A comprehensive evaluation method for the geological engineering compressibility of shale oil reservoirs

Abstract

The present invention relates to the field of petroleum engineering, and particularly relates to a comprehensive evaluation method for the geomechanical compressibility of shale oil reservoirs. The method is characterized by comprising the following steps: Step 1) establishing a fine geological model for the shale oil reservoir in the target block and determining the evaluation section, and obtaining the oil-bearing index per unit volume of the evaluation section; Step 2) obtaining downhole cores of the evaluation section, testing the mineral composition and rock mechanical parameters of the cores, and obtaining the mineral dispersion degree index and the fracture development degree index; Step 3) obtaining the engineering brittleness index according to the different mineral dispersion degree indexes and fracture development degree indexes of the cores; Step 4) performing weighted processing on the oil-bearing index per unit volume and the engineering brittleness index to obtain the compressibility factor, and conducting a comprehensive evaluation of the compressibility of the evaluation section. The present invention comprehensively considers the rock compressibility from a comprehensive perspective of geological engineering and proposes a new compressibility evaluation method.

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 geological engineering compressibility of a shale oil reservoir during the exploration and development of shale oil and gas reservoirs. Background Art

[0002] The compressibility of rock is a core factor affecting the volume fracturing effect of unconventional shale oil, and directly determines whether a large-scale volume fracturing can form a complex fracture network and the maximum fracture-controlled reserves. Scholars at home and abroad have conducted a large number of studies on the compressibility of conventional rocks, mainly using experimental methods, and establishing corresponding compressibility models relying on the mineral composition of rock samples or rock mechanical parameters. Representative methods in the prior art are as follows: (1) Patent CN202010189682.0 discloses a prediction method for the complexity of the fracture network formed by shale fracturing. This method measures the types and contents of mineral components of shale samples through indoor experiments, calculates the difference between different minerals and evaluates the differences between minerals, and establishes a shale brittleness evaluation model based on the heterogeneity of mineral composition, and then evaluates the shale compressibility potential. (2) Patent CN201911044838.X discloses a method for determining the compressibility of rocks in different well sections of a horizontal well in a reservoir with natural fractures. During the drilling process of the horizontal well, cuttings samples at different well sections are collected; the cuttings samples are observed by an electron scanning microscope to obtain the development of natural fractures, rock brittleness and the development of rock pores in the corresponding well sections, and the compressibility index of the rocks in the corresponding well sections is calculated by a weighted scoring method, so as to evaluate the compressibility of the rocks. (3) In the literature (Zhou Lihong, et al. Evaluation and Application of Influencing Factors of Rock Fracturability in Continental Shale Oil - Taking the Second Member of Kongdian Formation in Cangdong Sag as an Example [J]. Petroleum Exploration in China, 2019, 24(5): 670 - 678), by comprehensively considering three factors of rock brittleness, natural fractures and in-situ stress, a fracture network index model is established to qualitatively analyze and quantitatively characterize the compressibility of typical continental shale oil rocks developed in the second member of Kongdian Formation in Cangdong Sag of Dagang exploration area, and further optimize the perforation parameters and fracturing construction parameters of horizontal wells.

[0003] Through research, it can be known that most of the evaluation methods in the current prior art rely on rock mineral composition or rock mechanical parameters for quantitative evaluation. However, compared with North America, the continental shale oil reservoirs in China have strong heterogeneity. Through large-scale field tests, it is confirmed that the sand bodies in the continental shale oil reservoirs in China change rapidly, natural fractures and bedding are developed, and the compressibility evaluation is more important for the optimization design of reservoir stimulation, and for unconventional resources, whether a complex fracture network can be formed and high production can be obtained after volume fracturing is concerned.

