Complex fracture conductivity obtaining method and device, medium and electronic equipment

Abstract

The invention discloses a method and a device for acquiring the flow conductivity of a complex fracture, a medium and electronic equipment, and the method comprises the following steps: (A) extracting the specific form of the complex fracture formed in a stratum by hydrofracture, and calculating the average filling concentration of a proppant in the complex fracture; (B) the complex crack is divided into a plurality of simple and straight crack units, and the closing stress borne by each crack unit in the stratum is calculated; (C) carrying out a simple straight crack conductivity experiment to obtain a change curve of the crack conductivity along with the closed stress, and fitting to obtain a relational expression of the crack conductivity and the closed stress; (D) calculating to obtain the fracture conductivity corresponding to each fracture unit; and (E) calculating the flow conductivity of the whole complex crack by using the crack flow conductivity of each crack unit. The method is reliable in principle, easy to operate and high in practicability, the flow conductivity of the complex crack formed by hydrofracture can be accurately obtained, and then effective guidance is provided for hydrofracture construction effect evaluation.

Description

Technical Field

[0001] The present invention belongs to the technical field of oil and gas exploration and development, and in particular relates to a method, device, medium and electronic equipment for acquiring the conductivity of complex fractures. Background Art

[0002] Hydraulic fracturing technology is an important measure for increasing the production of low-permeability oil and gas reservoirs. Hydraulic fracturing uses a high-pressure ground pump set to pump fracturing fluid into the formation at a displacement that exceeds the absorption capacity of the formation to create cracks, and then continues to inject fracturing fluid with proppants (sand particles) to allow the cracks to continue to extend and fill them with proppants. When the fracturing fluid is returned, under the action of the formation closing stress, the proppants play a role in supporting the cracks in the cracks and prevent the cracks from closing, thereby forming sand-filled cracks with a certain length in the formation that allow fluid flow. At the same time, due to the heterogeneity of the formation rock, the cracks formed in the formation by hydraulic fracturing are not simple straight cracks, but complex cracks with winding and branching structures.

[0003] The conductivity of a fracture refers to the ability of a fracture to allow fluid to pass through it. It is generally expressed as the product of the permeability of the filling layer formed by the proppant (sand particles) in the fracture and the fracture width, and mainly depends on the proppant filling concentration and the closure stress of the fracture. The higher the conductivity of the fracture formed by hydraulic fracturing in the formation, the less resistance the oil and gas will encounter when passing through the fracture, and the greater the production of the oil and gas well. Therefore, the conductivity of the fracture is an important indicator for evaluating the quality of hydraulic fracturing construction, and directly determines the production increase effect of hydraulic fracturing.

[0004] The existing complex fracture conductivity is obtained mainly through experimental testing and theoretical calculation, which are as follows:

[0005] (1) With regard to experimental testing methods, the existing technical solutions mainly achieve actual measurement of conductivity by constructing a complex fracture device. For example, the document with publication number CN104295281A disclosed a shale gas reservoir complex fracture conductivity simulation experimental method on January 21, 2015, which includes: ① selecting a stratum shale core or a shale outcrop in the same layer for making a test piece, and processing the shale material into a shale plate with a length of 17.7 cm, a thickness of 1.5 cm, and a width of 3.8 cm and semicircular ends; ② further processing the plate to meet the requirements of a turning joint or a branching joint; ③ placing the processed plate into a diversion chamber for testing fracture conductivity, and laying a proppant with a certain sand concentration in the middle of the plate; ④ placing the diversion chamber with the proppant and the shale plate in place in a fracture conductivity test device for conducting a conductivity test. Although this method can realize the direct test of conductivity, its experimental objects are mainly simple straight cracks (that is, the cracks need to be in a vertical intersection state), which greatly simplifies the complex crack morphology and cannot obtain the conductivity of real complex cracks.

[0006] (2) Regarding theoretical calculation methods, the existing technical solutions mainly propose a calculation method for the conductivity of complex fractures based on the principle of hydroelectric similarity from the perspective of theoretical derivation. For example, the literature (Wang Xinhui. Fracture network conductivity calculation model based on hydroelectric similarity principle [J]. Petroleum Machinery, 2017, 45(05): 79-85.) discloses a solution method using series-parallel circuits to establish a numerical solution model for the conductivity of complex fractures. Although the principle of this method is relatively reliable, it only stays at the theoretical level and lacks practical operability. In addition, it still takes simple straight fractures as the main object and cannot obtain the conductivity of real complex fractures.

[0007] In summary, the industry has not yet developed practical means and methods for obtaining the conductivity of complex fractures after hydraulic fracturing. Summary of the invention

[0008] The purpose of the present invention is to overcome the above-mentioned problems existing in the prior art and to provide a method, device, medium and electronic equipment for obtaining the conductivity of complex fractures. The present invention has reliable principles, simple operation and strong practicality, and can more accurately obtain the conductivity of complex fractures formed by hydraulic fracturing, thereby providing effective guidance for the evaluation of hydraulic fracturing construction effects.

