Joint characterization method for micro-pore structure characteristics of shale reservoir

Abstract

The invention belongs to the field of unconventional oil and gas exploration and development, and particularly relates to a shale reservoir micro-pore structure feature joint characterization method. The method comprises the following steps: respectively obtaining a pore size distribution diagram A corresponding to the pore volume of shale according to a low-temperature nitrogen adsorption experiment result, a nuclear magnetic resonance experiment result and a high-pressure mercury injection experiment result carried out on a shale sample in a research area; a pore size distribution diagram B corresponding to the pore volume of the shale and a pore size distribution diagram C corresponding to the pore volume of the shale; correcting the pore size distribution diagram C corresponding to the pore volume of the shale according to the compression ratio of the shale sample to obtain a pore size distribution diagram D corresponding to the pore volume of the shale; and splicing and combining the aperture distribution diagram A, the aperture distribution diagram B and the aperture distribution diagram D to obtain a pore volume-aperture curve diagram S. By adopting the method disclosed by the invention, the accuracy of characterizing the micro-pore structure characteristics of the shale reservoir can be greatly improved.

Description

Technical Field

[0001] The present invention belongs to the field of unconventional oil and gas exploration and development, and specifically relates to a method for jointly characterizing microscopic pore structure characteristics of shale reservoirs. Background Art

[0002] The full-scale characterization technology of reservoir pore structure characteristics has an important impact on the occurrence state and gas content evaluation of shale gas. The study of multi-scale pore specific surface area and pore size distribution plays an important role in studying the influencing factors of pore development and gas content evaluation. With the deepening of unconventional oil and gas exploration and development, more and more characterization methods and technologies for reservoir pore specific surface area and pore size distribution have been derived. The commonly used low-temperature nitrogen adsorption experiment can test the pore size range mainly of micropores, nuclear magnetic resonance can indirectly test mesopores, and high-pressure mercury injection has certain advantages in reflecting pore roars, and can test larger pore volumes. Due to the strong reservoir heterogeneity, diverse pore types and wide distribution range, small throats, and complex pore throat connectivity of the shale reservoir in the study area. It is difficult to characterize the full-scale reservoir pore specific surface area and pore size distribution characteristics with a single test method, and the measurement values ​​of the overlapping parts of the two experiments are quite different and difficult to unify. A Chinese invention patent with authorization announcement number CN109060623B discloses a method for jointly characterizing the pore size distribution of dense sandstone, which combines the pore size distribution results obtained from high-pressure mercury injection experiments, the pore size distribution results obtained from XCT experiments, the pore size distribution results obtained from nuclear magnetic resonance experiments, and the pore size distribution results obtained from low-temperature nitrogen adsorption experiments, thereby jointly characterizing the pore size distribution of dense sandstone. However, due to the high content of brittle minerals in the shale in the study area, mercury cannot enter the semi-closed pores when testing with high-pressure mercury injection. Excessive mercury injection pressure will destroy the connectivity and structure of the pores, causing the mercury injection amount to be higher than the actual pore volume of the sample. The test results have a certain error, and the error will increase with the increase of mercury injection pressure. Therefore, there will be a certain error when using the method disclosed in the Chinese invention patent with authorization announcement number CN109060623B to characterize the microscopic pore structure characteristics of shale reservoirs; in addition, the above method can only characterize the microscopic pore structure characteristics of shale reservoirs from the dimension of pore volume, and the characterization results are not comprehensive, which leads to inaccurate evaluation results of the factors affecting the pore development of shale reservoirs and the gas content. Summary of the invention

[0003] The object of the present invention is to provide a method for jointly characterizing the microscopic pore structure characteristics of a shale reservoir, so as to solve the technical problem of errors existing in the prior art when jointly characterizing the microscopic pore structure characteristics of a shale reservoir.

