Fracturing method for longitudinal multi-layer horizontal well

Abstract

The invention discloses a fracturing method for a longitudinal multi-layer horizontal well, and relates to the technical field of oil and gas field exploitation, which comprises the following steps: constructing a multi-well fracturing geologic model; according to the constructed multi-well fracturing geologic model, interlayer ground stress difference is calculated, a low-stress-layer horizontal well and a high-stress-layer horizontal well are determined, and the stress value of the high-stress-layer horizontal well is larger than that of the low-stress-layer horizontal well; according to the interlayer crustal stress difference, a first stress change value of the low-stress layer horizontal well in the fracturing process is calculated, and the first stress change value is a first preset multiple of the interlayer crustal stress difference; according to the first stress change value and the interlayer crustal stress difference, a second stress change value of the high-stress-layer horizontal well in the fracturing process is determined, and the second stress change value is larger than 0 and smaller than or equal to the absolute value of the difference value of the first stress change value and the interlayer crustal stress difference; and according to the first stress change value and the second stress change value respectively.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field exploitation, and in particular to a vertical multi-layer horizontal well fracturing method. Background Art

[0002] Multi-layer horizontal well fracturing is an important technology for the development of unconventional reservoirs. Affected by the heterogeneity of inter-layer geostress and differences in mechanical properties, inter-well fractures are prone to "pressure channeling", that is, inter-well fractures communicate, which has an adverse impact on the production of adjacent wells.

[0003] In order to reduce the probability of pressure channeling, a zipper-type fracturing sequence is usually used based on experience, combined with a larger well spacing, a smaller construction scale or temporary plugging measures. However, there is a serious lack of theoretical and quantitative analysis in the empirical determination of multi-layer and multi-well fracturing schemes, and there is a lack of accurate, efficient and reliable design methods for designing multi-layer and multi-well fracturing sequences.

[0004] The above contents are only used to assist in understanding the technical solution of the present invention and do not constitute an admission that the above contents are prior art. Summary of the invention

[0005] The main purpose of the present invention is to provide a vertical multi-layer horizontal well fracturing method, aiming to solve or partially solve the above problems.

[0006] To achieve the above object, the present invention provides a method for fracturing a vertical multi-layer horizontal well, comprising: Constructing a multi-well fracturing geological model, wherein the parameters of the multi-well fracturing geological model include the spatial position of the fracturing wells, the wellbore parameters of the fracturing wells, the reservoir geological parameters, and the distribution of longitudinal geostress between layers; According to the constructed multi-well fracturing geological model, the inter-layer ground stress difference is calculated and the horizontal wells of the low stress layer and the horizontal wells of the high stress layer are determined, and the stress value of the horizontal wells of the high stress layer is greater than the stress value of the horizontal wells of the low stress layer; According to the interlayer in-situ stress difference, calculating a first stress change value of the low stress layer horizontal well during the fracturing process, the first stress change value being a first preset multiple of the interlayer in-situ stress difference; According to the first stress change value and the interlayer in-situ stress difference, the second stress change value of the high stress layer horizontal well during the fracturing process is determined, 0<second stress change value≤absolute value of the difference between the first stress change value and the interlayer in-situ stress difference.

[0007] According to the first stress change value and the second stress change value, a first construction parameter of the horizontal well in the low stress layer under the first stress change value and a second construction parameter of the horizontal well in the high stress layer under the second stress change value are solved respectively.

[0008] Preferably, in the vertical multi-layer horizontal well fracturing method, the first preset multiple is 1-1.5 times.

[0009] Preferably, in the vertical multi-layer horizontal well fracturing method, the first preset multiple is 1.5 times.

[0010] Preferably, in the fracturing method of the longitudinal multi-layer horizontal well, in the step of solving the first construction parameter of the low stress layer horizontal well under the first stress change value and the second construction parameter of the high stress layer horizontal well under the second stress change value according to the first stress change value and the second stress change value, the construction parameters include fracturing fluid viscosity, injection displacement, cluster spacing, and single-stage cluster number.