[0009] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0010] In a first aspect, the present invention provides a method for obtaining the conductivity of a complex fracture, which comprises the following steps:

[0011] (A) extracting the specific morphology of complex fractures formed in the formation by hydraulic fracturing, and calculating the average filling concentration of proppant in the complex fractures;

[0012] (B) dividing the complex fracture into multiple simple straight fracture units based on the specific morphology, and calculating the closure stress of each fracture unit in the formation;

[0013] (C) Conducting a simple straight fracture conductivity experiment using formation rocks to obtain a curve of fracture conductivity changing with closure stress under the condition of average proppant filling concentration, and fitting a relationship between fracture conductivity and closure stress;

[0014] (D) The fracture conductivity corresponding to each fracture unit is calculated using the relationship between fracture conductivity and closure stress;

[0015] (E) The conductivity of the entire complex fracture is calculated using the fracture conductivity of each fracture unit.

[0016] In step (A), the specific morphology of the complex crack mainly refers to the extension path of the crack along the length direction.

[0017] In step (A), the calculation method of the average filling concentration of the proppant in the complex fracture is:

[0018]

[0019] In the formula, K s ——Average filling concentration of proppant in complex fractures, kg / m 2 ;

[0020] M——Total amount of proppant used in hydraulic fracturing process, kg;

[0021] L is the total length of complex cracks, m;

[0022] H is the height of complex cracks, m.

[0023] In step (B), after the complex fractures are divided, the fracture units do not intersect with each other, and the calculation method of the closure stress of the fracture units in the formation is:

[0024]

[0025] In the formula, σ n ——closure stress of crack unit, MPa;

[0026] σ H ——maximum horizontal principal stress of the formation, MPa;

[0027] σ h ——minimum horizontal principal stress of the formation, MPa;

[0028] α is the angle between the fracture unit and the direction of the maximum horizontal principal stress of the formation, degrees.

[0029] In step (C), a simple straight fracture conductivity test using formation rock is carried out according to the following rules:

[0030] (a) The rocks used in the experiment should come from the target formation for hydraulic fracturing;

[0031] (b) The type of proppant used in the experiment should be consistent with the type of proppant used in the hydraulic fracturing process;

[0032] (c) The closing stress value during the experiment needs to change continuously and at equal intervals. The lower limit of the closing stress is set to 0.5 MPa, the upper limit is set to the maximum horizontal principal stress value of the formation, and the change interval is set to 0.5 MPa.

[0033] In step (C), the relationship between the fracture conductivity and the closure stress is fitted as follows:

[0034] F d =f(σ n)

[0035] In the formula, F d ——Crack conductivity, m 3 ;

[0036] σ n ——Closing stress of crack unit, MPa.

[0037] In step (E), the complex fractures include unbranched tortuous complex fractures, multi-branched complex fractures, and combined complex fractures having both unbranched tortuous complex fractures and multi-branched complex fractures; wherein,

[0038] (1) When the complex fracture is a non-branching tortuous complex fracture, the calculation method of the conductivity of the complex fracture is:

[0039]

[0040] In the formula, ——Conductivity of complex fractures, m 3 ;

[0041] M——total length of complex cracks, m;

[0042] L i ——the length of the i-th crack unit, m;

[0043] ——The conductivity of the i-th fracture unit, m 3 ;

[0044] N——Number of crack units, pieces;

[0045] (2) When the complex fracture is a multi-branch complex fracture, the calculation method of the conductivity of the complex fracture is:

[0046]

[0047] In the formula, ——Conductivity of complex fractures, m 3 ;

[0048] M——total length of complex cracks, m;

[0049] ——The conductivity of the i-th fracture unit, m 3 ;

[0050] L i ——the length of the i-th crack unit, m;

[0051] (3) When the complex fracture is a combined complex fracture, the conductivity of the complex fracture is calculated based on the calculation method of the unbranched tortuous complex fracture and the calculation method of the multi-branched complex fracture.

[0052] In a second aspect, the present invention provides a device for obtaining the conductivity of a complex fracture, comprising:

[0053] An extraction unit, used to extract the specific morphology of complex fractures formed in the formation by hydraulic fracturing;

[0054] The first calculation unit is used to calculate the average filling concentration of the proppant in the complex fracture;

[0055] Division unit, used to divide complex fractures into multiple simple straight fracture units according to specific shapes;

[0056] The second calculation unit is used to calculate the closure stress of each fracture unit in the formation;

[0057] An experiment acquisition unit is used to carry out a simple straight fracture conductivity experiment using formation rocks, to obtain a curve of fracture conductivity changing with closure stress, and to fit a relationship between fracture conductivity and closure stress;

[0058] A third calculation unit is used to calculate the fracture conductivity corresponding to each fracture unit by using a relationship between the fracture conductivity and the closure stress;

[0059] The fourth calculation unit is used to calculate the conductivity of the entire complex fracture using the fracture conductivity of each fracture unit.

[0060] In a third aspect, the present invention provides a computer-readable storage medium storing a computer program, which implements the method for acquiring the conductivity of complex fractures when executed by a processor.

[0061] In a fourth aspect, the present invention provides an electronic device, the electronic device comprising:

[0062] A memory storing executable instructions;

[0063] The processor runs the executable instructions in the memory to implement the method for acquiring the conductivity of complex fractures.

[0064] By adopting the above technical solution, the beneficial technical effects of the present invention are:

[0065] 1. The acquisition method of the present invention comprises five steps, wherein:

[0066] Advantages of step A: Based on the specific morphology of the extracted complex fractures, the calculation method of the average proppant filling concentration is quantitatively clarified from the physical meaning, which provides a basis for obtaining the conductivity of complex fractures.

