Optimal selection method of continental facies shale volume fracturing process technology

Abstract

The invention belongs to the technical field of oil-gas field development, and discloses a continental facies shale volume fracturing process technology optimization method, which comprises the following steps of: calculating a hydraulic fracture complexity index based on a reservoir rock brittleness index, a horizontal stress difference and a natural fracture density; calculating a hydraulic fracture crossing expansion index based on the interlayer interface shear strength, the interlayer stress difference, the vertical stress difference and the tensile strength difference; calculating a multi-cluster hydraulic fracture equilibrium expansion index based on ground stress heterogeneity, fracture toughness heterogeneity and Young modulus; and preferably selecting a continental facies shale volume fracturing process according to the three index evaluation indexes. According to the optimization method for the continental facies shale volume fracturing process technology, the hydraulic fracture complexity index, the hydraulic fracture crossing expansion index and the multi-cluster hydraulic fracture equilibrium expansion index are considered in parallel, an effective process optimization method is provided for continental facies shale volume fracturing, and the improvement volume of continental facies shale fracturing is increased.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field development, and in particular to a method for optimizing a continental shale volume fracturing process technology. Background Art

[0002] Domestic shale oil and gas resources are extremely rich, and have become a key area for unconventional oil and gas development. Due to the significant differences in the sedimentary environment, mineral composition and rock structure between marine shale and continental shale, the hydraulic fracturing effect varies greatly. Marine shale is usually more brittle, homogeneous and rich in organic matter. Its natural fracture system is relatively developed, and it is easy to form a complex fracture network structure after fracturing. However, continental shale reservoirs are characterized by strong heterogeneity and large differences in interlayer lithology. In the process of volume fracturing transformation, there are always problems such as single fracture morphology and small effective fracture volume, which leads to reduced oil and gas extraction efficiency. Combining the research progress at home and abroad and the practical experience of domestic continental shale gas exploration and development, it is believed that the complexity of hydraulic fractures, the degree of hydraulic fracture penetration and the degree of balanced expansion of multiple clusters of hydraulic fractures are the key to determining the effect of volume fracturing transformation. Therefore, it is urgent to propose a method for optimizing the volume fracturing technology of continental shale, and to recommend the volume fracturing construction technology of continental shale based on the calculation and comparison of the hydraulic fracture complexity index, the hydraulic fracture penetration extension index and the multi-cluster hydraulic fracture balanced extension index, so as to effectively avoid the above problems, which has guiding significance for guiding on-site construction and increasing the reservoir transformation volume.

[0003] At present, Chinese patent publication CN117034717A discloses a single cluster point fracturing transformation method for efficiently increasing the production of continental shale oil. The method is based on a simulation to determine the optimal fracture setting method for production, and achieves balanced expansion of the fracturing fractures. It is only applicable to fracturing transformation of a single cluster of fractures.

[0004] In summary, although the existing technical methods can achieve balanced expansion of single-cluster fractures in continental shale oil reservoirs, there is still a lack of systematic volume fracturing process support for increasing the complexity of hydraulic fractures, the degree of hydraulic fracture penetration and the balanced expansion of multiple clusters of fractures. Therefore, it is urgent to establish a method for optimizing continental shale volume fracturing technology to improve the reservoir transformation effect. Summary of the invention

[0005] The purpose of the present invention is to provide a method for optimizing the volume fracturing technology of continental shale, which considers the hydraulic fracture complexity index, the hydraulic fracture penetration expansion index, and the multi-cluster hydraulic fracture balanced expansion index in parallel, and provides an effective process optimization method for the volume fracturing of continental shale, which is beneficial to increasing the volume of continental shale fracturing transformation.

[0006] To achieve the above object, the present invention provides a method for optimizing the volume fracturing technology of continental shale, comprising the following steps:

[0007] Step S1, calculating the hydraulic fracture complexity index based on the reservoir rock brittleness index, horizontal stress difference and natural fracture density;

[0008] Step S2, calculating the hydraulic fracture penetration index based on the interlayer interface shear strength, interlayer stress difference, vertical stress difference and tensile strength difference;

[0009] Step S3, calculating the equilibrium expansion index of multiple clusters of hydraulic fractures based on the in-situ stress heterogeneity, fracture toughness heterogeneity and Young's modulus;

[0010] Step S4, analyzing and comparing the hydraulic fracture complexity index, the hydraulic fracture penetration expansion index and the multi-cluster hydraulic fracture balanced expansion index, and optimizing the continental shale volume fracturing process.

[0011] Preferably, in step S1, the hydraulic fracture complexity index is calculated based on the reservoir rock brittleness index, horizontal stress difference and natural fracture density, and the specific process is as follows:

[0012] Step S11, first, normalize the three parameters of natural fracture density, horizontal stress difference and rock brittleness index;

[0013] The normalized calculation formula for positive indicators is as follows:

[0014]

[0015] The normalized calculation formula for negative indicators is as follows:

[0016]

[0017] Among them, Y i It is the normalized value and dimensionless; X i is the value before normalization; X max With X min are the maximum and minimum values ​​of the sample data;

[0018] Step S12: Secondly, based on the fracture network expansion model, the positive and negative correlation and the primary and secondary order of the influence of three factors, namely, rock brittleness index, horizontal stress difference and natural fracture density of the target block on the complexity of hydraulic fractures are obtained;

[0019] Step S13, then, calculating the parameter weights a, b, c of the three factors of rock brittleness index, horizontal stress difference and natural fracture density based on the hierarchical analysis method;

[0020] Step S14: Finally, the hydraulic fracture complexity index is calculated as follows:

[0021] F net =aρ nf+bΔσ+cB rit (3);

[0022] Among them, F net is the hydraulic fracture complexity index, dimensionless; ρ nf is the normalized natural fracture density, dimensionless; Δσ is the normalized horizontal stress difference, dimensionless; B rit is the normalized rock brittleness index, dimensionless.