[0004] In order to solve the above technical problems, the present invention provides a method for jointly characterizing the microscopic pore structure characteristics of a shale reservoir, comprising the following steps:

[0005] Based on the results of low-temperature nitrogen adsorption experiments, nuclear magnetic resonance experiments, and high-pressure mercury injection experiments on shale samples in the study area, pore size distribution diagram A corresponding to the pore volume of shale, pore size distribution diagram B corresponding to the pore volume of shale, and pore size distribution diagram C corresponding to the pore volume of shale were obtained respectively;

[0006] The compression rate of the sample is calculated according to the compression coefficient β of the shale sample; the pore volume and pore volume of the shale sample are corrected according to the compression rate, and the pore size distribution diagram D corresponding to the corrected pore volume of the shale is obtained according to the corrected pore volume and pore volume of the shale sample;

[0007] According to the pore size range that can be tested by different testing methods, the pore size distribution diagram A, pore size distribution diagram B and pore size distribution diagram D corresponding to the pore volume of shale are spliced ​​and combined to obtain the pore volume-pore size curve diagram S, and then the microscopic pore structure characteristics of the shale reservoir are characterized based on the pore volume-pore size curve diagram S.

[0008] The beneficial effects are as follows: by correcting the pore volume and pore volume of the shale sample according to the compression rate of the sample, the pore size distribution diagram corresponding to the corrected pore volume of the shale can be obtained quickly and accurately; by correcting the pore size distribution diagram corresponding to the pore volume of the shale obtained by the high-pressure mercury injection experiment according to the compression rate of the shale sample, the distribution diagram finally obtained for jointly characterizing the influence of the pore size on the pore volume of the shale is more accurate, thereby greatly improving the accuracy of characterizing the microscopic pore structure characteristics of the shale reservoir; in addition, the method of the present invention performs multi-scale joint characterization of the pore structure characteristics of the shale reservoir by splicing the pore size distribution diagram corresponding to the pore volume of the shale obtained by the low-temperature nitrogen adsorption experiment, the pore size distribution diagram corresponding to the pore volume of the shale obtained by the nuclear magnetic resonance experiment, and the pore size distribution diagram corresponding to the pore volume of the shale obtained by the high-pressure mercury injection experiment, so that the characterization results of the pore structure characteristics of the shale reservoir are more comprehensive.

[0009] Preferably, the method for splicing and combining pore size distribution diagram A, pore size distribution diagram B and pore size distribution diagram D is: select a cutoff pore size rd1 near the pore size of 2nm, the difference between the pore volume a corresponding to the cutoff pore size rd1 in the pore size distribution diagram A and the pore volume b corresponding to the cutoff pore size rd1 in the pore size distribution diagram B is less than a first threshold value, select a cutoff pore size rd2 near the pore size of 50nm, the difference between the pore volume c corresponding to the cutoff pore size rd2 in the pore size distribution diagram B and the pore volume d corresponding to the cutoff pore size rd2 in the pore size distribution diagram D is less than a second threshold value, connect the pore size distribution diagram A and the pore size distribution diagram B at the cutoff pore size rd1, and connect the pore size distribution diagram D and the pore size distribution diagram B at the cutoff pore size rd2.

[0010] Preferably, the method for establishing a connection between pore size distribution diagram A and pore size distribution diagram B at the cutoff pore size rd1, and establishing a connection between pore size distribution diagram D and pore size distribution diagram B at the cutoff pore size rd2 is: using the weighted average method to calculate the average of a and b and the average of c and d, and using the average of a and b as the pore volume at the joint of pore size distribution diagram A and pore size distribution diagram B, and using the average of c and d as the pore volume at the joint of pore size distribution diagram B and pore size distribution diagram D.

[0011] The beneficial effects are as follows: low-temperature nitrogen adsorption has a high test accuracy for micropores below 2nm, nuclear magnetic resonance can effectively characterize the pore size distribution of mesopores of 2-50nm, and high-pressure mercury injection can effectively test macropores greater than 50nm; by selecting a cutoff pore size rd1 near the pore size of 2nm and a cutoff pore size rd2 near the pore size of 50nm, and using the weighted average method to splice the pore size distribution map corresponding to the pore volume of shale, the final distribution map for jointly characterizing the influence of pore size on pore volume of shale is more accurate.