[0004] Therefore, for the shale oil reservoirs in China, it is necessary to comprehensively consider the rock compressibility from the perspective of geology and engineering. On the one hand, it is the material basis for high production of rocks, that is, geological compressibility. On the other hand, it is whether the rocks can form complex fracture networks, that is, engineering compressibility. Summary of the Invention

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A comprehensive evaluation method for the geological and engineering compressibility of shale oil reservoirs, characterized by comprising the following steps:

[0007] Step 1) Establish a fine geological model for the shale oil reservoir in the target block, determine the evaluation section in the fine geological model, and obtain the oil-bearing index per unit volume of the evaluation section;

[0008] Step 2) Obtain the downhole core of the evaluation section, test the mineral composition and rock mechanical parameters of the core, and obtain the mineral dispersion degree index and the fracture development degree index;

[0009] Step 3) Obtain the engineering brittleness index according to the different mineral dispersion degree indexes and fracture development degree indexes of the core;

[0010] Step 4) Perform weighted processing on the oil-bearing index per unit volume and the engineering brittleness index to obtain the compressibility factor, and conduct a comprehensive evaluation of the compressibility of the evaluation section.

[0011] Further, in step 1), when determining the evaluation section in the fine geological model, it further includes:

[0012] According to the horizontal section length of the horizontal well, it is equally divided into n equal parts at equal distances, and each equal part is the evaluation section. According to the fine geological model, the three-dimensional space average porosity, oil saturation, reservoir thickness, and oil layer thickness of each equal part are obtained.

[0013] Further, the method for the oil-bearing index per unit volume is as follows:

[0014]

[0015] In the formula: RI is the oil-bearing index per unit volume of the evaluation section, dimensionless; h is the three-dimensional space average oil layer thickness of the evaluation section, m; H is the three-dimensional space average reservoir thickness of the evaluation section, m; is the three-dimensional space average porosity of the evaluation section, %; is the three-dimensional space average oil saturation of the evaluation section, dimensionless.

[0016] Further, in step 2), the mineral composition and the percentage content of different minerals of the core are tested by an X-ray diffractometer.

[0017] Further, in step 2), the Young's modulus of the core is tested by a triaxial mechanical testing system.

[0018] Further, obtaining the mineral dispersion degree in step 2) also includes:

[0019] Calculating the overall dispersion coefficient of different minerals in the rock sample and the mineral dispersion degree index.

[0020] Further, the calculation method of the overall dispersion coefficient of different minerals is as follows:

[0021]

[0022] In the formula: U is the overall dispersion coefficient of different minerals, dimensionless; n is the type of minerals, species; i is the mineral type number; m i is the percentage content of the i-th type of different minerals, %; M is the average value of the mineral percentage content, %.

[0023] Further, the calculation method of the mineral dispersion degree index is as follows:

[0024]

[0025] In the formula: E is the mineral dispersion degree index of different minerals in the rock sample, dimensionless.

[0026] Further, step 2) also includes: calculating the non-uniformity index of rock mechanical parameters according to the types of minerals measured in the core and the Young's modulus of the core.

[0027] Further, the calculation method of the non-uniformity index of rock mechanical parameters is as follows:

[0028]

[0029] In the formula: G i is the non-uniformity index of the rock mechanical parameters of the i-th type of mineral in the core, dimensionless; E i is the Young's modulus of the i-th type of mineral, MPa; E r is the Young's modulus measured for the core, MPa.

[0030] Further, based on the non-uniformity index of rock mechanical parameters and the types of minerals, determine the fracture development degree index.

[0031] Further, the calculation method of the fracture development degree index is as follows:

[0032]

[0033] Further, the calculation method of the engineering brittleness index in step 3) is as follows:

[0034] BI = E·F (6)

[0035] In the formula: BI is the rock engineering brittleness index, dimensionless.

[0036] On the other hand, the present invention provides a comprehensive evaluation device for the compressibility of a shale oil reservoir in geological engineering, which is characterized by comprising at least one processor and a memory communicatively connected to the processor; the memory stores instructions executable by the processor, and the instructions are executed by at least one processor so that at least one processor can execute the calculation method described in any one of the above.

[0037] On the other hand, the present invention provides a computer-readable storage medium, on which a computer program is stored, and is characterized in that when the computer program is executed by a processor, the steps of the comprehensive evaluation method described in any one of the above are realized.

