Comprehensive evaluation method for shale oil reservoir micro-pore flow capacity

Abstract

The invention relates to a comprehensive evaluation method for shale oil reservoir micro-pore flow capacity. The method comprises the following steps: taking a rock sample for a shale oil main development layer section in a to-be-researched area, and measuring the volume ratio of rock sample micro-cracks; calculating a macroscopic flow capacity index according to the physical property parameters of the rock sample and the viscosity of the crude oil, and evaluating the macroscopic flow capacity of the reservoir; calculating micro-crack dispersity and micro-crack connectivity by utilizing mineral components of the rock sample and rock mechanical parameters, and taking an arithmetic mean value as a micro-flow capacity index; and respectively constructing a macroscopic flow capacity index correlation chart, a microscopic flow capacity index correlation chart and a micro-crack volume ratio correlation chart, and defining a comprehensive flow capacity index which is positively correlated with the micro-pore flow capacity so as to evaluate the micro-pore flow capacity. According to the method, the evaluation accuracy and the practicability are qualitatively improved. The calculation method is simple and feasible, can be also suitable for the flowing capacity of the micro-pores of similar shale oil reservoirs, and has a good application prospect.

Description

Technical Field

[0001] The present invention relates to the field of oil and gas engineering, and in particular to a comprehensive evaluation method for the microscopic pore flow capacity of shale oil reservoirs during the exploration and development of shale oil and gas reservoirs. Background Art

[0002] Continental shale oil reservoirs in China usually develop multi-scale microscopic pores, and their flow capacity is the key to resource potential evaluation, the effectiveness of reservoir stimulation fracture network communication, and whether high production can be achieved. At the same time, it plays a core role in formulating shale oil development technical policies. China's shale oil and gas resources are extremely rich and have great development potential, becoming the most strategic oil replacement resources and the main force for crude oil reserve growth and production increase in the shale oil revolution of each oilfield. However, through core sampling, well logging fine description, 3D seismic, and high-precision nuclear magnetic resonance, CT and other means to finely describe the characteristics of continental shale oil reservoirs in China, each oilfield has confirmed that shale oil reservoirs have strong heterogeneity in the plane, longitudinal, and three-dimensional spaces, discontinuous reservoir sand bodies, multi-thin layer stacking development, large differences in physical property parameters in the same development area and development horizon, development of multi-scale micro-nano pores, complex development of microscopic fractures, and obvious changes in fracture development, resulting in extremely difficult evaluation of the fluidity of microscopic pores in shale oil reservoirs, and bringing huge challenges to aspects such as the deployment of shale reservoir development well patterns and the optimization of reservoir stimulation parameters. Since the pore flow capacity of microscopic pores in shale reservoirs is comprehensively affected by reservoir physical properties, rock mechanics, micro-fracture development and effectiveness, etc., there are many different factors and the relationships are complex. There is an urgent need for a quantitative evaluation of the microscopic pore flow capacity suitable for the characteristics of continental shale oil reservoirs to provide strong support for accelerating the efficient development of shale oil.

[0003] Through research and patent benchmarking, the current evaluation methods for rock pore flow capacity are mainly experimental and numerical simulation methods. Among them, Xu Yaodong et al. proposed a method for characterizing the nonlinear flow characteristics of shale oil microscale pores, patent number: CN202110688871.7. This method first measures the microscopic pore structure distribution of the mud shale core and its adsorption capacity for shale oil fluid. On this basis, the micro-tube flow model considering Darcy flow + non-Darcy flow + boundary layer thickness is used to calculate the flow value of shale oil in mud shale pores of different sizes as the driving pressure difference changes, and the calculation results are used to draw the nonlinear relationship curve between the displacement pressure gradient and the flow rate; thereby realizing the flow capacity. In addition, Song Wenhui et al. proposed a method for characterizing the oil and gas phase equilibrium and flow capacity of rock porous media, patent number: CN202111573757.6. The method obtains the relationship curve between oil and gas capillary force and gas saturation in rock through rock fractal dimension and pore size; establishes an oil-gas phase equilibrium model based on the relationship curve between gas saturation and oil and gas capillary force, and obtains gas saturation at a given temperature and pressure; inversely calculates capillary force based on gas saturation at a given temperature and pressure, and the curve between gas saturation and oil and gas capillary force, and obtains the distribution of oil and gas in pores of different sizes; establishes oil phase and gas phase flow models respectively through fractal dimension and pore size, and calculates oil phase and gas phase permeabilities according to the distribution of oil and gas in pores of different sizes, thereby achieving the purpose of evaluating pore flow capacity.