[0012] Preferably, the method further comprises: obtaining, based on the results of a low-temperature nitrogen adsorption experiment, a nuclear magnetic resonance experiment, and a high-pressure mercury injection experiment on shale samples in the study area, a pore size distribution diagram E corresponding to the pore specific surface area of ​​the shale, a pore size distribution diagram F corresponding to the pore specific surface area of ​​the shale, and a pore size distribution diagram G corresponding to the pore specific surface area of ​​the shale;

[0013] According to the pore size range that can be tested by different testing methods, the pore size distribution diagram E, pore size distribution diagram F and pore size distribution diagram G are spliced ​​and combined to obtain the pore specific surface area-pore size curve diagram Q; and then the pore specific surface area-pore size curve diagram Q is used to characterize the microscopic pore structure characteristics of the shale reservoir.

[0014] The beneficial effect is that the method of the present invention combines the results of low-temperature nitrogen adsorption experiments, nuclear magnetic resonance experiments and high-pressure mercury injection experiments to perform multi-scale joint characterization of the effect of pore size on the pore specific surface area of ​​shale, thereby achieving characterization of the microscopic pore structure characteristics of shale reservoirs in two dimensions of pore specific surface area and pore volume, making the characterization results more comprehensive, thereby improving the accuracy of the influencing factors of the pore development of the shale reservoir and the evaluation results of the gas content.

[0015] Preferably, the method for splicing and combining pore size distribution diagram E, pore size distribution diagram F and pore size distribution diagram G is: select a cutoff pore size rd3 near the pore size of 2nm, the difference between the pore specific surface area e corresponding to the cutoff pore size rd3 in the pore size distribution diagram E and the pore specific surface area f corresponding to the cutoff pore size rd3 in the pore size distribution diagram F is less than a third threshold value, select a cutoff pore size rd4 near the pore size of 50nm, the difference between the pore specific surface area g corresponding to the cutoff pore size rd4 in the pore size distribution diagram G and the pore specific surface area h corresponding to the cutoff pore size rd4 in the pore size distribution diagram F is less than a third threshold value, connect the pore size distribution diagram E and the pore size distribution diagram F at the cutoff pore size rd3, and connect the pore size distribution diagram G and the pore size distribution diagram F at the cutoff pore size rd4.

[0016] Preferably, the method of connecting the pore size distribution diagram E and the pore size distribution diagram F at the cutoff pore size rd3, and connecting the pore size distribution diagram G and the pore size distribution diagram F at the cutoff pore size rd4 is: using the weighted average method to calculate the mean of e and f and the mean of g and h, and using the mean of e and f as the pore specific surface area at the joint of the pore size distribution diagram A and the pore size distribution diagram B, and using the mean of g and h as the pore specific surface area at the joint of the pore size distribution diagram B and the pore size distribution diagram D.

[0017] Preferably, the porosity of the shale sample is greater than 1% and the permeability is greater than 0.001×10-3 μm2.

[0018] Preferably, the shale samples are shale samples at at least two depths of the target layer in the study area.

[0019] The beneficial effect is that by conducting experiments on shales at different depths in the target layer, the accuracy of the experimental results is guaranteed, and the accuracy of the joint characterization of the microscopic pore structure characteristics of the shale reservoir is further improved.

[0020] Preferably, the adsorption medium used in the low-temperature nitrogen adsorption experiment is high-purity nitrogen with a purity greater than 99.98% and a critical temperature of -195.8°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a flow chart of the method steps of the present invention;

[0022] Figure 2 is a pore size distribution diagram A corresponding to the pore volume of the shale of the present invention;

[0023] Figure 3 is the pore size distribution spectrum of the present invention;

[0024] Figure 4 is a pore size distribution diagram C corresponding to the pore volume of the shale of the present invention;

[0025] Figure 5 is a pore size distribution diagram D corresponding to the pore volume of the shale of the present invention;

[0026] Figure 6 is the pore volume-pore diameter curve S of the present invention;

[0027] Figure 7 It is the pore specific surface area-pore diameter curve Q of the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0029] Example of a joint characterization method for microscopic pore structure characteristics of shale reservoirs:

[0030] like Figure 1 As shown, the method for jointly characterizing the microscopic pore structure characteristics of shale reservoirs of the present invention comprises the following steps:

[0031] Step 1: Perform physical property analysis on the porosity and permeability of shale reservoir samples in the target layer in the study area, and select samples with porosity greater than a first threshold and permeability greater than a second threshold for conducting experiments.

