Dynamic change analysis method for crustal stress field of refracturing horizontal well

Abstract

The invention provides a dynamic change analysis method for a crustal stress field of a re-fractured horizontal well, which comprises the following steps of: establishing a geological model along a horizontal well track on the basis of geological data of a target area where the horizontal well is located, and endowing the geological model with corresponding rock mechanical parameters; according to the reservoir natural fracture development law, a natural fracture model conforming to the geological features of the target area is constructed, and the three-dimensional crustal stress field distribution condition of the target area is obtained through calculation; constructing a three-dimensional hydraulic fracturing simulation model based on a geologic model and a natural fracture model through the primary fracturing construction parameters to simulate a primary fracturing fracture form; according to the production time of the horizontal well, the size and direction distribution of the horizontal maximum principal stress and the horizontal minimum principal stress before re-fracturing of the horizontal well are determined in combination with the three-dimensional hydraulic fracturing simulation model. According to the method, the crustal stress field state analysis before the geology-oil reservoir-engineering integrated horizontal well refracturing is realized, and guidance is provided for the subsequent fracturing parameter optimization design.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas field development, and is applied to dynamic analysis of geostress field of horizontal wells subjected to repeated fracturing of tight oil and gas, shale oil and gas, etc., to improve transformation effect, and specifically relates to a method for analyzing dynamic changes of geostress field of horizontal wells subjected to repeated fracturing. Background Art

[0002] After the initial fracturing of a horizontal well, after a period of production, the production decreases due to geological, engineering and production factors, and the conditions for economic exploitation are not met. At this time, the horizontal well is re-fractured to open new fractures and restore the original fracture conductivity, so that the old well can resume production or achieve high production. This process is called repeated fracturing. This technology is mainly used for horizontal wells with low initial production capacity or rapid production decline due to imperfections in the initial fracturing design, construction, and post-fracturing management. For example: the initial fracturing scale is small, the amount of sand added is small, resulting in a small fracture network transformation volume and low conductivity. After the initial fracturing is completed, after a period of production, the gas well is polluted, resulting in a decrease in the permeability of the formation near the wellbore. The proppant is not laid reasonably in the initial fracturing, and the fracture cannot be effectively supported, or the proppant is broken during the post-fracturing production process, resulting in the failure of the initial fracturing fracture, resulting in a decrease in the gas well production.

[0003] Horizontal well re-fracturing technology is a relatively economical and efficient solution, and has been applied many times in shale oil and gas and tight oil and gas reservoirs at home and abroad. The overall idea of ​​​​re-fracturing design for horizontal wells is to first evaluate the initial horizontal well fracturing effect, mainly combining the construction pressure curve and the later production situation to invert the initial fracturing fracture parameters, analyze the current changes in the formation stress field, and further carry out re-fracturing well selection and section selection in combination with the distribution of remaining oil and gas, and optimize the re-fracturing fracture parameters and construction parameters.

[0004] When the remaining oil and gas in a horizontal well has been determined after a period of production, how to maximize the effect of repeated fracturing and improve the final recovery rate, and the accurate analysis and evaluation of the dynamic changes of the formation stress field are the key to whether repeated fracturing can achieve the design purpose, involving the fitting of the initial fracture and production dynamics, the distribution area of ​​the remaining reserves, the optimization of the sweet spot section of repeated fracturing, and the optimization of the repeated fracturing transformation plan. Therefore, the evaluation of the ground stress field is the focus before repeated fracturing, but it is also a big difficulty, involving various aspects such as fracture expansion and oil and gas seepage coupling. At present, most of the research in this area is based on qualitative or semi-numerical and semi-analytical methods, and a systematic research method has not yet been formed.

[0005] In view of the problems in the prior art, the present invention provides a method for analyzing the dynamic changes of the geostress field of a repeated fracturing horizontal well. Summary of the invention

[0006] In order to overcome the defects of the prior art, the present invention provides a method for analyzing the dynamic changes of the geostress field of a repeated fractured horizontal well, the method comprising:

[0007] Based on the geological data of the target area where the horizontal well is located, a geological model along the horizontal well trajectory is established, and corresponding rock mechanics parameters are assigned to the geological model;

[0008] According to the development law of natural fractures in the reservoir, a natural fracture model that conforms to the geological characteristics of the target area is constructed, and the three-dimensional distribution of the geostress field in the target area is calculated;

[0009] By using the initial fracturing construction parameters, a three-dimensional hydraulic fracturing simulation model based on the geological model and the natural fracture model is constructed to simulate the initial fracturing fracture morphology;

[0010] According to the production time of the horizontal well, combined with the three-dimensional hydraulic fracturing simulation model, the magnitude and direction distribution of the horizontal maximum principal stress and the horizontal minimum principal stress before repeated fracturing of the horizontal well are determined.

