A method for optimizing continental shale volume fracturing technology

Abstract

The present invention belongs to the technical field of oil and gas field development, and discloses a method for optimizing a volume fracturing process technology for continental shale, comprising the following steps: calculating a hydraulic fracture complexity index based on the reservoir rock brittleness index, horizontal stress difference, and natural fracture density; calculating a hydraulic fracture penetration index based on interlayer interface shear strength, interlayer stress difference, vertical stress difference, and tensile strength difference; calculating a multi-cluster hydraulic fracture equilibrium expansion index based on ground stress heterogeneity, fracture toughness heterogeneity, and Young's modulus; and optimizing a continental shale volume fracturing process based on the above three index evaluation indicators. The present invention adopts the above-mentioned method for optimizing a continental shale volume fracturing process technology, and considers the hydraulic fracture complexity index, hydraulic fracture penetration index, and multi-cluster hydraulic fracture equilibrium expansion index in parallel, providing an effective process optimization method for continental shale volume fracturing, which is conducive to increasing the volume of continental shale fracturing transformation.

Description

Technical Field

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

[0002] Domestic shale oil and gas resources are extremely abundant, making it 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 and terrestrial shales, the hydraulic fracturing effects vary greatly. Marine shales are generally more brittle, homogeneous, and rich in organic matter. Their natural fracture systems are relatively developed, and complex fracture networks are easily formed after fracturing. However, terrestrial shale reservoirs are characterized by strong heterogeneity and large differences in interlayer lithology. During volume fracturing, there are always problems such as single fracture morphology and small effective fracture volume, resulting in reduced oil and gas extraction efficiency. Combining domestic and international research progress and domestic terrestrial shale gas exploration and development practical experience, it is believed that the complexity of hydraulic fractures, the degree of hydraulic fracture penetration, and the balanced expansion of multiple clusters of hydraulic fractures are the key factors determining the effectiveness of volume fracturing. Therefore, it is urgent to propose a method for optimizing the volume fracturing technology of continental shale. Based on the calculation and comparison of the hydraulic fracture complexity index, the hydraulic fracture penetration expansion index and the multi-cluster hydraulic fracture balanced expansion index, the volume fracturing construction technology of continental shale can be recommended, so as to effectively avoid the above problems and have guiding significance for guiding on-site construction and increasing the reservoir transformation volume.

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

[0004] In summary, while existing methods can achieve balanced expansion of single-cluster fractures in continental shale reservoirs, they lack systematic volumetric fracturing technology support for increasing the complexity of hydraulic fractures, the extent of hydraulic fracture penetration, and the balanced expansion of multiple fracture clusters. Therefore, it is urgent to establish a method for optimizing continental shale volumetric fracturing technology to improve reservoir transformation effectiveness. 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 continental shale volume fracturing, which is conducive to increasing the volume of continental shale fracturing transformation.

[0006] To achieve the above objectives, the present invention provides a method for optimizing continental shale volume fracturing technology, 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 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: Analyze and compare the hydraulic fracture complexity index, the hydraulic fracture penetration expansion index, and the multi-cluster hydraulic fracture balanced expansion index to optimize 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. 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 is the normalized value, 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 the three factors of rock brittleness index, horizontal stress difference and natural fracture density on the complexity of hydraulic fractures in the target block are obtained;

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

[0020] Step S14: Finally, calculate the hydraulic fracture complexity index 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 shear strength, interlayer stress difference, vertical stress difference and tensile strength difference. The specific process is as follows:

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

[0025] Step S22: Secondly, a fluid-solid coupling model for hydraulic fracture propagation through layers in continental shale is established based on the finite element + cohesion element method, and the positive and negative correlations and the primary and secondary order of the effects of four factors, namely, interlayer shear strength, interlayer stress difference, tensile strength difference, and vertical stress difference, on hydraulic fracture propagation through layers 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 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, fracture toughness heterogeneity and Young's modulus, the equilibrium expansion index of multiple clusters of hydraulic fractures is calculated. 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 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 normalization 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 on the balanced expansion degree of the multi-cluster hydraulic fractures in the target block are obtained;

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

[0034] Step S34: Finally, calculate the balanced expansion index of multiple clusters of hydraulic fractures 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 within the fracture section, dimensionless; ΔK is the normalized fracture toughness difference within the fracture section, dimensionless; YM is the normalized Young's modulus, 0-1, dimensionless.

