Fractability evaluation method coupled with fracturing construction parameters

Abstract

The invention provides a fracturing construction parameter coupled fracturing performance evaluation method, which comprises the following steps: determining evaluation factors influencing the fracturing performance of a target reservoir, the evaluation factors comprising rock brittleness, crustal stress parameters, fracture toughness and net pressure; respectively calculating to obtain a weight value of each evaluation factor; and based on the evaluation factors and the weight value of each evaluation factor, in combination with a fracturing evaluation model, calculating to obtain the fracturing index of the target reservoir. The invention overcomes the defect that the comprehensive influence of net pressure influenced by construction parameters is not considered in the prior art, and provides a fracturing property evaluation model which comprehensively considers the elastic parameters of comprehensive characteristics such as reservoir rock composition, structure, pore, fluid and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of reservoir stimulation for production increase, and specifically, to a fracturability evaluation method coupling fracturing construction parameters. Background Art

[0002] Shale reservoirs have the characteristics of low porosity and low permeability. It is necessary to rely on large-scale fracturing to form a complex fracture system and increase the seepage channels to achieve commercial exploitation value. Evaluating the fracturability of the reservoir and determining the better fracturing position are crucial for the success of fracturing. As an effective reservoir stimulation technology for production increase, hydraulic fracturing technology is widely used in the exploration and development of unconventional oil and gas such as shale gas, shale oil, tight gas, and coalbed methane. The purpose of hydraulic fracturing is to form a complex fracture network and increase the stimulated volume, while fracturability characterizes the difficulty of effectively transforming shale reservoirs. However, the physical properties of different reservoirs vary greatly, and the heterogeneity also varies greatly. Therefore, it is necessary to evaluate the fracturability of the reservoir to ensure the formation of the optimal fracture network and thus increase the oilfield production.

[0003] The evaluation of reservoir fracturability needs to further identify the engineering sweet spot of the reservoir, that is, the engineering fracturability, on the basis of the geological sweet spot. At present, there are many studies on the evaluation models of reservoir fracturability. Initially, the fracturability evaluation was based on the brittle index evaluation method of the material composition of reservoir rocks, and the content of brittle minerals was determined by analyzing the mineral composition of reservoir rocks or the brittle index was calculated by rock mechanics parameters to determine the fracturability of the reservoir. Subsequently, some scholars proposed a fracturing evaluation model considering factors such as rock brittleness, fracture toughness of the reservoir, reservoir stress distribution, and natural fracture development. However, the current evaluation methods are all established based on reservoir geology and rock mechanics characteristics and cannot comprehensively evaluate the fracturability.

[0004] Therefore, the present invention provides a fracturability evaluation method coupling fracturing construction parameters. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a fracturability evaluation method coupling fracturing construction parameters, and the method includes:

[0006] Determine the evaluation factors affecting the fracturability of the target reservoir, wherein the evaluation factors include rock brittleness, in-situ stress parameters, fracture toughness, and net pressure;

[0007] Calculate the weight value of each evaluation factor respectively;

[0008] Based on the evaluation factors and the weight value of each evaluation factor, combined with the fracturing evaluation model, calculate the fracturability index of the target reservoir.

[0009] According to an embodiment of the present invention, the rock brittleness of the target reservoir is calculated through the following steps:

[0010] Determine the elastic modulus and Poisson's ratio of the target reservoir;

[0011] Normalize the elastic modulus and the Poisson's ratio;

[0012] Based on the normalized elastic modulus and the normalized Poisson's ratio, calculate the rock brittleness of the target reservoir by using the average weighted utilization formula.

[0013] According to an embodiment of the present invention, the in-situ stress parameters include vertical in-situ stress, maximum horizontal principal stress, and minimum horizontal principal stress. The in-situ stress parameters of the target reservoir are calculated through the following steps:

[0014] Use density logging data to calculate the overburden pressure as the vertical in-situ stress;

[0015] Assume that the rock is a homogeneous, isotropic linear elastic body, and assume that during the sedimentation and later geological tectonic movement processes, there is no relative displacement between strata, and the strains in the two horizontal directions of all strata are constants. According to the generalized Hooke's law, calculate the maximum horizontal principal stress and the minimum horizontal principal stress.

[0016] According to an embodiment of the present invention, the fracture toughness of the rock in the target reservoir is calculated through the following steps:

[0017] Determine the propagation type of the fractures in the target reservoir, where the propagation type includes opening type, shear type, and tearing type;

[0018] Based on the propagation type of the fractures in the target reservoir, combined with the confining pressure value and the tensile strength, calculate the fracture toughness of the rock in the target reservoir.