[0067] Advantages of step B: The complex cracks are divided into multiple simple straight crack units using a discrete method, and the closing stress of each unit is calculated separately, which simplifies the originally complex problem and reduces the difficulty of solving the problem.

[0068] Advantages of step C: By testing the curve of fracture conductivity changing with closure stress through indoor experiments and fitting the mathematical relationship between fracture conductivity and closure stress, the specific value of fracture conductivity under any closure stress condition can be quickly obtained without conducting conductivity experiments for all possible closure stress conditions.

[0069] Advantages of step D: The fracture conductivity corresponding to each fracture unit can be obtained quickly, quantitatively and accurately, providing a basis for obtaining the conductivity of complex fractures.

[0070] Advantages of step E: Based on a reliable theoretical basis, a direct calculation method for the conductivity of complex fractures is given, which can quickly, quantitatively and accurately obtain the conductivity of any complex fractures.

[0071] In summary, the present invention has reliable principles, simple operation, and strong practicability, and can relatively accurately obtain the conductivity of complex cracks formed by hydraulic fracturing, thereby providing effective guidance for the evaluation of hydraulic fracturing construction effects.

[0072] 2. The present invention adopts a combination of experimental and theoretical methods to propose a practical method for obtaining the conductivity of complex fractures. Each step has a strong theoretical basis and operability, and can quickly, quantitatively and accurately obtain the conductivity of any complex fracture, providing key parameters for the evaluation of hydraulic fracturing effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 is a flow chart of the present invention;

[0074] Figure 2 It is a schematic diagram of the specific morphology of complex fractures formed in the formation after hydraulic fracturing;

[0075] Figure 3 It is a schematic diagram of the result of dividing a complex fracture into multiple simple straight fracture units;

[0076] Figure 4 This is the curve of fracture conductivity changing with closure stress obtained through experiments. DETAILED DESCRIPTION

[0077] Example 1

[0078] The present invention provides a method for obtaining the conductivity of a complex fracture, which comprises the following steps:

[0079] (A) Extract the specific morphology of complex fractures formed by hydraulic fracturing in the formation and calculate the average filling concentration K of the proppant in the complex fractures s .

[0080] The specific form of complex fractures mainly refers to the extension path of the fractures along the length direction. The average filling concentration of proppant in complex fractures K s The calculation method is:

[0081]

[0082] In the formula, K s ——Average filling concentration of proppant in complex fractures, kg / m 2 ;

[0083] M——Total amount of proppant used in hydraulic fracturing process, kg;

[0084] L is the total length of the complex crack (obtained according to the extension path of the crack along the length direction), m;

[0085] H is the height of complex fractures (because the fractures formed by hydraulic fracturing need to penetrate the entire oil / gas reservoir section in the height direction, the height of complex fractures is regarded as equal to the thickness of the oil / gas reservoir section and remains constant), m.

[0086] (B) Based on the specific morphology obtained in step (A), the complex fracture is divided into a plurality of simple straight fracture units, and the closure stress of each fracture unit in the formation is calculated.

[0087] Among them, when dividing complex fractures, the intersection of two fracture units should be avoided, that is, the fracture units do not intersect after the complex fractures are divided, otherwise the subsequent calculation cannot be carried out normally. This goal can be achieved by reducing the length of the divided fracture unit. It should be noted that the simple fracture combination obtained by division is only an approximation of the original complex fracture. The smaller the length of the fracture unit, the finer the division, and the higher the approximation of the original complex fracture. At the same time, the calculation method of the closure stress of the fracture unit in the formation is:

[0088]

[0089] In the formula, σ n ——closure stress of crack unit, MPa;

[0090] σ H ——maximum horizontal principal stress of the formation, MPa;

[0091] σ h ——minimum horizontal principal stress of the formation, MPa;

[0092] α is the angle between the fracture unit and the direction of the maximum horizontal principal stress of the formation, degrees.

[0093] (C) Based on the results of step (A), a simple straight fracture conductivity test was carried out using formation rocks. The proppant filling concentration in the experiment was set to K s , thereby obtaining the average proppant filling concentration K s Fracture conductivity F under the condition d With closing stress σ n The change curve of the fracture conductivity F is obtained by fitting d and closing stress σ n The relationship formula.

[0094] Among them, the fracture conductivity F is obtained by fitting d and closing stress σ n The relationship is:

[0095] F d =f(σ n )

[0096] In the formula, F d ——Crack conductivity, m 3 ;

[0097] σ n ——Closing stress of crack unit, MPa.

[0098] It should be noted that when conducting a simple straight fracture conductivity experiment, in order to ensure that the obtained fracture conductivity versus closure stress curve can reflect the objective law and has a high degree of accuracy, the relevant experimental materials or parameters should be carried out according to the following rules:

[0099] (a) The rock used in the experiment should come from the target formation for hydraulic fracturing.

[0100] (b) The type of proppant used in the experiment should be consistent with the type of proppant used in the hydraulic fracturing process.

[0101] (c) The closing stress value during the experiment needs to change continuously and at equal intervals. The lower limit of the closing stress is set to 0.5 MPa, the upper limit is set to the maximum horizontal principal stress value of the formation, and the change interval is set to 0.5 MPa.

