A dynamic evaluation method for the opening and closing of lamellae

Abstract

The present invention provides a method for evaluating the opening and closing dynamics of lamellae fractures, which is applicable to the field of shale oil and gas geology. A plurality of test samples containing lamellae fractures are artificially prepared, and n test samples with the same opening and occurrence of the internal lamellae fractures are selected. Constant-rate mercury injection experiments and high-resolution field emission scanning electron microscopy are performed on the test samples respectively, so as to obtain the opening threshold A of the lamellae fracture opening in the tested area. c The true triaxial loading test samples were used and real-time CT scanning was performed. The control variable method was used to carry out cross physical simulation tests on the test samples. Based on the test result data volume analysis, the functional relationship between ground stress, pore pressure and lamellae fracture opening was established. The lamellae fracture opening under different ground stress and pore pressure conditions was analyzed. The lamellae fracture opening threshold A was used as the threshold value. c The method is simple in principle, highly operable and has high credibility.

Description

Technical Field

[0001] The invention relates to a lamella fracture opening and closing dynamics evaluation method, which is particularly applicable to the field of shale oil and gas geology. Background Art

[0002] With the deepening of oil and gas exploration and development, unconventional resources represented by shale oil and gas have become the main areas of exploration and development. my country is rich in shale oil and gas resources and has great potential for exploration and development. Usually, shale reservoirs develop natural fracture systems, including not only structural fractures formed under stress, but also a large number of lamellar fractures parallel to the bedding layers formed during the sedimentation and diagenesis process. They play an important role in the enrichment and accumulation of shale oil and gas, and affect the exploration and development effect.

[0003] The invention patent with application publication number CN113917554A proposes a method and electronic equipment for predicting the density of lamellae fractures in shale reservoirs, which obtains the density of lamellae fractures and the total organic carbon content of the coring section of the coring well, establishes a prediction relationship for the density of lamellae fractures based on the density of lamellae fractures and the total organic carbon content, and calculates the density of lamellae fractures in the uncored section of the horizontal well based on the quantitative prediction relationship of the density of lamellae fractures and the logging data of the horizontal well; the invention patent with authorization announcement number CN109870743B proposes a method and device for predicting the spatial distribution of lamellae fractures, which takes the longitudinal distribution of shale fracture phases in a single well as a constraint, establishes an equation with the shale fracture phase index as the objective function, and predicts the spatial distribution of lamellae fractures based on it; the invention patent with authorization announcement number CN110850502B provides a method, equipment and system for predicting the distribution law of lamellae fractures in shale oil and gas reservoirs, which obtains the development intensity of lamellae fractures in a single well, establishes its relationship with the main controlling factors of lamellae fractures, and predicts the distribution law of lamellae fractures in shale oil and gas reservoirs based on this relationship. The above methods all focus on the development degree and distribution pattern of lamellae fractures, but lack systematic research on key processes affecting shale oil and gas accumulation, such as the opening and closing of lamellae fractures. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the present invention provides a method for evaluating the opening and closing dynamics of lamellae fractures with simple steps and high reliability. The method is easy to use and can accurately obtain an evaluation by constructing a quantitative relationship between ground stress, pore pressure and lamellae fracture opening degree under the constraint of the lamellae fracture opening threshold.

[0005] In order to achieve the above objectives, the lamella crack opening and closing dynamics evaluation method of the present invention artificially prepares multiple test samples containing lamella cracks, selects n test samples with the same opening and occurrence of the internal lamella cracks, and performs constant-rate mercury injection experiment and high-resolution field emission scanning electron microscope on the n test samples, so as to obtain the opening threshold value A of the lamella crack opening of the test samples. cThe true triaxial loading test samples were used and real-time CT scanning was performed. The control variable method was used to carry out cross physical simulation tests on the test samples. Based on the test result data volume analysis, the functional relationship between ground stress, pore pressure and lamellae fracture opening was established. The lamellae fracture opening under different ground stress and pore pressure conditions was analyzed. The lamellae fracture opening threshold A was used as the threshold value. c To mark the page gap, find out whether it is open, so as to realize the evaluation of page gap opening and closing.

