Fracturing method for vertical multi-layer horizontal wells

Abstract

The present invention discloses a fracturing method for vertical multi-layer horizontal wells, which relates to the technical field of oil and gas field exploitation, and includes constructing a multi-well fracturing geological model; according to the constructed multi-well fracturing geological model, calculating the interlayer in-situ stress difference and determining the horizontal well in the low-stress layer and the horizontal well in the high-stress layer, wherein the stress value of the horizontal well in the high-stress layer > the stress value of the horizontal well in the low-stress layer; according to the interlayer in-situ stress difference, calculating the first stress change value of the horizontal well in the low-stress layer during the fracturing process, and the first stress change value is the first preset multiple of the interlayer in-situ stress difference; according to the first stress change value and the interlayer in-situ stress difference, determining the second stress change value of the horizontal well in the high-stress layer during the fracturing process, 0 < the second stress change value ≤ the absolute value of the difference between the first stress change value and the interlayer in-situ stress difference; respectively according to the first stress change value and the second stress change value.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field exploitation, and particularly to a fracturing method for vertical multi-layer horizontal wells. Background Art

[0002] Multi-layer horizontal well fracturing is an important technology for unconventional reservoir development. Affected by the heterogeneity of interlayer in-situ stresses and mechanical property differences, fractures between wells are prone to "fracture communication", that is, fractures between wells communicate, which has an adverse impact on the production of adjacent wells.

[0003] In order to reduce the probability of fracture communication, a zipper fracturing sequence is usually adopted according to experience, combined with a larger well spacing, a smaller construction scale or temporary plugging measures, etc. However, determining the multi-layer multi-well fracturing plan through experience seriously lacks theoretical and quantitative analysis, and there is a lack of an accurate, efficient and reliable design method for designing the multi-layer multi-well fracturing sequence.

[0004] The above content is only used to assist in understanding the technical solution of the present invention, and does not represent an admission that the above content is prior art. Summary of the Invention

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

[0006] To achieve the above object, the present invention provides a fracturing method for vertical multi-layer horizontal wells, including:

[0007] Constructing a multi-well fracturing geological model, the parameters of the multi-well fracturing geological model including the spatial position of the fracturing well, the wellbore parameters of the fracturing well, the reservoir geological parameters, and the interlayer vertical in-situ stress distribution;

[0008] According to the constructed multi-well fracturing geological model, calculating the interlayer in-situ stress difference and determining the low-stress layer horizontal well and the high-stress layer horizontal well, the stress value of the high-stress layer horizontal well > the stress value of the low-stress layer horizontal well;

[0009] 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;

[0010] According to the first stress change value and the interlayer in-situ stress difference, determining a second stress change value of the high-stress layer horizontal well during the fracturing process, 0 < the second stress change value ≤ the absolute value of the difference between the first stress change value and the interlayer in-situ stress difference.

[0011] Respectively according to the first stress change value and the second stress change value, solving the first construction parameters of the low-stress layer horizontal well under the first stress change value and the second construction parameters of the high-stress layer horizontal well under the second stress change value.

[0012] Preferably, in the fracturing method of the vertical multi-layer horizontal well, the first preset multiple is 1 - 1.5 times.

[0013] Preferably, in the fracturing method of the vertical multi-layer horizontal well, the first preset multiple is 1.5 times.

[0014] Preferably, in the fracturing method of the vertical multi-layer horizontal well, in the step of solving the first construction parameters of the horizontal well in the low stress layer under the first stress change value and the second construction parameters 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 construction parameters include fracturing fluid viscosity, injection displacement, cluster spacing, and number of clusters per single stage.