[0019] According to an embodiment of the present invention, the net pressure of the fluid in the fractures of the target reservoir is calculated through the following steps:

[0020] Based on Young's modulus, construction displacement, Poisson's ratio, fracturing fluid viscosity, fracture height, and injection time, calculate the fracture length:

[0021]

[0022] Through the fracture length, calculate the net pressure of the fluid in the fractures of the target reservoir:

[0023]

[0024] where, L f represents the fracture length; E represents Young's modulus, MPa; q represents the construction displacement, m 3 / s; ν represents the Poisson's ratio, dimensionless; μ represents the viscosity of the fracturing fluid, MPa·s; H f represents the fracture height, m; t represents the injection time, s; P net represents the net pressure of the fluid in the fracture of the target reservoir, MPa.

[0025] According to an embodiment of the present invention, the weight value of each evaluation factor is calculated through the following steps:

[0026] Based on the evaluation factors and the data points corresponding to each evaluation factor, an original evaluation matrix is constructed;

[0027] The original evaluation matrix is normalized to obtain a normalized evaluation matrix;

[0028] For the normalized evaluation matrix, calculate the proportion of each data point in a single evaluation factor to the sum of all data points in the single evaluation factor;

[0029] Based on the proportion and the number of data points of each evaluation factor, the entropy value of each evaluation factor is calculated respectively;

[0030] Based on the number of evaluation factors and the entropy value of each evaluation factor, the weight value of each evaluation factor is calculated respectively.

[0031] According to an embodiment of the present invention, the original evaluation matrix X is constructed based on n evaluation factors and m data points:

[0032]

[0033] The normalized evaluation matrix R obtained after normalization:

[0034]

[0035] The proportion p of each data point in a single evaluation factor to the sum of all data points in the single evaluation factor ij :

[0036]

[0037] The entropy value e of each evaluation factor j :

[0038]

[0039] The weight value c of each evaluation factor is calculated respectively j :

[0040]

[0041] Among them, X represents the original evaluation matrix; i represents the i-th data point; j represents the j-th evaluation factor; R represents the standardized evaluation matrix; p ij represents the proportion of each data point in a single evaluation factor to the sum of all data points in the single evaluation factor; e j represents the entropy value of the j-th evaluation factor, dimensionless; c j represents the weight value of the j-th evaluation factor, dimensionless.

[0042] According to an embodiment of the present invention, the fracability index of the target reservoir is calculated through the following steps:

[0043] For the rock brittleness and the net pressure, positive normalization processing is adopted to obtain the normalized rock brittleness and the normalized net pressure;

[0044] For the fracture toughness and the in-situ stress parameters, negative normalization processing is adopted to obtain the normalized fracture toughness and the normalized in-situ stress parameters;

[0045] Based on the normalized rock brittleness, the normalized net pressure, the normalized fracture toughness, and the normalized in-situ stress parameters, combined with the weight value of each evaluation factor, through the fracability evaluation model, the fracability index of the target reservoir is calculated:

[0046]

[0047] Among them, F rac represents the fracability index, dimensionless; S j represents the j-th normalized evaluation factor, dimensionless; c j represents the weight value of the j-th evaluation factor, dimensionless.

[0048] According to another aspect of the present invention, a storage medium is further provided, which contains a series of instructions for executing the method steps described in any one of the above.

[0049] According to another aspect of the present invention, a fracability evaluation device coupled with fracturing construction parameters is further provided, which executes the method described in any one of the above. The device includes:

[0050] An evaluation factor determination module, which is used to determine the evaluation factors affecting the fracability of the target reservoir. Among them, the evaluation factors include rock brittleness, in-situ stress parameters, fracture toughness, and net pressure;

[0051] A weight value calculation module, which is used to calculate the weight value of each evaluation factor respectively;

[0052] A fracability index module, which is used to calculate the fracability index of a target reservoir based on the evaluation factors and the weight value of each evaluation factor, in combination with a fracability evaluation model.

[0053] A fracability evaluation method coupling fracturing construction parameters provided by the present invention has the following advantages compared with the prior art: it overcomes the defect in the prior art that the comprehensive influence of net pressure affected by construction parameters is not considered, and provides a fracability evaluation model that comprehensively considers the elastic parameters of comprehensive characteristics such as reservoir rock composition, structure, pores, and fluids. After adding net pressure to the fracability evaluation method, the new fracability evaluation method simultaneously considers the influence of reservoir characteristics and fracturing construction parameters such as fracturing construction displacement and fracturing fluid viscosity, thereby measuring the fracability of the reservoir from both aspects of reservoir characteristics and pressure construction.