[0037] Preferably, in step S4, a fracturing construction plan for the target horizontal fracturing section is obtained based on three index evaluation indicators: the hydraulic fracture complexity index, the hydraulic fracture penetration expansion index, and the multi-cluster hydraulic fracture balanced expansion index of the target horizontal fracturing section, as shown below:

[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 expansion index is within the range of [0, 0.6], and the balanced expansion index of multiple clusters of hydraulic fractures 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-dropping 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 expansion 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 (0.3, 0.6], the "temporary plugging of fractures plus pre-injection of large-volume, high-viscosity fracturing fluid plus flow-limited 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 expansion 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 plus pre-placement of large-volume, high-viscosity fracturing fluid plus flow-limiting perforation and ball-dropping 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 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-dropping 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 expansion index is within the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced expansion index is within the range of (0.3, 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 expansion index is within the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced expansion index is within the range of (0.6, 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 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 "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 expansion index is within the range of [0, 0.6], and the multi-cluster hydraulic fracture balanced expansion index is within the range of (0.3, 0.6], the "pre-placement of large-volume, high-viscosity fracturing fluid plus flow-limited 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 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 "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 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-dropping 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 expansion index is within the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced expansion index is within the range of (0.3, 0.6], the "limited flow perforation" process is adopted 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 adopted 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 multi-cluster hydraulic fracture balanced expansion index in parallel, providing 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 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 expansion 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 are shown in Figure 2. (a) is E = 15 GPa; (b) is E = 30 GPa; (c) is E = 45 GPa.

[0057] Figure 6 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 the 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 with reference to 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: Calculate 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 is the normalized value, 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 the three factors of rock brittleness index, horizontal stress difference and natural fracture density on the complexity of hydraulic fractures in the target block are obtained.

[0069] Step S13: Then, the parameter weights a, b, and 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, calculate the hydraulic fracture complexity index 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 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 normalization calculation formulas are shown in formulas (1) and (2).

[0075] Step S22. Secondly, a fluid-solid coupling model of hydraulic fracture penetration expansion 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 expansion in the target block are obtained.

[0076] Step S23: Then, 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 based on the hierarchical analysis method.

[0077] Step S24: Finally, the hydraulic fracture penetration 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 fracture section, and the fracture toughness heterogeneity is characterized by the fracture toughness difference within the fracture section. The three parameters of the minimum horizontal in-situ stress difference, the fracture toughness difference, and the Young's modulus within the fracture section are normalized. The normalization 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 stress difference, fracture toughness difference and Young's modulus of the target block on the balanced expansion degree of multiple clusters of hydraulic fractures are obtained.

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

[0084] Step S34: Finally, calculate the balanced expansion index of multiple clusters of hydraulic fractures 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 within the fracture section, dimensionless; ΔK is the normalized fracture toughness difference within the fracture section, dimensionless; YM is the normalized Young's modulus, 0-1, dimensionless.

[0087] Step S4: Analyze and compare the hydraulic fracture complexity index, the hydraulic fracture penetration expansion index, and the multi-cluster hydraulic fracture balanced expansion index to optimize 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 balanced extension index of multiple clusters of hydraulic fractures 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-dropping 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 expansion 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 (0.3, 0.6], the "temporary plugging in the fracture + pre-placement of large-volume, high-viscosity fracturing fluid + flow-limited 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 expansion 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-dropping 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 balanced expansion index of multiple clusters of hydraulic fractures is in the range of [0, 0.3], the "temporary plugging in the fracture + flow-limiting perforation and ball-dropping 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 balanced expansion index of multiple clusters of hydraulic fractures 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 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 "pre-placement of large-volume, high-viscosity fracturing fluid + flow-limiting perforation and temporary plugging with ball dropping" 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 "pre-placement of large-volume, high-viscosity fracturing fluid + flow-limited 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 temporary plugging with ball dropping" 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 expansion index is within the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced expansion index is within the range of (0.3, 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 adopted for the target horizontal fracturing section.