[0015] Preferably, in the fracturing method of the vertical multi-layer horizontal well, in the step of solving the first construction parameters of the horizontal well in the low stress layer under the first stress change value and the second construction parameters 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 calculation formula for the first construction parameters of the horizontal well in the low stress layer under the first stress change value is:

[0016] ;

[0017] ;

[0018] ;

[0019] where, σ 1 is the first stress change value of the horizontal well in the low stress layer during fracturing;

[0020] n 1 is the number of fractures in the horizontal well in the low stress layer;

[0021] p 1i is the stress coefficient of the horizontal well in the low stress layer, Pa;

[0022] r 1ij is the attenuation coefficient of the horizontal well in the low stress layer, dimensionless;

[0023] μ 1 is the fracturing fluid viscosity for the construction of the horizontal well in the low stress layer, Pa·s;

[0024] E 1 ’ is the plane strain Young's modulus of the horizontal well in the low stress layer, Pa;

[0025] Q 1,i is the inflow rate of the i-th fracture in the horizontal well in the low stress layer, i.e., the injection displacement, m 3 / s;

[0026] h 1 is the reservoir thickness of the horizontal well in the low-stress layer, m;

[0027] t is the time, s;

[0028] d 1ij is the distance between the ith fracture and the jth fracture in the horizontal well of the low-stress layer, m;

[0029] δ is the Dirac function, dimensionless.

[0030] Preferably, in the fracturing method of the longitudinal multi-layer horizontal well, in the step of respectively 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:

[0031] ;

[0032] ;

[0033] ;

[0034] where σ 2 is the second stress change value of the horizontal well in the high-stress layer during fracturing;

[0035] n 2 is the number of fractures in the horizontal well of the high-stress layer;

[0036] p 2i is the stress coefficient of the horizontal well in the high-stress layer, Pa;

[0037] r 2ij is the attenuation coefficient of the horizontal well in the high-stress layer, dimensionless;

[0038] μ 2 is the viscosity of the fracturing fluid for horizontal well construction in the high-stress layer, Pa·s;

[0039] E 2 ’ is the plane strain Young's modulus of the horizontal well in the high-stress layer, Pa;

[0040] Q 2,i is the inflow rate of the ith fracture in the horizontal well of the high-stress layer, m 3 / s;

[0041] h 2 is the reservoir thickness of the horizontal well in the high-stress layer, m;

[0042] t is the time, s;

[0043] d 2ij is the distance, in m, from the i-th fracture to the j-th fracture in the high-stress layer horizontal well;

[0044] δ is the Dirac function, dimensionless.

[0045] Preferably, in the fracturing method for the longitudinal multi-layer horizontal well, in the step of constructing the multi-well fracturing geological model, 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 in-situ stress distribution,

[0046] the spatial position of the fracturing well includes the measured depth, the vertical depth, and the position of the fracturing well in the formation;

[0047] the wellbore parameters of the fracturing well include the roughness of the inner wall of the wellbore, the wellbore structure, and the well deviation angle;

[0048] the reservoir geological parameters include the Young's modulus of the rock, the Poisson's ratio, the fracture toughness, and the filtration coefficient;

[0049] the interlayer longitudinal in-situ stress distribution is the distribution of the minimum horizontal principal stress along each formation in the vertical direction.

[0050] Preferably, in the fracturing method for the longitudinal multi-layer horizontal well, in the step of constructing the multi-well fracturing geological model, 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 in-situ stress distribution, the multi-well fracturing geological model includes a fracture geometry model, a reservoir geological model, and a wellbore geometry model.

[0051] Preferably, in the fracturing method for the longitudinal multi-layer horizontal well, the step of 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:

[0052] Taking the second stress change value within the 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 in-situ stress difference.

