Method, device, medium and electronic equipment for obtaining complex fracture conductivity

Abstract

The application discloses a kind of acquisition methods, devices, media and electronic equipment of complex fracture conductivity, and its method includes: (A) extracting the specific form of complex fracture formed in stratum by hydraulic fracturing, calculating the average filling concentration of proppant in complex fracture;(B) complex fracture is divided into multiple simple straight fracture units, and the closure stress suffered by each fracture unit in stratum is calculated;(C) carry out simple straight fracture conductivity experiment, obtain the change curve of fracture conductivity with closure stress, and the relationship between fracture conductivity and closure stress is fitted;(D) the fracture conductivity corresponding to each fracture unit is calculated;(E) the fracture conductivity of each fracture unit is used to calculate the conductivity of the whole complex fracture.The application principle is reliable, simple to operate, and has strong practicability, can more accurately obtain the conductivity of complex fracture formed by hydraulic fracturing, and then provide effective guidance for hydraulic fracturing construction effect evaluation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of oil and gas exploration and development, and particularly relates to a method and device for obtaining complex fracture conductivity, a medium and an electronic device. BACKGROUND

[0002] Hydraulic fracturing technology is an important measure for stimulation and reconstruction of low-permeability oil and gas reservoirs. Hydraulic fracturing is to use a high-pressure pump group on the ground to pump fracturing fluid into the formation at a flow rate exceeding the absorption capacity of the formation to generate a fracture, and then continue to inject fracturing fluid with proppants (sand particles) to make the fracture continue to extend and fill the proppants, when the fracturing fluid is returned, the proppants in the fracture play a role in supporting the fracture under the action of the closure stress of the formation, preventing the fracture from closing, thereby forming a sand-filled fracture with a certain length in the formation, allowing fluid to flow. At the same time, due to the heterogeneity of the formation rock, the fracture formed by hydraulic fracturing in the formation is not a simple straight fracture, but a complex fracture with a branching structure.

[0003] The conductivity of the fracture refers to the ability of the fracture to allow fluid to pass through, which is generally represented by the product of the permeability of the proppant (sand particle) filling layer formed in the fracture and the width of the fracture, 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 smaller the resistance of oil and gas flowing through the fracture, and the greater the production of the oil and gas well. Therefore, the fracture conductivity is an important indicator for evaluating the degree of hydraulic fracturing construction, and directly determines the stimulation effect of hydraulic fracturing.

[0004] The existing methods for obtaining complex fracture conductivity mainly include experimental testing and theoretical calculation, which are as follows:

[0005] (1) For the experimental testing method, the existing technical solutions mainly realize actual measurement of the conductivity by constructing a complex fracture device. For example, a shale gas reservoir complex fracture conductivity simulation experiment method is disclosed in document CN104295281A, which was published on January 21, 2015, and includes: ① selecting formation shale core or shale outcrop of the same layer to make a test piece, and processing the shale material into a shale rock plate with a length of 17.7 cm, a thickness of 1.5 cm, and a width of 3.8 cm with a semicircular shape at both ends; ② further processing the rock plate to meet the requirements of a turning fracture or a branch fracture; ③ placing the processed rock plate into a conductivity chamber for testing the fracture conductivity, and placing proppants with a certain sand laying concentration in the middle of the rock plate; ④ placing the conductivity chamber with the proppants and the shale rock plate into a fracture conductivity testing device to test the conductivity. Although this method can directly test the conductivity, the experimental object is mainly a simple straight fracture (i.e., the fracture needs to be in a perpendicular intersection state), and the complex fracture morphology is greatly simplified, so it is impossible to obtain the conductivity of the real complex fracture.

[0006] (2) For theoretical calculation means, the prior art mainly proposes a complex fracture conductivity calculation idea based on the water and electricity similarity principle from the perspective of theoretical derivation. For example, the document (Wang Xin-hui. Fracture network conductivity calculation model based on water and electricity similarity principle [J]. Petroleum machinery, 2017, 45(05): 79-85.) discloses a numerical solution model of complex fracture conductivity by means of the solution of series-parallel circuit. Although the principle of this method is relatively reliable, it only stays at the theoretical level and lacks practical operability, and it is still mainly aimed at simple straight fractures, and cannot obtain the conductivity of real complex fractures.

