Method for optimizing shale oil reservoir multi-layer system three-dimensional exploitation well release mode

Abstract

The invention relates to an optimization method of a shale oil reservoir multi-layer system three-dimensional exploitation well spacing mode. The method comprises the following steps: acquiring a difference stress coefficient between two adjacent reservoirs and a spacing layer in a development layer section of a platform to be subjected to well spacing and a development layer section corresponding to an adjacent platform of the development layer section to be subjected to well spacing; the single well final recoverable reserves of the produced horizontal wells of the adjacent platforms are obtained; making a correlation chart of the interlayer thickness and the differential stress coefficient of the adjacent platforms and the final recoverable reserves of the single well, determining a longitudinal crossing geological engineering parameter boundary, and further determining a well spacing mode; performing three-dimensional geological modeling on the platform to be subjected to well spacing, calculating a comprehensive dessert coefficient according to the three-dimensional geological dessert coefficient and the engineering dessert coefficient, and classifying reservoirs according to the comprehensive dessert coefficient; and carrying out productivity numerical simulation of different well spacing, carrying out correlation analysis on the different well spacing and the oil production of the single well of the to-be-distributed well platform in the first year, and determining the optimal well spacing. The method can provide a basis for multi-layer three-dimensional efficient economic development of similar shale oil reservoirs, and has a good application prospect.

Description

Technical Field

[0001] The invention relates to the field of petroleum and natural gas engineering, and in particular to a method for optimizing a well drilling mode for three-dimensional development of a shale oil reservoir multilayer system during the exploration and development of a shale oil and gas reservoir. Background Art

[0002] China's shale oil and gas resources are extremely rich, mainly distributed in large basins such as Ordos, Junggar, Songliao, Bohai Bay, and Sichuan. They have huge development potential and are the most strategic oil replacement resources. They have become the main force for increasing reserves and production in the shale oil revolution of various oil fields. However, through the core sampling, logging precision, 3D seismic, high-precision nuclear magnetic resonance, CT and other means of the mine hydraulic fracturing test site, the characteristics of shale oil reservoirs are finely described. All oil fields have confirmed that shale oil reservoirs have strong heterogeneity in the plane, vertical and three-dimensional space, discontinuous reservoir sand bodies, multiple thin layers are superimposed, the physical parameters of the same development area and development layer are very different, and natural fractures or faults are developed, resulting in obvious pressure channeling problems between horizontal wells, which seriously affects the production of single wells. At the same time, the production of oil wells corresponding to different well layout methods varies greatly. Therefore, the well layout method is the primary key link in the three-dimensional development of multi-layer systems in shale oil reservoirs and the core factor affecting the efficient and economic development of shale oil. The well layout method is jointly affected by the geological and engineering parameters of the reservoir, and its optimization method also brings huge challenges. Therefore, there is an urgent need for a three-dimensional well layout method suitable for the characteristics of shale oil reservoirs to provide strong support for accelerating the efficient and economic development of shale oil.

[0003] Through research and patent benchmarking, the current optimization methods for unconventional tight reservoir well layout are mainly based on big data and reservoir numerical simulation methods. Among them, Li Jinbu et al. proposed a factory-based large well group layout method with multi-factor collaborative analysis, patent number: CN201711385221.5. This method is mainly aimed at optimizing the factory-based well layout of large well groups in tight gas and shale gas reservoirs, and realizes factory-based large well group layout through detailed reservoir description and combined drilling engineering factors. In addition, Fan Jianming et al. proposed a shale oil well layout method with long horizontal wells with small well spacing, multi-layer system and dense cutting, patent number: CN201910636274.2. This method is based on the classification of shale oil oil-bearing reservoir patterns, establishes the determination principles of horizontal well types and lengths under different oil-bearing reservoir patterns, and uses reservoir decline analysis methods and mine microseismic monitoring data to optimize horizontal well spacing.

[0004] None of the above representative methods targets the characteristics of unconventional reservoirs. How to achieve efficient production by three-dimensional well placement under the influence of multiple geological and engineering factors such as multi-layer systems, strong vertical heterogeneity, and development of natural fractures? Therefore, it is urgent to establish a multi-layer three-dimensional development well placement method that conforms to the actual shale oil reservoirs, so as to provide important support for the efficient production of shale oil and the realization of the shale oil revolution. Summary of the invention

[0005] The present invention aims to solve the above problems and proposes a method for optimizing the well drilling mode of multi-layer three-dimensional development of shale oil reservoirs.