[0053] The present invention has at least the following beneficial effects:

[0054] The present invention constructs 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 inter - layer longitudinal in - situ stress distribution. According to the constructed multi - well fracturing geological model, the inter - layer in - situ stress difference is calculated, and the horizontal wells in the low - stress layer and the horizontal wells in the high - stress layer are determined. The stress value of the horizontal wells in the high - stress layer > the stress value of the horizontal wells in the low - stress layer. According to the inter - layer in - situ stress difference, the first stress change value during the fracturing process of the horizontal wells in the low - stress layer is calculated, and the first stress change value is the first preset multiple of the inter - layer in - situ stress difference. According to the first stress change value and the inter - layer in - situ stress difference, the second stress change value during the fracturing process of the horizontal wells in the high - stress layer is determined, where 0 < the second stress change value ≤ the absolute value of the difference between the first stress change value and the inter - layer in - situ stress difference. The first construction parameters of the horizontal wells in the low - stress layer under the first stress change value and the second construction parameters of the horizontal wells in the high - stress layer under the second stress change value are solved respectively according to the first stress change value and the second stress change value. In this way, an efficient and reliable design method for the fracturing sequence of multiple layers and multiple wells can be provided.

[0055] Furthermore, the present invention obtains the spatial position of the fracturing wells, the fracturing completion information, the reservoir geological parameters, and the inter - layer longitudinal in - situ stress distribution. Then, according to the spatial position of the fracturing wells, the fracturing completion information, the reservoir geological parameters, and the inter - layer longitudinal in - situ stress distribution, the inter - layer in - situ stress difference is determined, so as to determine the fracturing sequence as "first the horizontal wells in the low - stress layer, and then the horizontal wells in the high - stress layer". Then, the first stress change value is estimated according to the reservoir geological parameters, and the first stress change value is selected and its value is about 1 - 1.5 times the inter - layer in - situ stress difference, so as to further calculate the first construction parameters of the horizontal wells in the low - stress layer. According to the estimated second stress change value, the second stress change value is selected and its value is numerically less than or equal to the absolute value of the difference between the first stress change value and the inter - layer in - situ stress difference, and then the second construction parameters of the horizontal wells in the high - stress layer are further calculated.

[0056] Furthermore, compared with the current design based on experience, for the fracturing sequence of multi - horizontal wells, it is mostly designed according to experience, especially for the case of longitudinal multiple layers. The present invention proposes a design method for the fracturing sequence of multi - layer horizontal wells based on the idea of making artificial stress barriers, and adopts the fracturing sequence of "first the horizontal wells in the low - stress layer, and then the horizontal wells in the high - stress layer". Since the horizontal wells in the low - stress layer are the first to be fractured, most of the fractures are located in the horizontal wells in the low - stress layer after the fracturing of the horizontal wells in the low - stress layer. Under the influence of the first stress change value, the in - situ stress of the horizontal wells in the low - stress layer increases significantly, forming an "artificial stress barrier", which hinders the cross - layer propagation of the fracturing fractures of the horizontal wells in the high - stress layer and reduces the possibility of well - to - well fracture connection and the probability of fracturing through.

[0057] Furthermore, assuming a fracturing sequence of "high-stress layer horizontal well first, then low-stress layer horizontal well", the fractures of the high-stress layer horizontal well tend to extend towards the low-stress layer horizontal well, which will increase the possibility of inter-well fracture connection, increase the probability of fracturing channeling, and affect the final production. Description of the Drawings

[0058] Figure 1 It is a flowchart of the fracturing method for the vertical multi-layer horizontal well of the present invention;

[0059] Figure 2 It is a schematic diagram of the multi-layer horizontal well layout model of the present invention;

[0060] Figure 3 It is a fracture morphology diagram after fracturing the horizontal well of the present invention with "low-stress layer horizontal well first, then high-stress layer horizontal well";

[0061] Figure 4 It is a fracture morphology diagram after fracturing the horizontal well with "high-stress layer horizontal well first, then low-stress layer horizontal well".

[0062] The realization, functional features and advantages of the object of the present invention will be further described with reference to the accompanying drawings in combination with the embodiments. Detailed Embodiments

[0063] In the embodiments of the present invention, the term "and / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0064] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily describe a specific order or sequence.

[0065] In the embodiments of the present invention, the term "plurality" refers to two or more, and other quantifiers are similar.