[0032] First, samples at different depths of the target layer are collected. Preferably, samples at five depth values ​​are selected for collection. Then, ordinary rock thin section observation and rock mineral composition determination experiments are carried out on the samples at the five depth values. According to the experimental results, the physical properties of the shale reservoir in the study area are analyzed and evaluated, so as to screen out shale samples with a porosity greater than 1% and a permeability greater than 0.001×10-3μm2. Finally, the screened shale samples are divided into five categories according to their depth values ​​and numbered, namely sample 1, sample 2, sample 3, sample 4 and sample 5.

[0033] Step 2: Conduct a low-temperature nitrogen adsorption experiment on the shale sample to obtain its pore size distribution diagram.

[0034] The five types of shale samples selected were subjected to low-temperature nitrogen adsorption tests on an ASAP2460 physical adsorption instrument. The adsorption medium was high-purity nitrogen greater than 99.98%, and the critical temperature was -195.8°C. According to the national standard "Measurement of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method" (GB / T19587-2004), the pore size distribution characteristics of the specific surface area of ​​the pores were calculated using the BET model, i.e., the pore size distribution diagram corresponding to the specific surface area of ​​the pores of the shale samples; the desorption branch of the nitrogen adsorption isotherm was calculated using the DFT model to obtain the pore size distribution characteristics of the pore volume of the sample, i.e., the pore size distribution diagram E corresponding to the specific surface area of ​​the pores of the shale.

[0035] Figure 2 Figure A is the pore size distribution diagram corresponding to the pore volume of shale obtained by low-temperature nitrogen adsorption experiment. The results show that the low-temperature nitrogen adsorption experiment has a good characterization of the micropores in the shale sample. When the pore size is less than 2nm, the inheritance is more obvious. However, since the low-temperature nitrogen adsorption experiment is greatly affected by the particle size, when the pore size is greater than 10nm, an obvious "strong right-biased peak type" appears, causing the measured values ​​of the mesopores and macropores to change in the opposite direction.

[0036] Step 3: Conduct a nuclear magnetic resonance experiment on the shale sample to obtain its pore size distribution spectrum.

[0037] The five types of shale samples selected were tested on MicroMr23-060H-1 nuclear magnetic resonance analyzer. To ensure the accuracy of the experimental results, the shale samples used in the test were all regular samples. The pore size distribution diagram E and the nuclear magnetic resonance T2 spectrum curve corresponding to the pore specific surface area of ​​the shale were obtained according to the nuclear magnetic resonance experimental results, and then the nuclear magnetic resonance T2 relaxation time was converted into a pore size distribution spectrum that characterizes the reservoir. Figure 3 It can be seen that the T2 spectrum peak is negatively correlated with the pore size, indicating that the micropores in the shale sample are relatively developed, which is consistent with the results of the low-temperature nitrogen adsorption experiment to characterize the micropores. The pores corresponding to the T2 spectrum peak increase from left to right, the pore size distribution is complex, the span range is wide, and the peak area is large, indicating that mesopores and macropores are also developed in the shale sample. The pore size distribution diagram B corresponding to the pore volume of the shale is obtained according to the pore size distribution spectrum.

[0038] Step 4: Conduct a high-pressure mercury injection experiment on the shale sample to obtain its pore size distribution diagram.

