Method for determining dosage of temporary plugging agent in tight reservoir fracturing crack

Abstract

The invention relates to a method for determining the dosage of a temporary plugging agent in a tight reservoir fracturing fracture. The method comprises the following steps: calculating a brittleness complex index according to brittleness values at different positions of a reservoir fracturing section to be evaluated; constructing a rock sample group formed by rock samples with different brittleness values, obtaining brittleness complex indexes of the corresponding rock sample group, carrying out in-crack temporary plugging experiments with different temporary plugging concentrations, evaluating crack diffusion indexes of the rock sample group according to the number of cracks, and establishing a regression function of the crack diffusion indexes of the rock sample group and the temporary plugging concentrations; the optimal temporary plugging concentration of the rock sample group is obtained by combining the target crack diffusion index; fitting the optimal temporary plugging concentration of the rock sample group with the brittleness complex index to obtain a temporary plugging concentration function; and the optimal use amount of the temporary plugging agent in the fracture of the to-be-evaluated reservoir fracturing section is obtained by combining the design liquid amount of the to-be-evaluated reservoir fracturing section. The method has an important guiding effect on optimization and improvement of an unconventional main body temporary plugging fracturing technology and implementation of a mine field.

Description

Technical Field

[0001] This invention relates to the field of oil and gas engineering, and in particular to a method for determining the amount of temporary plugging agent used in the fracture of tight reservoirs during exploration and development. Background Technology

[0002] Volumetric fracturing of horizontal or vertical wells is a key technology for enhancing production in tight reservoirs. It typically employs multi-cluster perforation fracturing. However, due to the strong heterogeneity of tight reservoirs in terms of geological sweet spots, the propagation of multi-cluster fractures is extremely uneven. Therefore, temporary plugging and diversion techniques are often used to increase fracture complexity and the volume of fracture network stimulation. Through research and benchmarking, the evaluation of temporary plugging agents used in fracturing mainly includes the following methods: The existing technical solution (patent number CN202410065984.5) discloses an optimization method for the addition of temporary plugging agents in volumetric fracturing. This method collects parameters affecting the single-well productivity of horizontal wells that have undergone temporary plugging fracturing, establishes a comprehensive big data productivity evaluation model, and calculates the reservoir geological quality factors for each fracturing section of the evaluation horizontal well. It also performs downhole coring on sections corresponding to different temporary plugging agent addition methods in the evaluation horizontal well to calculate the distribution factor of natural fractures and the volumetric factor controlling the fracture network. By comprehensively considering reservoir geological quality, engineering quality, and stimulation effect, it obtains the temporary plugging efficiency coefficient and optimizes the temporary plugging agent addition method based on this coefficient.

[0003] The existing technical solution (patent number CN202210165687.9) discloses a device and method for evaluating the plugging capability of temporary plugging and diverting agents in non-uniform cracks. This evaluation device includes a simulated crack system, with an annular rubber cylinder and a stainless steel outer cylinder arranged sequentially outside the simulated crack system. The simulated crack system comprises a fourth simulated crack and crack modules arranged sequentially; wherein the fourth simulated crack is a bell-mouth module, and the crack module includes three simulated cracks of different widths arranged sequentially; the front end of the bell-mouth module is connected to an inlet pipe, and the end end is connected to the crack module; it also includes a pumping system, a ring pressure system, and a monitoring system. This invention simulates both static and dynamic plugging methods through two systems and two methods.

[0004] The existing technical solution (patent number CN201821879734.1) discloses a device for evaluating the performance of a temporary plugging ball. This utility model discloses a device for evaluating the performance of a temporary plugging ball, comprising: a pumping module, a first fluid manifold, a temporary plugging and turning level testing module, a slotted orifice temporary plugging and turning simulation module, and a data acquisition module. The output end of the pumping module is connected to the temporary plugging and turning level testing module via the first fluid manifold. Multiple orifices are provided on the side wall of the temporary plugging and turning level testing module, and the temporary plugging and turning level testing module is connected to an input end of the slotted orifice temporary plugging and turning simulation module via these multiple orifices. The output end of the slotted orifice temporary plugging and turning simulation module is connected to the data acquisition module, which is used to collect the first flow rate of the fluid output by the slotted orifice temporary plugging and turning simulation module, and to evaluate the turning performance of the temporary plugging ball based on the first flow rate.