[0066] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, those of ordinary skill in the art can understand that in the embodiments of the present invention, many technical details are provided for 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 solutions required to be protected by the present invention can still be realized. The following division of each embodiment is for convenience of description and should not constitute any limitation to the specific implementation manner of the present invention. Each embodiment can be combined and cross-referenced with each other on the premise of not conflicting.

[0067] The prior art (such as CN109933860A) discloses a method for optimizing the cluster spacing of horizontal wells in shale gas fracturing. Specifically, it discloses a method for optimizing the cluster spacing of horizontal wells in a single horizontal well. The fracturing of the horizontal well disclosed in this patent is carried out in stages. The fractures in the fractured section will generate induced stress, which will change the formation stress distribution, thus causing stress interference to the fractures to be fractured next. This patent optimizes the optimal cluster spacing of the horizontal well by calculating the stress interference generated by multiple clusters of fractures in the fractured section of a horizontal well on multiple clusters of fractures in the unfractured section. Therefore, the core problem it reflects is the optimization problem of the cluster spacing of a single horizontal well considering the stress interference between fractures. That is, this patent aims at the optimization problem of the cluster spacing of multi-cluster staged fracturing in a single-layer horizontal well and is applicable to the single-layer fracturing scenario of a single shale gas horizontal well.

[0068] That is, the prior art only considers the correlation between the staged fractures in a single horizontal well and does not consider the case of multiple horizontal wells in multiple longitudinal layers. In the prior art, the target is a single horizontal well. The fracturing of the horizontal well is carried out in stages. The fractures in the fractured section will generate induced stress, which will change the formation stress distribution, thus causing stress interference to the fractures to be fractured next. This patent optimizes the optimal cluster spacing of the horizontal well by calculating the stress interference generated by multiple clusters of fractures in the fractured section of a horizontal well on multiple clusters of fractures in the unfractured section. Therefore, the core problem it reflects is the optimization problem of the cluster spacing of a single horizontal well considering the stress interference between fractures.

[0069] However, the object of the present invention is the case of multiple horizontal wells in multiple longitudinal layers. When there are horizontal wells in multiple longitudinal layers, during construction, it is necessary to avoid the connection of fractures between wells and the situation of fracturing through caused by fractures penetrating layers. That is, the focus of the present invention lies in the problem of the difference in in-situ stress between layers and the communication of fractures between wells, and it is applicable to the fracturing design and construction of multiple horizontal wells. The present invention first calculates the stress difference between layers, clarifies the fracturing sequence of multiple longitudinal layers, then gives a preset range of the change value of the in-situ stress of each layer based on the idea of forming an artificial stress isolation layer, proposes a calculation method for the formation stress change caused by fracture interference after fracturing, and then optimizes the fracturing construction parameters of each layer of horizontal wells based on this to form a set of fracturing design methods for multiple horizontal wells. It is a completely different problem from the prior art which targets a single horizontal well.

[0070] Furthermore, the present invention and the prior art are completely directed to different technical problems and are different in terms of application environment, determination of fracturing sequence, optimization objectives, complexity of models and methods, and optimization of construction parameters.

[0071] Specifically, the application environment of the present invention is different from that of the prior art. In the above prior art, the stress distribution in a single-layer horizontal well and the interaction between fractures are mainly considered. The model assumes that fractures propagate within the same horizontal layer, and focuses on the stress interference effect between fractures. The present invention relates to vertical multi-layer multi-horizontal wells. The fracture propagation behaviors in low-stress layers and high-stress layers are affected by the interlayer in-situ stress difference, and the transfer of interlayer stress and the interlayer effect need to be considered. The models and methods given in the prior art cannot directly handle the complex stress relationships between multiple layers.