[0054] Other features and advantages of the present invention will be described in the following specification, and part of them will become obvious from the specification, or be understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the structures specifically pointed out in the specification, claims, and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The drawings are used to provide a further understanding of the present invention, and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the present invention, and do not constitute a limitation to the present invention. In the drawings:

[0056] Figure 1 Shows a flowchart of a fracability evaluation method coupling fracturing construction parameters according to an embodiment of the present invention;

[0057] Figure 2 Shows a flowchart of a method for calculating the weight value of each evaluation factor according to an embodiment of the present invention;

[0058] Figure 3 Shows a flowchart of a method for calculating the fracability index of a target reservoir according to an embodiment of the present invention;

[0059] Figure 4 Shows a distribution diagram of the fracability index with well depth according to an embodiment of the present invention;

[0060] Figure 5 Shows a comparison chart of the production of Well GY-X and adjacent wells according to an embodiment of the present invention.

[0061] In the drawings, the same components are denoted by the same reference numerals. In addition, the drawings are not drawn to actual scale. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0062] To make the objectives, technical solutions, and advantages of the present invention clearer, the following further details the embodiments of the present invention with reference to the accompanying drawings.

[0063] The prior art (CN105134156A) provides a modeling method for a three-dimensional fracturability model of a tight sandstone reservoir, and mainly establishes a fracturability evaluation method by considering elastic parameters, internal friction angle, critical strain energy release rate, fracture toughness, etc. The prior art (CN115034636A) provides a fracturing risk assessment method based on the three-dimensional distribution of the double sweet spots of the reservoir fracturability, divides the encounter risks of faults and water layers in the fracturing intervals, and guides the fracturing design to avoid risks. The prior art (CN113962605A) provides a method, system, and storage medium for evaluating the fracturability of rock formations, and improves the effectiveness and reliability of the evaluation results by taking into account the effective information in the subjective and objective weights. The prior art (Evaluation Technology of Fracturability of Shale Gas Reservoirs, Acta Petrolei Sinica, 2013) provides an evaluation technology for the fracturability of shale gas reservoirs, and studies the evaluation technology for the fracturability of shale gas reservoirs in China from three aspects: brittleness index, fracture toughness, and rock mechanical properties of shale gas reservoir rocks. The prior art (An Integrated Petrophysics and Geomechanics Approach for Fracability Evaluation in Shale Reservoirs, SPE Journal) provides an integrated petrophysics and geomechanics method for evaluating the fracturability of shale reservoirs. The prior art (An Improved Fracability-Evaluation Method for Shale Reservoirs Based on New Fracture Toughness-Prediction Models, SPE Journal) provides an improved method for evaluating the fracturability of shale reservoirs based on a new fracture toughness prediction model.

[0064] However, the above prior art for fracturability evaluation is all based on reservoir geology and rock mechanical properties, and does not consider the influence of fracturing construction parameters on fracturability, so it is impossible to comprehensively evaluate fracturability.

[0065] The present invention takes into account the influence of fracturing construction parameters on the fracturability of the reservoir (realized by the net pressure of the fluid in the fracture) on the basis of considering the geology and rock mechanical properties of the reservoir itself, and establishes a new fracturability index evaluation method by using the entropy weight method to assign weights to different factors affecting fracturability, which can accurately reflect the fracturability of the reservoir under certain construction conditions.

[0066] Figure 1Shows a flowchart of a method for evaluating the fracability of coupling fracturing construction parameters according to an embodiment of the present invention.

[0067] As Figure 1 shown, in step S101, evaluation factors affecting the fracability of the target reservoir are determined, where the evaluation factors include rock brittleness, in-situ stress parameters, fracture toughness, and net pressure.

[0068] In one embodiment, the rock brittleness of the target reservoir is calculated through the following steps: determining the elastic modulus and Poisson's ratio of the target reservoir. Normalizing the elastic modulus and Poisson's ratio. Based on the normalized elastic modulus and the normalized Poisson's ratio, the rock brittleness of the target reservoir is calculated using the average weighted utilization formula.

[0069] Specifically, the rock brittleness of the target reservoir is characterized by the mechanical parameters of elastic modulus and Poisson's ratio. A high elastic modulus indicates that the rock property is hard and brittle, and the ability to maintain fractures after being fractured is strong. A low Poisson's ratio reflects that the rock is more likely to fracture under pressure. In the present invention, after normalizing the elastic modulus and Poisson's ratio, the average weighted utilization formula is used to calculate the rock brittleness. Further, the elastic modulus is normalized through the following expression:

[0070]

[0071] The Poisson's ratio is normalized through the following expression:

[0072]

[0073] The average weighted utilization formula calculates the rock brittleness:

[0074] B rit =(E Brit +v Brit ) / 2(3)

[0075] Where, E Brit represents the normalized elastic modulus; E represents the elastic modulus, GPa; E min represents the lowest elastic modulus of the formation in the target reservoir; E max represents the highest elastic modulus of the formation in the target reservoir; v Brit represents the normalized Poisson's ratio; v max represents the maximum Poisson's ratio of the formation in the target reservoir; v represents Poisson's ratio; v min represents the minimum Poisson's ratio of the formation in the target reservoir; B rit represents the brittleness index, dimensionless.