[0039] High-pressure mercury injection experiments were carried out on the five types of screened shale samples. The high-pressure mercury injection experiment can be carried out using the AutoPoreIV9510 instrument. The experimental process is to first inject mercury into the sample tube under vacuum conditions, and then put the sample tube into the high-pressure station for analysis, and continuously change the injection pressure. Finally, the pore size distribution diagram corresponding to the pore volume, the pore size distribution diagram corresponding to the pore specific surface area, and the capillary pressure curve can be obtained. Compared with low-temperature nitrogen adsorption and nuclear magnetic resonance experiments, high-pressure mercury injection can detect a larger pore throat range and more pore types, and has certain advantages in characterizing large pores in shale reservoirs. The pore size distribution diagram C corresponding to the pore volume of shale measured by the high-pressure mercury injection experiment of shale samples is shown in Figure 2. Figure 4As shown in the figure, the experimental results show that shale samples are distributed from nanometer to micrometer, showing the characteristics of "overall double peaks and strong right-biased peaks". The large peak and small peak represent the distribution of pore sizes of different particle sizes: the large peak pore throat radius is about 10nm, mainly large pores in shale samples, and the weak small peak pore throat radius is about 10nm, mainly medium pores in shale samples. When the sample particle size is greater than 10nm, the contribution rate of large pores to the total porosity of shale samples is higher.

[0040] Step 5: Perform compression correction on the high-pressure mercury injection data to obtain a pore size distribution diagram corresponding to the pore volume of the corrected shale sample and a pore size distribution diagram corresponding to the pore specific surface area of ​​the shale sample.

[0041] Due to the high content of brittle minerals in the shale in the study area, mercury cannot enter the semi-closed pores when testing using high-pressure mercury injection. Excessive mercury injection pressure will destroy the connectivity and structure of the pores, causing the mercury injection amount to be higher than the actual pore volume of the sample. The test results have a certain error, and the error will increase with the increase of mercury injection pressure. Therefore, the mercury injection data needs to be corrected when connecting.

[0042] When the sample is placed under static pressure, the forces acting on it in all directions are the same. When the mercury injection pressure gradually increases, all pore walls invaded by mercury will be affected by the above stress. Solid samples are compressible, so it is necessary to calculate the compression rate of the sample through the compression coefficient β of the shale sample, that is, the volume per unit pressure is v s The change ratio of shale samples is as follows:

[0043]

[0044] Where β is the compression coefficient of shale sample; v s is the volume of shale sample, cm 3 / g;d p The unit pressure is MPa.

[0045] The pore volume and pore volume of shale samples are corrected by the compressibility factor:

[0046] V pi =v cpi -β·v s (pi)·pi (2)

[0047]

[0048] In formula (2) to formula (3), V pi is the corrected pore volume corresponding to the mercury injection pressure pi, cm 3 / g;

[0049] v cpiis the pore volume test value corresponding to the mercury injection pressure, cm3 / g;

[0050] pi is the mercury inlet pressure corresponding to the data to be corrected, MPa;

[0051] v s (pi) is the volume of shale sample after the mercury injection pressure changes, cm 3 / g;

[0052] According to the corrected pore volume and volume of the shale sample, the following can be obtained: Figure 5 The pore volume of the shale obtained after correction is shown in pore size distribution diagram D.

[0053] By correcting the pore volume and pore capacity of the shale sample according to the compression rate of the sample, the pore size distribution diagram corresponding to the corrected shale pore volume can be quickly and accurately obtained.

[0054] Step 6: Establish a joint characterization of pore volume based on the results of nuclear magnetic resonance experiments, low-temperature nitrogen adsorption experiments and high-pressure mercury injection experiments.

[0055] From the test results, the above three experiments all have the advantage of testing pore size and can accurately characterize the pore structure of different pore sizes. According to the analysis of the experimental test results, low-temperature nitrogen adsorption has a high test accuracy for micropores below 2nm, nuclear magnetic resonance can effectively characterize the pore size distribution of mesopores of 2-50nm, and high-pressure mercury injection can effectively test macropores larger than 50nm.