[0101] Example

[0102] This embodiment takes the horizontal well Y9 in the continental shale oil block X 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, as shown in the following figure: 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: 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 the influencing factors were calculated using the sum method, and the relative weights of natural fracture density, horizontal stress difference, and rock brittleness index were 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, a fluid-solid coupling model of hydraulic fracture propagation through layers in continental shale was established based on the finite element + cohesion unit method in combination with the parameters of the target X block. 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 obtained by simulation, as shown in the following figure: Figure 4 Based on orthogonal experimental analysis, the order of influence of these four factors on the penetration of hydraulic fractures is determined to be: interlaminar interface shear strength > interlaminar 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 propagation of hydraulic fractures through layers

[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 were calculated based on the hierarchical analysis method, and the judgment matrix B of the factors affecting the propagation of hydraulic fractures through layers was constructed, as shown in Table 6:

[0123] Table 6 Judgment matrix B of factors affecting hydraulic fracture penetration and expansion

[0124] Interlayer interface shear strength interlaminar stress difference Poor tensile strength Vertical stress difference Interlayer 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 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, as shown in the figure below: 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 hydraulic fractures is: geostress heterogeneity > fracture toughness heterogeneity > Young's modulus, as shown in Figure 2. Figure 6 shown.

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

[0133] Table 8 Judgment matrix C of factors affecting the balanced expansion of multiple 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 the influencing factors were calculated using the sum method, and the relative weights of in-situ stress heterogeneity, fracture toughness heterogeneity, and Young's modulus were found to be 0.5476, 0.3155, and 0.1369, respectively.

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

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

[0138] Calculation of the hydraulic fracture complexity index F of each layer in Well Y9 net , hydraulic fracture penetration index F cc , balanced expansion index F of multiple hydraulic fractures jh The values ​​are shown in Table 9.

[0139] Table 9F of each layer of Well Y9 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 expansion index F cc , balanced expansion index F of multiple hydraulic fractures jh The fracturing operation plan of Well Y9 was dynamically adjusted and optimized based on the value of the fracturing operation plan. 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 sweep volume, complexity and vertical penetration degree of Well Y9 are all good. Figure 7 As shown, the daily oil production of a single well exceeds 25 tons, which is 80% higher than that of the 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 multi-cluster hydraulic fracture balanced expansion index in parallel, providing 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 solutions of the present invention rather than to limit the same. 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 solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions 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: Calculate the hydraulic fracture complexity index 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: （1）； The normalized calculation formula for negative indicators is as follows: （2）； in, Y i It is the normalized value and dimensionless; X i is the value before normalization; X max and 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 the three factors of rock brittleness index, horizontal stress difference and natural fracture density on the complexity of hydraulic fractures in the target block are obtained; Step S13: Then, the parameter weights a, b, and c of the three factors of rock brittleness index, horizontal stress difference, and natural fracture density are calculated based on the hierarchical analysis method; Step S14: Finally, calculate the hydraulic fracture complexity index as follows: （3）； in, F net is the hydraulic fracture complexity index, dimensionless; ρ nf is the normalized natural fracture density, dimensionless; ∆ σ is the normalized horizontal stress difference, dimensionless; B rit is the normalized rock brittleness index, dimensionless; 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: Analyze and compare the hydraulic fracture complexity index, the hydraulic fracture penetration expansion index, and the multi-cluster hydraulic fracture balanced expansion index to optimize the continental shale volume fracturing process.