[0023] Preferably, in step S2, the hydraulic fracture penetration index is calculated based on the interlayer interface shear strength, interlayer stress difference, vertical stress difference and tensile strength difference, and the specific process is as follows:

[0024] Step S21, first, normalize the four parameters of interlayer interface shear strength, interlayer stress difference, tensile strength difference and vertical stress difference; the normalized calculation formulas are shown in formulas (1) and (2);

[0025] Step S22, secondly, a fluid-solid coupling model of hydraulic fracture penetration and propagation in continental shale is established based on the finite element + cohesion unit method, and the positive and negative correlation and primary and secondary order of the influence of four factors, namely, interlayer shear strength, interlayer stress difference, tensile strength difference and vertical stress difference, on hydraulic fracture penetration and propagation in the target block are obtained;

[0026] Step S23, then, calculating the parameter weights d, e, f, g of the four factors of interlayer interface shear strength, interlayer stress difference, tensile strength difference and vertical stress difference based on the hierarchical analysis method;

[0027] Step S24: Finally, the hydraulic fracture penetration extension index is calculated as follows:

[0028] F cc =dμ in +eΔσ in +fΔT in +gΔσ v (4);

[0029] Among them, F cc is the hydraulic fracture penetration index, dimensionless; μ in is the normalized interlaminar interface shear strength, dimensionless; Δσ in is the normalized interlaminar stress difference, dimensionless; ΔT in is the normalized tensile strength difference, dimensionless; Δσ v is the normalized vertical stress difference and is dimensionless.

[0030] Preferably, in step S3, based on the in-situ stress heterogeneity, the fracture toughness heterogeneity and the Young's modulus, the equilibrium expansion index of multiple clusters of hydraulic fractures is calculated, and the specific process is as follows:

[0031] Step S31: First, the in-situ stress heterogeneity is characterized by the minimum horizontal in-situ stress difference in the fracturing section, and the fracture toughness heterogeneity is characterized by the fracture toughness difference in the fracturing section; the three parameters of the minimum horizontal in-situ stress difference, the fracture toughness difference and the Young's modulus in the fracturing section are normalized; the normalized calculation formulas are shown in formulas (1) and (2);

[0032] Step S32, secondly, based on the multi-fracture non-planar dynamic expansion model, the positive and negative correlation and the primary and secondary order of the influence of the three parameters of the minimum horizontal ground stress difference, the fracture toughness difference and the Young's modulus of the target block on the balanced expansion degree of the multi-cluster hydraulic fractures are obtained;

[0033] Step S33, then, calculating the parameter weights h, i, j of the three factors of in-situ stress heterogeneity, fracture toughness heterogeneity and Young's modulus based on the hierarchical analysis method;

[0034] Step S34: Finally, the balanced expansion index of multiple clusters of hydraulic fractures is calculated as follows:

[0035] F jh =hΔσ h +iΔK+jYM(5);

[0036] Among them, F jh is the equilibrium expansion index of multiple cluster hydraulic fractures, dimensionless; Δσ h is the normalized minimum horizontal stress difference in the fracturing section, dimensionless; ΔK is the normalized fracture toughness difference in the fracturing section, dimensionless; YM is the normalized Young's modulus, 0-1, dimensionless.

[0037] Preferably, in step S4, according to the three index evaluation indicators of the hydraulic fracture complexity index, the hydraulic fracture penetration extension index and the multi-cluster hydraulic fracture balanced extension index of the target horizontal fracturing section, the fracturing construction plan of the target horizontal fracturing section is obtained as follows:

[0038] ① When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of [0, 0.6], the hydraulic fracture penetration index is within the range of [0, 0.6], and the multi-cluster hydraulic fracture balanced expansion index is within the range of [0, 0.3], the "temporary plugging in the fracture plus pre-placement of large-volume, high-viscosity fracturing fluid plus flow-limiting perforation and ball-throwing temporary plugging" process is adopted for the fracturing construction of the target horizontal fracturing section;

[0039] ② When the hydraulic fracture complexity index of the target horizontal fracturing section is in the range of [0, 0.6], the hydraulic fracture penetration index is in the range of [0, 0.6], and the multi-cluster hydraulic fracture balanced expansion index is in the range of (0.3, 0.6], the "temporary plugging in the fracture plus pre-placement of large-volume, high-viscosity fracturing fluid plus flow-limiting perforation" process is selected for the fracturing construction of the target horizontal fracturing section;

[0040] ③ When the hydraulic fracture complexity index of the target horizontal fracturing section is in the range of [0, 0.6], the hydraulic fracture penetration index is in the range of [0, 0.6], and the multi-cluster hydraulic fracture balanced expansion index is in the range of (0.6, 1], the "temporary plugging in the fracture plus pre-placement of large-volume, high-viscosity fracturing fluid plus flow-limiting perforation and ball-throwing temporary plugging" process is selected for the fracturing construction of the target horizontal fracturing section;