[0102] (D) Based on the results of step (B) and step (C), the fracture conductivity F d and closing stress σ n The fracture conductivity corresponding to each fracture unit is calculated by the relationship between

[0103] (E) Based on the result of step (D), the conductivity of the entire complex fracture is calculated using the fracture conductivity of each fracture unit.

[0104] Since complex fractures have different morphologies, they usually include unbranched tortuous complex fractures, multi-branched complex fractures, and combined complex fractures that have both unbranched tortuous complex fractures and multi-branched complex fractures. Therefore, when calculating the conductivity of complex fractures, it is necessary to calculate them separately for different morphologies.

[0105] Specifically, assuming that a complex fracture is divided into N fracture units, the calculation methods of their conductivity are as follows:

[0106] (1) If N fracture units form a complex fracture without branches (similar to N resistors forming a series circuit), the calculation method for the conductivity of the complex fracture is:

[0107]

[0108] In the formula, ——Conductivity of complex fractures, m 3 ;

[0109] M is the total length of complex fractures (equal to the sum of the lengths of each fracture unit), m;

[0110] L i ——the length of the i-th crack unit, m;

[0111] ——The conductivity of the i-th fracture unit, m 3 ;

[0112] N is the number of crack units.

[0113] (2) If N fracture units form a multi-branch complex fracture with N branches (similar to N resistors forming a parallel circuit), the calculation method for the conductivity of the complex fracture is:

[0114]

[0115] In the formula, ——Conductivity of complex fractures, m 3 ;

[0116] M is the total length of complex fractures (equal to the sum of the lengths of each fracture unit), m;

[0117] ——The conductivity of the i-th fracture unit, m 3 ;

[0118] L i ——the length of the i-th crack unit, m;

[0119] (3) If N crack units form a complex crack that has both a tortuous structure and a multi-branched structure (similar to N resistors forming a circuit that combines series and parallel connections), it can be regarded as a complex crack composed of multiple tortuous cracks and multi-branched cracks. Combining the calculation methods in (1) and (2) above and the specific morphology of the complex cracks, a calculation method for the conductivity of the combined complex cracks can be obtained.

[0120] In addition, the applicant also provides a derivation process for the calculation method of non-branching tortuous complex cracks and the calculation method of multi-branching complex cracks, as follows:

[0121] The fluid flow in the fracture can be described by Darcy's law (Zhen Huaibin, Zhao Haifeng, Wang Chengwang, et al. Physical simulation of conductivity of artificial fractures in sandstone, Xinjiang Petroleum Geology, 2021, 42(01): 81-87.):

[0122]

[0123] Where, Q is the flow rate of fluid passing through the crack, m 3 / s;

[0124] K——Permeability of the proppant filling layer in the fracture, m 2 ;

[0125] A——the area of ​​the crack flow cross section, m 2 ;

[0126] μ——fluid viscosity, Pa·s;

[0127] L——crack length, m;

[0128] ΔP——pressure difference between crack inlet and outlet, Pa.

[0129] In formula (1), the area A of the crack flow cross section can be expressed as:

[0130] A=W·H (2)

[0131] Where A is the area of ​​the crack flow cross section, m 2 ;

[0132] W——crack width, m;

[0133] H——crack height, m.

[0134] Substituting formula (2) into formula (1), we get:

[0135]

[0136] Where, Q is the flow rate of fluid passing through the crack, m 3 / s;

[0137] K——Permeability of the proppant filling layer in the fracture, m 2 ;

[0138] W——crack width, m;

[0139] H——crack height, m;

[0140] μ——fluid viscosity, Pa·s;

[0141] L——crack length, m;

[0142] ΔP——pressure difference between crack inlet and outlet, Pa.

[0143] The fracture conductivity can be expressed as (Zhen Huaibin, Zhao Haifeng, Wang Chengwang, et al. Physical simulation of artificial fracture conductivity in conglomerate. Xinjiang Petroleum Geology, 2021, 42(01): 81-87.):

[0144] F d =KW (4)

[0145] In the formula, F d ——The conductivity of the crack, m 3 ;

[0146] K——Permeability of the proppant filling layer in the fracture, m 2 ;

[0147] W——crack width, m.

[0148] Substituting formula (4) into formula (3) yields:

[0149]

[0150] Where, Q is the flow rate of fluid passing through the crack, m 3 / s;

[0151] F d ——The conductivity of the crack, m 3 ;

[0152] H——crack height, m;

[0153] μ——fluid viscosity, Pa·s;

[0154] L——crack length, m;

[0155] ΔP——pressure difference between crack inlet and outlet, Pa.

[0156] Based on the principle of hydroelectric similarity, the flow of fluid in the fracture can be regarded as the flow of current in the circuit, and the resistance of the fracture to the fluid can be regarded as the resistance in the circuit (Wang Xinhui. Calculation model of fracture network conductivity based on hydroelectric similarity principle. Petroleum Machinery, 2017, 45(05): 79-85.), so formula (5) can be further expressed as:

[0157]

[0158] Where, Q is the flow rate of fluid passing through the crack, m 3 / s;

[0159] ΔP——pressure difference between crack inlet and outlet, Pa;

[0160] R——Resistance of crack to fluid flow, Pa·s·m -3 ;

[0161] μ——fluid viscosity, Pa·s;

[0162] L——crack length, m;

[0163] F d ——The conductivity of the crack, m 3 ;

[0164] H——crack height, m.