[0072] The optimization objectives of the present invention are different from those of the prior art. The optimization objective of the prior art is the cluster spacing of a single well, and the optimal fracture spacing is determined through the induced stress curve. The optimization objective of the present invention is the fracturing sequence and construction parameters of multi-layer multi-wells. By designing artificial stress interlayers, the possibility of fracture communication between wells is reduced, and the probability of fracturing crossflow is decreased. The prior art cannot achieve the optimization objective of this patent.

[0073] The complexity of the models and methods involved in the present invention is completely different. The models and methods in the prior art mainly focus on the stress distribution and fracture propagation in a single-layer horizontal well, and the calculation is relatively simple, mainly focusing on the optimization of fracture spacing. While the present invention needs to consider the stress distribution between multiple layers, the probability of fracture communication between wells, and the influence of fracturing sequence and multiple construction parameters on fracture 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.

[0074] Therefore, the present invention proposes a fracturing method for vertical multi-layer horizontal wells. The object targeted is the situation of vertical multi-layer multi-horizontal wells. When there are horizontal wells in multiple vertical layers during construction, it is necessary to avoid the wellbore fracture connection and fracturing crossflow caused by fracture penetration through layers. This application first calculates the interlayer stress difference, clarifies the fracturing sequence of vertical multi-layers, then gives the preset range of the in-situ stress change value of each layer based on the idea of forming artificial stress interlayers, proposes a calculation method for the formation stress change caused by fracture 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 multi-horizontal wells.

[0075] The present invention provides a schematic diagram of a fracturing method for vertical multi-layer horizontal wells, as Figure 1 shown.

[0076] At step S100, a multi-well fracturing geological model is constructed. 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 vertical in-situ stress distribution.

[0077] 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.

[0078] Among them, the spatial position of the fracturing well includes the measured depth, vertical depth, and the position of the fracturing well in the formation.

[0079] The wellbore parameters of the fracturing well include the roughness of the wellbore inner wall, well structure, and well deviation angle.

[0080] The reservoir geological parameters include Young's modulus of the rock, Poisson's ratio, fracture toughness, and filtration coefficient. In this embodiment, the reservoir geological parameters (reservoir geological parameters) can be obtained through logging technology.

[0081] The interlayer longitudinal in-situ stress distribution is the distribution of the minimum horizontal principal stress along each formation in the vertical direction.

[0082] Among them, the multi-well fracturing geological model includes a fracture geometry model, a reservoir geological model, and a wellbore geometry model.

[0083] 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 for quantitatively characterizing the geological characteristics of the reservoir. The wellbore geometry model is a model used to describe the characteristics of wellbores such as oil wells and gas wells in terms of spatial shape, size, etc.

[0084] Taking a well platform as an example below, the reservoir geology, engineering parameters, and wellbore parameters are shown in Table 1.

[0085] Table 1 Partial parameters of the multi-well fracturing geological model

[0086]

[0087] At step S200, according to the constructed multi-well fracturing geological model, calculate the interlayer in-situ stress difference and determine the horizontal well in the low-stress layer and the horizontal well in the high-stress layer, where the stress value of the horizontal well in the high-stress layer > the stress value of the horizontal well in the low-stress layer.

[0088] More specifically, determine the stress values of the horizontal well in the low-stress layer and the horizontal well in the high-stress layer according to the interlayer longitudinal in-situ stress distribution in the multi-well fracturing geological model. When the horizontal well in the high-stress layer and the horizontal well in the low-stress layer are not determined, compare the minimum horizontal principal stress of the first stress layer and the minimum horizontal principal stress of the second stress layer. When the minimum horizontal principal stress of the first stress layer is greater than the minimum horizontal principal stress of the second stress layer, determine the first stress layer as the horizontal well in the high-stress layer and the second stress layer as the horizontal well in the low-stress layer. The absolute value of the difference between the minimum horizontal principal stress of the first stress layer minus the minimum horizontal principal stress of the second stress layer is used as the interlayer in-situ stress difference. For example, the interlayer in-situ stress difference is 1.3 MPa.