[0056] A cut-off pore size rd1 is preferably selected near the 2nm pore size, a curve with a pore size smaller than rd1 is retained on the pore size distribution diagram A corresponding to the pore volume measured by the low-temperature nitrogen adsorption experiment, and a curve with a pore size larger than rd1 is retained on the pore size distribution diagram B corresponding to the pore volume measured by the nuclear magnetic resonance experiment, so as to ensure that the difference between the pore volume a corresponding to the cut-off pore size rd1 in the pore size distribution diagram A and the pore volume b corresponding to the cut-off pore size rd1 in the pore size distribution diagram B is less than a first threshold value, and a cut-off pore size rd2 is preferably selected near the 50nm pore size, so as to ensure that the cut-off pore size in the pore size distribution diagram B is less than a first threshold value. The difference between the pore volume c corresponding to the cutoff pore diameter rd2 and the pore volume d corresponding to the cutoff pore diameter rd2 in the pore size distribution diagram D is less than a second threshold value, and the weighted average method is used to calculate the average of a and b and the average of c and d, and the average of a and b is used as the pore volume at the joint of the pore size distribution diagram A and the pore size distribution diagram B, and the average of c and d is used as the pore volume at the joint of the pore size distribution diagram B and the pore size distribution diagram D, and the pore size distribution diagram A and the pore size distribution diagram B are connected at the cutoff pore diameter rd1, and the pore size distribution diagram D and the pore size distribution diagram B are connected at the cutoff pore diameter rd2.

[0057] Figure 6The pore volume-pore size curve S is used to jointly characterize the effect of pore size on pore volume of shale samples based on the experimental data obtained after connection, which is based on the low-temperature nitrogen adsorption experiment, nuclear magnetic resonance experiment and high-pressure mercury injection correction. The experimental results show that the pore size distribution of shale samples in a certain work area has the characteristics of wide distribution range and large span. With the increase of pore size, the pore volume of micropores and mesopores shows a trend of increasing first and then decreasing, while the macropore volume increases with the increase of pore size. The pore size detected by these three types of experiments can better characterize the multi-scale pore structure characteristics of shale, which has important guiding significance for exploring the controlling factors of the microscopic pore structure characteristics of shale reservoirs in the study area and pore development.

[0058] The weighted average method is used to splice the pore size distribution maps corresponding to the pore volume of the shale, so that the final distribution map for jointly characterizing the influence of the pore size on the pore volume of the shale is more accurate.

[0059] Step 7: Establish a joint characterization of pore specific surface area based on the results of nuclear magnetic resonance experiments, low-temperature nitrogen adsorption experiments and high-pressure mercury injection experiments.

[0060] The pore size distribution diagram F corresponding to the pore specific surface area of ​​shale obtained by nuclear magnetic resonance experiment, the pore size distribution diagram E corresponding to the pore specific surface area of ​​shale obtained by nitrogen adsorption experiment, and the pore size distribution diagram G corresponding to the pore specific surface area of ​​shale obtained by high-pressure mercury injection experiment are spliced ​​to obtain the pore specific surface area-pore size curve diagram Q for jointly characterizing the effect of the pore size of the shale sample on the pore specific surface area. The splicing method is as follows:

[0061] The pore surface area distribution and pore volume of shale samples have similar characteristics. On the whole, they first increase and then decrease with the increase of pore diameter, and reach the maximum value before it is less than 2nm. As the pore diameter increases, the pore surface area gradually decreases, indicating that the pore surface area of ​​shale samples is mainly contributed by micropores. A cutoff pore size rd3 is selected near the 2nm pore size, and the difference between the pore specific surface area e corresponding to the cutoff pore size rd3 in the pore size distribution diagram E and the pore specific surface area f corresponding to the cutoff pore size rd3 in the pore size distribution diagram F is less than the third threshold value. A cutoff pore size rd4 is selected near the pore size of 50nm, and the difference between the pore specific surface area g corresponding to the cutoff pore size rd4 in the pore size distribution diagram G and the pore specific surface area h corresponding to the cutoff pore size rd4 in the pore size distribution diagram F is less than the third threshold value. The weighted average method is used to calculate the average of e and f and the average of g and h, and the average of e and f is used as the pore specific surface area at the joint of the pore size distribution diagram A and the pore size distribution diagram B, and the average of g and h is used as the pore specific surface area at the joint of the pore size distribution diagram B and the pore size distribution diagram D, so that the pore size distribution diagram E and the pore size distribution diagram F are connected at the cutoff pore size rd3, and the pore size distribution diagram G and the pore size distribution diagram F are connected at the cutoff pore size rd4. The pore specific surface area-pore diameter curve Q obtained after the connection is established is as follows Figure 7 shown.