[0007] In summary, there is no practical means and method for obtaining the conductivity of complex fractures after hydraulic fracturing in the industry at present. SUMMARY

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

[0009] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

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

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

[0012] (B) Dividing the complex fractures into a plurality of simple straight fracture units based on the specific form, and calculating the closure stress suffered by each fracture unit in the formation;

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

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

[0015] (E) Calculating the conductivity of the whole complex fracture by using the fracture conductivity of each fracture unit.

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

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

[0018]

[0019] In the formula, K s —average proppant packing concentration in the complex fracture, kg / m 2 ;

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

[0021] L—total length of the complex fracture, m;

[0022] H—height of the complex fracture, m.

[0023] In step (B), the complex fracture is divided into non-intersecting fracture units, and the calculation method of the closure stress of each fracture unit in the formation is as follows:

[0024]

[0025] In the formula, σ n —closure stress of the fracture 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—angle between the fracture unit and the direction of the maximum horizontal principal stress of the formation, degree.

[0029] In step (C), the simple straight fracture conductivity experiment is carried out according to the following rules:

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

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

[0032] (c) The closure stress value in the experiment process needs to be continuously and equally spaced, the lower limit value of the closure stress is set to 0.5 MPa, the upper limit value 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 fitting formula of the relationship between the fracture conductivity and the closure stress is as follows:

[0034] F d =f(σ n)

[0035] F d fracture conductivity, m 3 ;

[0036] σ n closure stress of the fracture element, MPa.

[0037] In step (E), the complex fracture includes a non-branching and tortuous complex fracture, a multi-branch complex fracture, and a combined complex fracture having both the non-branching and tortuous complex fracture and the multi-branch complex fracture; wherein,

[0038] (1) when the complex fracture is the non-branching and tortuous complex fracture, the calculation method of the conductivity of the complex fracture is as follows:

[0039]

[0040] F conductivity of the complex fracture, m 3 ;

[0041] M - total length of the complex fracture, m;

[0042] L i length of the i-th fracture element, m;

[0043] conductivity of the i-th fracture element, m 3 ;

[0044] N - number of fracture elements, pieces;

[0045] (2) when the complex fracture is the multi-branch complex fracture, the calculation method of the conductivity of the complex fracture is as follows:

[0046]

[0047] F conductivity of the complex fracture, m 3 ;

[0048] M - total length of the complex fracture, m;

[0049] conductivity of the i-th fracture element, m 3 ;

[0050] L i length of the i-th fracture element, m;

[0051] (3) when the complex fracture is a combined complex fracture, the flow conductivity of the complex fracture is calculated according to the calculation method of the unbranched tortuous complex fracture and the calculation method of the multi-branch complex fracture.

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

[0053] a extracting unit configured to extract a specific form of the complex fracture formed by hydraulic fracturing in a formation;

[0054] a first calculating unit configured to calculate the average proppant concentration in the complex fracture;

[0055] a dividing unit configured to divide the complex fracture into a plurality of simple straight fracture units according to the specific form;

[0056] a second calculating unit configured to calculate the closure stress of each fracture unit in the formation;

[0057] an experimental obtaining unit configured to perform a simple straight fracture flow conductivity experiment using formation rock, to obtain a curve of the fracture flow conductivity changing with the closure stress, and to fit a relationship between the fracture flow conductivity and the closure stress;

[0058] a third calculating unit configured to calculate the fracture flow conductivity corresponding to each fracture unit using the relationship between the fracture flow conductivity and the closure stress;

[0059] a fourth calculating unit configured to calculate the flow conductivity of the whole complex fracture using the fracture flow conductivity of each fracture unit.

[0060] In a third aspect, the present application provides a computer readable storage medium storing a computer program, which, when executed by a processor, implements the method for obtaining the flow conductivity of a complex fracture.

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

[0062] a memory storing executable instructions;

[0063] a processor running the executable instructions in the memory to implement the method for obtaining the flow conductivity of a complex fracture.