[0011] According to one embodiment of the present invention, the geological model is established by the following steps:

[0012] Import the actual horizontal well trajectory, determine the position, size, shape, truncation relationship, and other fault parameter layers of the fault according to the fault data interpreted by seismic, and establish a structural model that conforms to the actual stratigraphic conditions of the fracturing horizontal well by combining well logging and structural layer data;

[0013] Based on the structural model, the reservoir phase boundary is determined and the distribution range of physical properties is clarified by using fine layer division and comparative data combined with the distribution of sand bodies along the horizontal well trajectory;

[0014] Data analysis is performed on the physical property parameters of the well points to determine the distribution characteristics of the rock mechanical parameters around the horizontal wellbore and between wells, and the results are compared with the logging data to correct the geological model.

[0015] According to one embodiment of the present invention, the rock mechanical parameters are calculated by the following steps: rock dynamic mechanical parameters are calculated by rock density and longitudinal wave time difference; and rock static mechanical parameters are converted into rock dynamic mechanical parameters as the rock mechanical parameters, wherein:

[0016] Based on the rock density and the longitudinal wave time difference, the transverse wave time difference is calculated;

[0017] Based on the shear wave time difference, the rock density, and the longitudinal wave time difference, Young's modulus is calculated;

[0018] Based on the transverse wave time difference and the longitudinal wave time difference, the Poisson's ratio is calculated.

[0019] According to one embodiment of the present invention, the natural fracture model is constructed by the following steps: based on the target area fractures and core description of the natural fracture occurrence, combined with the natural fracture coherent volume data, the natural fracture model of the high-angle structure around the well is constructed.

[0020] According to one embodiment of the present invention, the three-dimensional geostress field distribution in the target area is calculated by the following steps: combining the stress background and the heterogeneous rock mechanics parameter field of the target area, using the finite element method to calculate the stress and strain of each node, fitting the well point geostress test data, and obtaining the three-dimensional geostress field distribution in the target area.

[0021] According to one embodiment of the present invention, the three-dimensional hydraulic fracturing simulation model is constructed by the following steps:

[0022] A computational model for calculating the aperture of natural fractures is constructed by integrating local rock elastic properties, fluid pressure, and the path distance from the fracture unit to the injection section location;

[0023] Set the natural fracture activation capability priority parameter to characterize the priority of natural fracture opening when hydraulic fracture expansion encounters multiple activatable natural fractures at the same time;

[0024] According to the Mohr-Coulomb criterion, the stress variation of natural fractures in the three-dimensional stress system is considered, and a shear analysis model is constructed to describe the shear failure of natural fractures during hydraulic fracturing.

[0025] According to one embodiment of the present invention, the method further comprises: considering the interaction between hydraulic fractures and natural fractures, simulating the initial fracture morphology through the three-dimensional hydraulic fracturing simulation model, and correcting the fracture size based on the fracture monitoring data and the production dynamic fitting results.

[0026] According to one embodiment of the present invention, the magnitude and direction distribution of the maximum horizontal principal stress and the minimum horizontal principal stress before refracturing of a horizontal well are determined by the following steps:

[0027] Based on the geological model and the three-dimensional hydraulic fracturing simulation model, according to the mass conservation equation, Darcy flow equation and fluid state equation, combined with the natural fracture model, the flow of fluid in the reservoir is simulated, the production history of the oil well is fitted, and the pressure distribution and ground stress changes in the reservoir production process are clarified by using the production curve characteristics and reservoir distribution characteristics, and the reservoir utilization degree is clarified, and the magnitude and direction distribution of the horizontal maximum principal stress and the horizontal minimum principal stress before repeated fracturing of the current horizontal well are obtained.

[0028] According to another aspect of the present invention, a storage medium is provided, which contains a series of instructions for executing the method steps as described in any one of the above.