[0011] Preferably, in the fracturing method for the vertical multi-layer horizontal well, in the step of solving the first construction parameter of the low stress layer horizontal well under the first stress change value and the second construction parameter of the high stress layer horizontal well under the second stress change value according to the first stress change value and the second stress change value, the calculation formula of the first construction parameter of the low stress layer horizontal well under the first stress change value is: ; ; ; Among them, σ1 is the first stress change value of the horizontal well in the low stress layer during the fracturing process; n1 is the number of fractures in the horizontal well of the low stress layer; p 1i is the stress coefficient of the horizontal well in the low stress layer, Pa; r 1ij is the attenuation coefficient of the horizontal well in the low stress layer, dimensionless; μ1 is the fracturing fluid viscosity for horizontal well construction in low stress layer, Pa·s; E1' is the plane strain Young's modulus of the horizontal well in the low stress layer, Pa; Q 1,i is the liquid inflow rate of the i-th fracture in the horizontal well of the low stress layer, that is, the injection displacement, m 3 / s; h1 is the reservoir thickness of the horizontal well in the low stress layer, m; t is time, s; d 1ij is the distance from the i-th fracture to the j-th fracture in the horizontal well of the low stress layer, m; δ is the Dirac function, dimensionless.

[0012] Preferably, in the fracturing method for the vertical multi-layer horizontal well, in the step of solving the first construction parameter of the low stress layer horizontal well under the first stress change value and the second construction parameter of the high stress layer horizontal well under the second stress change value respectively according to the first stress change value and the second stress change value, the calculation formula of the second construction parameter of the high stress layer horizontal well under the second stress change value is: ; ; ; Among them, σ2 is the second stress change value of the horizontal well in the high stress layer during the fracturing process; n2 is the number of fractures in the horizontal well of the high stress layer; p 2i is the stress coefficient of the horizontal well in the high stress layer, Pa; r 2ij is the attenuation coefficient of the horizontal well in the high stress layer, dimensionless; μ2 is the fracturing fluid viscosity for horizontal well construction in high stress layers, Pa·s; E2' is the plane strain Young's modulus of the horizontal well in the high stress layer, Pa; Q 2,i is the fluid inflow rate of the i-th fracture in the horizontal well of the high stress layer, m 3 / s; h2 is the reservoir thickness of the horizontal well in the high stress layer, m; t is time, s; d 2ij is the distance from the i-th fracture to the j-th fracture in the horizontal well of the high stress layer, m; δ is the Dirac function, dimensionless.

[0013] Preferably, in the method for fracturing a longitudinal multi-layer horizontal well, in the step of constructing a multi-well fracturing geological model, the parameters of the multi-well fracturing geological model include the spatial position of the fracturing wells, the wellbore parameters of the fracturing wells, the reservoir geological parameters, and the longitudinal geostress distribution between layers, The spatial position of the fracturing well includes the measured depth, the vertical depth, and the position of the fracturing well in the formation; The wellbore parameters of the fracturing well include the roughness of the inner wall of the wellbore, the wellbore structure, and the well inclination angle; The reservoir geological parameters include Young's modulus, Poisson's ratio, fracture toughness, and filtration coefficient of rock; The interlayer longitudinal geostress distribution is the distribution of the minimum horizontal principal stress along each stratum vertically.

[0014] Preferably, in the fracturing method of the longitudinal multi-layer horizontal wells, in the step of constructing a multi-well fracturing geological model, the parameters of which include the spatial position of the fracturing wells, the wellbore parameters of the fracturing wells, the reservoir geological parameters, and the distribution of longitudinal geostress between layers, the multi-well fracturing geological model includes a fracture geometry model, a reservoir geological model and a wellbore geometry model.

[0015] Preferably, in the vertical multi-layer horizontal well fracturing method, determining the second stress change value of the high stress layer horizontal well during the fracturing process according to the first stress change value and the interlayer in-situ stress difference includes: The second stress change value is taken within a range greater than 0 and less than or equal to the absolute value of the difference between the first stress change value and the interlayer stress difference.