[0062] The method of the present invention performs multi-scale joint characterization of the pore structure characteristics of the shale reservoir by splicing the pore size distribution map corresponding to the pore volume of the shale obtained by the low-temperature nitrogen adsorption experiment, the pore size distribution map corresponding to the pore volume of the shale obtained by the nuclear magnetic resonance experiment, and the pore size distribution map corresponding to the pore volume of the shale obtained by the high-pressure mercury injection experiment, so that the characterization results of the pore structure characteristics of the shale reservoir are more comprehensive; the pore size distribution map corresponding to the pore volume of the shale obtained by the high-pressure mercury injection experiment is corrected by the compression rate of the shale sample, so that the distribution map of the influence of the pore size on the pore volume obtained for the joint characterization of the shale is more accurate, thereby greatly improving the accuracy of the characterization of the microscopic pore structure characteristics of the shale reservoir. In addition, the method of the present invention can realize the multi-scale joint characterization of the microscopic pore structure characteristics of the shale reservoir in two dimensions of pore specific surface area and pore volume, so that the characterization results are more comprehensive, thereby improving the accuracy of the evaluation results of the influencing factors of the pore development of the shale reservoir and the gas content; it can realize the quantitative evaluation of the contribution of pores of different scales to the specific surface area and pore volume of the shale reservoir.

[0063] Finally, it should be noted that the pore volume and pore volume in this embodiment are the same concept and have the same meaning.

Claims

1. A method for jointly characterizing microscopic pore structure characteristics of shale reservoirs, characterized in that: The following steps are involved: Based on the results of low-temperature nitrogen adsorption experiments, nuclear magnetic resonance experiments, and high-pressure mercury injection experiments on shale samples in the study area, pore size distribution diagram A corresponding to the pore volume of shale, pore size distribution diagram B corresponding to the pore volume of shale, and pore size distribution diagram C corresponding to the pore volume of shale were obtained respectively; The compression rate of the sample is calculated based on the compression coefficient β of the shale sample; The pore volume and pore volume of the shale sample are corrected according to the compression rate, and a pore size distribution diagram D corresponding to the corrected pore volume of the shale is obtained according to the corrected pore volume and pore volume of the shale sample; According to the pore size range that can be tested by different testing methods, the pore size distribution diagram A, pore size distribution diagram B and pore size distribution diagram D corresponding to the pore volume of shale are spliced ​​and combined to obtain the pore volume-pore size curve diagram S, and then the microscopic pore structure characteristics of the shale reservoir are characterized based on the pore volume-pore size curve diagram S.

2. The method for jointly characterizing the microscopic pore structure characteristics of a shale reservoir according to claim 1, characterized in that: The method for splicing and combining pore size distribution diagram A, pore size distribution diagram B and pore size distribution diagram D is: select a cutoff pore size rd1 near the pore size of 2nm, the difference between the pore volume a corresponding to the cutoff pore size rd1 in the pore size distribution diagram A and the pore volume b corresponding to the cutoff pore size rd1 in the pore size distribution diagram B is less than a first threshold value, select a cutoff pore size rd2 near the pore size of 50nm, the difference between the pore volume c corresponding to the cutoff pore size rd2 in the pore size distribution diagram B and the pore volume d corresponding to the cutoff pore size rd2 in the pore size distribution diagram D is less than a second threshold value, connect the pore size distribution diagram A and the pore size distribution diagram B at the cutoff pore size rd1, and connect the pore size distribution diagram D and the pore size distribution diagram B at the cutoff pore size rd2.