[0076] In one embodiment, the in-situ stress parameters include vertical in-situ stress, maximum horizontal principal stress, and minimum horizontal principal stress. The in-situ stress parameters of the target reservoir are calculated through the following steps: Using density logging data to calculate the overburden pressure, which is used as the vertical in-situ stress. Assuming that the rock is a homogeneous, isotropic linear elastic body, and assuming that there is no relative displacement between strata during sedimentation and subsequent geological tectonic movements, and the strains in the two horizontal directions of all strata are constant. According to Hooke's law in generalized form, the maximum horizontal principal stress and the minimum horizontal principal stress are calculated.

[0077] Specifically, for the determination of vertical stress, the present invention adopts the mode that the vertical stress is equal to the overburden pressure. The overburden pressure is the pressure generated by the total weight of the rock and pore fluid, and it is usually expressed in the form of equivalent density, which is called the overburden pressure gradient. The curve of its variation with depth is called the overburden pressure gradient curve or profile. The overburden pressure gradient mainly depends on the variation of the rock mass density with well depth, and the overburden pressure gradients in different regions are different. Density logging and acoustic logging can intuitively reflect the formation compaction law and can obtain the rock bulk density value. If there is density logging data, the average bulk density can be easily calculated. Otherwise, the rock bulk density can be calculated from the acoustic logging curve, but compaction correction must be performed. In one embodiment, the formula for calculating the overburden pressure using density logging data is as follows:

[0078]

[0079] where, σ v represents the vertical stress at depth h, MPa; ρ(h) represents the overlying rock mass density varying with depth, kg / m 3 ; h represents the formation depth, m.

[0080] Specifically, the maximum horizontal principal stress and the minimum horizontal principal stress are related to the formation pore pressure, skeleton stress, and tectonic stresses in two directions on the horizontal plane. Assuming that the rock is a homogeneous, isotropic linear elastic body, and assuming that there is no relative displacement between strata during sedimentation and subsequent geological tectonic movements, and the strains in the two horizontal directions of all strata are constant. From Hooke's law in generalized form, we have:

[0081]

[0082]

[0083] where, σ H is the maximum horizontal principal stress, MPa; α s is the effective stress coefficient; p p is the pore pressure, MPa; v represents the Poisson's ratio, dimensionless; K His the structural coefficient in the direction of the maximum horizontal principal stress, which is a constant within the same fault block, m -1 ; E is Young's modulus, MPa; σ h is the minimum horizontal principal stress, MPa; K h is the structural coefficient in the direction of the minimum horizontal principal stress, which is a constant within the same fault block, m -1 .

[0084] In one embodiment, the fracture toughness of the target reservoir rock is calculated by the following steps: determining the expansion type of the target reservoir fracture, wherein the expansion type includes opening type, shear type and tearing type. Based on the expansion type of the target reservoir fracture, combined with the confining pressure value and the tensile strength, the fracture toughness of the target reservoir rock is calculated.

[0085] Specifically, fracture toughness characterizes the ability of hydraulic fractures to extend forward. The higher the fracture toughness of the rock, the greater the energy required to generate the fracture, the more difficult it is to perform hydraulic fracturing, and the lower the degree of fracturing. In one embodiment, the expansion types of fractures include opening type (Type I), shear type (Type II), and tearing type (Type III). In practice, Type I and Type II fractures are usually produced during shale gas fracturing, and mixed fractures may be produced in formations with large changes in ground stress or lithology. At present, there are two main methods for determining fracture toughness: experimental determination and empirical formula determination. Due to the difficulty in obtaining cores, it is inconvenient to experimentally determine the fracture toughness of rocks. Therefore, the present invention uses the following empirical formula to calculate the fracture toughness of the target reservoir rock:

[0086]

[0087] Among them, K IC is the fracture toughness of mode I, MPa·m 1 / 2 ; K IIC is the type II fracture toughness, MPa·m 1 / 2 ;P c is the confining pressure value, MPa; S t is the tensile strength, calculated by the following formula:

[0088]

[0089] Among them, V cl is the mud content; E d is the dynamic Young's modulus of rock, MPa; K is a constant, which is taken as 12.26.

[0090] In one embodiment, the net pressure of the fluid in the target reservoir fracture is calculated by the following steps:

[0091] Based on Young's modulus, construction displacement, Poisson's ratio, fracturing fluid viscosity, fracture height, and injection time, the fracture length is calculated:

[0092]

[0093] Based on the fracture length, the net pressure of the fluid in the fractures of the target reservoir is calculated as follows:

[0094]

[0095] where L f represents the fracture length; E represents Young's modulus, in MPa; q represents the construction displacement, in m 3 / s; ν represents Poisson's ratio, dimensionless; μ represents the viscosity of the fracturing fluid, in MPa·s; H f represents the fracture height. Assuming the fracture height is constant, the reservoir thickness can be taken during calculation, in m; t represents the injection time, in s; P net represents the net pressure of the fluid in the fractures of the target reservoir, in MPa.