[0064] By adopting the above technical solution, the present application has the following beneficial technical effects:

[0065] 1. The method for obtaining the flow conductivity of a complex fracture comprises five steps, wherein,

[0066] The advantage of step A is that based on the specific form of the extracted complex fracture, the average proppant filling concentration calculation method is quantitatively determined from the physical meaning, and the complex fracture conductivity is obtained.

[0067] The advantage of step B is that the complex fracture is divided into a plurality of simple straight fracture units by using the discrete method, and the closure stress of each unit is calculated, so that the originally complex problem is simplified, and the problem solving difficulty is reduced.

[0068] The advantage of step C is that the mathematical relationship between the fracture conductivity and the closure stress is obtained by testing the change curve of the fracture conductivity with the closure stress through the laboratory experiment, so that the specific value of the fracture conductivity under the condition of any closure stress can be quickly obtained without carrying out the conductivity experiment for all possible closure stress conditions.

[0069] The advantage of step D is that the fracture conductivity corresponding to each fracture unit can be quickly, quantitatively and accurately obtained, and the complex fracture conductivity is obtained.

[0070] The advantage of step E is that based on the reliable theoretical basis, the direct calculation method of the complex fracture conductivity is given, and the conductivity of any complex fracture can be quickly, quantitatively and accurately obtained.

[0071] In summary, the principle of the present application is reliable, simple to operate and strong in practicality, and the conductivity of the complex fracture formed by hydraulic fracturing can be accurately obtained, and then the effective guidance for the hydraulic fracturing construction effect evaluation is provided.

[0072] 2, the present application adopts the combination of experiment and theory, and provides a practical complex fracture conductivity obtaining method, each step has strong theoretical basis and operability, and the conductivity of any complex fracture can be quickly, quantitatively and accurately obtained, and the key parameter for the hydraulic fracturing effect evaluation is provided. BRIEF DESCRIPTION OF DRAWINGS

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

[0074] Figure 2 is a specific form diagram of the complex fracture formed in the formation after hydraulic fracturing;

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

[0076] Figure 4 is a change curve of the fracture conductivity with the closure stress obtained through the experiment. DETAILED DESCRIPTION

[0077] Example 1

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

[0079] (A) extracting the specific form of complex fractures formed by hydraulic fracturing in the formation, and calculating the average proppant filling concentration K of the complex fractures s .

[0080] Wherein, the specific form of the complex fracture mainly refers to the extension path of the fracture along the length direction, and the calculation method of the average proppant filling concentration K of the complex fracture s is as follows:

[0081]

[0082] In the formula, K s is the average proppant filling concentration of the complex fracture, kg / m 2 ;

[0083] M is the total amount of proppant in the process of hydraulic fracturing, kg;

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

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

[0086] (B) dividing the complex fracture into a plurality of simple straight fracture units based on the specific form obtained in step (A), and calculating the closure stress of each fracture unit in the formation.

[0087] Wherein, when the complex fracture is divided, the intersection of two fracture units should be avoided, that is, each fracture unit after the complex fracture is divided is not intersected, otherwise the subsequent calculation cannot be normally carried out, and the above target 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 more refined the division, and the higher the approximation degree of the original complex fracture. Meanwhile, the calculation method of the closure stress of the fracture unit in the formation is as follows:

[0088]

[0089] In the formula, σ n is the closure stress of the fracture unit, MPa;

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

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

[0092] α—The angle between the fracture element and the direction of the maximum horizontal principal stress of the formation, in degrees.

[0093] (C) Based on the results of step (A), a simple straight fracture conductivity experiment was conducted using formation rocks. The proppant filling concentration in the experiment was set to K. s Thus, the average proppant filling concentration K is obtained. s Crack conductivity F under certain conditions d With closing stress σ n The variation curve was obtained by fitting the fracture conductivity F. d With closing stress σ n The relational expression.

[0094] Among them, the fracture conductivity F was obtained by fitting. d With closing stress σ n The relation is:

[0095] F d =f(σ n )

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

[0097] σ n —The closing stress of the crack element, MPa.

