability when the core texture is perpendicular to the core end face, L is the core height, and h′ is the true permeability value.i To create a core section along the midline of the opposite end faces of the arc, the height of the i-th layer on the section is given.

[0075] When the core texture is perpendicular to the core end face, and fluid flows in perpendicular to the direction of lamination development, the core is divided into layers 1, 2, ..., and n according to the development of the laminations. The permeability of each layer corresponds to k1, k2, ..., and k, respectively. n The thicknesses of each layer are H1, H2, ... and H. n A cuboid was constructed, with the core end face a square with the core diameter as its side length. The height of the cuboid was the height of the core. The permeability of each layer was designed based on the core end face, and the thickness distribution ratio was kept consistent with the core end face. The cuboid was designed with an input pressure of 1 MPa on the left side and an output pressure of 0 on the right side, with no fluid flow on other faces. A finite element mesh was established, and the seepage field distribution of the cuboid was obtained according to Darcy's law. The cuboid core was divided into 2l+1 equal parts from top to bottom. The average seepage flow values ​​kc1, kc2, ..., kc of each section were read from the numerical simulation results. 2m+1 The permeability values ​​through the left and right sides of the cuboid were calculated using Equation 3.

[0076]

[0077] in, This is a simulated permeability value passing through the left and right sides of the cuboid. Let be the average seepage flow rate at the i-th cross section;

[0078] c. Calculate the simulated values ​​of the core test results, and set up a three-dimensional cylindrical model. The permeability of each layer is determined according to k1, k2, ... and k n The fluid is set to flow in from end A and out from end B. A finite element mesh is established, and the seepage field distribution is obtained according to Darcy's law. The core sample is divided into 2m+1 equal parts from top to bottom. The average seepage flow values ​​q1, q2, ..., q of each section are read from the numerical simulation results of the seepage field. 2m+1 The simulated value k of the core test results is calculated using Equation 4. * ;

[0079]

[0080] Where, k * q represents the simulated value of the core test results. i Let be the average seepage flow rate at the i-th cross section;

[0081] d. Calculate the radial permeability test error value ε of the core using Equation 5;

[0082]

[0083] Where ε is the radial permeability test error value of the core, and k * These are simulated values ​​of the test results from the rock core.

[0084] In step a, core preparation specifically refers to re-preparing the core if the lamination development direction of the obtained core shows a broken line or a turn, until a core with a single lamination development direction is obtained.

[0085] In step a, recording the relationship between the direction of the airflow through the core and the core texture specifically refers to recording whether the core texture is perpendicular or parallel to the core end face after the airflow is added.

[0086] When the core end face is perpendicular to the core texture, the flow direction of the fluid is observed.

[0087] The observed flow direction of the fluid specifically refers to whether the fluid flows in along or perpendicular to the lamination development direction. If the flow direction of the fluid is at an angle to the lamination development direction, the position of the core is readjusted until the fluid flows in along or perpendicular to the lamination development direction.

[0088] It can objectively evaluate the accuracy or systematic error of core radial permeability test results, solving the previous problem that there was no other effective method to evaluate the accuracy of core radial permeability test results.

[0089] For different internal structures of the core sample, different calculation methods are used to numerically simulate the true permeability value, which effectively ensures the objectivity of the true permeability calculation and improves the accuracy of the systematic error evaluation.

[0090] It can simulate and calculate the impact of a system composed of materials with different properties on the overall permeability, and can be used to study the degree of influence of the degree of difference in the properties of the components on the system error.

[0091] Example 3

[0092] See Figure 1 A method for calculating the error of radial permeability testing of full-diameter core samples includes the following steps:

[0093] a. Prepare core samples, record the direction of the core texture and the core end face, and record the relationship between the direction of airflow through the core and the core texture;

[0094] b. When the core texture is parallel to the core end face, the core is divided into layers 1, 2, ..., and n according to the development of the lamellarity. The permeability of each layer corresponds to k1, k2, ..., and k, respectively. n The thicknesses of each layer are h1, h2, ... and h, respectively. n The true permeability k is calculated using Equation 1 when the core texture is parallel to the core end face. / / ;

[0095]

[0096] Where, k / / h represents the true permeability when the core texture is parallel to the core end face. i Let k be the thickness of the i-th layer of the core. i Let be the permeability of the i-th layer of the core.

[0097] When the core texture is perpendicular to the core end face, fluid flows in along the direction of lamination development. Based on the development of the laminations, the core is divided into layers 1, 2, ..., and n, with the permeabilities of each layer corresponding to k1, k2, ..., and k, respectively. n Draw a core section along the midline of the opposite end faces of the arc surface, and denote the heights of each layer on the section as h′1, h′2, ... and h′. n The true permeability value when the core texture is perpendicular to the core end face is calculated using Equation 2.

[0098]

[0099] in, h′ represents the true permeability when the core texture is perpendicular to the core end face, L is the core height, and h′ is the true permeability value. i To create a core section along the midline of the opposite end faces of the arc, the height of the i-th layer on the section is given.