[0165] Now assume that a complex fracture is divided into N fracture units. Based on equation (6), the flow equation in each fracture unit can be written as:

[0166]

[0167] In the formula, Q i ——The flow rate of fluid passing through the i-th fracture unit, m 3 / s;

[0168] ΔP i ——pressure difference between the inlet and outlet of the i-th fracture unit, Pa;

[0169] R i ——The resistance of the i-th fracture unit to fluid flow, Pa·s·m -3 .

[0170] Similarly, the overall flow equation of complex fractures can be expressed as:

[0171]

[0172] In the formula, Q s ——The flow rate of fluid passing through the entire complex fracture, m 3 / s;

[0173] ΔPs ——The pressure difference between the entrance and exit of the entire complex crack, Pa;

[0174] R s ——The resistance of the entire complex fracture to fluid flow, Pa·s·m -3 .

[0175] (a) If N fracture units form a complex fracture without branches (i.e., a zigzag fracture, similar to N resistors forming a series circuit), based on the principle of conservation of matter, the flow rate of fluid passing through each fracture unit should be equal, and the following relationship can be obtained:

[0176]

[0177] Where ΔP i ——pressure difference between the inlet and outlet of the i-th fracture unit, Pa;

[0178] Q i ——The flow rate of fluid passing through the i-th fracture unit, m 3 / s;

[0179] R i ——The resistance of the i-th fracture unit to fluid flow, Pa·s·m -3 ;

[0180] Q s ——The flow rate of fluid through the entire complex fracture (related to Q i equal), m 3 / s;

[0181] N is the number of crack units.

[0182] Substituting formula (8) into formula (9) yields:

[0183]

[0184] Where ΔP i ——Pressure difference between the inlet and outlet of the i-th fracture unit, Pa.

[0185] ΔP s ——The pressure difference between the entrance and exit of the entire complex crack, Pa;

[0186] R s ——The resistance of the entire complex fracture to fluid flow, Pa·s·m -3 ;

[0187] R i ——The resistance of the i-th fracture unit to fluid flow, Pa·s·m -3 ;

[0188] N is the number of crack units.

[0189] Because the fracture units are arranged end to end, that is, the outlet of the i-th fracture unit is the same as the inlet of the i+1-th fracture unit, the sum of the pressure differences between the inlet and outlet of each fracture unit should be equal to the pressure difference between the inlet and outlet of the entire complex fracture:

[0190]

[0191] Where ΔP i ——pressure difference between the inlet and outlet of the i-th fracture unit, Pa;

[0192] ΔP s ——The pressure difference between the entrance and exit of the entire complex crack, Pa.

[0193] Substituting formula (11) into formula (10) yields:

[0194]

[0195] In the formula, R s ——The resistance of the entire complex fracture to fluid flow, Pa·s·m -3 ;

[0196] R i ——The resistance of the i-th fracture unit to fluid flow, Pa·s·m -3 ;

[0197] N is the number of crack units.

[0198] Substituting the expression of R in formula (6) into formula (12), we get:

[0199]

[0200] In the formula, ——Conductivity of complex fractures, m 3 ;

[0201] M is the total length of complex fractures (equal to the sum of the lengths of each fracture unit), m;

[0202] L i ——the length of the i-th crack unit, m;

[0203] ——The conductivity of the i-th fracture unit, m 3 ;

[0204] N is the number of crack units.

[0205] Furthermore, by transforming equation (13), we can obtain the conductivity expression of non-branching tortuous complex fractures.

[0206] (b) If N fracture units form a multi-branch complex fracture with N branches (i.e., a multi-branch fracture with N branches, similar to N resistors forming a parallel circuit), based on the principle of conservation of matter, the total flow rate of the fluid through the complex fracture should be equal to the sum of the flow rates of the fluid through each fracture unit, then the following relationship holds:

[0207]

[0208] In the formula, Q s ——The flow rate of fluid passing through the entire complex fracture, m 3 / s;

[0209] Q i ——The flow rate of fluid passing through the i-th fracture unit, m 3 / s;

[0210] ΔP i ——pressure difference between the inlet and outlet of the i-th fracture unit, Pa;

[0211] R i ——The resistance of the i-th fracture unit to fluid flow, Pa·s·m -3 ;

[0212] N is the number of crack units.

[0213] Similarly, substituting formula (8) into formula (15) yields:

[0214]

[0215] Where ΔP s ——The pressure difference between the entrance and exit of the entire complex crack, Pa;

[0216] R s ——The resistance of the entire complex fracture to fluid flow, Pa·s·m -3 ;

[0217] ΔP i ——pressure difference between the inlet and outlet of the i-th fracture unit, Pa;

[0218] R i ——The resistance of the i-th fracture unit to fluid flow, Pa·s·m -3 ;

[0219] N is the number of crack units.