[0016] The present invention has at least the following beneficial effects: The present invention constructs a multi-well fracturing geological model, wherein the parameters of the multi-well fracturing geological model include the spatial position of the fracturing well, the wellbore parameters of the fracturing well, the reservoir geological parameters, and the interlayer longitudinal geostress distribution; according to the constructed multi-well fracturing geological model, the interlayer geostress difference is calculated and the low stress layer horizontal well and the high stress layer horizontal well are determined, wherein the stress value of the high stress layer horizontal well is greater than the stress value of the low stress layer horizontal well; according to the interlayer geostress difference, the first stress change value of the low stress layer horizontal well during the fracturing process is calculated, wherein the first stress change value is a first preset multiple of the interlayer geostress difference; according to the first stress change value and the interlayer geostress difference, the second stress change value of the high stress layer horizontal well during the fracturing process is determined, wherein 0 is less than the second stress change value and the absolute value of the difference between the first stress change value and the interlayer geostress difference; according to the first stress change value and the second stress change value, the first construction parameter of the low stress layer horizontal well under the first stress change value and the second construction parameter of the high stress layer horizontal well under the second stress change value are solved respectively, thereby providing an efficient and reliable design method for designing a multi-layer multi-well fracturing sequence.

[0017] Furthermore, the present invention obtains the spatial position of the fracturing well, the fracturing completion information, the reservoir geological parameters, and the interlayer longitudinal geostress distribution; then determines the interlayer geostress difference according to the spatial position of the fracturing well, the fracturing completion information, the reservoir geological parameters, and the interlayer longitudinal geostress distribution, thereby determining the fracturing sequence as "first low stress layer horizontal well, then high stress layer horizontal well". Then, the first stress change value is estimated according to the reservoir geological parameters, the first stress change value is selected and its value is about 1-1.5 times of the interlayer geostress difference, thereby further calculating the first construction parameter of the low stress layer horizontal well. According to the estimated second stress change value, the second stress change value is selected and its value is less than or equal to the absolute value of the difference between the first stress change value and the interlayer geostress difference, and then the second construction parameter of the high stress layer horizontal well is further calculated.

[0018] Furthermore, compared with the current design based on experience, the fracturing sequence of multiple horizontal wells is mostly designed based on experience, especially for the situation of multiple vertical layers; the present invention proposes a multi-layer horizontal well fracturing sequence design method based on the idea of ​​making an artificial stress barrier, and adopts the fracturing sequence of "low stress layer horizontal well first, then high stress layer horizontal well". Since the low stress layer horizontal well is the first layer to be fractured, most of the cracks in the low stress layer horizontal well are located in the low stress layer horizontal well after fracturing. Under the influence of the first stress change value, the ground stress of the low stress layer horizontal well is significantly increased, forming an "artificial stress barrier" to hinder the penetration and expansion of fracturing cracks in the high stress layer horizontal well, thereby reducing the possibility of fracture connectivity between wells and the probability of pressure channeling.

[0019] Furthermore, assuming that the fracturing sequence of "high stress layer horizontal wells first, then low stress layer horizontal wells" is adopted, the cracks in the high stress layer horizontal wells will tend to extend toward the low stress layer horizontal wells, which will increase the possibility of inter-well fracture connectivity and the probability of pressure channeling, affecting the final production. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A flow chart of a vertical multi-layer horizontal well fracturing method according to the present invention; Figure 2 It is a schematic diagram of a multi-layer horizontal well arrangement model of the present invention; Figure 3 This is a fracture morphology diagram after fracturing of a horizontal well of the present invention "horizontal well of low stress layer first, horizontal well of high stress layer later"; Figure 4 This is the fracture morphology diagram after fracturing of the horizontal well "horizontal well in high stress layer first, horizontal well in low stress layer later".

[0021] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0022] In the embodiments of the present invention, the term "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent three situations: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0023] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0024] In the embodiments of the present invention, the term "plurality" refers to two or more than two, and other quantifiers are similar.

[0025] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. However, it can be understood by those skilled in the art that in the embodiments of the present invention, many technical details are proposed in order to enable the reader to better understand the present invention. However, even without these technical details and various changes and modifications based on the following embodiments, the technical scheme claimed in the present invention can also be implemented. The division of the following embodiments is for the convenience of description and should not constitute any limitation on the specific implementation of the present invention. The various embodiments can be combined and referenced with each other under the premise of no contradiction.