[0004] The above methods mainly characterize flow capacity through experimental testing and model building. The numerical model assumes many conditions and it is difficult to prepare and characterize the strong heterogeneous reservoir of shale oil to establish an ideal model. The evaluation results need to be further demonstrated. None of them has the core solution to the vertical heterogeneity characteristics of the reservoir, that is, the comprehensive evaluation of the key influence of its own storage capacity, micro-fracture development, effectiveness, etc. on the microscopic pore capacity of the rock. Therefore, it is urgent to establish a rock microscopic pore flow capacity evaluation method that conforms to the actual shale oil reservoir to provide a basis for evaluating the characteristics of shale oil reservoirs. Summary of the invention

[0005] The present invention aims to solve the above problems and propose a comprehensive evaluation method for the microscopic pore flow capacity of shale oil reservoirs.

[0006] The technical solution of the present invention is.

[0007] A comprehensive evaluation method for microscopic pore flow capacity of shale oil reservoirs is as follows: Take rock samples from the main shale oil development layers in the area to be studied to determine the volume ratio of micro-fractures in the rock samples; The macroscopic flowability index is calculated based on the physical properties of the rock sample and the viscosity of the crude oil to evaluate the macroscopic flowability of the reservoir; the microfracture dispersion and microfracture connectivity are calculated using the mineral composition and rock mechanics parameters of the rock sample, and their arithmetic mean is used as the microscopic flowability index; The correlation diagrams of macro flow capacity index, micro flow capacity index and microcrack volume ratio were constructed respectively, and a comprehensive flow capacity index positively correlated with the micro pore flow capacity was defined to evaluate the micro pore flow capacity.

[0008] Specifically, the specific calculation process of the macro flowability index is: Dimensionless conversion of rock sample physical parameters and crude oil viscosity; The macroscopic flowability index was calculated by the following formula (2): Where: RI is the macro flowability index, dimensionless; is the dimensionless value of the permeability of the i-th rock sample; is the dimensionless value of the porosity of the i-th rock sample; is the dimensionless value of the fluid viscosity of the i-th rock sample.

[0009] The specific process of dimensionless transformation is as follows: Where: is the dimensionless value of parameter j of the i-th rock sample; R i (j) is the dimensionless value of parameter j of the i-th rock sample; (R i (j)) max is the maximum value of the dimensionless value of the j parameter of the i-th rock sample; Among them, j is specifically porosity, permeability and fluid viscosity.

[0010] Specifically, the specific calculation process of the micro-flowability index is: DI=0.5(FD+FE) (6) Where: DI is the microscopic flowability index, dimensionless; FD is the dispersion of microcracks and is dimensionless; FE is the connectivity of microcracks and is dimensionless.

[0011] The specific calculation process of the microcrack dispersion is as follows: Where: m h is the percentage of mineral content, %; M is the average percentage of mineral content, %; h is the type of mineral component, with a value of 1-1.

[0012] The specific calculation process of the microcrack connectivity is as follows: in, Where: V h is the weight coefficient of Poisson's ratio difference of different minerals, dimensionless; v h It is the Poisson's ratio corresponding to different minerals and is dimensionless.

[0013] Specifically, the specific calculation process of the comprehensive flow capacity index is: CI=α·RI+β·DI (7) Where: CI is the comprehensive flow capacity index, dimensionless; α is the weight factor of the macroscopic flowability index and the overall flowability of the rock sample, which is dimensionless; β is the weight factor of the microscopic flowability index and the overall flowability of the rock sample, which is dimensionless.

[0014] Specifically, the specific process of obtaining the volume ratio of microcracks in the rock sample is as follows: (1) Coring the reservoir section to be evaluated: Coring is performed in each sub-layer of the main shale oil development section in the study area and standard rock samples are prepared. The samples are placed in an oven and dried to constant weight; (2) Physical property parameter testing: The porosity and permeability of the dried standard rock samples were tested using a helium porosity automatic tester and an ultra-low permeability tester; (3) Mineral composition test: Use X-ray diffractometer to test the mineral composition of standard rock samples and the percentage of each mineral component; (4) Obtaining rock mechanical parameters: obtaining the Poisson's ratio of each mineral component; (5) Crude oil viscosity test of the reservoir section to be evaluated: Take a crude oil sample from the reservoir section to be evaluated and test its crude oil viscosity under reservoir temperature conditions; (6) Microcrack pore volume test: The volume ratio of microcracks in the standard rock sample after testing is determined.