[0100] When the core texture is perpendicular to the core end face, and fluid flows in perpendicular to the direction of lamination development, the core is divided into layers 1, 2, ..., and n according to the development of the laminations. The permeability of each layer corresponds to k1, k2, ..., and k, respectively. n The thicknesses of each layer are H1, H2, ... and H. n A cuboid was constructed, with the core end face a square with the core diameter as its side length. The height of the cuboid was the height of the core. The permeability of each layer was designed based on the core end face, and the thickness distribution ratio was kept consistent with the core end face. The cuboid was designed with an input pressure of 1 MPa on the left side and an output pressure of 0 on the right side, with no fluid flow on other faces. A finite element mesh was established, and the seepage field distribution of the cuboid was obtained according to Darcy's law. The cuboid core was divided into 2l+1 equal parts from top to bottom. The average seepage flow values ​​kc1, kc2, ..., kc of each section were read from the numerical simulation results. 2m+1 The permeability values ​​through the left and right sides of the cuboid were calculated using Equation 3.

[0101]

[0102] in, k is the simulated permeability value passing through the left and right sides of the cuboid. Ci Let be the average seepage flow rate at the i-th cross section;

[0103] c. Calculate the simulated values ​​of the core test results, and set up a three-dimensional cylindrical model. The permeability of each layer is determined according to k1, k2, ... and k n The fluid is set to flow in from end A and out from end B. A finite element mesh is established, and the seepage field distribution is obtained according to Darcy's law. The core sample is divided into 2m+1 equal parts from top to bottom. The average seepage flow values ​​q1, q2, ..., q of each section are read from the numerical simulation results of the seepage field. 2m+1 The simulated value k of the core test results is calculated using Equation 4. * ;

[0104]

[0105] Where, k * q represents the simulated value of the core test results. i Let be the average seepage flow rate at the i-th cross section;

[0106] d. Calculate the radial permeability test error value ε of the core using Equation 5;

[0107]

[0108] Where ε is the radial permeability test error value of the core, and k * These are simulated values ​​of the test results from the rock core.

[0109] In step a, core preparation specifically refers to re-preparing the core if the lamination development direction of the obtained core shows a broken line or a turn, until a core with a single lamination development direction is obtained.

[0110] In step a, recording the relationship between the direction of the airflow through the core and the core texture specifically refers to recording whether the core texture is perpendicular or parallel to the core end face after the airflow is added.

[0111] When the core end face is perpendicular to the core texture, the flow direction of the fluid is observed.

[0112] The observed flow direction of the fluid specifically refers to whether the fluid flows in along or perpendicular to the lamination development direction. If the flow direction of the fluid is at an angle to the lamination development direction, the position of the core is readjusted until the fluid flows in along or perpendicular to the lamination development direction.

[0113] In step b, the permeability values ​​of each layer are obtained by using a common permeability testing method based on core samples of the same type of material.

[0114] In step b, the thickness and area of ​​each layer are obtained through CT scans or MRI images.

[0115] In step c, the pressure at boundary A is set to 1 MPa, the pressure at boundary C is 0, and there is no flow at boundaries B and D.

[0116] In step d, k and k i Same, k i The true permeability k is the value when the core texture is parallel to the core end face. / / True permeability when core texture is perpendicular to the core end face Or the simulated permeability values ​​passing through the left and right sides of the cuboid.

[0117] The calculation of the true permeability value fully considers the usual habits of permeability measurement, making it convenient for operators to compare with the axial permeability test method.

[0118] A feasible algorithm is presented, which can effectively evaluate the impact of conformal transformation using complex functions on the test results of the radial permeability test when the assumption of isotropy is assumed.

[0119] The calculation of the true permeability value fully considers the usual habits of permeability measurement, making it convenient for operators to compare with the axial permeability test method.

[0120] The invention will now be described with reference to specific examples:

[0121] Observation of the core sample using CT scans or nuclear magnetic resonance imaging (NMR) revealed two layers: Layer 1 and Layer 2. The permeabilities of each layer correspond to k1 = 1 mD and k2 = 0.1 mD, respectively. A cross-section of the core sample was created along the midline of the opposite end face of the arc surface. The heights of each layer on the cross-section were denoted as h′1 = 0.785 m and h′2 = 0.041 m, respectively. The true permeability value at this point is:

[0122]

[0123] A three-dimensional cylindrical core model was constructed, with the permeability of each layer set according to k1 = 1 mD and k2 = 0.1 mD, respectively. Fluid flowed in from end A and out from end B. The boundary pressure at A was set to 1 MPa, the boundary pressure at C to 0, and there was no fluid flow at boundaries B and D. A finite element mesh was established, and the seepage field distribution was obtained according to Darcy's law. The cylindrical core was divided into 5 equal parts from top to bottom. The average flow rate of each section, q1≈q2≈q3≈q4≈q5 = 0.85 L / s, was read from the numerical simulation results. The permeability value simulated using the formula was then calculated.

[0124]

[0125] Therefore, the error value for the radial permeability test of the full-diameter core is:

[0126]

[0127] This specific example illustrates that even when the permeability of two parts differs by a factor of 10 and their area by a factor of 19, the radial permeability testing method remains reliable.