[0098] It should be noted that, when conducting experiments on the conductivity of simple straight fractures, in order to ensure that the obtained curve of fracture conductivity versus closure stress reflects objective laws and has high accuracy, the relevant experimental materials or parameters should be handled according to the following rules:

[0099] (a) The rocks used in the experiment should come from the target formation of the 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 must 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 steps (B) and (C), the fracture conductivity F is used. d With closing stress σ n The crack conductivity corresponding to each crack element is obtained by calculating the relational formula.

[0103] (E) Based on the result of step (D), the conductive capacity of the whole complex fracture is calculated by using the conductive capacity of each fracture unit.

[0104] Since the complex fracture has different forms, it usually includes non-branching and tortuous complex fracture, multi-branch complex fracture, and combined complex fracture with non-branching and tortuous complex fracture and multi-branch complex fracture, so the conductive capacity of the complex fracture needs to be calculated respectively for different forms.

[0105] Specifically, assuming that a complex fracture is divided into N fracture units, the conductive capacity calculation method is as follows:

[0106] (1) If the N fracture units form a non-branching and tortuous complex fracture (similar to N resistors forming a series circuit), the conductive capacity calculation method of the complex fracture is:

[0107]

[0108] In the formula, the conductive capacity of the complex fracture, m 3 ;

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

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

[0111] the conductive capacity of the i-th fracture unit, m 3 ;

[0112] N - the number of fracture units, pieces.

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

[0114]

[0115] In the formula, the conductive capacity of the complex fracture, m 3 ;

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

[0117] the conductive capacity of the i-th fracture unit, m 3 ;

[0118] L i Length of the i-th fracture unit, m;

[0119] (3) If N fracture units form a complex fracture with both tortuous structure and multi-branch structure (similar to a circuit formed by N resistors in series and parallel combination), it can be regarded as a complex fracture composed of multiple tortuous fractures and multi-branch fractures. By combining the calculation methods in (1) and (2) above and the specific form of the complex fracture, the calculation method of the conductivity of the combined complex fracture can be obtained.

[0120] In addition, the applicant also provides the derivation process for the calculation method of the tortuous complex fracture without branches and the calculation method of the multi-branch complex fracture, as follows:

[0121] The fluid flow in the fracture can be described by Darcy's law (ZHEN Huai-bin, ZHAO Hai-feng, WANG Cheng-wang, et al. Physical simulation of conductivity of artificial fracture in sandy conglomerate. Xinjiang Petroleum Geology, 2021, 42(01): 81-87.):

[0122]

[0123] In the formula, Q is the flow rate of fluid through the fracture, m 3 / s;

[0124] K is the permeability of the proppant packing layer in the fracture, m 2 ;

[0125] A is the area of the fracture flow cross section, m 2 ;

[0126] μ is the fluid viscosity, Pa·s;

[0127] L is the length of the fracture, m;

[0128] ΔP is the pressure difference between the inlet and outlet of the fracture, Pa.

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

[0130] A = W·H (2)

[0131] In the formula, A is the area of the fracture flow cross section, m 2 ;

[0132] W is the fracture width, m;

[0133] H is the fracture height, m.

[0134] Substituting formula (2) into formula (1) gives:

[0135]

[0136] In the formula, Q is the flow rate of the fluid through the crack, in meters. 3 / s;

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

[0138] W—Crack width, in meters;

[0139] H—Crack height, in meters;

[0140] μ — fluid viscosity, Pa·s;

[0141] L—Crack length, in meters;

[0142] ΔP — Pressure difference between the inlet and outlet of the crack, Pa.

[0143] The conductivity of fractures can be expressed as (Zhen Huaibin, Zhao Haifeng, Wang Chengwang, et al. Physical simulation of conductivity of artificial fractures in sandstone and 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-filled layer within the fracture, in m 2 ;

[0147] W – Crack width, in meters.

[0148] Substituting equation (4) into equation (3), we get:

[0149]

[0150] In the formula, Q is the flow rate of the fluid through the crack, in meters. 3 / s;

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

[0152] H—Crack height, in meters;

[0153] μ — fluid viscosity, Pa·s;

[0154] L—Crack length, in meters;

[0155] ΔP — Pressure difference between the inlet and outlet of the crack, Pa.