[0015] The technical effects of the present invention are: (1) The present invention realizes the quantitative evaluation of the macroscopic and microscopic flow capacity of shale oil reservoir pores by defining a comprehensive flow capacity index. The macroscopic flow capacity quantitative evaluation is realized by dimensionless transformation of porosity, permeability and fluid viscosity; (2) The present invention considers for the first time the influence of rock microcrack density and effectiveness on rock flow capacity by taking into account the differences in mineral composition and rock mechanical parameters; (3) Compared with the previous evaluation of flow capacity by testing permeability and establishing models, the present invention has a qualitative improvement in evaluation accuracy and practicality. The calculation method is simple and feasible, and can be applied to the microscopic pore flow capacity of similar shale oil reservoirs, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a macroscopic flowability index diagram of a specific experimental example of the present invention.

[0017] Figure 2 This is a microcrack dispersion diagram of a specific experimental example of the present invention.

[0018] Figure 3 This is a microcrack connectivity diagram of a specific experimental example of the present invention.

[0019] Figure 4 This is a microscopic flow capacity index diagram of a specific experimental example of the present invention.

[0020] Figure 5 This is a graph showing the correlation between the macroscopic flow capacity index and the volume percentage of microcracks in a specific experimental example of the present invention.

[0021] Figure 6 This is a correlation chart between the microscopic flow capacity index and the volume proportion of microcracks in a specific experimental example of the present invention. DETAILED DESCRIPTION

[0022] A comprehensive evaluation method for microscopic pore flow capacity of shale oil reservoirs is as follows: Step 1: Take rock samples from the main shale oil development layer in the area to be studied and determine the volume proportion of micro-fractures in the rock samples; the specific process is: (1) Coring of the reservoir section to be evaluated: Coring of each sublayer of the main shale oil development layer in the study area is carried out downhole to prepare standard rock samples, which are then placed in a 100°C oven and dried to constant weight; (2) Physical property parameter testing: The porosity and permeability of the dried standard rock samples were tested using a helium porosity automatic tester and an ultra-low permeability tester; (3) Mineral composition test: Use X-ray diffractometer to test the mineral composition of standard rock samples and the percentage of each mineral component; (4) Obtaining rock mechanical parameters: obtaining the Poisson's ratio of each mineral component; (5) Crude oil viscosity test of the reservoir section to be evaluated: Take a crude oil sample from the reservoir section to be evaluated and test its crude oil viscosity under reservoir temperature conditions; (6) Microcrack pore volume test: The volume ratio of microcracks in the standard rock sample after testing is determined.

[0023] Step 2: Calculate the macro flowability index based on the physical parameters of the rock sample and the viscosity of the crude oil to evaluate the macro flowability of the reservoir. The specific process is as follows: adopt the maximum value method to make the porosity, permeability and crude oil viscosity of the rock sample dimensionless through formula (1); then calculate the macro flowability index through formula (2) to evaluate the macro flowability of the reservoir.

[0024] Step 3: Calculate the microcrack dispersion and microcrack connectivity using the mineral composition and rock mechanical parameters of the rock sample, and use their arithmetic mean as the micro-flow capacity index; the specific process is: calculate the microcrack dispersion using formula (3), the larger the value, the greater the microcrack density; calculate the microcrack connectivity using formula (4) and formula (5) to evaluate the effectiveness of microcrack flow; take the arithmetic mean of the microcrack dispersion and microcrack connectivity as the micro-flow capacity index.

[0025] Step 4: Construct the correlation charts of the macro flow capacity index, micro flow capacity index and microcrack volume ratio respectively, and define a comprehensive flow capacity index that is positively correlated with the micro pore flow capacity, specifically as formula (7). The larger the comprehensive flow capacity index, the stronger the micro pore flow capacity.

[0026] Specific experimental examples The main shale oil development layer in the case study area is divided into four small layers vertically, numbered Y1~Y4; the early downhole coring, logging interpretation, reservoir transformation, etc. show that the reservoir characteristics of each small layer are obviously different, with strong heterogeneity. After the reservoir transformation, the production of the corresponding horizontal wells of each small layer is very different. It is urgent to evaluate the flow capacity of the reservoir itself to provide a basis for the optimization of reservoir characteristics and volume fracturing schemes.

[0027] A comprehensive evaluation method for microscopic pore flow capacity of shale oil reservoirs is as follows.