[0038] In summary, the present invention proposes a comprehensive evaluation method for the compressibility of a shale oil reservoir in geological engineering. On the one hand, by calculating the three-dimensional oil content index per unit volume, the material basis of the reservoir and the geological compressibility are evaluated. On the other hand, through the mineral composition and rock mechanics parameters of the core, the mineral dispersion degree index and the fracture development degree index are calculated respectively, and based on this, the rock engineering brittleness index is calculated to evaluate the engineering compressibility. Thus, the comprehensive evaluation of the compressibility of the shale oil reservoir is realized based on both geological compressibility and engineering compressibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a three-dimensional geological model diagram in an embodiment of the present invention;

[0040] Figure 2 It is the calculation result of the oil content index per unit volume of the evaluation reservoir section in an embodiment of the present invention;

[0041] Figure 3 It is the calculation result of the Young's modulus of different minerals of the reservoir section rock sample in an embodiment of the present invention;

[0042] Figure 4 It is the calculation result of the mineral dispersion degree index of different minerals of the reservoir section rock sample in an embodiment of the present invention;

[0043] Figure 5 It is the calculation result of the fracture development degree index of the reservoir section rock sample in an embodiment of the present invention;

[0044] Figure 6 It is the calculation result of the rock engineering brittleness index of the reservoir section rock sample in an embodiment of the present invention;

[0045] Figure 7 It is the compressibility comparison diagram of the reservoir section rock sample in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0046] The present invention will be described in detail below with reference to the accompanying drawings.

[0047] A comprehensive evaluation method for the geological engineering compressibility of shale oil reservoirs, which successively includes the following steps:

[0048] In step 1), a fine geological model is established using the geological data of the shale oil reservoir and the basic data of horizontal wells to obtain the physical property distribution in the three-dimensional space of the evaluation section, calculate the oil-bearing index per unit volume of the evaluation section, and evaluate the geological compressibility. The specific content is as follows:

[0049] (1) Based on the basic geological data such as the structural interpretation results and well logging interpretation data of the shale oil reservoir where the evaluation section is located, a three-dimensional geological model of a typical well group in the shale oil reservoir is established. On this basis, according to the length of the horizontal section of the horizontal well, it is equally divided into n equal parts, and each equal part is the evaluation section. The three-dimensional space average porosity, oil saturation, reservoir thickness, and oil layer thickness of each equal part are obtained using the three-dimensional geological model.

[0050] (2) Using the three-dimensional geological model to obtain the three-dimensional space average porosity, oil saturation, reservoir thickness, and oil layer thickness of the evaluation section, and calculate the oil-bearing index per unit volume. The calculation formula is as follows:

[0051]

[0052] In the formula: RI is the oil-bearing index per unit volume of the evaluation section, dimensionless; h is the three-dimensional space average oil layer thickness of the evaluation section, m; H is the three-dimensional space average reservoir thickness of the evaluation section, m; is the three-dimensional space average porosity of the evaluation section, %; is the three-dimensional space average oil saturation of the evaluation section, dimensionless.

[0053] In step 2), downhole cores of the evaluation section are obtained, and the mineral composition and rock mechanical parameters of the cores are tested. On this basis, the degree of mineral dispersion and the degree of fracture development are calculated respectively, and the rock engineering brittleness index is calculated to evaluate the engineering compressibility. The specific content is as follows:

[0054] (1) Core samples are taken from the evaluation section divided by the length of the horizontal section of the horizontal well in step 1), and the core samples are processed into standard rock samples with a diameter of 2.5 cm and a length of 5 cm.

[0055] (2) Use an X-ray diffractometer to test the mineral composition and the percentage content of different minerals of the rock sample.

[0056] (3) Test the Young's modulus of the rock mechanical parameters of the rock sample through a triaxial mechanical testing system, and obtain the Young's modulus of different minerals of the rock sample tested in step (2).