[0026] The prior art (such as CN109933860A) discloses a method for optimizing the spacing between clusters of shale gas fracturing horizontal wells, and specifically discloses a method for optimizing the spacing between clusters of horizontal wells in a single horizontal well. The horizontal well fracturing disclosed in the patent is carried out in stages, and the fractures in the fractured sections will produce induced stress, change the formation stress distribution, and thus form stress interference on the fractures to be fractured next. The patent optimizes the optimal cluster spacing of the horizontal well by calculating the stress interference caused by the multiple clusters of fractures in the fractured section of a certain horizontal well to the multiple clusters of fractures in the unfractured section. Therefore, the core issue it reflects is the optimization problem of the spacing between clusters of a single horizontal well under the consideration of stress interference between fractures. That is, the patent is aimed at the optimization problem of the spacing between clusters of segmented multi-cluster fracturing of a single-layer horizontal well, and is applicable to the single-layer fracturing scenario of a single shale gas horizontal well.

[0027] That is, the prior art only considers the correlation between segmented fractures in a single horizontal well, and does not consider the situation of vertical multi-layer and multi-horizontal wells. The prior art is for a single horizontal well, and the horizontal well fracturing is carried out in stages. The fractures in the fractured section will produce induced stress, change the formation stress distribution, and thus form stress interference on the next fractured fracture. This patent calculates the stress interference caused by the multiple clusters of fractures in the fractured section of a horizontal well to the multiple clusters of fractures in the unfractured section, and optimizes the optimal cluster spacing of the horizontal well. Therefore, the core issue it reflects is the optimization problem of the cluster spacing of a single horizontal well under the stress interference between fractures.

[0028] The present invention is aimed at the situation of multi-layer and multi-horizontal wells in the vertical direction. When there are horizontal wells in multiple layers in the vertical direction, it is necessary to avoid the connection of inter-well cracks and pressure channeling caused by cracks penetrating the layers during construction. That is, the present invention focuses on the difference in inter-layer ground stress and the communication of inter-well cracks, and is suitable for the fracturing design and construction of multi-layer horizontal wells. The present invention first calculates the inter-layer stress difference and clarifies the fracturing sequence of multiple layers in the vertical direction. Then, based on the idea of ​​forming an artificial stress barrier, a preset range of ground stress change values ​​for each layer is given, and a calculation method for formation stress changes caused by crack interference after fracturing is proposed. Then, based on this, the fracturing construction parameters of each layer of horizontal wells are optimized to form a set of fracturing design methods for multi-layer and multi-horizontal wells. These are two completely different problems from those for a single horizontal well in the prior art.

[0029] Furthermore, the present invention and the prior art are aimed at completely different technical problems and are different in application environment, fracturing sequence determination, optimization target, complexity of models and methods, and construction parameter optimization.

[0030] Specifically, the present invention is different from the application environment in the prior art. The above-mentioned prior art mainly considers the stress distribution in a single-layer horizontal well and the interaction between cracks. Its model assumes that the cracks expand in the same horizontal layer, focusing on the stress interference effect between cracks. The present invention relates to vertical multi-layer and multi-horizontal wells. The crack expansion behavior of the low-stress layer and the high-stress layer is affected by the inter-layer stress difference. The transfer of inter-layer stress and the interlayer effect need to be considered. The models and methods given in the prior art cannot directly handle the complex stress relationship between multiple layers.

[0031] The optimization target of the present invention is different from that of the prior art. The optimization target of the prior art is the cluster spacing of a single well, and the optimal fracture spacing is determined by the induced stress curve. The optimization target of the present invention is the fracturing sequence and construction parameters of multiple layers and multiple wells. By designing artificial stress barriers, the possibility of fracture communication between wells is reduced, and the probability of pressure channeling is reduced. The prior art cannot achieve the optimization target of this patent.

[0032] The complexity of the model and method involved in the present invention is completely different. The models and methods in the prior art mainly focus on the stress distribution and crack extension in a single-layer horizontal well, and the calculation is relatively simple, focusing on the optimization of the crack spacing. However, the present invention needs to consider the stress distribution between multiple layers, the probability of crack communication between wells, and the influence of the fracturing sequence and multiple construction parameters on the crack morphology. The calculation complexity is higher and more comprehensive geological and engineering parameters are required, which are not considered and involved in the prior art.