[0220] Because the conductivity of the fracture unit depends on the nature of the fracture itself, and has nothing to do with the pressure difference between the fracture inlet and outlet. The pressure difference between the fracture inlet and outlet will only affect the flow rate of the fluid through the fracture. At the same time, each fracture unit constitutes a multi-branch fracture, and its outlets are the same, so the pressure difference between the inlet and outlet of each fracture unit can be regarded as the same, and equal to the pressure difference between the inlet and outlet of the entire complex fracture, that is:

[0221] ΔP s =ΔP i (17)

[0222] Where ΔP s ——The pressure difference between the entrance and exit of the entire complex crack, Pa;

[0223] ΔP i ——Pressure difference between the inlet and outlet of the i-th fracture unit, Pa.

[0224] Substituting formula (17) into formula (16), we have:

[0225]

[0226] In the formula, R s ——The resistance of the entire complex fracture to fluid flow, Pa·s·m -3 ;

[0227] R i ——The resistance of the i-th fracture unit to fluid flow, Pa·s·m -3 ;

[0228] N is the number of crack units.

[0229] Substituting the expression of R in equation (6) into equation (18), we can obtain the conductivity expression of multi-branch complex fractures.

[0230] It should be noted that the conductivity of the fracture mainly depends on the proppant filling concentration and the closure stress of the fracture. The complex fractures formed by hydraulic fracturing are divided into several simple straight fracture units. Since the proppant filling concentration in different fracture units can be regarded as the same, the difference in their conductivity mainly comes from the different closure stresses. Based on the above understanding, the present invention first extracts the specific morphology of the complex fractures in the formation and calculates the average filling concentration of the proppant in the complex fractures; secondly, the complex fractures are divided into a plurality of simple straight fracture units, and the closure stress of each fracture unit is calculated; then, the simple straight fracture conductivity experiment is carried out using the formation rock to obtain the curve of the change of fracture conductivity with closure stress under the condition of the average proppant filling concentration, and the specific functional relationship is fitted; then, the conductivity corresponding to each fracture unit is calculated based on the functional relationship between the fracture conductivity and the closure stress; finally, the conductivity of the entire complex fracture can be obtained by further calculation using the conductivity of each fracture unit.

[0231] Example 2

[0232] The present invention provides a device for obtaining the conductivity of complex fractures, which comprises:

[0233] The extraction unit is used to extract the specific morphology of complex fractures formed in the formation by hydraulic fracturing.

[0234] The first calculation unit is used to calculate the average filling concentration of the proppant in the complex fracture.

[0235] The division unit is used to divide the complex fracture into multiple simple straight fracture units according to the specific shape.

[0236] The second calculation unit is used to calculate the closing stress of each fracture unit in the formation.

[0237] The experimental acquisition unit is used to carry out a simple straight fracture conductivity experiment using formation rocks, to obtain a curve of fracture conductivity changing with closure stress, and to fit a relationship between fracture conductivity and closure stress.

[0238] The third calculation unit is used to calculate the fracture conductivity corresponding to each fracture unit by using the relationship between the fracture conductivity and the closure stress.

[0239] The fourth calculation unit is used to calculate the conductivity of the entire complex fracture using the fracture conductivity of each fracture unit.

[0240] It should be noted that, based on the same innovative concept, the implementation scheme and method of the device for obtaining the conductivity of complex fractures provided in this embodiment are similar to each other, so the implementation of the specific device in this embodiment can refer to the implementation of the aforementioned method, and the repeated parts will not be repeated.

[0241] Example 3

[0242] The present invention provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, the method for obtaining the conductivity of complex fractures is implemented.

[0243] The computer-readable storage medium of this embodiment stores non-transitory computer-readable instructions, and when the non-transitory computer-readable instructions are executed by a processor, all or part of the steps of the aforementioned embodiment method are executed.

[0244] The above-mentioned computer-readable storage media include, but are not limited to: optical storage media (e.g., CD-ROM and DVD), magneto-optical storage media (e.g., MO), magnetic storage media (e.g., magnetic tape or mobile hard disk), media with built-in rewritable non-volatile memory (e.g., memory card) and media with built-in ROM (e.g., ROM box).

[0245] Example 4

[0246] The present invention provides an electronic device, the electronic device comprising:

[0247] A memory storing executable instructions;

[0248] The processor runs the executable instructions in the memory to implement the method for acquiring the conductivity of complex fractures.

[0249] The electronic device of this embodiment includes a memory and a processor, and the memory is used to store non-temporary computer-readable instructions. Specifically, the memory may include one or more computer program products, and the computer program product may include various forms of computer-readable storage media, such as volatile memory and / or non-volatile memory, the volatile memory may include, for example, random access memory (RAM) and / or cache memory (cache), etc., and the non-volatile memory may include, for example, read-only memory (ROM), hard disk, flash memory, etc. The processor may be a central processing unit (CPU) or other forms of processing units with data processing capabilities and / or instruction execution capabilities, and may control other components in the electronic device to perform desired functions. In this embodiment, the processor is used to run the computer-readable instructions stored in the memory.

[0250] The method of the present invention is further described in detail below with reference to the accompanying drawings and specific examples.

[0251] The oil and gas resources in the tight sandstone reservoirs of the Sichuan Basin are very rich. A large number of hydraulic fracturing operations have been carried out in the early stage. However, due to the lack of effective methods to obtain the conductivity of complex fractures, the hydraulic fracturing effect has not been evaluated from the perspective of fracture conductivity, resulting in limitations in the design and optimization of hydraulic fracturing schemes.