[0005] The three representative methods mentioned above mainly involve integrated geological and engineering research, experimental device development, and evaluation of the performance and effectiveness of temporary plugging agents. However, the core factor affecting the effectiveness of temporary plugging fracturing is the dosage of the temporary plugging agent. Currently, based on surveys of field operations in various oilfields, the focus is mainly on temporary plugging fracturing at the fracture opening, with the agent added empirically according to a certain proportion based on the number of perforations. However, the dosage for fracturing within the fracture is still in the exploratory and field experience stage, and a quantitative optimization method has not yet been developed. Therefore, it is necessary to propose an optimization method for the addition of temporary plugging agents within the fracture at the field scale to support the efficient development of tight reservoirs. Summary of the Invention

[0006] The present invention aims to address the above-mentioned problems by proposing a method for determining the amount of temporary plugging agent used in the fracture of tight reservoirs.

[0007] The technical solution of this invention is as follows: A method for determining the dosage of temporary plugging agent in the fracture of tight reservoirs is as follows: The brittle complexity index was calculated based on the brittleness values ​​at different locations in the fracturing section of the reservoir to be evaluated. A rock sample group consisting of rock samples with different brittleness values ​​was constructed to obtain the brittleness complexity index of the corresponding rock sample group. In-fracture plugging experiments with different plugging concentrations were carried out. The fracture diffusion index of the rock sample group was evaluated based on the number of fractures. A regression function between the fracture diffusion index and the plugging concentration of the rock sample group was established. Then, the optimal plugging concentration of the rock sample group was obtained by combining the target fracture diffusion index. The optimal temporary plugging concentration of the rock sample group was fitted with the brittle complexity index to obtain the temporary plugging concentration function; then, combined with the design fluid volume of the fracturing section of the reservoir to be evaluated, the optimal amount of temporary plugging agent in the fracture section of the reservoir to be evaluated was obtained.

[0008] The specific process for obtaining the brittle complexity index is as follows: take rock samples from different depths of the reservoir to be evaluated to make core samples, obtain the Young's modulus of each core sample, and then calculate the brittleness value of each core sample as the brittleness value at different locations in the fracturing section of the reservoir to be evaluated. Calculate the average brittleness value, and then calculate the brittleness deviation coefficient and the brittle complexity index in sequence.

[0009] The specific calculation process for the brittleness value is as follows: g i =( f i - f min ) / ( f max - f min (1) In the formula: f i For the first i Young's modulus of the core sample, MPa; f max The maximum Young's modulus of the test core in this block, in MPa; f min The minimum Young's modulus of the test core in this block, in MPa; g i For the first i The brittleness value of each core sample is dimensionless. Then calculate the average brittleness value: (2) In the formula: g m This is the average brittleness value, dimensionless; n To obtain the number of core samples, blocks were used.

[0010] The specific calculation process for the brittle complexity index is as follows: B = g z / g m (4) (3) In the formula: g z This is the brittleness deviation coefficient, which is dimensionless. B It is a brittle complexity index and has no dimension.

[0011] The specific process for obtaining the fracture diffusion index of the rock sample group is as follows: u = m / mmax (5) In the formula: u is the fracture diffusion index of the rock sample group, dimensionless; m The number of cracks; m max The theoretical maximum number of cracks is given by the number of cracks.

[0012] The specific process for obtaining the optimal temporary plugging concentration of the rock sample group is as follows: The regression function between the fracture diffusion index and the temporary plugging concentration of the rock sample group is established as follows: u = a ln( d )+ b (6) Then, based on the target fracture diffusion index and the following formula, the optimal temporary plugging concentration for the rock sample group is calculated: (7) In the formula: a The first regression coefficient is dimensionless; b The coefficients are the second regression coefficients and have no dimension. d Temporary blocking concentration, kg / m³ 3 ; d h The optimal temporary plugging concentration for the rock sample group is kg / m³. 3 ; u m The target crack propagation index is dimensionless.