[0041] ④ When the hydraulic fracture complexity index of the target horizontal fracturing section is in the range of [0, 0.6], the hydraulic fracture penetration index is in the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced expansion index is in the range of [0, 0.3], the "temporary plugging in the fracture plus flow-limiting perforation and ball-throwing temporary plugging" process is selected for the fracturing construction of the target horizontal fracturing section;

[0042] ⑤ When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of [0, 0.6], the hydraulic fracture penetration index is within the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced expansion index is within the range of (0.3, 0.6], the "temporary plugging in the fracture plus flow-limiting perforation" process is adopted for the fracturing construction of the target horizontal fracturing section;

[0043] ⑥ When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of [0, 0.6], the hydraulic fracture penetration index is within the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced expansion index is within the range of (0.6, 1], the "temporary plugging in the fracture" process is adopted for the fracturing construction of the target horizontal fracturing section;

[0044] ⑦ When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of (0.6, 1], the hydraulic fracture penetration index is within the range of [0, 0.6], and the multi-cluster hydraulic fracture balanced expansion index is within the range of [0, 0.3], the "pre-placement of large-volume, high-viscosity fracturing fluid plus flow-limiting perforation and ball-throwing temporary plugging" process is adopted for the fracturing construction of the target horizontal fracturing section;

[0045] ⑧ When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of (0.6, 1], the hydraulic fracture penetration index is within the range of [0, 0.6], and the multi-cluster hydraulic fracture balanced expansion index is within the range of (0.3, 0.6], the "pre-placement of large-volume, high-viscosity fracturing fluid plus flow-limiting perforation" process is adopted for the fracturing construction of the target horizontal fracturing section;

[0046] ⑨ When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of (0.6, 1], the hydraulic fracture penetration index is within the range of [0, 0.6], and the multi-cluster hydraulic fracture balanced expansion index is within the range of (0.6, 1], the "pre-placement of large-volume, high-viscosity fracturing fluid" process is adopted for the fracturing construction of the target horizontal fracturing section;

[0047] ⑩ When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of (0.6, 1], the hydraulic fracture penetration index is within the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced expansion index is within the range of [0, 0.3], the "pre-placement of large-volume, high-viscosity fracturing fluid plus flow-limiting perforation and ball-throwing temporary plugging" process is adopted for the fracturing construction of the target horizontal fracturing section;

[0048] When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of (0.6, 1], the hydraulic fracture penetration index is within the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced expansion index is within the range of (0.3, 0.6], the "limited flow perforation" process is used for the fracturing construction of the target horizontal fracturing section;

[0049] When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of (0.6, 1], the hydraulic fracture penetration extension index is within the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced extension index is within the range of (0.6, 1], conventional volume fracturing is used for the target horizontal fracturing section.

[0050] Therefore, the present invention adopts the above-mentioned method for optimizing the volume fracturing technology of continental shale, and considers the hydraulic fracture complexity index, the hydraulic fracture penetration expansion index, and the balanced expansion index of multiple clusters of hydraulic fractures in parallel, to provide an effective process optimization method for the volume fracturing of continental shale, which is beneficial to increasing the volume of continental shale fracturing transformation.

[0051] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 This is a schematic diagram of the process optimization method of the present invention;

[0053] Figure 2 The cloud diagram of the simulation results of hydraulic fracture network extension morphology with different natural fracture surface densities; among them, the surface density of (a) is 0.02m -1 ; (b) The surface density is 0.1m -1 ;

[0054] Figure 3 The range diagram of hydraulic fracture plane network complexity index for natural fracture density, horizontal stress difference and rock brittleness index;

[0055] Figure 4 The cloud diagram of the influence of interlayer shear strength, interlayer stress difference, tensile strength difference and vertical stress difference on the distribution of crack height; among them, (a) is the interface shear strength; (b) is the interlayer stress difference; (c) is the tensile strength difference; (d) is the vertical stress difference;

[0056] Figure 5 The equilibrium expansion cloud diagrams of hydraulic fractures with different Young's moduli; (a) is E = 15 GPa; (b) is E = 30 GPa; (c) is E = 45 GPa;

[0057] Figure 6 It is the range diagram of the balanced development index of multiple clusters of hydraulic fractures of in-situ stress heterogeneity, fracture toughness heterogeneity, and elastic modulus;

[0058] Figure 7 This is a microseismic map of the example well after fracturing transformation in the present invention. DETAILED DESCRIPTION

[0059] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0060] like Figure 1 As shown, a preferred method for continental shale volume fracturing technology includes the following steps:

[0061] Step S1, calculating the hydraulic fracture complexity index based on the reservoir rock brittleness index, horizontal stress difference and natural fracture density.

[0062] Step S11: First, the three parameters of natural fracture density, horizontal stress difference and rock brittleness index are normalized.

[0063] The normalized calculation formula for positive indicators is as follows:

[0064]

[0065] The normalized calculation formula for negative indicators is as follows:

[0066]

[0067] Among them, Y i It is the normalized value and dimensionless; X i is the value before normalization; X max With X min are the maximum and minimum values ​​of the sample data.

[0068] Step S12: Secondly, based on the fracture network expansion model, the positive and negative correlation and the primary and secondary order of the influence of three factors, namely, the rock brittleness index, horizontal stress difference and natural fracture density of the target block on the complexity of hydraulic fractures are obtained.

[0069] Step S13: Then, the parameter weights a, b, c of the three factors of rock brittleness index, horizontal stress difference and natural fracture density are calculated based on the hierarchical analysis method.