[0252] Taking the hydraulic fracturing construction of a well in the tight sandstone reservoir in the Sichuan Basin as an example, the method provided by the present invention is used to obtain the conductivity of complex fractures after hydraulic fracturing. The main steps are as follows:

[0253] (A) Extract the specific morphology of complex fractures formed in the formation by hydraulic fracturing (see Figure 2 ), the total length of the complex fracture is 214m, the height is 40m, and the total amount of proppant added during the hydraulic fracturing construction is 47080kg. From this, the average filling concentration K of the proppant in the complex fracture can be calculated s 5.5kg / m 2 .

[0254] (B) Divide the complex fracture into 14 straight fracture units (see Figure 3 ), the minimum horizontal principal stress of the target formation is 23MPa, and the maximum horizontal principal stress is 41MPa. From this, the closing stress of each fracture unit in the formation can be calculated, and the results are shown in the following table.

[0255] Crack unit number Crack unit length / m Angle with the maximum horizontal principal stress direction / degree Closing stress / MPa 1 10 2 23.0 2 15 11 23.7 3 12 55 35.1 4 23 178 23.0 5 21 178 23.0 6 17 158 25.5 7 11 5 23.1 8 12 42 31.1 9 7 39 30.1 10 9 162 24.7 11 22 155 26.2 12 18 15 24.2 13 16 133 32.6 14 21 5 23.1

[0256] (C) A simple straight fracture conductivity test was conducted using the target formation rock, with the proppant filling concentration set at 5.5 kg / m 2 The proppant type is 40 / 70 mesh ceramsite, which is consistent with the proppant type used in the hydraulic fracturing process. The closing stress value changes continuously and at equal intervals during the experiment. The lower limit of the closing stress is set to 0.5MPa, the upper limit is set to 41MPa, and the change interval is set to 0.5MPa. Finally, the fracture conductivity F d With closing stress σ n The change curve F d -σ n (See Figure 4 ), and fitted to get F d With σ n The relationship is as follows:

[0257]

[0258] (D) Combined with the calculation results of the closure stress of each fracture unit and the fracture conductivity F d and closing stress σ nThe conductivity of each fracture unit is calculated based on the relationship between them. The results are shown in the following table.

[0259] Crack unit number Closing stress / MPa <![CDATA[Conductivity / 10 -14 m 3 > 1 23.0 26.36 2 23.7 25.61 3 35.1 16.87 4 23.0 26.36 5 23.0 26.36 6 25.5 23.61 7 23.1 26.22 8 31.1 19.19 9 30.1 19.82 10 24.7 24.43 11 26.2 22.95 12 24.2 25.00 13 32.6 18.20 14 23.1 26.22

[0260] (E) According to Figure 2 The specific morphology of complex fractures in the present invention is combined with the conductivity calculation rules described in the present invention to obtain the calculation formula of the conductivity of complex fractures as follows:

[0261] (1) For the complex cracks ①-③ composed of crack units ①, ②, and ③, they can be regarded as three resistors in series, and the calculation formula for their conductivity is:

[0262]

[0263] In the formula, ——Flow conductivity of complex fractures ①-③ (similar to the following), m 3 ;

[0264] L 1-3 ——The length of complex cracks ①-③ (similar to the following), m;

[0265] L 1 , L 2 , L 3 ——The length of crack units ①, ②, ③ (similar to the following), m;

[0266] ——Conductivity of fracture units ①, ②, ③ (similar to the following), m 3 .

[0267] (2) Similarly, for the complex fracture ④-⑥ composed of fracture units ④, ⑤, and ⑥, the calculation formula for its conductivity is:

[0268]

[0269] (3) The complex fracture ①-⑥ composed of fracture units ①, ②, ③, ④, ⑤, and ⑥ can be regarded as a combination of complex fractures ①-③ and complex fractures ④-⑥, which are two resistors in parallel. The calculation formula for its conductivity is:

[0270]

[0271] (4) For the complex cracks ①-⑧ composed of crack units ①, ②, ③, ④, ⑤, ⑥, ⑦, and ⑧, it can be regarded as a combination of complex cracks ①-⑥ and crack units ⑦ and ⑧, which are three resistors in series. The calculation formula for its conductivity is:

[0272]

[0273] (5) By analogy, the calculation formulas for the conductivity of each level of complex fractures and the entire complex fracture can be obtained as follows:

[0274]

[0275]

[0276]

[0277]

[0278] (6) Substituting the length and conductivity of each fracture unit into the above formula, the conductivity of each level of complex fractures and the entire complex fracture can be calculated in turn, as shown in the following table. The conductivity of the complex fractures formed in the formation after this hydraulic fracturing is 108.82×10 -14 m 3 .

[0279]

[0280] In order to verify the accuracy of the calculation results of this method, a production test operation was further carried out on the well to invert the actual conductivity of the complex fractures formed by hydraulic fracturing. During the production test, the formation pressure was 42MPa, the bottom hole flow pressure was 33MPa, the fluid viscosity was 12mPa·s, and the single well production was 13.96m 3 / d, the actual conductivity of the complex fracture is inverted using the following formula (Formula 5 in Step E) to obtain 115.23×10 -14 m 3 .

[0281]

[0282] Wherein, ΔP = 42-33 = 9 MPa; H = 40 m; L = 214 m; μ = 12 mPa·s; Q = 13.96 m 3 / d.