[0013] The specific process for obtaining the temporary blocking concentration function is as follows: d u = r˙B + t (8) In the formula: d u The temporary blocking concentration function is expressed in kg / m³. 3 ; r The first fitting coefficient is dimensionless. b The second fitting coefficient is dimensionless.

[0014] The specific solution process for determining the optimal amount of temporary plugging agent in the fractured section of the reservoir to be evaluated is as follows: D = d u ˙c m (9) In the formula: d u The optimal temporary plugging concentration within the fractured section of the reservoir to be evaluated is kg / m³. 3; c m For the design liquid volume, m 3 ; D The optimal amount of temporary plugging agent in the fractured section of the reservoir to be evaluated is kg.

[0015] The number of cracks was obtained by CT scanning of rock samples that had undergone temporary plugging experiments within the cracks.

[0016] The technical effects of this invention are as follows: This invention innovatively establishes a fitting function between the optimal temporary plugging concentration and the brittle complexity index by combining reservoir geomechanical differences and experimental testing methods, enabling dynamic prediction of temporary plugging agents within fractures at the mine scale. This method is simple to operate and can significantly reduce testing and experimental costs, showing great promise for application at the mine scale. It also provides important guidance for optimizing and improving unconventional main temporary plugging fracturing technology and its implementation in mines. Attached Figure Description

[0017] Figure 1 This is a comparison chart showing the calculation of the brittleness complexity index for different rock samples in this invention. Detailed Implementation

[0018] A method for determining the dosage of temporary plugging agent in the fracture of tight reservoirs is as follows: Step 1: Take rock samples from different depths of the reservoir to be evaluated to make core samples, and calculate the Young's modulus of each core sample according to formula (1). f i Then, the average brittleness value is calculated according to equation (2). g m The brittleness deviation coefficient is calculated according to equation (3). g z Then, the brittle complexity index is calculated according to equation (4). B ; Step 2: Construct a rock sample group consisting of rock samples with different brittleness values, and conduct intra-fracture plugging experiments on each rock sample group with different temporary plugging concentrations. Obtain the brittleness complexity index of each rock sample group according to Equation (5). u The fracture diffusion index of the rock sample group was established according to formula (6). u With temporary blocking concentration d The regression function yields the first regression coefficient. a and the second regression coefficient b ; and then the optimal temporary plugging concentration of the rock sample group is obtained according to equation (7). d h ; Step 3: Calculate the optimal temporary plugging concentration for the rock sample group according to formula (8). d h With brittle complexity index B The temporary blocking concentration function was obtained by fitting. du Furthermore, based on equation (9) and the design fluid volume of the fracturing section of the reservoir to be evaluated, the optimal amount of temporary plugging agent in the fracturing section of the reservoir to be evaluated is obtained.

[0019] Specific Implementation Cases The following describes the specific implementation of the present invention in detail with reference to the attached figures and rock sample results from a tight sandstone reservoir development area in a certain block.

[0020] A typical tight sandstone reservoir in western China was selected as the reservoir to be evaluated. Taking one vertical well, HJ-1, as an example, rock samples were obtained at 3000m in the main development section. The amount of temporary plugging agent used in the fractured tight reservoir of the fractured section of the HJ-1 vertical well was evaluated using the method provided in this application. The specific implementation steps are as follows.

[0021] Step 1: Obtain rock mechanical parameters at different locations within the fractured section of the reservoir to be evaluated. This is used to determine the brittleness values ​​at different locations. The average brittleness value and brittleness deviation coefficient of the fractured section are then calculated based on these values. Furthermore, the brittleness complexity index is calculated to evaluate the mechanical differences at different locations within the fractured section. Smaller differences indicate a more homogeneous reservoir, easier propagation of multiple fracture clusters, and a smaller amount of temporary plugging agent required. Details are as follows: (1) Calculate the brittleness value at different locations: Take rock samples from different depths of the reservoir to be evaluated to make core samples. Take rock samples within 9m of the reservoir to be evaluated. The sampling locations are 3m, 6m and 9m of the sampling range. Use the samples to make core samples. Use a triaxial rock mechanics testing system to test the Young's modulus of the core samples. Calculate the brittleness value of each core sample to serve as the brittleness value at different locations. Among them, the maximum Young's modulus of the core samples in this block is used. f max The minimum Young's modulus of the test core from this block is 34078.25 MPa. f min The value is 26218.93 MPa; the results are shown in Table 1; combined with formula (1), the brittleness value of each layer is calculated. f 1- f 3; Combined with formula (2), the average brittleness value is calculated. g m Combined with formula (3), the brittleness deviation coefficient is calculated. g z Combined with formula (4), the brittle complexity index is calculated. B The results are shown in Table 1. Table 1. Brittleness-Complexity Index B Calculation process .