[0070] Step S14: Finally, the hydraulic fracture complexity index is calculated as follows:

[0071] F net =aρ nf +bΔσ+cB rit (3);

[0072] Among them, F net is the hydraulic fracture complexity index, dimensionless; ρ nf is the normalized natural fracture density, dimensionless; Δσ is the normalized horizontal stress difference, dimensionless; B rit is the normalized rock brittleness index, dimensionless.

[0073] Step S2: Calculate the hydraulic fracture penetration index based on the interlayer interface shear strength, interlayer stress difference, vertical stress difference and tensile strength difference.

[0074] Step S21: First, the four parameters of interlayer interface shear strength, interlayer stress difference, tensile strength difference and vertical stress difference are normalized. The normalized calculation formulas are shown in formulas (1) and (2).

[0075] Step S22. Secondly, a fluid-solid coupling model of hydraulic fracture penetration extension in continental shale is established based on the finite element + cohesion unit method, and the positive and negative correlation and primary and secondary order of the four factors of interlayer shear strength, interlayer stress difference, tensile strength difference and vertical stress difference on the hydraulic fracture penetration extension in the target block are obtained.

[0076] Step S23, then, based on the hierarchical analysis method, the parameter weights d, e, f, g of the four factors of interlayer interface shear strength, interlayer stress difference, tensile strength difference and vertical stress difference are calculated.

[0077] Step S24: Finally, the hydraulic fracture penetration extension index is calculated as follows:

[0078] F cc =dμ in +eΔσ in +fΔT in +gΔσ v (4);

[0079] Among them, F cc is the hydraulic fracture penetration index, dimensionless; μ in is the normalized interlaminar interface shear strength, dimensionless; Δσ in is the normalized interlaminar stress difference, dimensionless; ΔT in is the normalized tensile strength difference, dimensionless; Δσ v is the normalized vertical stress difference and is dimensionless.

[0080] Step S3: Calculate the equilibrium expansion index of multiple clusters of hydraulic fractures based on the in-situ stress heterogeneity, fracture toughness heterogeneity and Young's modulus.

[0081] Step S31: First, the in-situ stress heterogeneity is characterized by the minimum horizontal in-situ stress difference within the fracturing section, and the fracture toughness heterogeneity is characterized by the fracture toughness difference within the fracturing section; the three parameters of the minimum horizontal in-situ stress difference, the fracture toughness difference and the Young's modulus within the fracturing section are normalized. The normalized calculation formulas are shown in formulas (1) and (2).

[0082] Step S32, secondly, based on the multi-fracture non-planar dynamic expansion model, the positive and negative correlation and the primary and secondary order of the influence of the three parameters of the minimum horizontal ground stress difference, the fracture toughness difference and the Young's modulus of the target block on the balanced expansion degree of the multi-cluster hydraulic fractures are obtained.

[0083] Step S33: Then, the parameter weights h, i, j of the three factors of geostress heterogeneity, fracture toughness heterogeneity and Young's modulus are calculated based on the hierarchical analysis method.

[0084] Step S34: Finally, the balanced expansion index of multiple clusters of hydraulic fractures is calculated as follows:

[0085] F jh =hΔσ h +iΔK+jYM(5);

[0086] Among them, F jh is the equilibrium expansion index of multiple cluster hydraulic fractures, dimensionless; Δσ h is the normalized minimum horizontal stress difference in the fracturing section, dimensionless; ΔK is the normalized fracture toughness difference in the fracturing section, dimensionless; YM is the normalized Young's modulus, 0-1, dimensionless.

[0087] Step S4, analyzing and comparing the hydraulic fracture complexity index, the hydraulic fracture penetration expansion index and the multi-cluster hydraulic fracture balanced expansion index, and optimizing the continental shale volume fracturing process.

[0088] According to the three index evaluation indicators of the target horizontal fracturing section, the fracturing construction plan of the target horizontal fracturing section is obtained as follows:

[0089] ① When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of [0, 0.6], the hydraulic fracture penetration extension index is within the range of [0, 0.6], and the multi-cluster hydraulic fracture balanced extension index is within the range of [0, 0.3], the "temporary plugging in the fracture + pre-placement of large-volume, high-viscosity fracturing fluid + flow-limiting perforation and ball-throwing temporary plugging" process is adopted for the fracturing construction of the target horizontal fracturing section.

[0090] ② When the hydraulic fracture complexity index of the target horizontal fracturing section is in the range of [0, 0.6], the hydraulic fracture penetration index is in the range of [0, 0.6], and the multi-cluster hydraulic fracture balanced expansion index is in the range of (0.3, 0.6], the "temporary plugging in the fracture + pre-placement of large-volume, high-viscosity fracturing fluid + flow-limiting perforation" process is selected for the fracturing construction of the target horizontal fracturing section.

[0091] ③ When the hydraulic fracture complexity index of the target horizontal fracturing section is in the range of [0, 0.6], the hydraulic fracture penetration index is in the range of [0, 0.6], and the balanced expansion index of multiple clusters of hydraulic fractures is in the range of (0.6, 1], the "temporary plugging in the fracture + pre-placement of large-volume, high-viscosity fracturing fluid + flow-limiting perforation and ball-throwing temporary plugging" process is selected for the fracturing construction of the target horizontal fracturing section.