[0006] The specific steps are as follows:

[0007] Step 1: collect core samples with foliation fractures, perform argon ion polishing on the core samples, observe the polished core samples using a high-resolution field emission scanning electron microscope, and extract the foliation fracture aperture value in the core samples; perform a constant-rate mercury injection experiment on the core samples, and obtain the throat information of the core samples through the constant-rate mercury injection experiment, and then observe the minimum aperture value A of the core samples through a scanning electron microscope. 1 And the minimum throat value A obtained from the constant-rate mercury injection experiment 2 Calculate the arithmetic mean to obtain the threshold value A for the opening of the leaf gap c ,Right now:

[0008]

[0009] Step 2: Collect shale, grind it into powder, mix it with a binder and put it into a mold. Insert a temperature-sensitive material into the shale powder in the mold. Control the temperature to make the temperature-sensitive material generate lamellae in the cube. Prepare multiple test samples containing lamellae. Drill a hole vertically on any cube surface on each test sample. Select the lamellae with an opening less than the opening threshold A. c Carry out CT scanning on the test samples, and select n test samples with the same lamellae opening and occurrence from all the prepared test samples according to the CT scanning results;

[0010] Step 3, performing true triaxial loading and real-time CT scanning on the n test samples selected in step 2: applying two horizontal loads and one vertical load to the test sample with a cubic structure through true triaxial loading, wherein the horizontal load represents the maximum horizontal and minimum horizontal principal stresses applied to the test sample, and the vertical load represents gravity; injecting fluid into the test sample from the borehole, and performing CT scanning on the test sample with a cubic structure after the injection pressure of the fluid is equal to the preset pressure value, and observing the change in the opening degree of the lamellae in the cubic test sample in real time;

[0011] Step 4: the page seam opening threshold A determined in step 1 is cUnder the constraints, the control variable method is used to carry out cross physical simulation experiments. Multiple test samples with the same opening and occurrence are used to carry out different true triaxial loading and fluid injection tests. At the same time, the corresponding CT data are scanned and recorded in real time, and the different true triaxial loading data, injection pressure and CT scanning data are matched to generate multiple sample data bodies. The functional relationship between ground stress, pore pressure and lamellae fracture opening is established using multiple sample data bodies to realize the evaluation of lamellae fracture opening and closing.

[0012] The functional relationship between ground stress, pore pressure and lamellar fracture opening is:

[0013]

[0014] Where: A is the arithmetic mean of the openings of multiple lamellae obtained by CT scanning during any true triaxial and fluid injection pressure loading, S Hmax , S hmin , S v are the horizontal load 1, horizontal load 2 and vertical load in the true triaxial loading of the experimental data body, respectively, and P p is the injection pressure of the fluid, A c The opening threshold of the page gap.

[0015] Furthermore, in step 1, the sample size of the constant rate mercury injection experiment was 25 mm in diameter × 50 mm in height, the rate was set to 0.00005 mL / min, and the pressure dropped and rose periodically during the mercury injection process. The experiment ended when the pressure reached 900 psi.

[0016] Furthermore, in step 1, the constant rate mercury injection experiment is performed on at least 20 samples and the scanning electron microscope is performed at least 20 times.

[0017] Furthermore, the size of the cube experimental sample in step 2 is 50mm×50mm×50mm, the drilled hole diameter is 2mm, the number of cube experimental samples selected is at least 36, and the cross-physical simulation experiment carried out in step 4 must be carried out at least 36 times.

[0018] Furthermore, the horizontal load, vertical load and injection pressure of the true triaxial loading in step 3 are all preset in the range of 5 to 50 MPa, with a step length of 5 MPa; the lamella opening exceeds the threshold value A c The number of physical simulation experiments is at least 20.

[0019] Beneficial effects:

[0020] This method obtains the opening threshold value Ac of the opening of lamellae fractures through constant-rate mercury injection experiment and high-resolution field emission scanning electron microscope. On the basis of artificial sample preparation, experimental samples with consistent opening and occurrence are selected. With the help of true triaxial loading real-time CT scanning system, a cross physical simulation experiment is carried out by using the control variable method. Based on the analysis of the experimental result data body, the functional relationship between ground stress, pore pressure and lamellae fracture opening is established to realize the evaluation of lamellae fracture opening and closing in rock areas. The method has simple steps, accurate evaluation and wide practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic flow chart of the lamella crack opening and closing dynamics evaluation method of the present invention. DETAILED DESCRIPTION

[0022] The embodiments of the present invention are further described below in conjunction with the accompanying drawings:

[0023] like Figure 1 As shown, a method for evaluating the opening and closing dynamics of lamellae fractures of the present invention is characterized by: artificially preparing multiple test samples containing lamellae fractures, selecting n test samples with the same opening and occurrence of the inner lamellae fractures, and performing constant-speed mercury injection experiment and high-resolution field emission scanning electron microscope on the n test samples respectively, so as to obtain the opening threshold value A of the lamellae fracture opening of the test samples. c The true triaxial loading test samples were used and real-time CT scanning was performed. The control variable method was used to carry out cross physical simulation tests on the test samples. Based on the test result data volume analysis, the functional relationship between ground stress, pore pressure and lamellae fracture opening was established. The lamellae fracture opening under different ground stress and pore pressure conditions was analyzed. The lamellae fracture opening threshold A was used as the threshold value. c To mark the page gap, find out whether it is open, so as to realize the evaluation of page gap opening and closing.