[0057] (4) According to the mineral composition and the percentage content of different minerals of the rock sample tested in step (2), calculate the overall dispersion coefficient of different minerals of the rock sample. The calculation formula is as follows:

[0058]

[0059] Where: U is the overall dispersion coefficient of different minerals in the rock sample, dimensionless; n is the type of minerals, species; i is the mineral type number; m i is the percentage content of different minerals of the i-th type in the rock sample, %; M is the average value of the mineral percentage content in the rock sample, %.

[0060] (5) According to the overall dispersion coefficient of different minerals in the rock sample in step (4), calculate the dispersion degree index of different minerals in the rock sample. The larger its value, the higher the dispersion degree of different minerals, and the more easily the rock for engineering fracturing is broken. The calculation formula is as follows:

[0061]

[0062] Where: E is the dispersion degree index of different minerals in the rock sample, dimensionless.

[0063] (6) According to the type of minerals tested in the rock sample in step (2) and the rock mechanics parameters of the rock sample tested in step (3), namely Young's modulus and Young's modulus of different minerals, calculate the non-uniformity index of the rock mechanics parameters of different minerals in the rock sample. The calculation formula is as follows:

[0064]

[0065] Where: G i is the non-uniformity index of the rock mechanics parameters of the i-th type of mineral in the rock sample, dimensionless; E i is the Young's modulus of the i-th type of mineral, MPa; E r is the overall Young's modulus of the rock sample tested, MPa.

[0066] (7) According to the non-uniformity index of the rock mechanics parameters of different minerals in the rock sample and the type of minerals, calculate the fracture development degree index to evaluate the development degree of the original fractures. The larger its value, the more developed the fractures in the rock sample, and the more easily the rock for engineering fracturing is broken. The calculation formula is as follows:

[0067]

[0068] In step 3), based on the calculation of the mineral dispersion degree index and the fracture development degree index calculated in steps (5) and (7) of step 2), calculate the rock engineering brittleness index to evaluate the engineering compressibility. The calculation formula is as follows:

[0069] BI = E·F (6)

[0070] Where: BI is the rock engineering brittleness index, dimensionless.

[0071] In the present invention, in step 4), comprehensively considering the geology and engineering compressibility of the evaluation section, obtain the compressibility factor. The larger its value, the stronger the compressibility, so as to achieve the purpose of quantitative evaluation of the geological engineering compressibility of the shale oil reservoir. The specific content is as follows:

[0072] Comprehensively considering the geological and engineering compressibility of the evaluation section, the compressibility factor is obtained. The larger the value, the stronger the compressibility. The larger the value, the stronger the geological and engineering compressibility of the evaluation section.

[0073] The calculation formula for the compressibility factor is as follows:

[0074] EI = α·RI + β·BI (7)

[0075] In the formula: EI is the rock compressibility factor, dimensionless; α and β are the weight coefficients of geological and engineering compressibility, which are fitted or selected according to the actual situation.

[0076] Specifically, it can be divided into four grades according to its value. When the rock compressibility factor 0 < EI ≤ 0.25, it is a poor compressibility reservoir; when the rock compressibility factor 0.25 < EI ≤ 0.50, it is a medium compressibility reservoir; when the rock compressibility factor 0.50 < EI ≤ 0.75, it is a relatively good compressibility reservoir; when the rock compressibility factor 0.75 < EI ≤ 1.0, it is a strong compressibility reservoir.

[0077] Example 1

[0078] The following takes the core samples of a horizontal well in a shale oil reservoir in a certain block as an example to describe the specific implementation manner of the present invention in detail. This example provides a comprehensive evaluation method for the geological and engineering compressibility of a shale oil reservoir, as follows:

[0079] 1) Use the basic data of the shale oil reservoir geology and horizontal well to establish a fine geological model, obtain the three-dimensional physical property distribution of the evaluation section, calculate the oil-bearing index per unit volume, and evaluate the geological compressibility. The specific content is as follows:

[0080] (1) Taking the typical Y platform of shale oil as an example, there are 5 horizontal wells on this platform. The basic geological data such as the structural interpretation results and logging interpretation data of the shale oil reservoir are respectively obtained to establish a three-dimensional geological model of the typical well group of the shale oil reservoir. As Figure 1 shown, taking one of the horizontal wells Y1 on the platform as an example, the horizontal section length of this well is 1860 m, the well spacing of adjacent wells is 400 m, and the horizontal section is divided into 31 evaluation sections at an equal interval of 60 m. Taking three of these sections as an example, numbered Y1-1 to Y1-3, the three-dimensional spatial average porosity, oil saturation, reservoir thickness, and oil layer thickness of these three sections are obtained by using the three-dimensional geological model. See Table 1.

