Lamellar shale gas permeability test method

Abstract

The present application provides a kind of laminated shale gas permeability test method, comprising: step 1, select the laminated shale sample of certain study block, obtain the length L and diameter D of laminated shale;Step 2, measure the laminated shale gas permeability value under different confining pressures;Step 3, draw the curve of laminated shale permeability with net overburden pressure;Step 4, draw the curve of permeability-net overburden pressure logarithm;Step 5, according to the curve of permeability-net overburden pressure logarithm, obtain the inflection point value;Step 6, establish the curve of net overburden pressure-permeability in rectangular coordinate;Step 7, calculate the curve of laminated shale gas permeability and net overburden pressure relationship.The method accurately determines the laminated shale gas permeability value, has strong reliability and accuracy, provides effective technical support for laminated shale oilfield productivity prediction and development plan.

Description

Technical Field

[0001] The present invention relates to the technical field of shale oil exploration and development, and in particular to a method for testing the gas permeability of laminated shale. Background Art

[0002] Laminated shale is an important lithofacies type in shale oil in the Jiyang Depression. In laminated shale reservoirs, muddy and gray laminae are abundantly developed, with one gray lamina developing alternately with another. The bedding fractures between the muddy and gray laminae are important seepage channels in shale reservoirs. Accurate characterization of the permeability of this laminated shale is of great significance for shale oil production capacity prediction, development plan formulation, and mining optimization.

[0003] Chinese patent application CN 111650108 A discloses a shale matrix permeability measurement device and method. The device comprises: a gas cylinder; a booster pump connected to the gas cylinder; an automatic gas replenishment and pressure-increasing system connected to the booster pump via a pressure regulating valve, configured to replenish and pressurize the reference and sample chambers with gas from the booster pump's gas tank when the pressure in the reference and sample chambers is less than a preset target pressure during the experiment; a temperature control device for accommodating the reference and sample chambers, wherein the sample chamber is used to hold the shale rock sample to be measured; and a pressure sensor for measuring the pressure data in the reference and sample chambers. The solution provided in this application avoids the problem of a sharp drop in system pressure after gas has filled the intergranular spaces, eliminating the influence of filling level on permeability measurement, reducing measurement error, and improving the accuracy of permeability measurement. This method cannot characterize bedding fractures opened in laminar shale samples during pre-experimental processing.

[0004] Chinese patent application CN 112730198 A discloses a method for calculating the permeability of natural fractures in shale. The method includes the following steps: preparing a standard shale core column; obtaining single-fracture shale samples with different roughness; obtaining multiple-fracture shale samples with the same roughness but different numbers of fractures; determining the quantitative relationship between fracture surface roughness and single-fracture permeability in shale; determining the quantitative relationship between fracture slip distance and single-fracture permeability in shale; determining the quantitative relationship between effective pressure and single-fracture permeability in shale; determining the quantitative relationship between the number of fractures and the permeability of multiple-fracture shale; establishing a characterization equation for single-fracture permeability in shale that takes into account effective pressure, fracture slip distance, and fracture surface roughness; establishing an expression for calculating the permeability of multiple-fracture shale using single-fracture permeability and the number of fractures in shale; substituting the established characterization equation for single-fracture permeability in shale into the established characterization equation for multiple-fracture permeability in shale to obtain a comprehensive characterization equation for multiple-fracture permeability in shale. The permeabilities of different types of natural fractures in shale calculated by this method are more closely aligned with the actual conditions under reservoir conditions. This method is mainly used to calculate the permeability of fractures, and it is impossible to test the permeability of the matrix part in laminated shale.

[0005] Chinese patent application CN 112329240 A discloses a method for calculating the apparent permeability of shale gas reservoirs based on fuzzy theory. The method includes: establishing a concentration cloud model for free and adsorbed gas based on the shale reservoir's occurrence mechanism and fuzzy theory; establishing a flux model for the shale gas reservoir that considers viscous flow, Knudsen diffusion, and surface diffusion due to the slippage effect of gas molecules; optimizing a ridge-shaped distribution membership calculation function based on the pore throat structure characteristics of the shale reservoir that considers viscous flow, Knudsen diffusion, and surface diffusion; and calculating the membership of the concentration cloud model. Based on the flux model, the apparent permeability of the shale gas reservoir is derived based on the transport flux relationship within nanopores. Based on the adsorption and desorption characteristics of the shale reservoir, the method considers migration mechanisms such as viscous flow, Knudsen diffusion, and surface diffusion, and establishes a gas concentration cloud model based on fuzzy theory to rationally describe the apparent permeability of shale gas, which is influenced by the interactions between molecules. This method primarily calculates shale permeability from a numerical perspective, but is not suitable for testing core samples.