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

[0157]

[0158] In the formula, Q——flow rate of fluid through the fracture, m 3 / s;

[0159] ΔP——pressure difference between the inlet and outlet of the fracture, Pa;

[0160] R——resistance of the fracture to the fluid flow, Pa·s·m -3 ;

[0161] μ——viscosity of the fluid, Pa·s;

[0162] L——length of the fracture, m;

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

[0164] H——height of the fracture, m.

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

[0166]

[0167] In the formula, Q i ——flow rate of fluid 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 ——resistance of the i-th fracture unit to the fluid flow, Pa·s·m -3 .

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

[0171]

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

[0173] ΔPs ΔP —— the pressure difference between the inlet and the outlet of the whole complex fracture, Pa;

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

[0175] (a) If N fracture units constitute a complex fracture without branch (i.e. a tortuous fracture, similar to N resistors forming a series circuit), based on the conservation of mass, the flow rate of fluid through each fracture unit should be equal, then the following relationship is obtained:

[0176]

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

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

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

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

[0181] N —— the number of fracture units, units.

[0182] Substituting equation (8) into equation (9) gives:

[0183]

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

[0185] ΔP s ΔP —— the pressure difference between the inlet and the outlet of the whole complex fracture, Pa;

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

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

[0188] N —— the number of fracture units, units.

[0189] Because each fracture unit is arranged in a head-to-tail manner, 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 inlets and outlets of each fracture unit should be equal to the pressure difference between the inlet and outlet of the whole complex fracture:

[0190]

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

[0192] ΔP s is the pressure difference between the inlet and outlet of the whole complex fracture, Pa.

[0193] Substituting equation (11) into equation (10) gives:

[0194]

[0195] where R s is the resistance of the whole complex fracture to fluid flow, Pa·s·m -3 ;

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

[0197] N is the number of fracture units.

[0198] Substituting the expression of R in equation (6) into equation (12) gives:

[0199]

[0200] where is the conductivity of the complex fracture, m 3 ;

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

[0202] L i is the length of the i-th fracture unit, m;

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

[0204] N is the number of fracture units.

[0205] Further, equation (13) can be transformed to obtain the expression of the conductivity of a complex fracture without branch and meander.

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

[0207]

[0208] where Q s — the flow rate of fluid through the whole complex fracture, m 3 / s;

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

[0210] ΔP i — the 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 — the number of fracture units, units.

[0213] Similarly, substituting equation (8) into equation (15) gives:

[0214]

[0215] where ΔP s — the pressure difference between the inlet and outlet of the whole complex fracture, Pa;

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

[0217] ΔP i — the 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 — the number of fracture units, units.

[0220] Because the flow conductivity of the fracture unit depends on the properties 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 only affects the flow rate of the fluid through the fracture; at the same time, each fracture unit forms a multi-branch fracture, and the outlets of each fracture unit are the same, so the pressure difference between the inlet and outlet of each fracture unit can be regarded as the same, and is equal to the pressure difference between the inlet and outlet of the whole complex fracture, that is:

[0221] ΔP s = ΔP i (17)

[0222] In the formula, ΔP s is the pressure difference between the inlet and outlet of the whole complex fracture, Pa;

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

[0224] Substituting formula (17) into formula (16) gives:

[0225]

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

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

[0228] N is the number of fracture units, units.

[0229] Substituting the expression of R in formula (6) into formula (18) gives the flow conductivity expression of the multi-branch complex fracture.

[0230] It should be noted that the flow conductivity of the fracture mainly depends on the proppant filling concentration and the closure stress of the fracture, the complex fracture formed by hydraulic fracturing is divided into a plurality of simple straight fracture units, since the proppant filling concentration in different fracture units can be regarded as uniform, so the difference of the flow conductivity mainly comes from the different closure stresses. Based on the above understanding, the specific form of the complex fracture in the formation is extracted first, and the average filling concentration of the proppant in the complex fracture is calculated; secondly, the complex fracture is divided into a plurality of simple straight fracture units, and the closure stress of each fracture unit is calculated; then the simple straight fracture flow conductivity experiment is carried out by using the formation rock, the change curve of the fracture flow conductivity with the closure stress under the condition of the average filling concentration of the proppant is obtained, and the specific function relationship is fitted; then the flow conductivity corresponding to each fracture unit is calculated based on the function relationship between the fracture flow conductivity and the closure stress; finally, the flow conductivity of the whole complex fracture can be obtained by further calculating the flow conductivity of each fracture unit.