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

[0007] A method for optimizing the well drilling method for multi-layer three-dimensional development of shale oil reservoirs is as follows: Step 1: Obtain the differential stress coefficients of the two adjacent reservoirs and the interlayer in the development layer section of the platform to be well-placed and the corresponding development layer section of the adjacent platform; obtain the final recoverable reserves of the single well of the produced horizontal wells of the adjacent platform; make a correlation chart of the thickness of the interlayer of the adjacent platform, the differential stress coefficient and the final recoverable reserves of the single well, determine the limit of the vertical interlayer geological engineering parameters, and then determine the well-placement mode; Step 2: Conduct 3D geological modeling for the well platform to be deployed, calculate the comprehensive sweet spot coefficient using the 3D geological sweet spot coefficient and the engineering sweet spot coefficient, and classify the reservoir according to the comprehensive sweet spot coefficient; Step 3: Carry out numerical simulation of production capacity at different well spacings, conduct correlation analysis between different well spacings and the cumulative oil production of a single well in the first year of the platform to be deployed, and determine the optimal well spacing.

[0008] Wherein, the calculation formula of the differential stress coefficient is: Where: F is the differential stress coefficient between the reservoir and the interlayer of the shale oil development formation, dimensionless; σ H is the average minimum horizontal principal stress of the interlayer, MPa; σ h1 is the average minimum horizontal principal stress of the reservoir in the development layer, MPa; σ h2 is the average minimum horizontal principal stress of the reservoir below the development layer, MPa.

[0009] The process of determining the limits of the longitudinal interlayer geological engineering parameters is as follows: The interlayer thickness and differential stress coefficient of adjacent platforms are sorted from small to large, and a correlation chart is drawn with the final recoverable reserves of a single well. The preliminary interlayer thickness limit and preliminary differential stress coefficient limit are determined by the inflection point method; the determined preliminary interlayer thickness limit and preliminary differential stress coefficient limit are calculated as follows by the following formula; Where: DI is the final recoverable reserves growth coefficient of the kth producing horizontal well corresponding to the initial barrier thickness limit, %; FI is the final recoverable reserves growth coefficient of the jth producing horizontal well corresponding to the initial differential stress coefficient limit, %; E Skis the final recoverable reserves of the kth producing horizontal well, 10,000 tons; E Sk+1 The ultimate recoverable reserves of the single well of k+1 producing horizontal wells, 10,000 tons; E Fj is the final recoverable reserves of the jth producing horizontal well, 10,000 tons; E Fj+1 is the final recoverable reserves of the j+1th producing horizontal well, 10,000 tons; When the calculated values ​​of DI and FI are both less than 5%, the corresponding preliminary interlayer thickness limit and preliminary differential stress coefficient limit are the interlayer thickness limit S h Sum and difference stress coefficient limit F h ; If the calculated values ​​of DI and FI do not meet the condition of being both less than 5%, DI and FI will be recalculated at the next inflection point until the calculated values ​​of DI and FI are both less than 5%.

[0010] The determination rule of the well layout pattern is: if the interlayer thickness ≥ interlayer thickness limit S h And the differential stress coefficient ≥ differential stress coefficient limit F h When the shale oil development layer is developed, the upper and lower reservoirs are developed separately in a three-dimensional manner, that is, a mountain-shaped development; otherwise, the wells are developed in a staggered manner, that is, a W-shaped development.

[0011] The calculation process of the three-dimensional geological sweet spot coefficient is as follows: Where: GQ is the three-dimensional geological sweet spot coefficient of the well platform to be deployed, dimensionless; h is the average oil layer thickness in the three-dimensional space of the well platform to be deployed, m; H is the average reservoir thickness in the three-dimensional space of the well platform to be deployed, m; is the average porosity of the three-dimensional space of the well platform to be deployed, %; S o It is the average oil saturation in the three-dimensional space of the well platform to be deployed, which is dimensionless.

[0012] The calculation process of the engineering sweet spot coefficient is as follows: Where: EQ is the engineering sweet spot coefficient, dimensionless; i is the type of mineral, dimensionless, and has a value of 1-n; m i is the percentage of the i-th mineral, %; M is the average value of mineral content, %.