[0006] Currently, shale permeability testing is mainly divided into steady-state and non-steady-state methods. However, none of the above methods can eliminate the influence of bedding fracture opening on shale permeability during experimental treatment. At the same time, there are few systematic studies and mature methods for analyzing the permeability of laminated shale containing bedding fractures.

[0007] The above existing technologies are all significantly different from the present invention and fail to solve the technical problem we want to solve. Therefore, we have invented a new method for testing the gas permeability of laminated shale. Summary of the Invention

[0008] The purpose of the present invention is to provide a laminar shale gas permeability testing method for accurately measuring the laminar shale gas permeability value.

[0009] The purpose of the present invention can be achieved by the following technical measures: a method for testing the gas permeability of laminated shale, the method comprising:

[0010] Step 1: Select a laminar shale sample from a certain research area and obtain the laminar shale length L and diameter D;

[0011] Step 2, measuring the gas permeability of laminated shale under different confining pressures;

[0012] Step 3, plotting the variation curve of laminar shale permeability with net overburden pressure;

[0013] Step 4, draw a relationship curve between permeability and logarithm of net overburden pressure;

[0014] Step 5: Obtain the inflection point value based on the relationship curve of permeability and net overburden pressure logarithm;

[0015] Step 6, establishing a net overburden pressure-permeability relationship curve in rectangular coordinates;

[0016] Step 7: Calculate and obtain the relationship curve between the gas permeability of the laminated shale and the net overburden pressure.

[0017] The purpose of the present invention can also be achieved by the following technical measures:

[0018] In step 1, the length L and diameter D of the laminated shale are obtained by measurement.

[0019] In step 2, an overburden permeability experiment is conducted. The confining pressure is set to 1.5 MPa, and the permeability value of the laminated shale gas is measured; the confining pressure is gradually increased to 1.5 MPa, 3.5 MPa, 7 MPa, 10 MPa, 15 MPa, 20 MPa, and 30 MPa, and the permeability values ​​under different confining pressures are measured respectively.

[0020] In step 3, a curve of the permeability of laminated shale versus net overburden pressure is obtained based on the permeability values ​​of the shale sample under different net overburden pressures.

[0021] In step 4, the logarithm of the net overburden pressure value on the abscissa of the obtained permeability-net overburden pressure variation curve is taken to obtain a relationship curve between the logarithm of the permeability and the net overburden pressure.

[0022] In step 5, the inflection point value is obtained according to the relationship curve of permeability-net overburden pressure logarithm and the intersection point of two straight lines in the graph.

[0023] In step 6, the net overburden pressure data and permeability data at a value greater than or equal to the inflection point are used to establish a net overburden pressure-permeability relationship curve in rectangular coordinates, and exponential fitting is performed to obtain a fitting relationship.

[0024] In step 6, the fitting relationship is obtained as follows:

[0025] k=Ae -Bx

[0026] Where: k is the permeability of laminated shale, mD; A and B are parameter values ​​obtained according to the fitting formula; x is the net overburden pressure.

[0027] In step 7, the net overburden pressure is set to 1.5 MPa, and the gas permeability value of the laminated shale under ground conditions is calculated according to the fitting relationship. The relationship curve between the gas permeability of the laminated shale and the net overburden pressure is obtained by the fitting relationship.