[0092] ④ When the hydraulic fracture complexity index of the target horizontal fracturing section is in the range of [0, 0.6], the hydraulic fracture penetration index is in the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced expansion index is in the range of [0, 0.3], the "temporary plugging in the fracture + flow-limiting perforation and ball-throwing temporary plugging" process is selected for the fracturing construction of the target horizontal fracturing section.

[0093] ⑤ When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of [0, 0.6], the hydraulic fracture penetration extension index is within the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced extension index is within the range of (0.3, 0.6], the "temporary plugging in the fracture + flow limiting perforation" process is adopted for the fracturing construction of the target horizontal fracturing section.

[0094] ⑥ When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of [0, 0.6], the hydraulic fracture penetration index is within the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced expansion index is within the range of (0.6, 1], the "temporary plugging in the fracture" process is adopted for the fracturing construction of the target horizontal fracturing section.

[0095] ⑦ When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of (0.6, 1], the hydraulic fracture penetration index is within the range of [0, 0.6], and the multi-cluster hydraulic fracture balanced expansion index is within the range of [0, 0.3], the "pre-placement of large-volume, high-viscosity fracturing fluid + flow-limiting perforation and temporary plugging with ball throwing" process is adopted for the fracturing construction of the target horizontal fracturing section.

[0096] ⑧ When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of (0.6, 1], the hydraulic fracture penetration extension index is within the range of [0, 0.6], and the multi-cluster hydraulic fracture balanced extension index is within the range of (0.3, 0.6], the "front-end large-volume, high-viscosity fracturing fluid + flow-limiting perforation" process is adopted for the fracturing construction of the target horizontal fracturing section.

[0097] ⑨ When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of (0.6, 1], the hydraulic fracture penetration extension index is within the range of [0, 0.6], and the multi-cluster hydraulic fracture balanced extension index is within the range of (0.6, 1], the "front-end large-volume, high-viscosity fracturing fluid" process is adopted for the fracturing construction of the target horizontal fracturing section.

[0098] ⑩ When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of (0.6, 1], the hydraulic fracture penetration extension index is within the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced extension index is within the range of [0, 0.3], the "pre-placement of large-volume, high-viscosity fracturing fluid + flow-limiting perforation and ball-throwing temporary plugging" process is adopted for the fracturing construction of the target horizontal fracturing section.

[0099] When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of (0.6, 1], the hydraulic fracture penetration extension index is within the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced extension index is within the range of (0.3, 0.6], the "limited flow perforation" process is adopted for the fracturing construction of the target horizontal fracturing section.

[0100] When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of (0.6, 1], the hydraulic fracture penetration extension index is within the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced extension index is within the range of (0.6, 1], conventional volume fracturing is used for the target horizontal fracturing section.

[0101] Example

[0102] This embodiment takes the horizontal well Y9 in the X block of continental shale oil in a certain region as an example.

[0103] Step S1: First, calculate the natural fracture density ρ of Well Y9 according to formula (1): nf , horizontal stress difference Δσ and rock brittleness index B rit The normalized values ​​are shown in Table 1.

[0104] Table 1ρ nf , Δσ, B rit Normalized results

[0105]

[0106]

[0107] Secondly, based on the fracture network expansion model and combined with the parameters of the target block X, a cloud map of the influence of the natural fracture surface density on the complexity of hydraulic fractures in this block is simulated, such as Figure 2As shown in Figure 2. Based on the range analysis, the order of influence of natural fracture density, horizontal stress difference and rock brittleness index on the complexity of hydraulic fractures is as follows: natural fracture density > horizontal stress difference > rock brittleness index. Figure 3 shown.

[0108] Then, the relative weights of natural fracture density, horizontal stress difference, and rock brittleness index were calculated based on the analytic hierarchy process, and the hydraulic fracture complexity factor judgment matrix A was constructed, as shown in Table 2:

[0109] Table 2 Judgment matrix of factors affecting the complexity of hydraulic fractures A

[0110] Natural fracture density Horizontal stress difference Rock brittleness index Natural fracture density 1 2 3 Horizontal stress difference 1 / 2 1 2 Rock brittleness index 1 / 3 1 / 2 1

[0111] The relative weights of influencing factors were calculated using the sum method, and the relative weights of natural fracture density, horizontal stress difference, and rock brittleness index were obtained to be 0.5390, 0.2970, and 0.1638, respectively.

[0112] Therefore, the hydraulic fracture complexity index of the target block is as follows:

[0113] F net =0.5390ρ nf +0.2973Δσ+0.1638B rit (6);

[0114] Step S2: First, calculate the interlayer shear strength μ of the Y9 well according to formula (1): in , interlaminar stress difference Δσ in , tensile strength difference ΔT in and vertical stress difference Δσ v The normalized values ​​are shown in Table 3.