[0024] 2. A method for evaluating the opening and closing dynamics of a sheet joint according to claim 1, characterized in that the specific steps are as follows:

[0025] Step 1: collect core samples with foliation fractures, perform argon ion polishing on the core samples, observe the polished core samples using a high-resolution field emission scanning electron microscope, and extract the foliation fracture aperture value in the core samples; perform a constant-rate mercury injection experiment on the core samples, and obtain the throat information of the core samples through the constant-rate mercury injection experiment, and then observe the minimum aperture value A of the core samples through a scanning electron microscope. 1 And the minimum throat value A obtained from the constant-rate mercury injection experiment 2 Calculate the arithmetic mean to obtain the threshold value A for the opening of the leaf gap c ,Right now:

[0026]

[0027] The sample size of the rapid mercury injection experiment is 25 mm in diameter × 50 mm in height, and the rate is set to 0.00005 mL / min. The pressure drops and rises periodically during the mercury injection process, and the experiment ends when the pressure reaches 900 psi. The constant-rate mercury injection experiment is performed on at least 20 samples and the scanning electron microscope is performed at least 20 times.

[0028] Step 2: Collect shale, grind it into powder, mix it with a binder and put it into a mold. Insert a temperature-sensitive material into the shale powder in the mold. Control the temperature to make the temperature-sensitive material generate lamellae in the cube. Prepare multiple test samples containing lamellae. Drill a hole vertically on any cube surface on each test sample. Select the lamellae with an opening less than the opening threshold A. c Carry out CT scanning on the test samples, and select n test samples with the same lamellae opening and occurrence from all the prepared test samples according to the CT scanning results; the size of the cube test sample is 50mm×50mm×50mm, the drilled hole diameter is 2mm, the number of cube test samples selected is at least 36, and the cross physical simulation experiment carried out in step 4 must be carried out at least 36 times;

[0029] Step 3, performing real-time CT scanning of the n test samples selected in step 2 by true triaxial loading: applying two horizontal loads and one vertical load to the test sample with a cubic structure by true triaxial loading, wherein the horizontal load represents the maximum horizontal and minimum horizontal principal stresses applied to the test sample, and the vertical load represents gravity; injecting fluid into the test sample from the borehole, and performing CT scanning on the test sample with the cubic structure after the injection pressure of the fluid is equal to the preset pressure value, and observing the change of the lamella opening in the cubic test sample in real time; the horizontal load, vertical load and injection pressure of the true triaxial loading are all preset in the range of 5 to 50 MPa, with a step length of 5 MPa; the lamella opening exceeds the threshold value A c The number of physical simulation experiments is at least 20.

[0030] Step 4: the page seam opening threshold A determined in step 1 is c Under the constraints, the control variable method is used to carry out cross physical simulation experiments. Multiple test samples with the same opening and occurrence are used to carry out different true triaxial loading and fluid injection tests. At the same time, the corresponding CT data are scanned and recorded in real time, and the different true triaxial loading data, injection pressure and CT scanning data are matched to generate multiple sample data bodies. The functional relationship between ground stress, pore pressure and lamellae fracture opening is established using multiple sample data bodies to realize the evaluation of lamellae fracture opening and closing.

[0031] The functional relationship between ground stress, pore pressure and lamellar fracture opening is:

[0032]

[0033] Where: A is the arithmetic mean of the openings of multiple lamellae obtained by CT scanning during any true triaxial and fluid injection pressure loading, S Hmax , S hmin , S v are the horizontal load 1, horizontal load 2 and vertical load in the true triaxial loading of the experimental data body, respectively, and P p is the injection pressure of the fluid, A c The opening threshold of the page gap.