[0096] Specifically, the net pressure of the fluid in the fractures during fracturing is the direct driving force for the propagation of hydraulic fractures, affecting the propagation trajectory, length, and width of hydraulic fractures, and thus affecting the fracturing treatment effect. The net pressure is affected by parameters such as the formation Young's modulus, Poisson's ratio, construction displacement during fracturing, and viscosity of the fracturing fluid. Therefore, it is very necessary to introduce the net pressure into the evaluation of engineering fracturability in the present invention, and at the same time, the influence of construction parameters on fracturability can also be considered.

[0097] As Figure 1 shown, in step S102, the weight values of each evaluation factor are calculated respectively. Specifically, the present invention considers rock brittleness, fracture toughness, net pressure, and in-situ stress parameters, assigns a certain weight value to each evaluation factor, and establishes a new fracturability evaluation method. The weight values are determined according to the entropy weight method.

[0098] Figure 2 shows a flowchart of the method for calculating the weight value of each evaluation factor according to an embodiment of the present invention.

[0099] As Figure 2 shown, in step S201, an original evaluation matrix is constructed based on the evaluation factors and the data points corresponding to each evaluation factor.

[0100] In one embodiment, an original evaluation matrix X is constructed based on n evaluation factors and m data points:

[0101]

[0102] As Figure 2As shown in the figure, in step S202, the original evaluation matrix is standardized to obtain a standardized evaluation matrix. Specifically, considering that there are multiple data points for evaluation factors and there are significant differences in the dimensions of different evaluation factors, the present invention needs to standardize the original evaluation matrix.

[0103] In one embodiment, for the type where the larger the value, the better:

[0104]

[0105] In one embodiment, for the type where the smaller the value, the better:

[0106]

[0107] In one embodiment, after the original evaluation matrix undergoes the above-mentioned standardization process, a standardized evaluation matrix R can be constructed:

[0108]

[0109] As Figure 2 shown, in step S203, for the standardized evaluation matrix, calculate the proportion of each data point in a single evaluation factor to the sum of all data points in the single evaluation factor.

[0110] In one embodiment, calculate the proportion p of each data point in a single evaluation factor to the sum of all data points in the single evaluation factor ij :

[0111]

[0112] As Figure 2 shown, in step S204, based on the proportion and the number of data points of each evaluation factor, calculate the entropy value of each evaluation factor respectively.

[0113] In one embodiment, calculate the entropy value e of each evaluation factor j :

[0114]

[0115] As Figure 2 shown, in step S205, based on the number of evaluation factors and the entropy value of each evaluation factor, calculate the weight value of each evaluation factor respectively. Specifically, the entropy weight method believes that the higher the difference in the data samples of each evaluation index, the greater the weight that should be assigned to this index. However, the higher the difference in the samples, the smaller the entropy value of this index. Therefore, there is an inverse relationship between the entropy value and the weight.

[0116] In one embodiment, calculate the weight value c of each evaluation factor respectively j :

[0117]

[0118] Among them, X represents the original evaluation matrix; i represents the i-th data point; j represents the j-th evaluation factor; R represents the standardized evaluation matrix; p ij represents the proportion of each data point in a single evaluation factor to the sum of all data points in the single evaluation factor. When p ij = 0, p ij lnp ij = 0; e j represents the entropy value of the j-th evaluation factor, dimensionless; c j represents the weight value of the j-th evaluation factor, dimensionless.

[0119] As Figure 1 shown, in step S103, based on the evaluation factors and the weight value of each evaluation factor, combined with the fracturing evaluation model, the fracturability index of the target reservoir is calculated.

[0120] Figure 3 shows the flowchart of the method for calculating the fracturability index of the target reservoir according to an embodiment of the present invention.

[0121] As Figure 3 shown, in step S301, for rock brittleness and net pressure, positive normalization processing is adopted to obtain the normalized rock brittleness and the normalized net pressure.

[0122] In one embodiment, the positive normalization processing:

[0123]

[0124] As Figure 3 shown, in step S302, for fracture toughness and in-situ stress parameters, negative normalization processing is adopted to obtain the normalized fracture toughness and the normalized in-situ stress parameters.

[0125] In one embodiment, the negative normalization processing:

[0126]

[0127] Among them, S j represents the j-th normalized evaluation factor, dimensionless; S represents the unnormalized evaluation factor; S min , S max represent the minimum value and the maximum value in the unnormalized single evaluation factor.