[0013] The calculation process of the comprehensive sweet spot coefficient is as follows: R = α·GQ + β·EQ (6) In the formula: R is the comprehensive sweet spot coefficient, dimensionless; α is the weight of the three-dimensional geological sweet spot coefficient, dimensionless; β is the weight of the engineering sweet spot coefficient, dimensionless.

[0014] Among them, the specific process of classifying the reservoir according to the comprehensive sweet spot coefficient is as follows: when the comprehensive sweet spot coefficient 0 < R ≤ 0.35, it is a Class III reservoir; when 0.35 < R ≤ 0.70, it is a Class II reservoir; when 0.70 < R ≤ 1, it is a Class I reservoir.

[0015] The specific process of step 3 is as follows: (1) Conduct numerical simulations of production capacity at different well spacings, where the half-length of the horizontal well volume fracturing fracture is half of the well spacing, and obtain the cumulative oil production of a single well on the well platform to be drilled in the first year under different well spacings; (2) Conduct a correlation analysis between different well spacings and the cumulative oil production of a single well on the well platform to be drilled in the first year, and obtain the optimal well spacing of the well platform to be drilled by the inflection point method.

[0016] The technical effects of the present invention are as follows: (1) By establishing a correlation chart of field production data and geological engineering parameters, the present invention quantifies the problem of the longitudinal cross-layer geological engineering parameter boundaries in the multi-layer development of shale oil, and innovatively proposes a well pattern under different cross-layer boundaries; (2) The present invention realizes the quantitative evaluation and reservoir classification of the three-dimensional geological engineering sweet spots of the well platform, and quantifies the well spacing of different formations with the maximum production capacity as the goal. Its calculation method is simple and feasible, which can provide a basis for the three-dimensional efficient and economic development of multi-layer shale oil reservoirs of the same type, and has good application prospects. Description of the Drawings

[0017] Figure 1 It is a flow chart of the present invention.

[0018] Figure 2 It is a mountain-shaped schematic diagram.

[0019] Figure 3 It is a W-shaped schematic diagram.

[0020] Figure 4 It is a correlation chart of the interlayer thickness and the ultimate recoverable reserve of a single well in a specific experimental example.

[0021] Figure 5 It is a correlation chart of the differential stress coefficient and the ultimate recoverable reserve of a single well in a specific experimental example.

[0022] Figure 6 It is a correlation chart of different well spacings and the cumulative oil production of a single well on the H1 platform in the first year in a specific experimental example. Detailed Embodiments

[0023] A method for optimizing the well drilling method for multi-layer three-dimensional development of shale oil reservoirs is as follows:

[0024] Step 1: Obtain the differential stress coefficients of the two adjacent reservoirs and the interlayer in the development interval of the platform to be well-placed and the corresponding development interval of the adjacent platform; obtain the final recoverable reserves of the single well of the produced horizontal wells of the adjacent platform; make a correlation chart of the thickness of the interlayer of the adjacent platform, the differential stress coefficient and the final recoverable reserves of the single well, determine the limit of the vertical interlayer geological engineering parameters, and then determine the well-placement mode; the specific process is as follows: The development layer section where the well platform is to be deployed includes an upper reservoir and a lower reservoir, and the upper reservoir and the lower reservoir are separated by a barrier layer; Collect the thickness of the interlayer in the development layer section of the platform to be well-placed and the corresponding development layer section of the adjacent platform, and the minimum horizontal principal stress of each reservoir and interlayer, and calculate the differential stress coefficient based on this; at the same time, collect the final recoverable reserves of the single well of the horizontal wells that have been produced in the adjacent platform; the calculation process of the differential stress coefficient is shown in formula (1); The interlayer thickness and differential stress coefficient of adjacent platforms are sorted from small to large, and a correlation chart is drawn with the final recoverable reserves of a single well. The preliminary interlayer thickness limit and the preliminary differential stress coefficient limit are determined by the inflection point method. The final recoverable reserves growth coefficient DI of the kth producing horizontal well corresponding to the preliminary interlayer thickness limit is calculated by formula (2), and the final recoverable reserves growth coefficient FI of the jth producing horizontal well corresponding to the preliminary differential stress coefficient limit is calculated by formula (3); When the calculated values ​​of DI and FI are both less than 5%, the corresponding preliminary interlayer thickness limit and preliminary differential stress coefficient limit are the interlayer thickness limit S h Sum and difference stress coefficient limit F h ; If the calculated values ​​of DI and FI do not meet the condition of being both less than 5%, recalculate DI and FI at the next inflection point until the calculated values ​​of DI and FI are both less than 5%; If the interlayer thickness ≥ interlayer thickness limit S h And the differential stress coefficient ≥ differential stress coefficient limit F h When the shale oil development layer is developed, the upper and lower reservoirs are developed separately in a three-dimensional manner, that is, a mountain-shaped development; otherwise, the wells are developed in a staggered manner, that is, a W-shaped development.