[0081] Table 1 Statistical table of three-dimensional geological parameters of the evaluation section

[0082]

[0083] (2) Obtain the three-dimensional spatial average porosity, oil saturation, reservoir thickness, and oil layer thickness of the evaluation section using a three-dimensional geological model, and calculate the oil-bearing index per unit volume of the evaluation reservoir section Y1-1 to Y1-3 using formula (1), as shown in Figure 2 .

[0084] 2) Obtain downhole cores of the evaluation reservoir section, and test the mineral composition and rock mechanical parameters of the cores. On this basis, calculate the mineral dispersion degree and fracture development degree respectively, and calculate the rock engineering brittleness index to evaluate the engineering compressibility. The specific content is as follows:

[0085] (1) Conduct downhole coring of the evaluation sections Y1-1 to Y1-3 for the horizontal section length division of the horizontal well in step 1). Take one typical core for each, numbered W1 to W3, and process the cores into standard rock samples with a diameter of 2.5 cm and a length of 5 cm.

[0086] (2) Use an X-ray diffractometer to test that the main mineral components of the rock samples in step (1) are 5 types, quartz, feldspar, calcite, dolomite, and clay minerals, and the percentage contents of different minerals are shown in Table 2.

[0087] Table 2 Test table of mineral composition and percentage content of rock samples W1-W3

[0088]

[0089] (3) Test the rock mechanical parameters of the rock samples W1-W3 in step (1) through a triaxial mechanical testing system. The Young's moduli are 36207 MPa, 28768 MPa, and 46572 MPa respectively, and obtain the Young's moduli of different minerals of the rock samples tested in step (2), as shown in Figure 3 .

[0090] (4) According to the mineral composition of the rock samples tested in step (2) and the percentage contents of different minerals, calculate the overall dispersion coefficients of different minerals of the rock samples W1 to W3 using formula (2), which are 41.0%, 69.4%, and 46.4% respectively.

[0091] (5) According to the overall dispersion coefficients of different minerals of the rock samples in step (4), calculate the dispersion degree indices of different minerals of the rock samples W1 to W3 using formula (3). The larger the value, the higher the dispersion degree of different minerals, and the easier it is for the rock to be broken during engineering fracturing, as shown in Figure 4 .

[0092] (6) According to the types of minerals tested in the rock samples in step (2) and the Young's modulus of the rock mechanical parameters and the Young's moduli of different minerals tested in the rock samples in step (3), calculate the non-uniformity indices of the rock mechanical parameters of different minerals of the rock samples W1 to W3, as shown in Table 3.

[0093] Table 3 Calculation result table of non-uniformity indices of rock mechanical parameters of different minerals of rock samples W1-W3

[0094]

[0095] (7) According to the non-uniformity index and mineral types of the mechanical parameters of different mineral rocks in the rock samples, use formula (5) to calculate the fracture development degree index of rock samples W1 to W3, and evaluate the development degree of the original fractures. The larger the value, the more developed the fractures in the rock samples, and the easier the rock is to be broken during engineering fracturing. See Figure 5 .

[0096] 3) Based on the calculation of the mineral dispersion degree and fracture development degree in steps (5) and (7) of step 2), use formula (6) to calculate the rock engineering brittleness index of rock samples W1 to W3, and evaluate the engineering compressibility. See Figure 6 .