[0128] As Figure 3As shown, in step S303, based on the normalized rock brittleness, normalized net pressure, normalized fracture toughness and normalized geostress parameters, combined with the weight value of each evaluation factor, the fracturing index of the target reservoir is calculated through the fracturing evaluation model.

[0129] In one embodiment, the fracturing evaluation model may:

[0130]

[0131] Among them, F rac represents the fracturability index, dimensionless; S j represents the jth normalized evaluation factor, dimensionless; c j Represents the weight value of the jth evaluation factor, dimensionless.

[0132] The present invention takes into account the influence of fracturing construction parameters on the fracturing of the reservoir on the basis of considering the geological and rock mechanical properties of the reservoir itself, and establishes a new fracturing index evaluation method. The new fracturing evaluation method not only includes rock brittleness that characterizes the ability to form complex cracks during fracturing, rock fracture toughness parameters that describe the ability of hydraulic fractures to extend forward, and ground stress difference parameters that describe the multi-directional extension of cracks, but also couples the net pressure in the crack during fracturing construction. Specifically, the net pressure characterizes the difference between the fluid pressure in the crack and the minimum horizontal principal stress during fracturing. The net pressure is controlled by construction parameters such as fracturing fluid viscosity and construction displacement. The greater the net pressure, the stronger the overall ability to break up the reservoir, which is beneficial to the control of hydraulic fracture morphology. The present invention can measure the fracturing of the reservoir from both reservoir characteristics and pressure construction.

[0133] The method for evaluating the fracturability of coupled fracturing construction parameters provided by the present invention can also be used in conjunction with a computer-readable storage medium, on which a computer program is stored, and the computer program is executed to run the method for evaluating the fracturability of coupled fracturing construction parameters. The computer program can run computer instructions, which include computer program codes, which can be in source code form, object code form, executable file, or some intermediate form, etc.

[0134] Computer-readable storage media may include: any entity or device that can carry computer program code, recording media, USB flash drives, mobile hard disks, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc.

[0135] It should be noted that the content included in the computer-readable storage medium can be appropriately increased or decreased according to the requirements of legislation and patent practice within the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, the computer-readable storage medium does not include electrical carrier signals and telecommunication signals.

[0136] According to another aspect of the present invention, there is also provided a fracability evaluation device for coupling fracturing construction parameters, which executes a fracability evaluation method for coupling fracturing construction parameters. The device includes: an evaluation factor determination module, a weight value calculation module, and a fracability index module.

[0137] The evaluation factor determination module is used to determine the evaluation factors that affect the fracability of the target reservoir. Among them, the evaluation factors include rock brittleness, in-situ stress parameters, fracture toughness, and net pressure. The weight value calculation module is used to calculate the weight value of each evaluation factor respectively. The fracability index module is used to calculate the fracability index of the target reservoir based on the evaluation factors and the weight value of each evaluation factor, in combination with the fracability evaluation model.

[0138] In one embodiment, actual calculations are performed based on Well GY-X. The average thickness of the reservoir in the block where the well is located is 35m, the construction displacement is 3m 3 / min, the viscosity of the fracturing fluid is 40 mPa·s, and the stage pumping time is 60 minutes. Mainly considering the brittleness of the rock, Mode I fracture toughness and Mode II fracture toughness, the maximum and minimum horizontal stress differences, and the net pressure, the data of rock brittleness, fracture toughness, maximum and minimum horizontal principal stress differences, and net pressure calculated based on well logging data such as AC, GR, and DEN are shown in Table 1. At the same time, the fracability indices calculated by the fracability evaluation model established in this paper and compared with the YUAN model in the prior art (An Improved Fracability-Evaluation Method for Shale Reservoirs Based on New Fracture Toughness-Prediction Models, SPE Journal) are also listed in Table 1.

[0139] Table 1 Input data and calculation results for fracability calculation

[0140]

[0141]

[0142] The fracability index calculated by the YUAN model is as follows:

[0143]

[0144] In the formula: B nis the brittleness of rock, dimensionless; K IC and K IIC are the fracture toughnesses of type I and type II, MPa·m 0.5 ; σ h is the minimum horizontal principal stress gradient, MPa / 100m; a and b are the fracture toughness weight values, taking 0.5.

[0145] The model of the present invention is compared with the YUAN model. As Figure 4 shown, when the result of evaluating the fracability by the YUAN model is a relatively low value, such as at a depth of 3933 meters, since the present invention takes into account the influence of the net pressure on the fracability and the net pressure is relatively high at this position, the evaluation result of the fracability is relatively high. When evaluating the fracability of a reservoir, the present invention not only considers reservoir parameters such as the brittleness of the reservoir rock, fracture toughness, and in-situ stress, but also considers construction parameters such as the construction displacement, fracturing fluid viscosity, and construction time. Evaluating the fracability of a reservoir under certain construction parameters can better optimize the perforation position than evaluating from the perspective of reservoir characteristics alone, thereby increasing the production.