[0025] Step 2: Carry out 3D geological modeling of the well platform to be deployed, calculate the comprehensive sweet spot coefficient by using the 3D geological sweet spot coefficient and the engineering sweet spot coefficient, and classify the reservoir according to the comprehensive sweet spot coefficient. The specific process is as follows: calculate the 3D geological sweet spot coefficient GQ by formula (4), calculate the engineering sweet spot coefficient EQ by formula (5), and then calculate the comprehensive sweet spot coefficient R by formula (6); and then classify the reservoir according to the value of the comprehensive sweet spot coefficient R.

[0026] Step 3: Carry out numerical simulation of production capacity at different well spacings, conduct correlation analysis between different well spacings and the first-year cumulative oil production of a single well of the platform to be deployed, and determine the optimal well spacing; the specific process is as follows: (1) Carry out numerical simulation of production capacity at different well spacings, where the half-length of the horizontal well volume fracturing fracture is half of the well spacing, and obtain the first-year cumulative oil production of a single well of the well platform to be deployed at different well spacings; (2) The correlation between different well spacings and the cumulative oil production of a single well in the first year of the well platform to be deployed is analyzed, and the optimal well spacing for the well platform to be deployed is obtained using the inflection point method.

[0027] Specific experimental example: a typical continental shale oil multi-layer development mine

[0028] The development layer section of the platform to be well-deployed (H1 platform) is divided into two sets of layers vertically, numbered as the upper reservoir C1 and the lower reservoir C2, with an interlayer G in the middle, which is a mudstone interlayer. Early downhole coring, logging interpretation, reservoir transformation, etc. show that the characteristics of the upper reservoir C1 and the lower reservoir C2 are significantly different, with strong heterogeneity. It is urgent to optimize the well layout method to provide a basis for optimizing the development technology policy in this area.

[0029] A method for optimizing the well drilling method for multi-layer three-dimensional development of shale oil reservoirs is as follows:

[0030] Step 1: Determine the well layout pattern; the specific process is as follows: (1) Collect the thickness of interlayer G, the average minimum horizontal principal stress of the upper reservoir of C1, the average minimum horizontal principal stress of the lower reservoir of C2, and the average minimum horizontal principal stress of interlayer G of the H1 platform; collect the thickness of interlayers in the corresponding development layers of the adjacent H2-H8 platforms, the average minimum horizontal principal stress of each reservoir and interlayer, and the ultimate recoverable reserves of single wells in the producing horizontal wells of the adjacent H2-H8 platforms, as shown in Table 1: Table 1 Basic parameters of the platform to be deployed and adjacent platforms (2) Calculate the differential stress coefficient using formula (2), see Table 1; (3) Sort the thickness of the interlayer and the differential stress coefficient of adjacent platforms from small to large, and make a correlation chart with the final recoverable reserves of a single well, see Figure 4 and Figure 5 ; Using the inflection point method, the interlayer thickness limit is preliminarily determined to be 8m and the differential stress coefficient limit is 0.27; DI is calculated by formula (2) and FI is calculated by formula (3); DI and FI are both less than 5%, and the interlayer thickness limit S is finally determined h is 8m, the limit of differential stress coefficient F h is 0.27; (4) The thickness of the interlayer of the H1 platform is 6.8m < the thickness limit S h, the differential stress coefficient is 0.19<the differential stress coefficient limit F h , it was determined that the well layout pattern of the H1 platform was staggered well layout and three-dimensional development, that is, W-type.