[0033] Therefore, the present invention proposes a fracturing method for longitudinal multi-layer horizontal wells. The target object is the situation of longitudinal multi-layer and multi-horizontal wells. When there are horizontal wells in multiple layers in the vertical direction, it is necessary to avoid the situation of inter-well crack connection and pressure channeling caused by crack penetration during construction. This application first calculates the inter-layer stress difference, clarifies the fracturing sequence of the longitudinal multi-layer, and then gives the preset range of the ground stress change value of each layer based on the idea of ​​forming an artificial stress barrier, and proposes a calculation method for the formation stress change caused by crack interference after fracturing, and then optimizes the fracturing construction parameters of each layer of horizontal wells based on this, forming a set of fracturing design methods for multi-layer and multi-horizontal wells.

[0034] The present invention provides a schematic diagram of a vertical multi-layer horizontal well fracturing method, as shown in Figure 1 shown.

[0035] In step S100, a multi-well fracturing geological model is constructed, and the parameters of the multi-well fracturing geological model include the spatial position of the fracturing wells, the wellbore parameters of the fracturing wells, the reservoir geological parameters, and the distribution of longitudinal geostress between layers.

[0036] It should be understood that the multi-well fracturing geological model includes a fracture geometry model, a reservoir geological model and a wellbore geometry model.

[0037] The spatial position of the fracturing well includes the measured depth, the vertical depth, and the position of the fracturing well in the formation.

[0038] The wellbore parameters of the fracturing well include the roughness of the inner wall of the wellbore, the wellbore structure, and the well inclination angle.

[0039] The reservoir geological parameters include Young's modulus, Poisson's ratio, fracture toughness, and fluid loss coefficient of rock. In this embodiment, the reservoir geological parameters (oil reservoir geological parameters) can be obtained through well logging technology.

[0040] The interlayer longitudinal geostress distribution is the distribution of the minimum horizontal principal stress along each stratum vertically.

[0041] The multi-well fracturing geological model includes a fracture geometry model, a reservoir geological model and a wellbore geometry model.

[0042] It should be noted that the fracture geometry model is a model used to describe the spatial shape and size of fractures. The reservoir geological model is a three-dimensional spatial model that quantitatively characterizes the geological characteristics of the reservoir. The wellbore geometry model is a model used to describe the spatial shape, size and other characteristics of the wellbore of oil wells, gas wells, etc.

[0043] The following takes a well platform as an example, where the reservoir geology, engineering parameters, and wellbore parameters are shown in Table 1.

[0044] Table 1 Some parameters of multi-well fracturing geological model In step S200, based on the constructed multi-well fracturing geological model, the interlayer stress difference is calculated and the low stress layer horizontal well and the high stress layer horizontal well are determined, and the stress value of the high stress layer horizontal well is greater than the stress value of the low stress layer horizontal well.

[0045] More specifically, the stress values ​​of the low stress layer horizontal well and the high stress layer horizontal well are determined according to the interlayer longitudinal geostress distribution in the multi-well fracturing geological model. When the high stress layer horizontal well and the low stress layer horizontal well are uncertain, the minimum horizontal principal stress of the first stress layer and the minimum horizontal principal stress of the second stress layer are compared. When the minimum horizontal principal stress of the first stress layer is greater than the minimum horizontal principal stress of the second stress layer, the first stress layer is determined to be a high stress layer horizontal well and the second stress layer is determined to be a low stress layer horizontal well. The absolute value of the minimum horizontal principal stress of the first stress layer minus the minimum horizontal principal stress of the second stress layer is taken as the interlayer geostress difference. For example, the interlayer geostress difference is 1.3MPa.

[0046] When calculating the first stress change value of the low stress layer horizontal well during the fracturing process and the second stress change value of the high stress layer horizontal well during the fracturing process, the horizontal wells with low stress layer first and high stress layer later are used.

[0047] It should be noted that the low stress layer horizontal well and the high stress layer horizontal well are different horizontal wells in the vertical direction, rather than different sections of the same horizontal well.