[0022] Step 2: Construct rock sample assemblies composed of rock samples with different brittleness values, and conduct intra-fracture plugging experiments on each rock sample assembly with different temporary plugging concentrations to determine the optimal temporary plugging concentration for each rock sample assembly; the specific details are as follows: (1) A three-layer rock sample group consisting of three rock samples with different brittleness values ​​was prepared. Each of the three rock samples was a cube with a side length of 100 mm. By using multiple rock sample groups with different brittleness values, the uniformity of different crack distributions could be quantitatively evaluated. The brittleness values ​​of each part of the rock sample group and the corresponding brittleness complexity index are shown in Table 2. Table 2. Calculation process of the brittle complexity index ; (2) Temporary plugging experiment in the fracture: For the same rock sample group, the temporary plugging concentration is stacked sequentially to conduct a temporary plugging experiment in the rock sample group and its parallel rock sample group. After the experiment, the rock sample group is CT scanned to determine the number of cracks. Combined with formula (5), where the theoretical maximum number of cracks is 20, the crack diffusion index is shown in Table 3. Table 3 Crack Propagation Index ; (3) Determine the optimal temporary plugging concentration for each rock sample group: Establish the fracture diffusion index for each rock sample group. u With temporary blocking concentration d The regression function is shown in equation (6); the target crack propagation index is set. u m Given a value of 0.8, and combining with equation (7), the optimal temporary plugging concentration for each rock sample group is determined. d h The results are shown in Table 4. Table 4 Optimal Temporary Plugging Concentration for Rock Sample Groups .

[0023] Step 3: Calculate the optimal temporary plugging concentration for the rock sample group according to formula (8). d h With brittle complexity index B The temporary blocking concentration function was obtained by fitting. d u : Optimal temporary plugging concentration for rock sample group d h Corresponding brittle complexity index B Perform a fitting operation to obtain the first fitting coefficient. r The second fitting coefficient is 9.745. b The value is 0.4167, thus yielding the temporary blocking concentration function. d u = 9.745 B +0.4167; The brittle complexity index of the fracturing section of the reservoir to be evaluated, calculated in step 1. BSubstituting into equation (8), the optimal temporary plugging concentration of the fracturing section of the reservoir to be evaluated is calculated. d u It is 2.21 kg / m 3 ; Design fluid volume of the reservoir fracturing section to be evaluated c m 50m 3 For example, by combining equation (9), the optimal amount of temporary plugging agent in the fractured section of the reservoir to be evaluated is calculated. D It weighs 110.5 kg.

[0024] The present invention has been specifically described above through embodiments. It should be noted that these embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way, nor are they limited to the forms disclosed herein, and should not be construed as excluding other embodiments. Modifications and simple variations made by those skilled in the art that do not depart from the technical concept and scope of the present invention are all within the protection scope of the present invention.

Claims

1. A method for determining the dosage of temporary plugging agent in the fracture of a tight reservoir, characterized in that, The method is as follows: The brittle complexity index was calculated based on the brittleness values ​​at different locations in the fracturing section of the reservoir to be evaluated. A rock sample group consisting of rock samples with different brittleness values ​​was constructed to obtain the brittleness complexity index of the corresponding rock sample group. In-fracture plugging experiments with different plugging concentrations were carried out. The fracture diffusion index of the rock sample group was evaluated based on the number of fractures. A regression function between the fracture diffusion index and the plugging concentration of the rock sample group was established. Then, the optimal plugging concentration of the rock sample group was obtained by combining the target fracture diffusion index. The optimal temporary plugging concentration of the rock sample group was fitted with the brittle complexity index to obtain the temporary plugging concentration function; then, combined with the design fluid volume of the fracturing section of the reservoir to be evaluated, the optimal amount of temporary plugging agent in the fracture section of the reservoir to be evaluated was obtained.