Claims

1. A method for calculating the error of radial permeability testing of full-diameter core samples, characterized in that, Includes the following steps: a. Prepare core samples, record the direction of the core texture and the core end face, and record the relationship between the direction of airflow through the core and the core texture; b. When the core texture is parallel to the core end face, the core is divided into layers 1, 2, ..., and n according to the development of the lamellarity. The permeability of each layer corresponds to k1, k2, ..., and k, respectively. n The thicknesses of each layer are h1, h2, ... and h, respectively. n The true permeability value when the core texture is parallel to the core end face is calculated using Equation 1. ; Formula 1 in, This represents the true permeability when the core texture is parallel to the core end face. Let be the thickness of the i-th layer of the core. Let be the permeability of the i-th layer of the core. When the core texture is perpendicular to the core end face, fluid flows in along the direction of lamination development. Based on the development of the laminations, the core is divided into layers 1, 2, ..., and n, with the permeabilities of each layer corresponding to k1, k2, ..., and k, respectively. n Draw a core section along the centerline of the opposite end face of the arc surface, and record the height of each layer on the section as follows: , ,……and The true permeability value when the core texture is perpendicular to the core end face is calculated using Equation 2. ; Formula 2 in, The true permeability value is given when the core texture is perpendicular to the core end face, and L is the core height. To create a core section along the midline of the opposite end faces of the arc, the height of the i-th layer on the section is given. When the core texture is perpendicular to the core end face, and fluid flows in perpendicular to the direction of lamination development, the core is divided into layers 1, 2, ..., and n according to the development of the laminations. The permeability of each layer corresponds to k1, k2, ..., and k, respectively. n The thicknesses of each layer are H1, H2, ... and H. n A cuboid was constructed, with the core end face a square with the core diameter as its side length. The height of the cuboid was the height of the core. The permeability of each layer was designed based on the core end face, and the thickness distribution ratio was consistent with the core end face. The cuboid was designed with an input pressure of 1 MPa on the left side and an output pressure of 0 on the right side, with no fluid flow on other faces. A finite element mesh was established, and the seepage field distribution of the cuboid was obtained according to Darcy's law. The cuboid core was divided into 2l+1 equal parts from top to bottom. The average seepage flow values ​​kc1, kc2, ..., of each section were read from the numerical simulation results. The permeability values ​​through the left and right sides of the cuboid were calculated using Equation 3. ; Formula 3 in, This is a simulated permeability value passing through the left and right sides of the cuboid. The average seepage flow rate at the i-th cross section; c. Calculate the simulated values ​​of the core test results, and set up a three-dimensional cylindrical model. The permeability of each layer is determined according to k1, k2, ... and k n The fluid is set to flow in from end A and out from end B. A finite element mesh is established, and the seepage field distribution is obtained according to Darcy's law. The core sample is divided into 2m+1 equal parts from top to bottom. The average seepage flow values ​​q1, q2, ..., q of each section are read from the numerical simulation results of the seepage field. 2m+1 The simulated values ​​of the core test results are calculated using Equation 4. ; Formula 4 in, These are simulated values ​​of the core test results. The average seepage flow rate at the i-th cross section; d. Calculate the radial permeability test error value of the core using Equation 5. ; Formula 5 in, This represents the radial permeability test error value of the rock core. These are simulated values ​​of the core test results; In step d, and same, The true permeability value when the core texture is parallel to the core end face. True permeability when core texture is perpendicular to the core end face Or the simulated permeability values ​​passing through the left and right sides of the cuboid. .

2. The method for calculating the radial permeability test error of a full-diameter core according to claim 1, characterized in that: In step a, core preparation specifically refers to re-preparing the core if the lamination development direction of the obtained core shows a broken line or a turn, until a core with a single lamination development direction is obtained.

3. The method for calculating the radial permeability test error of a full-diameter core according to claim 1, characterized in that: In step a, recording the relationship between the direction of the airflow through the core and the core texture specifically refers to recording whether the core texture is perpendicular or parallel to the core end face after the airflow is added.

4. The method for calculating the radial permeability test error of a full-diameter core according to claim 3, characterized in that: When the core end face is perpendicular to the core texture, the flow direction of the fluid is observed.

5. The method for calculating the radial permeability test error of a full-diameter core according to claim 4, characterized in that: The observation of the flow direction of the fluid specifically refers to whether the fluid flows in along or perpendicular to the direction of lamination development. If the flow direction of the fluid is at an angle to the direction of lamination development, the position of the core is readjusted until the fluid flows in along or perpendicular to the direction of lamination development.

6. The method for calculating the radial permeability test error of a full-diameter core according to claim 1, characterized in that: In step b, the permeability values ​​of each layer are obtained by using a common permeability testing method based on core samples of the same type of material.

7. The method for calculating the radial permeability test error of a full-diameter core according to claim 1, characterized in that: In step b, the thickness and area of ​​each layer are obtained through CT scans or MRI images.

8. The method for calculating the radial permeability test error of a full-diameter core according to claim 1, characterized in that: In step c, the pressure at boundary A is set to 1 MPa, the pressure at boundary C is 0, and there is no flow at boundaries B and D.

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