[0028] The present invention discloses a method for testing the gas permeability of laminated shale. When measuring the gas permeability of laminated shale, the net overburden pressure is varied to test the overburden permeability value of the laminated shale. A relationship curve is plotted between the overburden permeability of the shale and the logarithm of the net overburden pressure to obtain an inflection point in the curve. The relationship curve after the inflection point is exponentially fitted to obtain a fitting formula. The fitting formula is then used to calculate the gas permeability value of the laminated shale sample. The present invention can reflect the open state of existing cracks in the laminated shale under surface conditions, and can correct cracks caused by pre-experimental treatment to the closed state of bedding fractures under surface conditions. This allows for accurate measurement of the gas permeability value of laminated shale, overcoming the shortcomings of existing technologies.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] When calculating the gas permeability of laminated shale, this method can reflect the open state of the original cracks in the laminated shale under ground conditions, and the cracks caused by the experimental pre-treatment process can be corrected to the closed state of the bedding fractures under ground conditions. The gas permeability value of the laminated shale is accurately measured with strong reliability and accuracy. The method of the present invention provides effective technical support for the production capacity prediction and development plan formulation of laminated shale oil fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a flow chart of a specific embodiment of the method for testing the gas permeability of laminated shale according to the present invention;

[0032] Figure 2 This is a graph showing changes in shale permeability versus net overburden pressure in a specific embodiment of the present invention;

[0033] Figure 3A shale permeability change graph with net overburden pressure as a logarithm for a specific embodiment of the present application;

[0034] Figure 4 A fitting relationship graph of permeability after the inflection point and net overburden pressure for a specific embodiment of the present application;

[0035] Figure 5 A gas permeability calculation graph according to the fitting relationship for a specific embodiment of the present application. DETAILED DESCRIPTION

[0036] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0037] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments in accordance with the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0038] The present application provides a laminated shale gas permeability determination method - overpressure backstepping method, the method comprises:

[0039] Step 1, select a laminated shale sample in a certain research block, and obtain the length L and diameter D of the laminated shale by measuring method.

[0040] Step 2, set the confining pressure to 1.5Mpa, measure the laminated shale gas permeability value; gradually increase the confining pressure to 1.5MPa, 3.5MPa, 7MPa, 10MPa, 15MPa, 20MPa, 30MPa, and measure the permeability value under different confining pressures.

[0041] Step 3, according to the permeability value of the shale sample under different net overburden pressure, the change curve of the laminated shale permeability with the net overburden pressure is obtained.

[0042] Step 4, taking the logarithm of the net overburden pressure value in the obtained permeability-net overburden pressure change curve as the horizontal coordinate, the permeability-net overburden pressure logarithm relationship curve is obtained;

[0043] Step 5, according to the permeability-net overburden pressure logarithm relationship curve, the inflection point value is obtained according to the intersection point of the two straight lines in the graph.

[0044] Step 6: Use the net overburden pressure data and permeability data at or above the inflection point to establish a net overburden pressure-permeability relationship curve in rectangular coordinates, perform exponential fitting, and obtain the fitting relationship:

[0045] k=Ae -Bx

[0046] Where: k is the permeability of laminated shale, mD; A and B are parameter values ​​obtained according to the fitting formula; x is the net overburden pressure.

[0047] Step 7: Set the net overburden pressure to 1.5 MPa and calculate the gas permeability of the laminated shale under ground conditions based on the fitting relationship. The relationship curve between the gas permeability of the laminated shale and the net overburden pressure is obtained by fitting the relationship.

[0048] The following are several specific embodiments of the present invention.

[0049] Example 1

[0050] In the specific embodiment 1 of the present invention, Figure 1 As shown, the laminar shale gas permeability determination method - overburden pressure inversion method includes the following steps:

[0051] Step 101: Select a laminar shale sample from a certain research area, and obtain the laminar shale length L = 2.40 cm and diameter D = 2.51 cm by measurement.

[0052] Step 2: Set the confining pressure to 1.5 MPa and measure the permeability of the laminated shale gas; gradually increase the confining pressure to 1.5 MPa, 3.5 MPa, 7 MPa, 10 MPa, 15 MPa, 20 MPa, and 30 MPa, and measure the permeability values ​​under different confining pressures, see Table 1.

[0053] Table 1 Permeability under different net overburden pressures

[0054] Confining pressure (Mpa) Permeability (mD) 1.5 5.964 3.5 3.323 7 1.239 10 0.560 15 0.215 20 0.100 30 0.023

[0055] Step 3: Based on the permeability values ​​of the shale sample under different net overburden pressures, the curve of the permeability of the laminated shale versus the net overburden pressure is obtained, as shown in Figure 2 .