2. The method for determining the amount of temporary plugging agent used in the fractured tight reservoir according to claim 1, characterized in that, The specific process for obtaining the brittle complexity index is as follows: take rock samples from different depths of the reservoir to be evaluated to make core samples, obtain the Young's modulus of each core sample, and then calculate the brittleness value of each core sample as the brittleness value at different locations in the fracturing section of the reservoir to be evaluated. Calculate the average brittleness value, and then calculate the brittleness deviation coefficient and the brittle complexity index in sequence.

3. The method for determining the amount of temporary plugging agent used in the fractured tight reservoir according to claim 2, characterized in that, The specific calculation process for the brittleness value is as follows: g i =( f i － f min ) / ( f max － f min ) （1） In the formula: f i For the first i Young's modulus of the core sample, MPa; f max The maximum Young's modulus of the test core in this block, in MPa; f min The minimum Young's modulus of the test core in this block, in MPa; g i For the first i The brittleness value of each core sample is dimensionless. Then calculate the average brittleness value: （2） In the formula: g m This is the average brittleness value, dimensionless; n To obtain the number of core samples, blocks were used.

4. The method for determining the amount of temporary plugging agent used in the fractured tight reservoir according to claim 3, characterized in that, The specific calculation process for the brittle complexity index is as follows: B = g z / g m （4） （3） In the formula: g z This is the brittleness deviation coefficient, which is dimensionless. B It is a brittle complexity index and has no dimension.

5. The method for determining the amount of temporary plugging agent used in the fractured tight reservoir according to claim 1, characterized in that, The specific process for obtaining the fracture diffusion index of the rock sample group is as follows: u = m / m max （5） In the formula: u is the fracture diffusion index of the rock sample group, dimensionless; m The number of cracks; m max The theoretical maximum number of cracks is given by the number of cracks.

6. The method for determining the amount of temporary plugging agent used in the fractured tight reservoir according to claim 5, characterized in that, The specific process for obtaining the optimal temporary plugging concentration of the rock sample group is as follows: The regression function between the fracture diffusion index and the temporary plugging concentration of the rock sample group is established as follows: u = a ln( d )+ b （6） Then, based on the target fracture diffusion index and the following formula, the optimal temporary plugging concentration for the rock sample group is calculated: （7） In the formula: a The coefficient is the first regression coefficient and has no dimension. b The coefficient is the second regression coefficient, which is dimensionless. d Temporary blocking concentration, kg / m³ 3 ; d h The optimal temporary plugging concentration for the rock sample group is kg / m³. 3 ; u m The target crack propagation index is dimensionless.

7. The method for determining the amount of temporary plugging agent used in the fractured tight reservoir according to claim 6, characterized in that, The specific process for obtaining the temporary blocking concentration function is as follows: d u = r˙B + t （8） In the formula: d u The temporary blocking concentration function is expressed in kg / m³. 3 ; r The first fitting coefficient is dimensionless. b The second fitting coefficient is dimensionless.

8. The method for determining the amount of temporary plugging agent used in the fractured tight reservoir according to claim 7, characterized in that, The specific solution process for determining the optimal amount of temporary plugging agent in the fractured section of the reservoir to be evaluated is as follows: D = d u ˙c m （9） In the formula: d u The optimal temporary plugging concentration within the fractured section of the reservoir to be evaluated is kg / m³. 3 ; c m For the design liquid volume, m 3 ; D The optimal amount of temporary plugging agent in the fractured section of the reservoir to be evaluated is kg.

9. The method for determining the amount of temporary plugging agent used in the fracture of a tight reservoir according to claim 1, characterized in that, The number of cracks was obtained by CT scanning of rock samples that had undergone temporary plugging experiments within the cracks.

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