[0115] Table 3μ in , Δσ in , ΔT in , Δσ v Normalized results

[0116] Segment number <![CDATA[μ in ]]> <![CDATA[Δσ in ]]> <![CDATA[ΔT in ]]> <![CDATA[Δσ v ]]> 1 0.784 0.137 0.286 0.998 2 0.652 0.174 0.973 0.673 3 0.127 0.849 0.766 0.585 4 0.659 0.105 0.383 0.221 5 0.542 0.406 0.374 0.308 6 0.098 0.758 0.49 0.286 7 0.278 0.743 0.446 0.757 8 0.547 0.392 0.646 0.754 9 0.958 0.655 0.709 0.38 10 0.965 0.171 0.755 0.568 11 0.916 0.908 0.272 0.904 12 0.971 0.032 0.68 0.054 13 0.957 0.277 0.655 0.531 14 0.477 0.969 0.721 0.865 15 0.873 0.712 0.692 0.993 16 0.699 0.873 0.3 0.012 17 0.422 0.695 0.96 0.569 18 0.67 0.406 0.473 0.453 19 0.549 0.734 0.081 0.189 20 0.959 0.034 0.224 0.337

[0117] Secondly, based on the parameters of the target X block, a fluid-solid coupling model of hydraulic fracture penetration in continental shale was established based on the finite element + cohesion unit method. The cloud map of the influence of interlayer shear strength, interlayer stress difference, tensile strength difference and vertical stress difference on fracture height distribution was simulated, as shown in Figure 2. Figure 4 Based on orthogonal experimental analysis, the order of influence of these four factors on the penetration degree of hydraulic fractures is determined as follows: interlayer interface shear strength > interlayer stress difference > tensile strength difference > vertical stress difference, as shown in Tables 4 and 5.

[0118] Table 4 Orthogonal experimental table of factors affecting the penetration of hydraulic fractures

[0119]

[0120] Table 5 Extreme difference of seam height

[0121]

[0122] Then, the relative weights of interlayer shear strength, interlayer stress difference, tensile strength difference and vertical stress difference are calculated based on the hierarchical analysis method, and the judgment matrix B of the factors affecting the propagation of hydraulic fractures through layers is constructed, as shown in Table 6:

[0123] Table 6 Judgment matrix B of factors affecting the penetration of hydraulic fractures

[0124] Interlaminar interface shear strength Interlaminar stress difference Poor tensile strength Vertical stress difference Interlaminar interface shear strength 1 2 4 6 Interlaminar stress difference 1 / 2 1 2 3 Poor tensile strength 1 / 4 1 / 2 1 2 Vertical stress difference 1 / 6 1 / 3 1 / 2 1

[0125] The relative weights of the influencing factors were calculated using the sum method, and the relative weights of the interlaminar shear strength, interlaminar stress difference, tensile strength difference and vertical stress difference were 0.5192, 0.2596, 0.1402 and 0.0810, respectively.

[0126] Therefore, the hydraulic fracture penetration extension index is as follows:

[0127] F cc =0.5192μ in +0.2596Δσ in +0.1402ΔT in +0.0810Δσ v (7);

[0128] Step 3: First, calculate the minimum horizontal stress difference Δσ of Well Y9 according to formula (1): h , the normalized values ​​of fracture toughness difference ΔK and Young's modulus YM are shown in Table 7.

[0129] Table 7 Δσ h , ΔK, YM normalization results

[0130] Segment number <![CDATA[Δσ h ]]> ΔK YM 1 0.705 0.095 0.125 2 0.519 0.8 0.432 3 0.391 0.06 0.527 4 0.432 0.167 0.372 5 0.134 0.671 0.746 6 0.833 0.088 0.19 7 0.561 0.19 0.461 8 0.011 0.044 0.435 9 0.34 0.19 0.335 10 0.169 0.168 0.061 11 0.127 0.206 0.969 12 0.005 0.051 0.383 13 0.068 0.299 0.871 14 0.944 0.241 0.289 15 0.908 0.907 0.842 16 0.435 0.873 0.647 17 0.371 0.914 0.909 18 0.937 0.666 0.663 19 0.988 0.818 0.953 20 0.662 0.662 0.842

[0131] Secondly, combined with the target X block parameters, based on the multi-fracture non-planar dynamic expansion model, the cloud map of the influence of different Young's moduli on the balanced expansion degree of multiple clusters of hydraulic fractures is simulated, such as Figure 5 Based on the range analysis, the order of influence of geostress heterogeneity, fracture toughness heterogeneity and Young's modulus on the balanced expansion of multiple clusters of hydraulic fractures is: geostress heterogeneity > fracture toughness heterogeneity > Young's modulus, as shown in Figure 6 shown.

[0132] Then, based on the analytic hierarchy process, the relative weights of the in-situ stress heterogeneity, fracture toughness heterogeneity and Young's modulus are calculated, and the judgment matrix C of the influencing factors of the balanced expansion of multiple clusters of hydraulic fractures is constructed, as shown in Table 8:

[0133] Table 8 Judgment matrix C of factors affecting balanced expansion of multi-cluster hydraulic fractures

[0134] Heterogeneity of geostress Fracture toughness heterogeneity Elastic modulus Heterogeneity of geostress 1 2 4 Fracture toughness heterogeneity 1 / 2 1 3 Elastic modulus 1 / 4 1 / 3 1

[0135] The relative weights of influencing factors were calculated by the sum method, and the relative weights of in-situ stress heterogeneity, fracture toughness heterogeneity and Young's modulus were 0.5476, 0.3155 and 0.1369, respectively.

[0136] Therefore, the balanced expansion index of multiple cluster hydraulic fractures is as follows:

[0137] F jh =0.5476Δσ h +0.3155ΔK+0.1369YM (8);

[0138] Calculation of hydraulic fracture complexity index F for each layer of Well Y9 net , hydraulic fracture penetration index F cc , multi-cluster hydraulic fracture equilibrium expansion index F jh The values ​​are shown in Table 9.