2. The method for optimizing the continental shale volume fracturing technology according to claim 1, characterized in that: In step S2, the hydraulic fracture penetration index is calculated based on the interlayer shear strength, interlayer stress difference, vertical stress difference, and tensile strength difference. The specific process is as follows: Step S21: First, the four parameters of interlayer interface shear strength, interlayer stress difference, tensile strength difference, and vertical stress difference are normalized. The normalization calculation formula is as follows: The normalized calculation formula for positive indicators is as follows: （1）； The normalized calculation formula for negative indicators is as follows: （2）； in, Y i It is the normalized value and dimensionless; X i is the value before normalization; X max and X min are the maximum and minimum values ​​of the sample data; Step S22: Secondly, a fluid-solid coupling model for hydraulic fracture propagation through layers in continental shale is established based on the finite element + cohesion element method, and the positive and negative correlations and the primary and secondary order of the effects of four factors, namely, interlayer shear strength, interlayer stress difference, tensile strength difference, and vertical stress difference, on hydraulic fracture propagation through layers 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 index is calculated as follows: （4）； in, F cc is the hydraulic fracture penetration index, dimensionless; μ in is the normalized interlaminar interface shear strength, dimensionless; σ in is the normalized interlaminar stress difference, dimensionless; ∆ T in is the normalized tensile strength difference, dimensionless; ∆ σ v is the normalized vertical stress difference and is dimensionless.

3. The method for optimizing the continental shale volume fracturing technology according to claim 1, characterized in that: In step S3, the equilibrium growth index of multiple clusters of hydraulic fractures is calculated based on the in-situ stress heterogeneity, fracture toughness heterogeneity, and Young's modulus. The specific process is as follows: 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 normalization calculation formula is as follows: The normalized calculation formula for positive indicators is as follows: （1）； The normalized calculation formula for negative indicators is as follows: （2）； in, Y i It is the normalized value and dimensionless; X i is the value before normalization; X max and X min are the maximum and minimum values ​​of the sample data; 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 on the balanced expansion degree of the multi-cluster hydraulic fractures in the target block are obtained; Step S33: Then, the parameter weights h, i, j of the three factors of in-situ stress heterogeneity, fracture toughness heterogeneity and Young's modulus are calculated based on the hierarchical analysis method; Step S34: Finally, calculate the balanced expansion index of multiple clusters of hydraulic fractures as follows: （5）； in, F jh is the equilibrium expansion index of multiple hydraulic fractures, dimensionless; ∆ σ h is the normalized minimum horizontal stress difference within the fracture section, dimensionless; K is the normalized fracture toughness difference within the fracturing section, dimensionless; YM is the normalized Young's modulus, 0~1, dimensionless.

4. The method for optimizing the continental shale volume fracturing technology according to claim 1, characterized in that: In step S4, based on the three index evaluation indicators of the hydraulic fracture complexity index, the hydraulic fracture penetration expansion index, and the multi-cluster hydraulic fracture balanced expansion 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 balanced expansion index of multiple clusters of hydraulic fractures 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-dropping 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 within the range of [0, 0.6], the hydraulic fracture penetration expansion index is within the range of [0, 0.6], and the balanced expansion index of multiple clusters of hydraulic fractures is within the range of (0.3, 0.6]), the "temporary plugging of fractures plus pre-injection of large-volume, high-viscosity fracturing fluid plus flow-limited 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 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 (0.6, 1], the "temporary plugging in the fracture plus pre-placement of large-volume, high-viscosity fracturing fluid plus flow-limiting perforation and ball-dropping 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 balanced expansion index of multiple clusters of hydraulic fractures is in the range of [0, 0.3], the "temporary plugging in the fracture plus flow-limiting perforation and ball-dropping 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 expansion index is within the range of (0.6, 1], and the multi-cluster hydraulic fracture balanced expansion index is within the range of (0.3, 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 balanced expansion index of multiple clusters of hydraulic fractures 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 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 "pre-placement of large-volume, high-viscosity fracturing fluid with flow-limiting perforation and ball-dropping 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 expansion index is within the range of [0, 0.6], and the multi-cluster hydraulic fracture balanced expansion index is within the range of (0.3, 0.6], the "pre-placement of large-volume, high-viscosity fracturing fluid plus flow-limited 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 expansion index is within the range of [0, 0.6], and the multi-cluster hydraulic fracture balanced expansion index is within the range of (0.6, 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 with flow-limiting perforation and ball-dropping temporary plugging" process is adopted for the fracturing construction of the target horizontal fracturing section; ⑪ 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 adopted for the fracturing construction of the target horizontal fracturing section; ⑫ 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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