[0029] According to another aspect of the present invention, there is also provided a device for analyzing dynamic changes in the geostress field of a repeated fractured horizontal well, which performs the method described in any one of the above items, and the device comprises:

[0030] A geological model module, which establishes a geological model along the horizontal well trajectory based on the geological data of the target area where the horizontal well is located, and assigns corresponding rock mechanics parameters to the geological model;

[0031] The fracture model module is used to construct a natural fracture model that conforms to the geological characteristics of the target area according to the development law of natural fractures in the reservoir, and calculate the three-dimensional distribution of the geostress field in the target area;

[0032] A fracturing model module, which is used to construct a three-dimensional hydraulic fracturing simulation model based on the geological model and the natural fracture model through the initial fracturing construction parameters to simulate the initial fracturing fracture morphology;

[0033] The stress distribution module is used to determine the magnitude and direction distribution of the maximum horizontal principal stress and the minimum horizontal principal stress before repeated fracturing of the horizontal well according to the production time of the horizontal well and in combination with the three-dimensional hydraulic fracturing simulation model.

[0034] The present invention provides a method for analyzing dynamic changes in the geostress field of a repeated fracturing horizontal well, which has the following advantages over the prior art:

[0035] The present invention establishes a geological model along the trajectory of a horizontal well, a three-dimensional discrete natural fracture model, and combines logging data to give the geological model corresponding attribute parameters such as porosity, permeability, pore pressure, Young's modulus, Poisson's ratio, and far-field three-dimensional geostress. The finite element method is used to calculate the regional three-dimensional geostress field distribution. Then, according to the initial fracturing construction parameters, a three-dimensional hydraulic fracturing simulation model based on the geological model is constructed. The interaction between hydraulic fractures and natural fractures is considered to simulate the initial fracturing fracture morphology. At the same time, based on the fracturing fracture monitoring data and the production dynamic fitting results, the fracture size is corrected. Finally, according to the production time of the horizontal well, the pressure distribution in the reservoir production process and the dynamic change law of geostress are clarified, and the size and direction distribution of the maximum horizontal principal stress and the minimum horizontal principal stress before repeated fracturing of the horizontal well are determined, laying a foundation for the subsequent repeated fracturing optimization design.

[0036] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0038] Figure 1 A flowchart showing the steps of a method for analyzing dynamic changes in the geostress field of a repeated fractured horizontal well according to an embodiment of the present invention is shown;

[0039] Figure 2 A schematic diagram of a single well geological model according to an embodiment of the present invention is shown;

[0040] Figure 3 A schematic diagram of Young's modulus distribution according to an embodiment of the present invention is shown;

[0041] Figure 4 shows a fracture occurrence rose diagram according to an embodiment of the present invention;

[0042] Figure 5 shows a fracture dip statistical histogram according to an embodiment of the present invention;

[0043] Figure 6 A schematic diagram of a natural fracture model according to an embodiment of the present invention is shown;

[0044] Figure 7 A schematic diagram of simulating stress field using a finite element method according to an embodiment of the present invention is shown;

[0045] Figure 8 A schematic diagram of horizontal minimum principal stress field distribution according to an embodiment of the present invention is shown;

[0046] Fig. 9 A schematic diagram of the distribution direction of the horizontal minimum principal stress field according to an embodiment of the present invention is shown;

[0047] Fig.10 A schematic diagram of a Mohr-Coulomb circle according to an embodiment of the present invention is shown;

[0048] Fig.11 A schematic diagram showing the stress state of any point in a rock according to an embodiment of the present invention is shown;

[0049] Fig.12 A schematic diagram of the initial fracturing simulation results according to an embodiment of the present invention is shown;

[0050] Fig.13 The distribution diagram of the horizontal minimum principal stress and the horizontal maximum principal stress on the 30th day according to one embodiment of the present invention is shown;

[0051] Fig.14The horizontal minimum principal stress and the horizontal maximum principal stress distribution diagram at the 180th day according to one embodiment of the present invention are shown;

[0052] Fig.15 The horizontal minimum principal stress and the horizontal maximum principal stress distribution diagram on the 540th day according to one embodiment of the present invention are shown;

[0053] Fig.16 The distribution diagram of the horizontal minimum principal stress and the horizontal maximum principal stress at the 900th day according to one embodiment of the present invention is shown;

[0054] Fig.17 The diagram shows the distribution of ground stress after production and after shut-in pressure recovery according to an embodiment of the present invention.

[0055] In the accompanying drawings, the same reference numerals are used for the same components. In addition, the accompanying drawings are not drawn according to the actual scale. DETAILED DESCRIPTION

[0056] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0057] Horizontal well re-fracturing technology has been applied in many unconventional oil and gas reservoirs such as tight gas and shale oil and gas at home and abroad. The understanding of the current geostress field is the key to the design of subsequent re-fracturing schemes. The existing technology has not yet formed a systematic research method in this regard, which affects the effect of re-fracturing.