[0056] Step 4: Take the logarithm of the net overburden pressure value on the horizontal axis of the obtained permeability-net overburden pressure change curve to obtain the relationship curve between the logarithm of permeability and net overburden pressure, see Figure 3 .

[0057] Step 5: Based on the relationship curve between permeability and the logarithm of net overburden pressure, the inflection point value is obtained according to the intersection of the two straight lines in the graph. The inflection point coordinate value is (10.0.56), indicating that the net overburden pressure at the inflection point is 10.0 MPa.

[0058] Step 6: Use the net overburden pressure data and permeability data at the inflection point, that is, the net overburden pressure data and permeability data at the inflection point greater than or equal to 10.0 MPa, to establish a rectangular coordinate net overburden pressure-permeability relationship curve, see Figure 4 , perform exponential fitting and obtain the fitting relationship:

[0059] k=2.592e -0.162x (1)

[0060] Where: k is the permeability of laminated shale, mD; A = 2.592 and B = 0.162 are parameter values ​​obtained according to the fitting formula; x is the net overburden pressure.

[0061] Step 7: Calculate the gas permeability of the laminated shale according to the fitting relationship. Under the ground conditions, the net overburden pressure is 1.5 MPa. Substituting it into formula (1), the gas permeability value is 2.03 mD. The permeability curve is obtained by back-calculating the overburden pressure. Figure 5 .

[0062] Example 2:

[0063] In the specific embodiment 2 of the present invention, as Figure 1 As shown, the laminar shale gas permeability determination method - overburden pressure inversion method includes the following steps:

[0064] Step 101: Select a laminar shale sample from a certain research area, and obtain the laminar shale length L = 2.56 cm and diameter D = 2.46 cm by measurement.

[0065] Step 2: Set the confining pressure to 1.5 MPa and measure the permeability of the laminated shale gas; gradually increase the confining pressure to 1.5 MPa, 3.5 MPa, 7 MPa, 10 MPa, 15 MPa, 20 MPa, and 30 MPa, and measure the permeability values ​​under different confining pressures.

[0066] Step 3: According to the permeability values ​​of the shale sample under different net overburden pressures, a curve of the permeability of the laminated shale versus the net overburden pressure is obtained.

[0067] Step 4: Take the logarithm of the net overburden pressure value on the horizontal axis of the obtained permeability-net overburden pressure variation curve to obtain a relationship curve between the logarithm of permeability and net overburden pressure.

[0068] Step 5: Based on the relationship curve between permeability and the logarithm of the net overburden pressure, the inflection point value is obtained according to the intersection of the two straight lines in the graph. The inflection point coordinate value is (10.0, 0.0132), indicating that the net overburden pressure at the inflection point is 10.0 MPa.

[0069] Step 6: Use the net overburden pressure data and permeability data at a value greater than or equal to the inflection point, i.e., the net overburden pressure data and permeability data at a value greater than or equal to 10.0 MPa, to establish a net overburden pressure-permeability relationship curve in rectangular coordinates, perform exponential fitting, and obtain the fitting relationship:

[0070] k=0.0438e -0.148x (1)

[0071] Where: k is the permeability of laminated shale, mD; A = 0.0438, B = 0.148 are the parameter values ​​obtained according to the fitting formula; x is the net overburden pressure.

[0072] Step 7: Calculate the gas permeability of the laminated shale according to the fitting relationship. Under the ground condition, the net overburden pressure is 1.5 MPa. Substituting it into formula (1), the gas permeability value is 0.035 mD. The permeability curve is obtained by inverse calculation of the overburden pressure.

[0073] Example 3:

[0074] In the specific embodiment 3 of the present invention, Figure 1 As shown, the laminar shale gas permeability determination method - overburden pressure inversion method includes the following steps:

[0075] Step 101: Select a laminar shale sample from a certain research area, and obtain the laminar shale length L = 2.52 cm and diameter D = 2.46 cm by measurement.

[0076] Step 2: Set the confining pressure to 1.5 MPa and measure the permeability of the laminated shale gas; gradually increase the confining pressure to 1.5 MPa, 3.5 MPa, 7 MPa, 10 MPa, 15 MPa, 20 MPa, and 30 MPa, and measure the permeability values ​​under different confining pressures.