[0031] Step 2: Carry out 3D geological modeling for the well platform to be deployed, calculate the comprehensive sweet spot coefficient based on the 3D geological sweet spot coefficient and engineering sweet spot coefficient, and classify the reservoir according to the comprehensive sweet spot coefficient; the specific process is as follows: (1) A three-dimensional geological model of the H1 platform was established based on basic geological data such as the structural interpretation of the H1 platform and the fine interpretation of vertical well logging. The average porosity of the H1 platform in three dimensions was The average oil saturation S is 10.2%. o The average reservoir thickness is 67.5%, the average reservoir thickness H is 18.6m, and the average oil layer thickness h is 16.7m. The three-dimensional geological sweet spot coefficient GQ is calculated by formula (4) to be 0.62. (2) Two typical rock samples are taken from the upper reservoir C1 and the lower reservoir C2 of the H1 platform to make standard rock samples numbered S1 to S4. The standard rock samples are placed in a 100°C oven and dried to constant weight. The mineral types and the percentage of each mineral type are tested by X-ray diffractometer, and the average percentage of each mineral content is calculated to represent the mineral percentage of the H1 platform, see Table 2. The engineering sweet spot coefficient EQ is calculated by formula (5) to be 0.81. Table 2 Mineral composition test results (3) The comprehensive sweet spot coefficient R calculated by formula (6) is 0.72, which is judged to be a Class I reservoir.

[0032] Step 3: Carry out numerical simulation of production capacity at different well spacings, conduct correlation analysis between different well spacings and the first-year cumulative oil production of a single well of the platform to be deployed, and determine the optimal well spacing; the specific process is as follows: (1) Numerical simulations of production capacity were conducted when the well spacing was 300, 350, 400, 450, and 500 m, respectively. The half-length of the horizontal well volume fracturing fracture was uniformly set to half of the well spacing, and the first-year cumulative oil production of a single well on the H1 platform was obtained at different well spacings. (2) Correlation analysis was performed between different well spacings and the first-year cumulative oil production of a single well on the H1 platform. Figure 6 , using the inflection point method, the optimal well spacing of the H1 platform is obtained to be 400m.

[0033] It was then determined that the optimal well layout for the H1 platform was a W-type well layout, with a Class I reservoir and an optimal well spacing of 400m.

Claims

1. A method for optimizing the well drilling method for multi-layer three-dimensional development of shale oil reservoirs, characterized in that: The method is as follows: Step 1: Obtain the differential stress coefficients of two adjacent reservoirs and the intervening layer in the development intervals of the platform to be drilled and the corresponding development intervals of adjacent platforms; obtain the ultimate recoverable reserves per well of the horizontal wells that have been produced in adjacent platforms; Make a correlation chart of the interlayer thickness, differential stress coefficient and ultimate recoverable reserves per well of adjacent platforms to determine the longitudinal cross-layer geological engineering parameter boundaries, and then determine the well pattern; Step 2: Conduct 3D geological modeling of the platform to be drilled, calculate the comprehensive sweet spot coefficient based on the 3D geological sweet spot coefficient and the engineering sweet spot coefficient, and classify the reservoirs according to the comprehensive sweet spot coefficient; Step 3: Carry out numerical simulations of production capacity for different well spacings, conduct a correlation analysis between different well spacings and the cumulative oil production of the first year per well of the platform to be drilled, and determine the optimal well spacing.

2. The method for optimizing the well drilling method for multi-layer three-dimensional development of shale oil reservoirs according to claim 1, characterized in that: The calculation formula of the differential stress coefficient is: In the formula: F is the differential stress coefficient of the reservoir and the interlayer in the shale oil development series, dimensionless; σ H is the average minimum horizontal principal stress of the interlayer, MPa; σ h1 is the average minimum horizontal principal stress of the reservoir in the development layer, MPa; σ h2 is the average minimum horizontal principal stress of the reservoir below the development layer, MPa.