[0231] Embodiment 2

[0232] The application provides a device for obtaining the flow conductivity of a complex fracture, which comprises:

[0233] The extraction unit is used for extracting the specific form of the complex fracture formed by hydraulic fracturing in the formation.

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

[0235] The division unit is used for dividing the complex fracture into a plurality of simple straight fracture units according to the specific form.

[0236] The second calculation unit is used for calculating the closure stress of each fracture unit in the formation.

[0237] The experimental acquisition unit is used for carrying out the simple straight fracture flow conductivity experiment by using the formation rock, for obtaining the change curve of the fracture flow conductivity with the closure stress, and for fitting the relationship between the fracture flow conductivity and the closure stress.

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

[0239] The fourth calculation unit is used for calculating the flow conductivity of the whole complex fracture by using the fracture flow conductivity of each fracture unit.

[0240] It should be noted that based on the same innovative concept, the device for obtaining the flow conductivity of the complex fracture provided in the embodiment solves the problem in a similar way, so the specific device implementation of the embodiment can be referred to the implementation of the foregoing method, and the repeated parts will not be described here.

[0241] Embodiment 3

[0242] The application provides a computer readable storage medium, which stores a computer program, and the computer program is executed by a processor to realize the method for obtaining complex fracture conductivity.

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

[0244] The computer readable storage medium includes, but is not limited to, an optical storage medium (for example, a CD-ROM and a DVD), a magneto-optical storage medium (for example, an MO), a magnetic storage medium (for example, a magnetic tape or a mobile hard disk), a medium with a built-in rewritable non-volatile memory (for example, a memory card), and a medium with a built-in ROM (for example, a ROM cartridge).

[0245] Embodiment 4

[0246] The application provides an electronic device, which comprises:

[0247] a memory storing executable instructions;

[0248] a processor running the executable instructions in the memory to realize the method for obtaining complex fracture conductivity.

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

[0250] The method of the application will be further described in detail below in combination with the accompanying drawings and specific examples.

[0251] The tight sandstone reservoirs in the Sichuan Basin are rich in oil and gas resources. 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 effect of hydraulic fracturing has not been evaluated from the perspective of fracture conductivity, which has limited the design and optimization methods of hydraulic fracturing schemes.

[0252] Taking the hydraulic fracturing operation of a well in a tight sandstone reservoir in the Sichuan Basin as an example, the main steps of obtaining the conductivity of complex fractures after hydraulic fracturing using the method provided by this invention are as follows:

[0253] (A) Extracting the specific morphology of complex fractures formed in the formation by hydraulic fracturing (see...) Figure 2 The complex fracture has a total length of 214m and a height of 40m. The total amount of proppant added during the hydraulic fracturing operation was 47080kg. Therefore, the average proppant concentration K in the complex fracture can be calculated. s It is 5.5 kg / m 2 .

[0254] (B) The complex crack was divided into 14 straight crack units (see...). Figure 3 The minimum horizontal principal stress of the target stratum is 23 MPa, and the maximum horizontal principal stress is 41 MPa. The closure stress of each fracture element in the stratum can be calculated from this, and the results are shown in the table below.

[0255] Fracture element number Fracture element length / m Angle with the direction of the maximum horizontal principal stress / deg Closure 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) Conduct a simple straight fracture conductivity test using the target formation rock, with the proppant filling concentration set at 5.5 kg / m³. 2 The proppant type selected was 40 / 70 mesh ceramsite, consistent with the proppant type used in hydraulic fracturing. The closure stress value varied continuously and at equal intervals during the experiment. The lower limit of the closure stress was set to 0.5 MPa, the upper limit to 41 MPa, and the variation interval to 0.5 MPa. The fracture conductivity F was ultimately obtained. d With closing stress σ n The change curve F d -σ n (See Figure 4 ), and fitted to obtain F d With σ n The relationship is as follows:

[0257]

[0258] (D) Combining the calculation results of the closure stress of each fracture element and the fracture conductivity F d With closing stress σ nThe conductive capacity corresponding to each fracture unit is calculated according to the relational expression, and the results are shown in the following table.