[0283] It can be seen that the error of the conductivity calculated by this method is only 5.56%, which is highly accurate and thus has high innovation and practicality.

[0284] The above description is only a specific implementation mode of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other alternative features that are equivalent or have similar purposes; all the disclosed features, or all the steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A method for obtaining the conductivity of complex fractures, characterized in that The following steps are involved: (A) extracting the specific morphology of complex fractures formed in the formation by hydraulic fracturing, and calculating the average filling concentration of proppant in the complex fractures; (B) dividing the complex fracture into multiple simple straight fracture units based on the specific morphology, and calculating the closure stress of each fracture unit in the formation; (C) Conducting a simple straight fracture conductivity experiment using formation rocks to obtain a curve of fracture conductivity changing with closure stress under the condition of average proppant filling concentration, and fitting a relationship between fracture conductivity and closure stress; (D) The fracture conductivity corresponding to each fracture unit is calculated using the relationship between fracture conductivity and closure stress; (E) The conductivity of the entire complex fracture is calculated using the fracture conductivity of each fracture unit.

2. The method for obtaining the conductivity of complex fractures according to claim 1, characterized in that: In step (A), the specific shape of the complex crack refers to the extension path of the crack along the length direction.

3. The method for obtaining the conductivity of complex fractures according to claim 1, characterized in that: In step (A), the calculation method of the average filling concentration of the proppant in the complex fracture is: In the formula, K s ——Average filling concentration of proppant in complex fractures, kg / m 2 ; M——Total amount of proppant used in hydraulic fracturing process, kg; L is the total length of complex cracks, m; H is the height of complex cracks, m.

4. The method for obtaining the conductivity of complex fractures according to claim 3, characterized in that: In step (B), after the complex fractures are divided, the fracture units do not intersect with each other, and the calculation method of the closure stress of the fracture units in the formation is: In the formula, σ n ——closure stress of crack unit, MPa; σ H ——maximum horizontal principal stress of the formation, MPa; σ h ——minimum horizontal principal stress of the formation, MPa; α is the angle between the fracture unit and the direction of the maximum horizontal principal stress of the formation, degrees.

5. The method for obtaining the conductivity of complex fractures according to claim 1, characterized in that: In step (C), a simple straight fracture conductivity test using formation rock is carried out according to the following rules: (a) The rocks used in the experiment should come from the target formation for hydraulic fracturing; (b) The type of proppant used in the experiment should be consistent with the type of proppant used in the hydraulic fracturing process; (c) The closing stress value during the experiment needs to change continuously and at equal intervals. The lower limit of the closing stress is set to 0.5 MPa, the upper limit is set to the maximum horizontal principal stress value of the formation, and the change interval is set to 0.5 MPa.

6. The method for obtaining the conductivity of complex fractures according to claim 4, characterized in that: In step (C), the relationship between the fracture conductivity and the closure stress is fitted as follows: F d =f(σ n ) In the formula, F d ——Crack conductivity, m 3 ; σ n ——Closing stress of crack unit, MPa.

7. The method for obtaining the conductivity of complex fractures according to claim 6, characterized in that: In step (E), the complex fractures include unbranched tortuous complex fractures, multi-branched complex fractures, and combined complex fractures having both unbranched tortuous complex fractures and multi-branched complex fractures; wherein, (1) When the complex fracture is a non-branching tortuous complex fracture, the calculation method of the conductivity of the complex fracture is: In the formula, ——Conductivity of complex fractures, m 3 ; M——total length of complex cracks, m; L i ——the length of the i-th crack unit, m; ——The conductivity of the i-th fracture unit, m 3 ; N——Number of crack units, pieces; (2) When the complex fracture is a multi-branch complex fracture, the calculation method of the conductivity of the complex fracture is: In the formula, ——Conductivity of complex fractures, m 3 ; M——total length of complex cracks, m; ——The conductivity of the i-th fracture unit, m 3 ; L i ——the length of the i-th crack unit, m; (3) When the complex fracture is a combined complex fracture, the conductivity of the complex fracture is calculated based on the calculation method of the unbranched tortuous complex fracture and the calculation method of the multi-branched complex fracture.

8. A device for obtaining the conductivity of complex fractures, characterized in that include: An extraction unit, used to extract the specific morphology of complex fractures formed in the formation by hydraulic fracturing; The first calculation unit is used to calculate the average filling concentration of the proppant in the complex fracture; Division unit, used to divide complex fractures into multiple simple straight fracture units according to specific shapes; The second calculation unit is used to calculate the closure stress of each fracture unit in the formation; An experiment acquisition unit is used to carry out a simple straight fracture conductivity experiment using formation rocks, to obtain a curve of fracture conductivity changing with closure stress, and to fit a relationship between fracture conductivity and closure stress; A third calculation unit is used to calculate the fracture conductivity corresponding to each fracture unit by using a relationship between the fracture conductivity and the closure stress; The fourth calculation unit is used to calculate the conductivity of the entire complex fracture using the fracture conductivity of each fracture unit.

9. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method for acquiring the complex fracture conductivity according to any one of claims 1 to 7 is implemented.

10. An electronic device, characterized in that: The electronic device includes: A memory storing executable instructions; The processor runs the executable instructions in the memory to implement the method for acquiring the conductivity of a complex fracture according to any one of claims 1 to 7.

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