3. The method for optimizing the well drilling method for multi-layer three-dimensional development of shale oil reservoirs according to claim 2, characterized in that: The determination process of the longitudinal cross-layer geological engineering parameter boundaries is: Sort the interlayer thickness and differential stress coefficient of adjacent platforms from small to large respectively, make a correlation chart with the ultimate recoverable reserves per well, and determine the preliminary interlayer thickness boundary and the preliminary differential stress coefficient boundary by the inflection point method; calculate as follows through the following formula with the determined preliminary interlayer thickness boundary and preliminary differential stress coefficient boundary; In the formula: DI is the growth coefficient of the ultimate recoverable reserves per well of the kth horizontal well produced corresponding to the preliminary interlayer thickness boundary, %; FI is the growth coefficient of the ultimate recoverable reserves per well of the jth horizontal well produced corresponding to the preliminary differential stress coefficient boundary, %; E Sk is the final recoverable reserves of the kth producing horizontal well, 10,000 tons; E Sk+1 The ultimate recoverable reserves of the single well of k+1 producing horizontal wells, 10,000 tons; E Fj is the final recoverable reserves of the jth producing horizontal well, 10,000 tons; F Fj+1 is the final recoverable reserves of the j+1th producing horizontal well, 10,000 tons; When the calculated values ​​of DI and FI are both less than 5%, the corresponding preliminary interlayer thickness limit and preliminary differential stress coefficient limit are the interlayer thickness limit S h Sum and difference stress coefficient limit F h .

4. The method for optimizing the well drilling method for multi-layer three-dimensional development of shale oil reservoirs according to claim 3, characterized in that: It also includes that if the calculated values of DI and FI do not meet the condition of being less than 5% both, then recalculate DI and FI with the next inflection point until the calculated values of DI and FI are both less than 5%.

5. The method for optimizing the well drilling method for multi-layer three-dimensional development of shale oil reservoirs according to claim 3 or 4, characterized in that: The determination rule of the well layout pattern is: if the interlayer thickness ≥ interlayer thickness limit S h And the differential stress coefficient ≥ differential stress coefficient limit F h When the shale oil development layer is developed, the upper and lower reservoirs are developed separately in a three-dimensional manner, that is, a mountain-shaped development; otherwise, the wells are developed in a staggered manner, that is, a W-shaped development.

6. The method for optimizing the well drilling method for multi-layer three-dimensional development of shale oil reservoirs according to claim 1, characterized in that: The calculation process of the 3D geological sweet spot coefficient is: In the formula: GQ is the 3D geological sweet spot coefficient of the platform to be drilled, dimensionless; h is the average oil layer thickness in the 3D space of the platform to be drilled, m; H is the average reservoir thickness in the 3D space of the platform to be drilled, m; is the average porosity of the three-dimensional space of the well platform to be deployed, %; S o It is the average oil saturation in the three-dimensional space of the well platform to be deployed, which is dimensionless.

7. The method for optimizing the well drilling method for multi-layer three-dimensional development of shale oil reservoirs according to claim 6, characterized in that: The calculation process of the engineering sweet spot coefficient is: In the formula: EQ is the engineering sweet spot coefficient, dimensionless; i is the mineral type, dimensionless; the value range is 1 - n; m i is the percentage of the i-th mineral, %; M is the average value of the mineral percentage content, %.

8. The method for optimizing the well drilling method for multi-layer three-dimensional development of shale oil reservoirs according to claim 7, characterized in that: The calculation process of the comprehensive sweet spot coefficient is: R = α·GQ + β·EQ (6) In the formula: R is the comprehensive sweet spot coefficient, dimensionless; α is the weight of the 3D geological sweet spot coefficient, dimensionless; β is the weight of the engineering sweet spot coefficient, dimensionless.

9. The method for optimizing the well drilling method for multi-layer three-dimensional development of shale oil reservoirs according to claim 8, characterized in that: The specific process of classifying the reservoirs according to the comprehensive sweet spot coefficient is: when 0 < R ≤ 0.35, it is a Class III reservoir; when 0.35 < R ≤ 0.70, it is a Class II reservoir; When 0.70 < R ≤ 1, it is a Class I reservoir.

10. The method for optimizing the well drilling method for multi-layer three-dimensional development of shale oil reservoirs according to claim 1, characterized in that: The specific process of Step 3 is: (1) Carry out numerical simulations of production capacity for different well spacings, where the half-length of the horizontal well volume fracturing cracks is half of the well spacing, and obtain the cumulative oil production of the first year per well of the platform to be drilled under different well spacings; (2) Conduct a correlation analysis between different well spacings and the cumulative oil production of the first year per well of the platform to be drilled, and obtain the optimal well spacing of the platform to be drilled by the inflection point method.

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