[0048] In step S300, a first stress change value of the low stress layer horizontal well during the fracturing process is calculated according to the interlayer in-situ stress difference, and the first stress change value is a first preset multiple of the interlayer in-situ stress difference.

[0049] The first preset multiple is 1-1.5 times. Preferably, the first preset multiple is 1.5 times. In other embodiments, the first preset multiple can also be 1.3.

[0050] Taking the interlayer stress difference of 1.3MPa as an example, when the first preset multiple is 1-1.5 times, the first stress change value can be 1.3MPa-1.95MPa.

[0051] For a horizontal well in a low stress layer, the first stress change value can be selected first. For a horizontal well in a low stress layer, different construction parameters correspond to different first stress change values, so the corresponding first construction parameters can be inferred from the first stress change value.

[0052] It should be noted that the first stress change value refers to the stress change in the formation caused by factors such as the formation and expansion of cracks and the loss of fracturing fluid during the fracturing process of the horizontal well in the low stress layer. It reflects the stress change in the layer (low stress layer) where the horizontal well is located.

[0053] In step S400, a second stress change value of the high stress layer horizontal well during the fracturing process is determined according to the first stress change value and the interlayer in-situ stress difference, 0<second stress change value≤absolute value of the difference between the first stress change value and the interlayer in-situ stress difference.

[0054] Specifically, the second stress change value is taken within a range greater than 0 and less than or equal to the absolute value of the difference between the first stress change value and the interlayer stress difference.

[0055] It should be noted that, taking the first stress change value of 1.9 MPa and the interlayer stress difference of 1.3 MPa as an example, the second stress change value is (0, 0.6] MPa, and a value in this range can be selected as the second stress change value.

[0056] It should be understood that for a horizontal well in a high stress layer, the second stress change value can be selected first. For a horizontal well in a high stress layer, different construction parameters correspond to different second stress change values, so the corresponding second construction parameters can be inferred from the second stress change value.

[0057] For example, if the absolute value of the difference between the first stress change value and the interlayer ground stress difference is 3 MPa, then the second stress change value can be selected to be a value between 0 and 3 MPa (except 0); and then the corresponding second construction parameter can be inferred based on the selected second stress change value.

[0058] It should be noted that the second stress change value refers to the stress change in the formation caused by factors such as the formation and expansion of cracks and the loss of fracturing fluid during the fracturing process of the horizontal well in the low stress layer. It reflects the stress change in the layer (high stress layer) where the horizontal well is located.

[0059] In step S500, a first construction parameter of a horizontal well in a low stress layer under a first stress change value and a second construction parameter of a horizontal well in a high stress layer under a second stress change value are solved according to the first stress change value and the second stress change value respectively.

[0060] It should be understood that the first construction parameter / the second construction parameter includes fracturing fluid viscosity, injection displacement, cluster spacing, and the number of clusters in a single stage.

[0061] Wherein, the calculation formula of the first construction parameter of the horizontal well in the low stress layer under the first stress change value is: ; ; ; Among them, σ1 is the first stress change value of the horizontal well in the low stress layer during the fracturing process; n1 is the number of fractures in the horizontal well of the low stress layer; p 1i is the stress coefficient of the horizontal well in the low stress layer, Pa; r 1ij is the attenuation coefficient of the horizontal well in the low stress layer, dimensionless; μ1 is the fracturing fluid viscosity for horizontal well construction in low stress layer, Pa·s; E1' is the plane strain Young's modulus of the horizontal well in the low stress layer, Pa; Q 1,i is the liquid inflow rate of the i-th fracture in the horizontal well of the low stress layer, that is, the injection displacement, m 3 / s; h1 is the reservoir thickness of the horizontal well in the low stress layer, m; t is time, s; d 1ij为 The distance from the i-th fracture to the j-th fracture in the horizontal well of the low stress layer, m; δ is the Dirac function, dimensionless.