[0058] In order to solve the problems of the current existing technology, the present invention uses a geological engineering integration method. First, according to the fault data, lithofacies data, and structural layer data around the initial fracturing horizontal well, a geological model along the horizontal well trajectory is established, and the corresponding porosity, permeability, pore pressure, Young's modulus, Poisson's ratio and other physical parameters are given to the geological model in combination with the logging data. Then, according to the results of the natural fracture development law analysis, a natural fracture model that meets the geological characteristics of the target area is constructed using three-dimensional discrete fracture geological modeling technology. Combined with the regional stress background and rock mechanics physical property field, the finite element method is used to calculate the regional The three-dimensional geostress field distribution is then inputted, and the initial fracturing construction parameters are then inputted to construct a three-dimensional hydraulic fracturing simulation model based on the geological model. The interaction between hydraulic fractures and natural fractures is considered to simulate the fracture morphology of the initial fracturing. At the same time, the fracture size is corrected based on the fracturing fracture monitoring data and the production dynamic fitting results. Finally, according to the production time of the horizontal well, the pressure distribution in the reservoir production process and the dynamic change law of geostress are clarified, which lays the foundation for the subsequent horizontal well repeated fracturing section selection and fracture morphology simulation, and finally realizes the geology-reservoir-engineering integrated horizontal well repeated fracturing The state analysis of the geostress field before the analysis.

[0059] Figure 1A flowchart of the steps of a method for analyzing dynamic changes in the geostress field of a repeated fractured horizontal well according to an embodiment of the present invention is shown.

[0060] like Figure 1 As shown, in step S101, based on the geological data of the target area where the horizontal well is located, a geological model along the horizontal well trajectory is established, and corresponding rock mechanics parameters are assigned to the geological model.

[0061] Specifically, based on the fault data, lithofacies data, and structural plane data around the initial fracturing horizontal well, a geological model along the horizontal well trajectory is established (e.g. Figure 2 As shown in Figure 1, model size: 1500m*2000m*80m, number of grids: 60*80*320=1.536 million, grid size: 25m*25m*0.25m), and the corresponding porosity, permeability, pore pressure, and Young's modulus (such as Figure 3 As shown), Poisson's ratio and other physical properties.

[0062] In one embodiment, in step S101, a geological model is established by the following steps: importing the trajectory of an actual horizontal well, determining the position, size, shape, truncation relationship, and other fault parameter layers of the fault according to the fault data interpreted by the seismic, and combining the well logging and structural layer data to establish a structural model that conforms to the actual stratigraphic conditions of the fracturing horizontal well. On the basis of the structural model, the reservoir phase boundary is determined by using fine layer division and comparative data, combined with the distribution of sand bodies along the trajectory of the horizontal well, and the distribution range of physical properties is clarified; data analysis is performed on the physical property parameters of the well points to determine the distribution characteristics of the rock mechanical parameters (physical parameters such as porosity, permeability, Young's modulus, Poisson's ratio, etc.) around the horizontal wellbore and between the wells, and the results are compared with the well logging data to correct the geological model.

[0063] In one embodiment, in step S101, the rock mechanical parameters are calculated by the following steps: the rock dynamic mechanical parameters are calculated by rock density and P-wave time difference; the rock dynamic mechanical parameters are converted into rock static mechanical parameters as rock mechanical parameters. Specifically, the shear wave time difference is calculated based on rock density and P-wave time difference; the Young's modulus is calculated based on the shear wave time difference, rock density, and P-wave time difference; and the Poisson's ratio is calculated based on the shear wave time difference and P-wave time difference.

[0064] In the prior art, rock mechanics parameters can be obtained by directly using underground cores through uniaxial and triaxial compression tests of rocks to carry out mechanical experimental tests. The mechanical data obtained has high accuracy and credibility. However, due to the small number of sample points, the results obtained cannot be directly used for modeling interpolation. The present invention combines logging data to calculate rock mechanics parameters, which can make up for the shortcomings of rock mechanics experiments to a certain extent, and also has the advantages of good continuity and low cost.