[0259] Fracture element number Closure stress / MPa Flow conducting capacity / 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 conductive capacity calculation formula of the complex fracture can be obtained according to the conductive capacity calculation rule described in the present application in combination with the specific form of the complex fracture in the middle.

[0261] (1) For the complex fracture ①-③ composed of fracture units ①, ② and ③, it can be regarded as three resistances in series, and the conductive capacity calculation formula is:

[0262]

[0263] In the formula, The conductive capacity of the complex fracture ①-③ (similar below), m 3 ;

[0264] L 1-3 The length of the complex fracture ①-③ (similar below), m

[0265] L 1 , L 2 , L 3 The length of the fracture units ①, ② and ③ (similar below), m

[0266] The conductive capacity of the fracture units ①, ② and ③ (similar below), m 3 .

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

[0268]

[0269] (3) For the complex fracture ①-⑥ composed of fracture units ①, ②, ③, ④, ⑤ and ⑥, it can be regarded as a combination of the complex fracture ①-③ and the complex fracture ④-⑥, which is two resistances in parallel, and the conductive capacity calculation formula is:

[0270]

[0271] (4) For the complex fracture ①-⑧ composed of fracture units ①, ②, ③, ④, ⑤, ⑥, ⑦ and ⑧, it can be regarded as a combination of the complex fracture ①-⑥ and the fracture unit ⑦ and the fracture unit ⑧, which is three resistances in series, and the conductive capacity calculation formula is:

[0272]

[0273] (5) in this way, can be obtained in turn each level of complex fracture and the whole complex fracture conductivity calculation formula as follows:

[0274]

[0275]

[0276]

[0277]

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

[0279]

[0280] To verify the accuracy of the calculation results of the method, further production testing operation is carried out on the well to obtain the real complex fracture conductivity formed by hydraulic fracturing. During the production test, the formation pressure is 42MPa, the bottom hole flowing pressure is 33MPa, the fluid viscosity is 12mPa·s, the single well production is 13.96m 3 / d, the real complex fracture conductivity is 115.23*10 -14 m 3 .

[0281]

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

[0283] Thus, the error of the conductivity calculated by the method is only 5.56%, which is high in accuracy, and thus has high innovation and practicality.

[0284] The above described, only for the specific embodiments of the present application, any feature disclosed in the specification, unless specifically described, can be replaced by other equivalent or similar purpose of the disclosed features to replace; All features disclosed, or all the steps in the method or process, in addition to mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A method for obtaining complex fracture conductivity, comprising: The method comprises the following steps: (A) extracting the specific shape of a complex fracture formed by hydraulic fracturing in a formation and calculating the average proppant filling concentration in the complex fracture; (B) dividing the complex fracture into a plurality of simple straight fracture units based on the specific shape and calculating the closure stress of each fracture unit in the formation; (C) conducting a simple straight fracture conductivity experiment using formation rock 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) calculating the fracture conductivity corresponding to each fracture unit by using the relationship between fracture conductivity and closure stress; (E) calculating the conductivity of the whole complex fracture by using the fracture conductivity of each fracture unit. In step (C), the relationship between fracture conductivity and closure stress is fitted as follows: In the formula, - fracture conductivity, m 3 ; — closure stress on the fracture element, MPa; In step (E), the complex fracture includes a non-branching and tortuous complex fracture, a multi-branch complex fracture, and a combined complex fracture having both the non-branching and tortuous complex fracture and the multi-branch complex fracture; wherein, (1) when the complex fracture is the non-branching and tortuous complex fracture, the calculation method of the conductivity of the complex fracture is as follows: In the formula, - complex fracture conductivity, m 3 ; M - total length of complex fractures, m; - length of the i-th crack element, m; - the conductivity of the i-th fracture element, m 3 ; N — number of crack elements, pieces; (2) when the complex fracture is the multi-branch complex fracture, the calculation method of the conductivity of the complex fracture is as follows: In the formula, - complex fracture conductivity, m 3 ; M - total length of complex fractures, m; - the flow conductivity of the i-th fracture element, m 3 ; - length of the i-th crack element, m; (3) when the complex fracture is the combined complex fracture, the conductivity of the complex fracture is calculated according to the calculation method of the non-branching and tortuous complex fracture and the calculation method of the multi-branch complex fracture.