[0139] Table 9F of each layer of Y9 well net 、F cc 、F jh Value Result

[0140]

[0141]

[0142] Step S4: Combine the hydraulic fracture complexity index F of each layer in Y9 well net , hydraulic fracture penetration index F cc , multi-cluster hydraulic fracture equilibrium expansion index F jh The fracturing operation plan of Well Y9 was dynamically adjusted and optimized according to the value. The results are shown in Table 10.

[0143] Table 10Fracturing technology of each layer in Well Y9

[0144]

[0145] After the above-mentioned fracturing treatment, the fracture network swept volume, complexity and vertical penetration of Well Y9 were good. Figure 7 As shown, the daily oil production of a single well exceeds 25 tons, which is 80% higher than the production of wells that have not implemented the hydraulic fracturing transformation process of the present invention.

[0146] Therefore, the present invention adopts the above-mentioned method for optimizing the volume fracturing technology of continental shale, and considers the hydraulic fracture complexity index, the hydraulic fracture penetration expansion index, and the balanced expansion index of multiple clusters of hydraulic fractures in parallel, to provide an effective process optimization method for the volume fracturing of continental shale, which is beneficial to increasing the volume of continental shale fracturing transformation.

[0147] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for optimizing continental shale volume fracturing technology, characterized in that: The following steps are involved: Step S1, calculating the hydraulic fracture complexity index based on the reservoir rock brittleness index, horizontal stress difference and natural fracture density; Step S2, calculating the hydraulic fracture penetration index based on the interlayer shear strength, interlayer stress difference, vertical stress difference and tensile strength difference; Step S3, calculating the equilibrium expansion index of multiple clusters of hydraulic fractures based on the in-situ stress heterogeneity, fracture toughness heterogeneity and Young's modulus; Step S4, analyzing and comparing the hydraulic fracture complexity index, the hydraulic fracture penetration expansion index and the multi-cluster hydraulic fracture balanced expansion index, and optimizing the continental shale volume fracturing process.

2. The method for optimizing the volume fracturing technology of continental shale according to claim 1, characterized in that: In step S1, the hydraulic fracture complexity index is calculated based on the reservoir rock brittleness index, horizontal stress difference and natural fracture density. The specific process is as follows: Step S11, first, normalize the three parameters of natural fracture density, horizontal stress difference and rock brittleness index; The normalized calculation formula for positive indicators is as follows: The normalized calculation formula for negative indicators is as follows: Among them, Y i It is the normalized value and dimensionless; X i is the value before normalization; X max With X min are the maximum and minimum values ​​of the sample data; Step S12: Secondly, based on the fracture network expansion model, the positive and negative correlation and the primary and secondary order of the influence of three factors, namely, rock brittleness index, horizontal stress difference and natural fracture density of the target block on the complexity of hydraulic fractures are obtained; Step S13, then, calculating the parameter weights a, b, c of the three factors of rock brittleness index, horizontal stress difference and natural fracture density based on the hierarchical analysis method; Step S14: Finally, the hydraulic fracture complexity index is calculated as follows: F net =aρ nf +bΔσ+cB rit (3); Among them, F net is the hydraulic fracture complexity index, dimensionless; ρ nf is the normalized natural fracture density, dimensionless; Δσ is the normalized horizontal stress difference, dimensionless; B rit is the normalized rock brittleness index, dimensionless.

3. The method for optimizing the volume fracturing technology of continental shale according to claim 1, characterized in that: In step S2, the hydraulic fracture penetration index is calculated based on the interlayer interface shear strength, interlayer stress difference, vertical stress difference and tensile strength difference. The specific process is as follows: Step S21, first, normalize the four parameters of interlayer interface shear strength, interlayer stress difference, tensile strength difference and vertical stress difference; the normalized calculation formulas are shown in formulas (1) and (2); Step S22, secondly, a fluid-solid coupling model of hydraulic fracture penetration and propagation in continental shale is established based on the finite element + cohesion unit method, and the positive and negative correlation and primary and secondary order of the influence of four factors, namely, interlayer shear strength, interlayer stress difference, tensile strength difference and vertical stress difference, on hydraulic fracture penetration and propagation in the target block are obtained; Step S23, then, calculating the parameter weights d, e, f, g of the four factors of interlayer interface shear strength, interlayer stress difference, tensile strength difference and vertical stress difference based on the hierarchical analysis method; Step S24: Finally, the hydraulic fracture penetration extension index is calculated as follows: F cc =dμ in +eΔσ in +fΔT in +gΔσ v (4); Among them, F cc is the hydraulic fracture penetration index, dimensionless; μ in is the normalized interlaminar interface shear strength, dimensionless; Δσ in is the normalized interlaminar stress difference, dimensionless; ΔT in is the normalized tensile strength difference, dimensionless; Δσ v is the normalized vertical stress difference and is dimensionless.