[0028] Step 1: Take rock samples from the main shale oil development layer section in the area to be studied to determine the volume ratio of micro-fractures in the rock samples; the specific process is: carry out downhole coring of 4 small layers in the main shale oil development layer section in the area to be studied, test the physical parameters, rock mechanical parameters and mineral composition of the corresponding rock samples and the viscosity of the crude oil fluid produced in each small layer, and use CT to test the volume ratio of micro-fracture pores in the rock samples: (1) Coring of the reservoir section to be evaluated: Coring of each sublayer Y1 to Y4 in the main shale oil development section of the study area is carried out to prepare standard rock samples, numbered Y1-1 to Y4-1, and the standard rock samples are placed in a 100°C oven to dry to constant weight; (2) Physical property parameter testing: The porosity and permeability of the dried standard rock samples were tested using a helium porosity automatic tester and an ultra-low permeability tester, respectively; the results are shown in Table 1; Table 1 Rock sample basic parameters

[0029] (3) Mineral composition test: X-ray diffractometer is used to test the mineral composition of the dried standard rock sample and the percentage of each mineral component; Table 2 Mineral composition test table Standard rock sample after drying quartz(%) Feldspar(%) Calcite(%) dolomite(%) Clay minerals (%) Y1-1 51.4 12.7 9.5 12.6 13.8 Y2-1 59.5 11.6 13.1 6.2 9.6 Y3-1 29.5 29.6 8.5 8.7 23.7 Y4-1 33.0 36.2 9.7 8.5 12.6

[0030] (4) Obtaining rock mechanical parameters: Based on the mineral composition and the percentage of each mineral component, obtain the Poisson's ratio and Poisson's ratio difference weight coefficient of each mineral component; Table 3 Rock mechanical parameters of different minerals in rock samples Mineral composition Poisson's ratio (dimensionless) Poisson's ratio difference weight coefficient (dimensionless) quartz 0.07 0.521 Feldspar 0.32 0.114 Calcite 0.31 0.118 dolomite 0.26 0.140 Clay Minerals 0.34 0.107

[0031] (5) Crude oil viscosity test of the reservoir section to be evaluated: Take a crude oil sample from the reservoir section to be evaluated and test its crude oil viscosity under reservoir temperature conditions, see Table 1; (6) Microcrack pore volume test: The microcrack volume ratio of the standard rock sample after drying was tested by CT, see Table 1.

[0032] Step 2: Calculate the macro flowability index based on the physical parameters of the rock sample and the viscosity of the crude oil to evaluate the macro flowability of the reservoir. The specific process is: use the maximum value method to make the porosity, permeability and crude oil viscosity dimensionless through formula (1); then calculate the macro flowability index through formula (2). The calculation results are shown in Figure 1 , which is used to evaluate the macroscopic flow capacity of the reservoir.

[0033] Step 3: Calculate the microcrack dispersion and microcrack connectivity using the mineral composition and rock mechanical parameters of the rock sample, and use their arithmetic mean as the microscopic flow capacity index; the specific process is: calculate the microcrack dispersion using formula (3), and the calculation results are shown in Figure 2 ; The larger its value, the greater the density of microcracks; According to the mineral composition and the Poisson's ratio of the corresponding mineral composition, the weight coefficient of the Poisson's ratio difference of different minerals is calculated by formula (4), and the calculation results are shown in Table 3; Based on the weight coefficient of the Poisson's ratio difference of different minerals and the percentage of each mineral component, the microcrack connectivity is calculated by formula (5), and the calculation results are shown in Figure 3 , used to evaluate the effectiveness of microcrack flow; the arithmetic mean of microcrack dispersion and microcrack connectivity is taken as the microscopic flow capacity index. The calculation results are shown in Figure 4 .

[0034] Step 4: Construct a correlation chart between the macroscopic flow capacity index and the volume proportion of microcracks, see Figure 5 ; Construct a correlation chart between the microscopic flow capacity index and the volume proportion of microcracks, see Figure 6; The macroscopic flowability index and the weight factor α of the overall flowability of the rock sample are 0.6840, and the microscopic flowability index and the weight factor β of the overall flowability of the rock sample are 0.3865; the comprehensive flowability indexes of rock samples Y1-1, Y2-1, Y3-1, and Y4-1 are calculated using formula (7) to be 0.74, 0.75, 0.81, and 0.64, respectively. The microscopic pore flow capacity of each small layer in the main shale oil development layer section of the study area is ranked as Y3>Y2>Y1>Y4.