[0146] According to the calculated results, the distribution of the fracability index considering construction parameters with the well depth is made. As Figure 5 shown, the relative high and low of the fracability is judged according to the distribution of the fracability index calculated by the present invention with the well depth, and then the segmented fracturing perforation clusters are preferably selected. Figure 4 The well depth corresponding to the position of the small dot is the preferably selected perforation cluster position; according to the method for preferably selecting the perforation position proposed by the present invention, a satisfactory production increase effect has been achieved after on-site application. As Figure 5 shown, the cumulative oil production per kilometer of this well in 12 months reached 8744.5 tons, and the production is much higher than that of the adjacent wells, fully proving the superiority of the present invention in evaluating the fracability considering construction parameters.

[0147] In summary, a method for evaluating the fracability coupling fracturing construction parameters provided by the present invention has the following advantages compared with the prior art: it overcomes the defect that the prior art does not consider the comprehensive influence of the net pressure affected by construction parameters, provides a fracability evaluation model considering the elastic parameters of the comprehensive characteristics of reservoir rock composition, structure, pores, fluids, etc. After adding the net pressure to the fracability evaluation method, the new fracability evaluation method simultaneously considers the influence of reservoir characteristics and fracturing construction parameters such as fracturing construction displacement and fracturing fluid viscosity, so as to measure the fracability of the reservoir from both aspects of reservoir characteristics and pressure construction.

[0148] It should be understood that the embodiments disclosed in the present invention are not limited to the specific structures, processing steps or materials disclosed herein, but should extend to equivalent alternatives of these features understood by those of ordinary skill in the relevant art. It should also be understood that the terms used herein are for the purpose of describing specific embodiments only and do not imply limitation.

[0149] In the description of the present invention, unless otherwise specified, the meaning of "a plurality of" is two or more; the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", "inner", "outer", "front end", "rear end", "head", "tail", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation of the present invention. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0150] In the description of the present invention, it should be noted that, unless otherwise clearly specified and defined, the terms "connected" and "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0151] Certain terms are used throughout this application document to refer to particular system components. As those skilled in the art will recognize, the same components may typically be referred to by different names, and thus this application document is not intended to distinguish components that differ only in name and not in function. In this application document, the terms "comprise", "include" and "have" are used in an open-ended fashion and should thus be interpreted to mean "including but not limited to...". Additionally, the terms "substantially", "essentially" or "approximately" as may be used herein refer to the industry-accepted tolerance for the corresponding term. As the term "coupled" as may be used herein includes direct coupling and indirect coupling via additional components, elements, circuits, or modules, where for indirect coupling the intervening components, elements, circuits, or modules do not change the information of the signal but may adjust its current level, voltage level, and / or power level. Inferred coupling (such as where one element is inferred to be coupled to another element) includes both direct and indirect coupling between the two elements in the same manner as "coupled".

[0152] As used herein, the term "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the phrases "one embodiment" or "an embodiment" that appear throughout the specification do not necessarily all refer to the same embodiment.

[0153] Embodiments of the present invention are provided for purposes of illustration and description, and are not intended to be exhaustive or to limit the invention to the disclosed form. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are chosen and described in order to best explain the principles of the invention and its practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications suited to the particular use contemplated.

[0154] Although the embodiments disclosed in the present invention are as described above, the above-described content is only an embodiment adopted for the convenience of understanding the present invention, and is not intended to limit the present invention. Any person skilled in the art within the technical field to which the present invention pertains may make any modifications and variations in the form and details of the implementation without departing from the spirit and scope disclosed by the present invention. However, the scope of patent protection of the present invention shall still be subject to the scope defined by the appended claims.

Claims

1. A method for evaluating fracability by coupling fracturing construction parameters, characterized in that, The method includes: Determining evaluation factors affecting the fracturability of the target reservoir, where the evaluation factors include rock brittleness, in-situ stress parameters, fracture toughness, and net pressure; Calculating the weight value of each evaluation factor respectively; Based on the evaluation factors and the weight value of each evaluation factor, combining with the fracturability evaluation model, calculating the fracturability index of the target reservoir.

2. The method for evaluating the fracability by coupling fracturing construction parameters as claimed in claim 1, wherein The rock brittleness of the target reservoir is calculated through the following steps: Determining the elastic modulus and Poisson's ratio of the target reservoir; Normalizing the elastic modulus and the Poisson's ratio; Based on the normalized elastic modulus and the normalized Poisson's ratio, calculating the rock brittleness of the target reservoir using the average weighted utilization formula.