[0065] In one embodiment, the rock mechanical parameters calculated by the logging data are called rock dynamic mechanical parameters. According to the rock mechanics theory, the present invention clarifies the relationship between the mechanical parameters of the reservoir rock such as elastic modulus E and Poisson's ratio μ and the longitudinal wave time difference Δt p , shear wave time difference Δt s and rock density ρ b The following relationship is satisfied:

[0066]

[0067]

[0068] In the formula, E d is Young's modulus, Pa; μ d is Poisson's ratio, dimensionless; ρ b is the rock density, kg / m 3 ; Δt p and Δt s are the time differences of longitudinal and transverse waves, us / m respectively; a, b, c can be determined by the method of undetermined coefficients, and the general values ​​are 2.12, 45.33, and -167.31.

[0069] Rock density and P-wave time difference are conventional logging data and are relatively easy to obtain, while S-wave time difference needs to be calculated through array logging or dipole acoustic logging. In view of the lack of S-wave time difference data, the present invention establishes a relationship (1) between S-wave time difference, P-wave time difference and rock density.

[0070] In one embodiment, there are differences between the dynamic and static rock mechanics parameters of the rock, and the static elastic parameters can better represent the loading conditions of the rock in petroleum engineering. In actual engineering, the static elastic parameters of the rock should be used. According to the relationship between the dynamic and static elastic parameters of the rock, acoustic data such as sonic logging are used to infer the static parameters of rock mechanics.

[0071] like Figure 1 As shown, in step S102, according to the development law of natural fractures in the reservoir, a natural fracture model that meets the geological characteristics of the target area is constructed, and the three-dimensional distribution of the geostress field in the target area is calculated.

[0072] Specifically, based on the analysis results of the development laws of natural fractures in the reservoir, the three-dimensional discrete fracture geological modeling technology is used to construct a natural fracture model that conforms to the geological characteristics of the target area. Combined with the regional far-field three-dimensional geostress and rock mechanics physical properties, the finite element method is used to calculate the regional three-dimensional geostress field distribution.

[0073] In one embodiment, in step S102, a natural fracture model is constructed by the following steps: describing the occurrence of natural fractures in the target area and the core (e.g. Figure 4 and Figure 5 ), combined with the natural fracture coherence volume data, a natural fracture model of the high-angle structure around the well is constructed (as shown in Figure 6 shown).

[0074] In one embodiment, in step S102, the three-dimensional ground stress field distribution of the target area is calculated by the following steps: combining the stress background of the target area and the inhomogeneous rock mechanical parameter field, using the finite element method (such as Figure 7 Calculate the stress and strain of each node, fit the well point geostress test data, and obtain the three-dimensional geostress field distribution of the target area (as shown in Figure 8 and Fig. 9 shown).

[0075] Based on the geological model, the finite element method is used to comprehensively consider factors such as boundary conditions, rock mechanical properties, structural characteristics, natural fractures and faults, and conduct geostress field analysis and simulation.

[0076] In the present invention, the geostress field analysis mainly uses imaging logging in the study area and online literature to clarify the geostress characteristics of the target area. The drilling induced fractures / well collapse fractures identified by electrical imaging logging data are combined to determine the geostress orientation; the geostress field size is clarified by logging interpretation, fracturing operation curves, acoustic emission experiments and other data.

[0077] Differential strain analysis (DSA) test: A method for determining the three-dimensional stress direction and stress value of the formation through indoor core experiments. For homogeneous cores without natural cracks from deep hole drilling, the values ​​of the three-dimensional principal stresses are different from each other, and the degree of unloading in different directions is also different when drilling the core. The release of the original stress produces micro-fracture strain proportional to the degree of unloading. When re-loaded with equal confining pressure, the recovery strain in different directions is also different. The direction with the maximum strain value is the direction in which the core was originally subjected to the maximum principal stress.

[0078] Kaiser effect: It can be considered that micro-fractures occur in rocks after being subjected to stress. The frequency of micro-fractures increases with increasing stress. The fracture process is irreversible, but since friction and sliding on the existing fracture surface can also generate acoustic emission signals, this friction and sliding is reversible. Therefore, when the stress is lower than the maximum stress that has been applied, acoustic emission may also occur. These are the acoustic emission events caused by reversible friction and sliding. When the stress exceeds the maximum stress that has been applied originally, new fractures will occur, resulting in a sudden increase in the frequency of acoustic emission activities. The acoustic emission Kaiser effect test can measure the maximum compressive stress that the rock mass has ever been subjected to.