[0077] Step 3: According to the permeability values ​​of the shale sample under different net overburden pressures, a curve of the permeability of the laminated shale versus the net overburden pressure is obtained.

[0078] Step 4: Take the logarithm of the net overburden pressure value on the horizontal axis of the obtained permeability-net overburden pressure variation curve to obtain a relationship curve between the logarithm of permeability and net overburden pressure.

[0079] Step 5: Based on the relationship curve between permeability and the logarithm of the net overburden pressure, the inflection point value is obtained according to the intersection of the two straight lines in the graph. The inflection point coordinate value is (10.0, 0.0032), indicating that the net overburden pressure at the inflection point is 10.0 MPa.

[0080] Step 6: Use the net overburden pressure data and permeability data at a value greater than or equal to the inflection point, i.e., the net overburden pressure data and permeability data at a value greater than or equal to 10.0 MPa, to establish a net overburden pressure-permeability relationship curve in rectangular coordinates, perform exponential fitting, and obtain the fitting relationship:

[0081] k=0.0118e -0.178x (1)

[0082] Where: k is the permeability of laminated shale, mD; A = 0.0118, B = 0.178 are the parameter values ​​obtained according to the fitting formula; x is the net overburden pressure.

[0083] Step 7: Calculate the gas permeability of the laminated shale according to the fitting relationship. The net overburden pressure under ground conditions is 1.5 MPa. Substituting it into formula (1), the gas permeability value is 0.009 mD. The permeability curve is obtained by inverse calculation of the overburden pressure.

[0084] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art may still modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features therein. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

[0085] Except for the technical features described in the specification, all other technical features are known technologies to those skilled in the art.

Claims

1. A method for testing the gas permeability of laminated shale, characterized in that: The laminar shale gas permeability testing method includes: Step 1: Select a laminar shale sample from a certain research area and obtain the laminar shale length L and diameter D; Step 2, measuring the gas permeability of laminated shale under different confining pressures; Step 3, plotting the variation curve of laminar shale permeability with net overburden pressure; Step 4, draw a relationship curve between permeability and logarithm of net overburden pressure; Step 5: Obtain an inflection point value based on the intersection of two straight lines in a permeability-net overburden pressure logarithm relationship curve; Step 6, establishing a net overburden pressure-permeability relationship curve in rectangular coordinates; Step 7: Calculate and obtain the relationship curve between the gas permeability of the laminated shale and the net overburden pressure; The net overburden pressure data and permeability data at a level greater than or equal to the inflection point are used to establish a net overburden pressure-permeability relationship curve in rectangular coordinates, and exponential fitting is performed to obtain a fitting relationship. The obtained fitting relationship is: ； Where: k is the permeability value of laminated shale, mD; A and B are parameter values ​​obtained according to the fitting formula; x is the net overburden pressure value.

2. The method for testing the gas permeability of laminated shale according to claim 1, characterized in that: In step 1, the length L and diameter D of the laminated shale are obtained by measurement.

3. The method for testing the gas permeability of laminated shale according to claim 1, characterized in that: In step 2, an overburden permeability experiment is conducted. The confining pressure is set to 1.5 MPa, and the permeability value of the laminated shale gas is measured; the confining pressure is gradually increased to 1.5 MPa, 3.5 MPa, 7 MPa, 10 MPa, 15 MPa, 20 MPa, and 30 MPa, and the permeability values ​​under different confining pressures are measured respectively.

4. The method for testing the gas permeability of laminated shale according to claim 1, characterized in that: In step 3, a curve of the permeability of the laminated shale versus the net overburden pressure is obtained based on the permeability values ​​of the laminated shale samples under different net overburden pressures.

5. The method for testing the gas permeability of laminated shale according to claim 1, characterized in that: In step 4, the logarithm of the net overburden pressure value on the abscissa of the obtained permeability-net overburden pressure variation curve is taken to obtain a relationship curve between the logarithm of the permeability and the net overburden pressure.

6. The method for testing the gas permeability of laminated shale according to claim 1, characterized in that: In step 7, the net overburden pressure is set to 1.5 MPa, and the gas permeability value of the laminated shale under ground conditions is calculated according to the fitting relationship. The relationship curve between the gas permeability of the laminated shale and the net overburden pressure is obtained by the fitting relationship.

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