2. The method of claim 1, wherein: In step (A), the specific shape of the complex fracture refers to the extension path of the fracture along the length direction.

3. The method of claim 1, wherein: In step (A), the calculation method of the average proppant filling concentration in the complex fracture is as follows: wherein - average proppant packing concentration in complex fractures, kg / m 2 ; - total amount of proppant used during the hydraulic fracturing process, kg; - total length of complex fractures, m; H - height of complex fracture, m.

4. The method of claim 3, wherein: In step (B), the fracture units after division are not intersected, and the calculation method of the closure stress of each fracture unit in the formation is as follows: wherein — closure stress on the fracture element, MPa; — Maximum horizontal principal stress of the formation, MPa; — minimum horizontal principal stress of the formation, MPa; - the angle between the fracture element and the direction of the maximum horizontal principal stress of the formation, degrees.

5. The method of claim 1, wherein: In step (C), the simple straight fracture conductivity experiment using formation rock is conducted according to the following rules: (a) the rock used in the experiment should come from the target formation of hydraulic fracturing; (b) the type of proppant used in the experiment should be consistent with that in the process of hydraulic fracturing; (c) the closure stress value in the experiment process needs to be continuous and equidistant, the lower limit value of the closure stress is set to 0.5 MPa, the upper limit value is set to the maximum horizontal principal stress value of the formation, and the change interval is set to 0.5 MPa.

6. An apparatus for obtaining complex fracture conductivity, comprising The method comprises: an extraction unit configured to extract the specific shape of a complex fracture formed by hydraulic fracturing in a formation; a first calculation unit configured to calculate the average proppant filling concentration in the complex fracture; a division unit configured to divide the complex fracture into a plurality of simple straight fracture units according to the specific shape; a second calculation unit configured to calculate the closure stress of each fracture unit in the formation; an experiment acquisition unit configured to conduct a simple straight fracture conductivity experiment using formation rock to obtain a curve of fracture conductivity changing with closure stress, and fit a relationship between fracture conductivity and closure stress; a third calculation unit configured to calculate the fracture conductivity corresponding to each fracture unit by using the relationship between fracture conductivity and closure stress; and a fourth calculation unit configured to calculate the conductivity of the whole complex fracture by using the fracture conductivity of each fracture unit. A fourth calculation unit is configured to calculate the conductive capacity of the whole complex fracture by using the fracture conductive capacity of each fracture unit; The fitting relationship between the fracture conductive capacity and the closure stress is as follows: In the formula, - fracture conductivity, m 3 ; — closure stress on the fracture element, MPa; The complex fracture includes a non-branching and tortuous complex fracture, a multi-branch complex fracture, and a combined complex fracture having both the non-branching and tortuous complex fracture and the multi-branch complex fracture. (1) When the complex fracture is the non-branching and tortuous complex fracture, the conductive capacity of the complex fracture is calculated by the following method: wherein - complex fracture conductivity, m 3 ; M - total length of complex fractures, m; - length of the i-th crack element, m; - the flow conductivity of the i-th fracture element, m 3 ; N — number of fracture elements, pieces; (2) When the complex fracture is the multi-branch complex fracture, the conductive capacity of the complex fracture is calculated by the following method: wherein - complex fracture conductivity, m 3 ; M - total length of complex fractures, m; - the conductivity of the i-th fracture element, m 3 ; - length of the i-th crack element, m; (3) When the complex fracture is the combined complex fracture, the conductive capacity of the complex fracture is calculated according to the calculation method of the non-branching and tortuous complex fracture and the calculation method of the multi-branch complex fracture.

7. A computer-readable storage medium, characterized in that: The computer readable storage medium stores a computer program, and the computer program is executed by the processor to implement the method for obtaining the conductive capacity of the complex fracture according to any one of claims 1-6.

8. An electronic device, comprising: The electronic device comprises: A memory storing executable instructions; A processor running the executable instructions in the memory to implement the method for obtaining the conductive capacity of the complex fracture according to any one of claims 1-6.

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