Claims

1. A method for evaluating the dynamics of opening and closing of a sheet joint, characterized in that: Artificially prepare multiple test samples containing lamellae fractures, select n test samples with the same opening and occurrence of the internal lamellae fractures, conduct constant-rate mercury injection experiments and high-resolution field emission scanning electron microscopy on the n test samples, and obtain the opening threshold A of the lamellae fracture opening of the test samples. c The true triaxial loading test samples were used and real-time CT scanning was performed. The control variable method was used to carry out cross physical simulation tests on the test samples. Based on the test result data volume analysis, the functional relationship between ground stress, pore pressure and lamellae fracture opening was established. The lamellae fracture opening under different ground stress and pore pressure conditions was analyzed. The lamellae fracture opening threshold A was used as the threshold value. c To check whether the page seam is open, so as to evaluate the opening and closing of the page seam; The specific steps are as follows: Step 1: collect core samples with foliation fractures, perform argon ion polishing on the core samples, observe the polished core samples using a high-resolution field emission scanning electron microscope, and extract the foliation fracture opening value in the core samples; perform a constant-rate mercury injection experiment on the core samples, and obtain the throat information of the core samples through the constant-rate mercury injection experiment, and then calculate the arithmetic mean of the minimum opening value A1 of the core samples observed by the scanning electron microscope and the minimum throat value A2 obtained by the constant-rate mercury injection experiment, so as to obtain the opening threshold value A of the foliation fracture opening. c ,Right now: Step 2, collect shale, grind it into powder, mix it with a binder and put it into a mold, embed a temperature-sensitive material in the shale powder in the mold, control the temperature to make the temperature-sensitive material generate lamellae in the cube, prepare multiple test samples containing lamellae, and drill a hole vertically perpendicular to any surface of the cube on each test sample; Select the page whose seam opening is less than the opening threshold A c Carry out CT scanning on the test samples, and select n test samples with the same lamellae opening and occurrence from all the prepared test samples according to the CT scanning results; Step 3, performing true triaxial loading real-time CT scanning on the n test samples selected in step 2: applying two horizontal loads and one vertical load to the test samples of the cubic structure through true triaxial loading, wherein the horizontal load represents the maximum horizontal and minimum horizontal principal stresses applied to the test samples, and the vertical load represents gravity; Fluid is injected into the test sample from the drill hole. When the injection pressure of the fluid is equal to the preset pressure value, CT scanning is performed on the test sample with a cubic structure to observe the changes in the opening of the lamellae in the cubic test sample in real time. Step 4: the page seam opening threshold A determined in step 1 is c Under the constraints, the control variable method is used to carry out cross physical simulation experiments. Multiple test samples with the same opening and occurrence are used to carry out different true triaxial loading and fluid injection tests. At the same time, the corresponding CT data are scanned and recorded in real time, and the different true triaxial loading data, injection pressure and CT scanning data are matched to generate multiple sample data bodies. The functional relationship between ground stress, pore pressure and lamellae fracture opening is established using multiple sample data bodies to realize the evaluation of lamellae fracture opening and closing. The functional relationship between ground stress, pore pressure and lamellar fracture opening is: Where: A is the arithmetic mean of the openings of multiple lamellae obtained by CT scanning during any true triaxial and fluid injection pressure loading, S Hmax , S hmin , S v are the horizontal load 1, horizontal load 2 and vertical load in the true triaxial loading of the experimental data body, respectively, and P p is the injection pressure of the fluid, A c The opening threshold of the page gap.

2. A method for evaluating the dynamics of opening and closing of a sheet joint according to claim 1, characterized in that: In step 1, the sample size of the constant rate mercury injection experiment is 25 mm in diameter and 50 mm in height. The rate is set to 0.00005 mL / min. During the mercury injection process, the pressure drops and rises periodically. The experiment ends when the pressure reaches 900 psi.

3. A method for evaluating the dynamics of opening and closing of a sheet joint according to claim 1, characterized in that: In step 1, perform constant rate mercury injection experiments on at least 20 samples and scanning electron microscopy at least 20 times.

4. A method for evaluating the dynamics of opening and closing of a sheet joint according to claim 1, characterized in that: The size of the cube experimental sample in step 2 is 50mm×50mm×50mm, the drilled hole diameter is 2mm, the number of cube experimental samples selected is at least 36, and the cross-physical simulation experiment carried out in step 4 must be carried out at least 36 times.

5. A method for evaluating the opening and closing dynamics of a sheet joint according to claim 1, characterized in that: In step 3, the horizontal load, vertical load and injection pressure of the true triaxial loading are preset in the range of 5 to 50 MPa, with a step length of 5 MPa; the lamella opening exceeds the threshold value A c The number of physical simulation experiments is at least 20.

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