[0089] When calculating the first stress change value of the horizontal well in the low-stress layer during fracturing and the second stress change value of the horizontal well in the high-stress layer during fracturing, the horizontal well in the low-stress layer is used first, and then the horizontal well in the high-stress layer.

[0090] It should be noted that the horizontal well in the low-stress layer and the horizontal well in the high-stress layer are different horizontal wells longitudinally, rather than different segments of the same horizontal well.

[0091] At step S300, according to the interlayer in-situ stress difference, calculate the first stress change value of the horizontal well in the low-stress layer during fracturing, and the first stress change value is the first preset multiple of the interlayer in-situ stress difference.

[0092] Wherein, 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.

[0093] Taking the interlayer in-situ stress difference of 1.3 MPa as an example, when the first preset multiple is 1 - 1.5 times, the first stress change value can be taken as 1.3 MPa - 1.95 MPa.

[0094] For the horizontal well in the low-stress layer, the first stress change value can be selected first. For the horizontal well in the low-stress layer, different construction parameters correspond to different first stress change values. Therefore, the corresponding first construction parameters can be deduced inversely according to the first stress change value.

[0095] It should be noted that the first stress change value refers to the stress change caused in the formation due to factors such as the formation and propagation of fractures and the filtration loss of fracturing fluid during the fracturing of the horizontal well in the low-stress layer, which reflects the stress change of this layer (low-stress layer) where the horizontal well is located.

[0096] At step S400, according to the first stress change value and the interlayer in-situ stress difference, determine the second stress change value of the horizontal well in the high-stress layer during fracturing, 0 < the second stress change value ≤ the absolute value of the difference between the first stress change value and the interlayer in-situ stress difference.

[0097] Specifically, within the 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 in-situ stress difference, take the second stress change value.

[0098] It should be noted that taking the first stress change value of 1.9 MPa and the interlayer in-situ stress difference of 1.3 MPa as an example, then the second stress change value takes (0, 0.6] MPa, and a value within this range can be selected as the second stress change value.

[0099] It should be understood that for horizontal wells in high-stress layers, the second stress change value can be selected first. For horizontal wells in high-stress layers, different construction parameters correspond to different second stress change values. Therefore, the corresponding second construction parameters can be deduced inversely based on the second stress change value.

[0100] For example, if the absolute value of the difference between the first stress change value and the interlayer in-situ stress difference is 3 MPa, then a second stress change value between 0 and 3 MPa (excluding 0) can be selected; and then the corresponding second construction parameters can be deduced inversely based on the selected second stress change value.

[0101] It should be noted that the second stress change value refers to the stress change caused in the formation during the fracturing process of horizontal wells in high-stress layers due to factors such as the formation and propagation of fractures and the filtration loss of fracturing fluid. It reflects the stress change of the layer (high-stress layer) where the horizontal well is located.

[0102] At step S500, the first construction parameters of the horizontal well in the low-stress layer under the first stress change value and the second construction parameters of the horizontal well in the high-stress layer under the second stress change value are solved respectively according to the first stress change value and the second stress change value.

[0103] It should be understood that the first construction parameters / second construction parameters include fracturing fluid viscosity, injection displacement, cluster spacing, and number of clusters per single stage.

[0104] Among them, the calculation formula for the first construction parameters of the horizontal well in the low-stress layer under the first stress change value is:

[0105] ;

[0106] ;

[0107] ;

[0108] Among them, σ 1 is the first stress change value of the horizontal well in the low-stress layer during the fracturing process;

[0109] n 1 is the number of fractures in the horizontal well in the low-stress layer;

[0110] p 1i is the stress coefficient of the horizontal well in the low-stress layer, Pa;

[0111] r 1ij is the attenuation coefficient of the horizontal well in the low-stress layer, dimensionless;

[0112] μ 1 is the fracturing fluid viscosity for the construction of the horizontal well in the low-stress layer, Pa·s;

[0113] E 1 is the plane strain Young's modulus of the horizontal well in the low stress layer, Pa;

[0114] Q 1,i is the liquid inflow rate of the i-th fracture in the horizontal well of the low stress layer, i.e., the injection displacement, m 3 / s;

[0115] h 1 is the reservoir thickness of the horizontal well in the low stress layer, m;

[0116] t is the time, s;

[0117] d 1ij is the distance between the i-th fracture and the j-th fracture in the horizontal well of the low stress layer, m;

[0118] δ is the Dirac function, dimensionless.