[0035] The present invention is specifically described through examples. It is necessary to point out that the examples are only preferred examples of the present invention and do not limit the present invention in any way, nor are they limited to the forms disclosed herein, and should not be regarded as excluding other examples. Modifications and simple changes made by those skilled in the art that do not depart from the technical concept and scope of the present invention all fall within the protection scope of the technical solution of the present invention.

Claims

1. A comprehensive evaluation method for microscopic pore flow capacity of shale oil reservoirs, characterized in that: Here’s how: Take rock samples from the main shale oil development layers in the area to be studied to determine the volume ratio of micro-fractures in the rock samples; The macroscopic flowability index is calculated based on the physical properties of the rock sample and the viscosity of the crude oil to evaluate the macroscopic flowability of the reservoir; the microfracture dispersion and microfracture connectivity are calculated using the mineral composition and rock mechanics parameters of the rock sample, and their arithmetic mean is used as the microscopic flowability index; The correlation diagrams of macro flow capacity index, micro flow capacity index and microcrack volume ratio were constructed respectively, and a comprehensive flow capacity index positively correlated with the micro pore flow capacity was defined to evaluate the micro pore flow capacity.

2. The comprehensive evaluation method for microscopic pore flow capacity of shale oil reservoir according to claim 1 is characterized in that: The specific calculation process of the macro flowability index is: Dimensionless conversion of rock sample physical parameters and crude oil viscosity; The macroscopic flowability index was calculated by the following formula (2): Where: RI is the macro flowability index, dimensionless; is the dimensionless value of the permeability of the i-th rock sample; is the dimensionless value of the porosity of the i-th rock sample; is the dimensionless value of the fluid viscosity of the i-th rock sample.

3. The comprehensive evaluation method for microscopic pore flow capacity of shale oil reservoir according to claim 2 is characterized in that: The specific process of dimensionless transformation is as follows: Where: is the dimensionless value of parameter j of the i-th rock sample; R i (j) is the dimensionless value of parameter j of the i-th rock sample; (R i (j)) max is the maximum value of the dimensionless value of the j parameter of the i-th rock sample; Among them, j is specifically porosity, permeability and fluid viscosity.

4. The comprehensive evaluation method for microscopic pore flow capacity of shale oil reservoir according to claim 3 is characterized in that: The specific calculation process of the micro-flowability index is: DI=0.5(FD+FE) (6) Where: DI is the microscopic flowability index, dimensionless; FD is the dispersion of microcracks and is dimensionless; FE is the connectivity of microcracks and is dimensionless.

5. The comprehensive evaluation method for microscopic pore flow capacity of shale oil reservoir according to claim 4 is characterized in that: The specific calculation process of the microcrack dispersion is: Where: m h is the percentage of mineral content, %; M is the average percentage of mineral content, %; h is the type of mineral component, with a value of 1-1.

6. The comprehensive evaluation method for microscopic pore flow capacity of shale oil reservoir according to claim 5 is characterized in that: The specific calculation process of the microcrack connectivity is as follows: in, Where: V h is the weight coefficient of the Poisson's ratio difference of different minerals, dimensionless; ν h It is the Poisson's ratio corresponding to different minerals and is dimensionless.

7. The comprehensive evaluation method for microscopic pore flow capacity of shale oil reservoirs according to claim 6 is characterized in that: The specific calculation process of the comprehensive flow capacity index is: CI=α·RI+β·DI (7) Where: CI is the comprehensive flow capacity index, dimensionless; α is the weight factor of the macroscopic flowability index and the overall flowability of the rock sample, which is dimensionless; β is the weight factor of the microscopic flowability index and the overall flowability of the rock sample, which is dimensionless.

8. The comprehensive evaluation method for microscopic pore flow capacity of shale oil reservoir according to claim 1, characterized in that: The specific process of obtaining the volume proportion of microcracks in the rock sample is as follows: (1) Coring the reservoir section to be evaluated: Coring each sublayer of the main shale oil development section in the study area is carried out downhole to prepare standard rock samples, which are then dried to constant weight; (2) Physical property parameter testing: The porosity and permeability of the dried standard rock samples were tested using a helium porosity automatic tester and an ultra-low permeability tester; (3) Mineral composition test: Use X-ray diffractometer to test the mineral composition of standard rock samples and the percentage of each mineral component; (4) Obtaining rock mechanical parameters: obtaining the Poisson's ratio of each mineral component; (5) Crude oil viscosity test of the reservoir section to be evaluated: Take a crude oil sample from the reservoir section to be evaluated and test its crude oil viscosity under reservoir temperature conditions; (6) Microcrack pore volume test: The volume ratio of microcracks in the standard rock sample after testing is determined.

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