[0062] Among them, the calculation formula of the second construction parameter of the horizontal well in the high stress layer under the second stress change value is: ; ; ; Among them, σ2 is the second stress change value of the horizontal well in the high stress layer during the fracturing process; n2 is the number of fractures in the horizontal well of the high stress layer; p 2i is the stress coefficient of the horizontal well in the high stress layer, Pa; r 2ij is the attenuation coefficient of the horizontal well in the high stress layer, dimensionless; μ2 is the fracturing fluid viscosity for horizontal well construction in high stress layers, Pa·s; E2' is the plane strain Young's modulus of the horizontal well in the high stress layer, Pa; Q 2,i is the fluid inflow rate of the i-th fracture in the horizontal well of the high stress layer, m 3 / s; h2 is the reservoir thickness of the horizontal well in the high stress layer, m; t is time, s; d 2ij is the distance from the i-th fracture to the j-th fracture in the horizontal well of the high stress layer, m; δ is the Dirac function, dimensionless.

[0063] It should be noted that in the construction parameters, the total number of clusters = the number of single-segment clusters * the total number of segments = the number of cracks, and the total number of segments is usually known; the cluster spacing = the distance between two adjacent cracks.

[0064] For example, the first construction parameters calculated may be: fracturing fluid viscosity 5mPa·s, injection displacement 12m 3 / min, cluster spacing 10m, 3 clusters in a single section.

[0065] The second construction parameters can be calculated as follows: fracturing fluid viscosity 1mPa·s, injection displacement 8m 3 / min, cluster spacing 20m, 2 clusters in a single section.

[0066] The crack morphology under the design parameters adopted by the present invention can be as follows Figure 3 As shown, the present invention forms an artificial stress barrier in the horizontal well of the low stress layer, which hinders the penetration extension of the cracks in the high stress layer, thereby reducing the possibility of fracture communication between wells. Figure 4 The diagram shows "horizontal wells in low stress layers first, then horizontal wells in high stress layers", which is the opposite of the present invention, i.e. "horizontal wells in high stress layers first, then horizontal wells in low stress layers". Figure 3 and Figure 4 , obviously, Figure 4 The more overlapping parts of the fractures are, the more likely it is that the fractures between the wells will communicate with each other, that is, the effect provided by the present invention is better.

[0067] Obviously, the embodiments described above are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, ordinary technicians in this field can make other different forms of changes or modifications without creative work, which should fall within the scope of protection of the present invention.

Claims

1. A method for fracturing a longitudinal multi-layer horizontal well, characterized in that: include: Constructing a multi-well fracturing geological model, wherein the parameters of the multi-well fracturing geological model include the spatial position of the fracturing wells, the wellbore parameters of the fracturing wells, the reservoir geological parameters, and the distribution of longitudinal geostress between layers; According to the constructed multi-well fracturing geological model, the inter-layer ground stress difference is calculated and the horizontal wells of the low stress layer and the horizontal wells of the high stress layer are determined, and the stress value of the horizontal wells of the high stress layer is greater than the stress value of the horizontal wells of the low stress layer; According to the interlayer in-situ stress difference, calculating a first stress change value of the low stress layer horizontal well during the fracturing process, the first stress change value being a first preset multiple of the interlayer in-situ stress difference; Determine a second stress change value of the high stress layer horizontal well during the fracturing process according to the first stress change value and the interlayer in-situ stress difference, 0<second stress change value≤absolute value of the difference between the first stress change value and the interlayer in-situ stress difference; According to the first stress change value and the second stress change value, a first construction parameter of the horizontal well in the low stress layer under the first stress change value and a second construction parameter of the horizontal well in the high stress layer under the second stress change value are solved respectively.

2. The method for fracturing a vertical multi-layer horizontal well according to claim 1, characterized in that: The first preset multiple is 1-1.5 times.

3. The method for fracturing a vertical multi-layer horizontal well according to claim 2, characterized in that: The first preset multiple is 1.5 times.

4. The method for fracturing a vertical multi-layer horizontal well according to claim 1, characterized in that: In the steps of solving the first construction parameter of the horizontal well in the low stress layer under the first stress change value and the second construction parameter of the horizontal well in the high stress layer under the second stress change value respectively according to the first stress change value and the second stress change value, the first construction parameter / the second construction parameter includes fracturing fluid viscosity, injection displacement, cluster spacing, and single-stage cluster number.