3. The frackability evaluation method for coupling fracturing construction parameters according to claim 1 or 2, characterized in that The in-situ stress parameters include vertical in-situ stress, maximum horizontal principal stress, and minimum horizontal principal stress. The in-situ stress parameters of the target reservoir are calculated through the following steps: Using density logging data to calculate the overburden pressure as the vertical in-situ stress; Assuming that the rock is a homogeneous and isotropic linear elastic body, and assuming that there is no relative displacement between formations during sedimentation and later geological tectonic movements, and the strains in the two horizontal directions of all formations are constant, calculating the maximum horizontal principal stress and the minimum horizontal principal stress according to the generalized Hooke's law.

4. A method for evaluating the fracability of coupling fracturing construction parameters according to any one of claims 1-3, characterized in that, The fracture toughness of the rock in the target reservoir is calculated through the following steps: Determining the crack propagation type in the target reservoir, where the propagation type includes opening type, shear type, and tearing type; Based on the crack propagation type in the target reservoir, combining with the confining pressure value and the tensile strength, calculating the fracture toughness of the rock in the target reservoir.

5. A method for evaluating the fracability of coupling fracturing construction parameters according to any one of claims 1-4, characterized in that, The net pressure of the fluid in the crack of the target reservoir is calculated through the following steps: Based on Young's modulus, construction displacement, Poisson's ratio, fracturing fluid viscosity, fracture height, and injection time, calculating the fracture length: Through the fracture length, calculating the net pressure of the fluid in the crack of the target reservoir: Among them, L f represents the crack length; E represents the Young's modulus, MPa; q represents the construction displacement rate, m 3 / s; ν represents the Poisson's ratio, dimensionless; μ represents the viscosity of the fracturing fluid, MPa·s; H f represents the crack height, m; t represents the injection time, s; P net represents the net pressure of the fluid in the crack of the target reservoir, MPa.

6. A method for evaluating the fracability of coupling fracturing construction parameters according to any one of claims 1-5, characterized in that, The weight value of each evaluation factor is calculated through the following steps: Based on the evaluation factors and the data points corresponding to each evaluation factor, constructing an original evaluation matrix; Performing standardization processing on the original evaluation matrix to obtain a standardized evaluation matrix; For the standardized evaluation matrix, calculating the proportion of each data point in a single evaluation factor to the sum of all data points in the single evaluation factor; Based on the proportion and the number of data points of each evaluation factor, calculating the entropy value of each evaluation factor respectively; Based on the number of evaluation factors and the entropy value of each evaluation factor, calculating the weight value of each evaluation factor respectively.

7. The fracturability evaluation method for coupling fracturing construction parameters according to claim 6, characterized in that Constructing the original evaluation matrix X based on n evaluation factors and m data points: The standardized evaluation matrix R obtained after performing standardization processing: The proportion p of each data point in a single evaluation factor to the sum of all data points in the single evaluation factor ij : The entropy value e of each evaluation factor j : Calculate the weight value c of each evaluation factor separately j : Among them, X represents the original evaluation matrix; i represents the i-th data point; j represents the j-th evaluation factor; R represents the standardized evaluation matrix; p ij represents the proportion of each data point in a single evaluation factor to the sum of all data points in the single evaluation factor; e j represents the entropy value of the j-th evaluation factor, dimensionless; c j represents the weight value of the j-th evaluation factor, dimensionless.

8. A method for evaluating the fracability of coupling fracturing construction parameters according to any one of claims 1-7, characterized in that, The fracturability index of the target reservoir is calculated through the following steps: For the rock brittleness and the net pressure, performing positive normalization processing to obtain the normalized rock brittleness and the normalized net pressure; For the fracture toughness and the in-situ stress parameters, performing negative normalization processing to obtain the normalized fracture toughness and the normalized in-situ stress parameters; Based on the normalized rock brittleness, normalized net pressure, normalized fracture toughness, and normalized in-situ stress parameters, combined with the weight values of each evaluation factor, through the said fracturability evaluation model, the fracturability index of the target reservoir is calculated: Among them, F rac represents the fracability index, dimensionless; S j represents the j-th normalized evaluation factor, dimensionless; c j represents the weight value of the j-th evaluation factor, dimensionless.

9. A storage medium, characterized in that, It includes a series of instructions for performing the method steps described in any one of claims 1-8.

10. A fracturability evaluation device for coupling fracturing construction parameters, characterized in that, When performing the method described in any one of claims 1-8, the device includes: An evaluation factor determination module, which is used to determine the evaluation factors affecting the fracturability of the target reservoir, wherein the evaluation factors include rock brittleness, in-situ stress parameters, fracture toughness, and net pressure; A weight value calculation module, which is used to calculate the weight values of each evaluation factor respectively; A fracturability index module, which is used to calculate the fracturability index of the target reservoir based on the evaluation factors and the weight values of each evaluation factor, in combination with the fracturability evaluation model.

Images