[0097] 4) Considering the geology and engineering compressibility of the evaluation section comprehensively, obtain the compressibility factor, so as to achieve the purpose of quantitative evaluation of the geological engineering compressibility of the shale oil reservoir. The specific content is as follows:

[0098] Considering the geology and engineering compressibility of the evaluation section comprehensively, use formula (7) to calculate the rock compressibility factor of rock samples W1 to W3. In this embodiment, α and β are respectively taken as 0.5. The calculation results are shown in Figure 7 , which are 0.45, 0.55, and 0.50 respectively. It can be seen from this that the compressibility ranking of the reservoirs corresponding to rock samples W1 to W3 in the evaluation sections Y1-1 to Y1-3 is: Y1-2 > Y1-3 > Y1-1. According to the reservoir compressibility grade division standard in step 4), the evaluation sections Y1-1 and Y1-3 are medium compressibility reservoirs, and Y1-2 is a better compressibility reservoir.

[0099] The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A comprehensive evaluation method for geological engineering compressibility of shale oil reservoirs, characterized in that: The following steps are involved: Step 1) establishing a fine geological model for the shale oil reservoir of the target block, determining an evaluation section in the fine geological model, and obtaining a unit volume oil content index of the evaluation section; The calculation method of the unit volume oil content index is: （1） Where: It is the oil content index per unit volume of the evaluation section, dimensionless; is the average oil layer thickness in the three-dimensional space of the evaluation section, ; is the average reservoir thickness in the three-dimensional space of the evaluation section, ; To evaluate the average porosity of the three-dimensional space of the segment, ; It is the average oil saturation in the three-dimensional space of the evaluation section, dimensionless; Step 2) Obtain downhole cores of the evaluation section, test the mineral composition and rock mechanical parameters of the cores, and obtain the mineral dispersion index and fracture development index; Obtaining the degree of mineral dispersion in step 2) also includes: Calculate the overall dispersion coefficient of different minerals in the rock sample and the mineral dispersion index. The calculation method of the mineral dispersion index is: （3） Where: E It is the index of the degree of dispersion of different minerals in the rock sample, dimensionless; n is the mineral type, species; U is the overall dispersion coefficient of different minerals, dimensionless; Step 2) also includes determining a fracture development index based on the rock mechanical parameter heterogeneity index and the mineral type; the fracture development index is calculated by: （5） G i is the rock mechanical parameter heterogeneity index of the i-th mineral in the core, dimensionless; Step 3) According to the dispersion index of different minerals in the core and the fracture development index, the engineering brittleness index is obtained. The calculation method of the engineering brittleness index is: （6） Where: BI Rock engineering brittleness index, dimensionless; Step 4) Weighted processing is performed on the unit volume oil content index and the engineering brittleness index to obtain the compressibility factor and conduct a comprehensive evaluation of the compressibility of the evaluation section.

2. The method for comprehensive evaluation of compressibility according to claim 1, wherein in step 1), determining the evaluation section in the fine geological model further comprises: According to the length of the horizontal section of the horizontal well, it is divided into n The three-dimensional average porosity, oil saturation, reservoir thickness and oil layer thickness of each equal section are obtained according to the fine geological model.

3. The method for comprehensive evaluation of compressibility according to claim 1, wherein in step 2) X X-ray diffractometer is used to test the mineral composition and percentage of different minerals in the core.

4. The method for comprehensive evaluation of compressibility as claimed in claim 1, wherein in step 2), the Young's modulus of the core is tested by a triaxial mechanical testing system.

5. The method for comprehensive evaluation of compressibility according to claim 1, wherein step 2) further comprises: The rock mechanical parameter heterogeneity index is calculated based on the mineral types measured in the core and the Young's modulus of the core.

6. A comprehensive evaluation device for the geological engineering compressibility of shale oil reservoirs, characterized in that: include: at least one processor and a memory in communication with the processor; The memory stores instructions executable by the processor, and the instructions are executed by at least one processor so that the at least one processor can execute the comprehensive evaluation method described in any one of claims 1-5.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the comprehensive evaluation method as described in any one of claims 1 to 5 are implemented.

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