5. The method for fracturing a vertical multi-layer horizontal well according to claim 4, characterized in that: In the step of solving the first construction parameter of the horizontal well in the low stress layer under the first stress change value and the second construction parameter of the horizontal well in the high stress layer under the second stress change value according to the first stress change value and the second stress change value, the calculation formula of the first construction parameter of the horizontal well in the low stress layer under the first stress change value is: ； ； ； Among them, σ1 is the first stress change value of the horizontal well in the low stress layer during the fracturing process; n1 is the number of fractures in the horizontal well of the low stress layer; p 1i is the stress coefficient of the horizontal well in the low stress layer, Pa; r 1ij is the attenuation coefficient of the horizontal well in the low stress layer, dimensionless; μ1 is the fracturing fluid viscosity for horizontal well construction in low stress layer, Pa·s; E1' is the plane strain Young's modulus of the horizontal well in the low stress layer, Pa; Q 1,i is the liquid inflow rate of the i-th fracture in the horizontal well of the low stress layer, that is, the injection displacement, m 3 / s; h1 is the reservoir thickness of the horizontal well in the low stress layer, m; t is time, s; d 1ij is the distance from the i-th fracture to the j-th fracture in the horizontal well of the low stress layer, m; δ is the Dirac function, dimensionless.

6. The method for fracturing a vertical multi-layer horizontal well according to claim 4, characterized in that: In the step of solving the first construction parameter of the horizontal well in the low stress layer under the first stress change value and the second construction parameter of the horizontal well in the high stress layer under the second stress change value according to the first stress change value and the second stress change value, the calculation formula of the second construction parameter of the horizontal well in the high stress layer under the second stress change value is: ； ； ； Among them, σ2 is the second stress change value of the horizontal well in the high stress layer during the fracturing process; n2 is the number of fractures in the horizontal well of the high stress layer; p 2i is the stress coefficient of the horizontal well in the high stress layer, Pa; r 2ij is the attenuation coefficient of the horizontal well in the high stress layer, dimensionless; μ2 is the fracturing fluid viscosity for horizontal well construction in high stress layers, Pa·s; E2' is the plane strain Young's modulus of the horizontal well in the high stress layer, Pa; Q 2,i is the fluid inflow rate of the i-th fracture in the horizontal well of the high stress layer, m 3 / s; h2 is the reservoir thickness of the horizontal well in the high stress layer, m; t is time, s; d 2ij is the distance from the i-th fracture to the j-th fracture in the horizontal well of the high stress layer, m; δ is the Dirac function, dimensionless.

7. The method for fracturing a vertical multi-layer horizontal well according to claim 1, characterized in that: In the step of constructing a multi-well fracturing geological model, the parameters of the multi-well fracturing geological model include the spatial position of the fracturing wells, the wellbore parameters of the fracturing wells, the reservoir geological parameters, and the distribution of longitudinal geostress between layers, The spatial position of the fracturing well includes the measured depth, the vertical depth, and the position of the fracturing well in the formation; The wellbore parameters of the fracturing well include the roughness of the inner wall of the wellbore, the wellbore structure, and the well inclination angle; The reservoir geological parameters include Young's modulus, Poisson's ratio, fracture toughness, and filtration coefficient of rock; The interlayer longitudinal geostress distribution is the distribution of the minimum horizontal principal stress along each stratum vertically.

8. The method for fracturing a vertical multi-layer horizontal well according to claim 6, characterized in that: In the step of constructing a multi-well fracturing geological model, the parameters of the multi-well fracturing geological model include the spatial position of the fracturing wells, the wellbore parameters of the fracturing wells, the reservoir geological parameters, and the distribution of longitudinal geostress between layers. The multi-well fracturing geological model includes a fracture geometry model, a reservoir geological model and a wellbore geometry model.

9. The method for fracturing a vertical multi-layer horizontal well according to claim 1, characterized in that: Determining the second stress change value of the high stress layer horizontal well during the fracturing process according to the first stress change value and the interlayer in-situ stress difference includes: The second stress change value is taken within a range greater than 0 and less than or equal to the absolute value of the difference between the first stress change value and the interlayer stress difference.

Images