3. The method for jointly characterizing the microscopic pore structure characteristics of a shale reservoir according to claim 2, characterized in that: The method of establishing a connection between pore size distribution diagram A and pore size distribution diagram B at cutoff pore size rd1, and establishing a connection between pore size distribution diagram D and pore size distribution diagram B at cutoff pore size rd2 is: using the weighted average method to calculate the mean of a and b and the mean of c and d, taking the mean of a and b as the pore volume at the joint of pore size distribution diagram A and pore size distribution diagram B, and taking the mean of c and d as the pore volume at the joint of pore size distribution diagram B and pore size distribution diagram D.

4. The method for jointly characterizing the microscopic pore structure characteristics of a shale reservoir according to claim 1, characterized in that: Also includes: Based on the results of low-temperature nitrogen adsorption experiments, nuclear magnetic resonance experiments, and high-pressure mercury injection experiments on shale samples in the study area, the pore size distribution diagram E corresponding to the pore specific surface area of ​​shale, the pore size distribution diagram F corresponding to the pore specific surface area of ​​shale, and the pore size distribution diagram G corresponding to the pore specific surface area of ​​shale were obtained respectively; According to the pore size range that can be tested by different testing methods, the pore size distribution diagram E, pore size distribution diagram F and pore size distribution diagram G are spliced ​​and combined to obtain the pore specific surface area-pore size curve diagram Q; and then the pore specific surface area-pore size curve diagram Q is used to characterize the microscopic pore structure characteristics of the shale reservoir.

5. The method for jointly characterizing the microscopic pore structure characteristics of a shale reservoir according to claim 4, characterized in that: The method for splicing and combining pore size distribution diagram E, pore size distribution diagram F and pore size distribution diagram G is: select a cutoff pore size rd3 near the pore size of 2nm, the difference between the pore specific surface area e corresponding to the cutoff pore size rd3 in the pore size distribution diagram E and the pore specific surface area f corresponding to the cutoff pore size rd3 in the pore size distribution diagram F is less than a third threshold value, select a cutoff pore size rd4 near the pore size of 50nm, the difference between the pore specific surface area g corresponding to the cutoff pore size rd4 in the pore size distribution diagram G and the pore specific surface area h corresponding to the cutoff pore size rd4 in the pore size distribution diagram F is less than a third threshold value, connect the pore size distribution diagram E and the pore size distribution diagram F at the cutoff pore size rd3, and connect the pore size distribution diagram G and the pore size distribution diagram F at the cutoff pore size rd4.

6. The method for jointly characterizing the microscopic pore structure characteristics of a shale reservoir according to claim 5, characterized in that: The method of connecting pore size distribution diagram E and pore size distribution diagram F at the cutoff pore size rd3, and connecting pore size distribution diagram G and pore size distribution diagram F at the cutoff pore size rd4 is: using the weighted average method to calculate the average of e and f and the average of g and h, and using the average of e and f as the pore specific surface area at the joint of pore size distribution diagram A and pore size distribution diagram B, and using the average of g and h as the pore specific surface area at the joint of pore size distribution diagram B and pore size distribution diagram D.

7. The method for jointly characterizing microscopic pore structure characteristics of shale reservoirs according to claim 1, characterized in that: The porosity of the shale sample is greater than 1% and the permeability is greater than 0.001×10-3μm 2 .

8. The method for jointly characterizing the microscopic pore structure characteristics of a shale reservoir according to claim 1, characterized in that: The shale samples are shale samples at at least two depths of the target layer in the study area.

9. The method for jointly characterizing the microscopic pore structure characteristics of a shale reservoir according to any one of claims 1 to 8, characterized in that: The adsorption medium used in the low-temperature nitrogen adsorption experiment is high-purity nitrogen with a purity greater than 99.98% and a critical temperature of -195.8°C.

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