4. The method for optimizing the volume fracturing technology of continental shale according to claim 1, characterized in that: In step S3, based on the in-situ stress heterogeneity, fracture toughness heterogeneity and Young's modulus, the equilibrium extension index of multiple clusters of hydraulic fractures is calculated. The specific process is as follows: Step S31, first, the in-situ stress heterogeneity is characterized by the minimum horizontal in-situ stress difference in the fracturing section, and the fracture toughness heterogeneity is characterized by the fracture toughness difference in the fracturing section; the three parameters of the minimum horizontal in-situ stress difference, the fracture toughness difference and the Young's modulus in the fracturing section are normalized; The normalized calculation formula is shown in formula (1) and (2); Step S32, secondly, based on the multi-fracture non-planar dynamic expansion model, the positive and negative correlation and the primary and secondary order of the influence of the three parameters of the minimum horizontal ground stress difference, the fracture toughness difference and the Young's modulus of the target block on the balanced expansion degree of the multi-cluster hydraulic fractures are obtained; Step S33, then, calculating the parameter weights h, i, j of the three factors of in-situ stress heterogeneity, fracture toughness heterogeneity and Young's modulus based on the hierarchical analysis method; Step S34: Finally, the balanced expansion index of multiple clusters of hydraulic fractures is calculated as follows: F jh [hΔσ h +iΔK+jYM(5): Among them, F jh is the equilibrium expansion index of multiple cluster hydraulic fractures, dimensionless; Δσ h is the normalized minimum horizontal stress difference in the fracturing section, dimensionless; ΔK is the normalized fracture toughness difference in the fracturing section, dimensionless; YM is the normalized Young's modulus, 0-1, dimensionless.

5. The method for optimizing the volume fracturing technology of continental shale according to claim 1, characterized in that: In step S4, according to the three index evaluation indicators of the hydraulic fracture complexity index, the hydraulic fracture penetration extension index and the multi-cluster hydraulic fracture balanced extension index of the target horizontal fracturing section, the fracturing construction plan of the target horizontal fracturing section is obtained as follows: ① When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of [0, 0.6], the hydraulic fracture penetration expansion index is within the range of [0, 0.6], and the multi-cluster hydraulic fracture balanced expansion index is within the range of [0, 0.3], the "temporary plugging in the fracture plus pre-placement of large-volume, high-viscosity fracturing fluid plus flow-limiting perforation and ball-throwing temporary plugging" process is adopted for the fracturing construction of the target horizontal fracturing section; ② When the hydraulic fracture complexity index of the target horizontal fracturing section is in the range of [0, 0.6], the hydraulic fracture penetration index is in the range of [0, 0.6], and the multi-cluster hydraulic fracture balanced expansion index is in the range of (0.3, 0.6], the "temporary plugging in the fracture plus pre-placement of large-volume, high-viscosity fracturing fluid plus flow-limiting perforation" process is selected for the fracturing construction of the target horizontal fracturing section; ③ When the hydraulic fracture complexity index of the target horizontal fracturing section is in the range of [0, 0.6], the hydraulic fracture penetration index is in the range of [0, 0.6], and the multi-cluster hydraulic fracture balanced expansion index is in the range of (0.6, 1], the "temporary plugging in the fracture plus pre-placement of large-volume, high-viscosity fracturing fluid plus flow-limiting perforation and ball-throwing temporary plugging" process is selected for the fracturing construction of the target horizontal fracturing section; ④ When the hydraulic fracture complexity index of the target horizontal fracturing section is in the range of [0, 0.6], the hydraulic fracture penetration expansion index is in the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced expansion index is in the range of [0, 0.3], the "temporary plugging in the fracture plus flow-limiting perforation and ball-throwing temporary plugging" process is selected for the fracturing construction of the target horizontal fracturing section; ⑤ When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of [0, 0.6], the hydraulic fracture penetration index is within the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced expansion index is within the range of (0.3, 0.6], the "temporary plugging in the fracture plus flow-limiting perforation" process is adopted for the fracturing construction of the target horizontal fracturing section; ⑥ When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of [0, 0.6], the hydraulic fracture penetration index is within the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced expansion index is within the range of (0.6, 1], the "temporary plugging in the fracture" process is adopted for the fracturing construction of the target horizontal fracturing section; ⑦ When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of (0.6, 1], the hydraulic fracture penetration index is within the range of [0, 0.6], and the multi-cluster hydraulic fracture balanced expansion index is within the range of [0, 0.3], the "pre-placement of large-volume, high-viscosity fracturing fluid plus flow-limiting perforation and ball-throwing temporary plugging" process is adopted for the fracturing construction of the target horizontal fracturing section; ⑧ When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of (0.6, 1], the hydraulic fracture penetration index is within the range of [0, 0.6], and the multi-cluster hydraulic fracture balanced expansion index is within the range of (0.3, 0.6], the "pre-placement of large-volume, high-viscosity fracturing fluid plus flow-limiting perforation" process is adopted for the fracturing construction of the target horizontal fracturing section; ⑨ When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of (0.6, 1], the hydraulic fracture penetration index is within the range of [0, 0.6], and the multi-cluster hydraulic fracture balanced expansion index is within the range of (0.6, 1], the "pre-placement of large-volume, high-viscosity fracturing fluid" process is adopted for the fracturing construction of the target horizontal fracturing section; ⑩ When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of (0.6, 1], the hydraulic fracture penetration expansion index is within the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced expansion index is within the range of [0, 0.3], the "pre-placement of large-volume, high-viscosity fracturing fluid plus flow-limiting perforation and ball-throwing temporary plugging" process is adopted for the fracturing construction of the target horizontal fracturing section; When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of (0.6, 1], the hydraulic fracture penetration index is within the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced expansion index is within the range of (0.3, 0.6], the "limited flow perforation" process is used for the fracturing construction of the target horizontal fracturing section; When the hydraulic fracture complexity index of the target horizontal fracturing section is within the range of (0.6, 1], the hydraulic fracture penetration extension index is within the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced extension index is within the range of (0.6, 1], conventional volume fracturing is used for the target horizontal fracturing section.

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