[0119] Among them, the calculation formula for the second construction parameter of the horizontal well in the high stress layer under the second stress change value is:

[0120] ;

[0121] ;

[0122] ;

[0123] Among them, σ 2 is the second stress change value during the fracturing process of the horizontal well in the high stress layer;

[0124] n 2 is the number of fractures in the horizontal well of the high stress layer;

[0125] p 2i is the stress coefficient of the horizontal well in the high stress layer, Pa;

[0126] r 2ij is the attenuation coefficient of the horizontal well in the high stress layer, dimensionless;

[0127] μ 2 is the viscosity of the fracturing fluid for the construction of the horizontal well in the high stress layer, Pa·s;

[0128] E 2 ’ is the plane strain Young's modulus of the horizontal well in the high stress layer, Pa;

[0129] Q 2,i is the liquid inflow rate of the i-th fracture in the horizontal well of the high stress layer, m 3 / s;

[0130] h 2 is the reservoir thickness of the horizontal well in the high stress layer, m;

[0131] t is the time, in s;

[0132] d 2ij is the distance from the i-th fracture to the j-th fracture in the horizontal well of the high-stress layer, in m;

[0133] δ is the Dirac function, dimensionless.

[0134] It should be noted that in the construction parameters, the total number of clusters = the number of clusters per single section * the total number of sections = the number of fractures, and the total number of sections is usually known; the cluster spacing = the distance between two adjacent fractures.

[0135] For example, the first construction parameter calculated can be: the viscosity of the fracturing fluid is 5 mPa·s, the injection displacement is 12 m 3 / min, the cluster spacing is 10 m, and there are 3 clusters per single section.

[0136] The second construction parameter calculated can be: the viscosity of the fracturing fluid is 1 mPa·s, the injection displacement is 8 m 3 / min, the cluster spacing is 20 m, and there are 2 clusters per single section.

[0137] The fracture pattern under the design parameters adopted by the present invention can be as Figure 3 shown. Since the present invention forms an artificial stress barrier in the horizontal well of the low-stress layer, which hinders the cross-layer extension of the fractures in the high-stress layer, the possibility of fracture communication between wells is reduced. Figure 4 What is schematically shown is "first the horizontal well in the high-stress layer, then the horizontal well in the low-stress layer", that is, a scheme opposite to the present invention, namely "first the horizontal well in the high-stress layer, then the horizontal well in the low-stress layer". Comparing Figure 3 and Figure 4 , obviously, Figure 4 has more fracture overlapping parts, meaning that fracture communication between wells is more likely to occur, that is, the effect provided by the present invention is better.

[0138] Obviously, the above-described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, those of ordinary skill in the art can make other different forms of changes or modifications without making creative efforts, and all should fall within the protection scope 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 the first stress change value of the low stress layer horizontal well during the fracturing process, the first stress change value is a first preset multiple of the interlayer in-situ stress difference, wherein the first preset multiple is 1.3-1.5 times; Determine, according to the first stress change value and the interlayer in-situ stress difference, a second stress change value of the high stress layer horizontal well during the fracturing process, including taking the second stress change value 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 in-situ stress difference; According to the first stress change value and the second stress change value, respectively, 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. The calculation formula of the first construction parameter of the horizontal well in the low stress layer under the first stress change value is: ； ； ； 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, 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; 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; 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.

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

3. 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.

4. 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.

5. The method for fracturing a vertical multi-layer horizontal well according to claim 4, 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.

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