[0079] In the present invention, when simulating and calculating the geostress field, the regional stress background and the inhomogeneous rock mechanical parameter field are combined, and the finite element method is used to calculate the stress and strain of each node, fit the well point geostress test data, and obtain an accurate three-dimensional geostress field distribution model.

[0080] In the mechanical model, an originally continuous object is discretized into a finite number of units of a certain size. These units are only connected at a finite number of nodes, and equivalent forces are introduced at the nodes to replace the external forces actually acting on the units. For each unit, according to the idea of ​​block approximation, a simple function is selected to represent the distribution law of displacement within the unit, and the relationship between the unit node force and the node displacement is established according to the energy principle in the elastic theory (or the variational principle). Finally, by combining the relationship formulas of all units, a set of algebraic equations with node displacement as the unknown quantity is obtained. Solving these equations can calculate the displacement of a finite number of discrete nodes on the object. "One division and one combination", breaking the whole into parts, and gathering the parts into a whole, a complex structure is regarded as a whole composed of a finite number of units. The method provided by the present invention can accurately describe the size and direction characteristics of the ground stress field around faults and cracks.

[0081] like Figure 1 As shown, in step S103, a three-dimensional hydraulic fracturing simulation model based on a geological model and a natural fracture model is constructed through the initial fracturing construction parameters to simulate the initial fracturing fracture morphology.

[0082] Specifically, according to the initial fracturing construction parameters, a three-dimensional hydraulic fracturing simulation model based on the geological model is constructed. The interaction between hydraulic fractures and natural fractures is considered to simulate the initial fracturing crack morphology. At the same time, the crack size is corrected based on the fracturing fracture monitoring data and production dynamic fitting results.

[0083] In one embodiment, in step S103, a three-dimensional hydraulic fracturing simulation model is constructed through steps S1031-S1033.

[0084] In step S1031, a calculation model for calculating the aperture of natural fractures is constructed by comprehensively considering the local rock elastic properties, fluid pressure, and the path distance from the fracture unit to the injection section.

[0085] Tight reservoirs often have natural fractures. During the hydraulic fracturing process, the natural fractures will be reactivated and expanded due to the injection of fracturing fluid. The reactivation of natural fractures is usually the flow path of reservoir oil and gas from the formation to the wellbore, which plays a vital role in improving the oil and gas recovery rate of tight oil reservoirs. In the present invention, when the hydraulic main fracture connects the natural fracture and the natural fracture opening condition is met (the pore pressure in the fracture is greater than the fracture normal stress (minimum principal stress), that is, P frac >σ N), the natural fractures will receive the fluid flowing into the ground from the wellbore. Following the material balance equation, the injected fluid is equal to the increment of the underground fracture network volume (when considering the filtration loss, it is equal to the increment of the underground fracture network volume and the filtration loss). The present invention adopts this material balance formula to make the calculation efficiency higher when processing a large number of discrete fractures (for multi-well scale problems, usually millions or tens of millions of finite elements).

[0086] In one embodiment, the seam pressure P frac Determined by the following formula (3):

[0087]

[0088] Where P pump is the pump pressure, MPa; σ N is the normal stress at the fracture tip, MPa; d is the flow distance from the well intersection to the fracture unit, m; d max is the maximum flow distance automatically adjusted according to the length of the hydraulic fracture at each time step, m; ρ is the mud density, kg / m 3 ; Δh is the vertical elevation difference from the well intersection point to the fracture unit, m.

[0089] In the present invention, the fracture aperture calculation uses the elastic equation of the relationship between the fracture aperture and pressure to calculate the evolution of the elliptical elastic fracture aperture. Specifically, the fracture aperture is integrated with the local rock elastic properties, fluid pressure, and the path distance from the fracture unit to the injection section to obtain a fracture aperture calculation model.

[0090]

[0091] Because the shear modulus G of the rock mass can be expressed as:

[0092]

[0093] Where G is the shear modulus, MPa.

[0094] Therefore, the crack opening calculation model is:

[0095]

[0096] Where, e is the crack width (crack opening), mm; v is the rock Poisson's ratio, dimensionless; E is the elastic modulus, MPa; P frac is the pressure inside the crack, MPa.

[0097] According to the fracture aperture calculation model, it can be seen that when the normal stress is greater than the fracture pore pressure, that is, σ N >P frac When the cracks are filled with water, they will not expand, but instead they will begin to crack.

[0098] In step S1032, a natural fracture activation capability priority parameter is set to characterize the priority of natural fracture activation when the hydraulic fracture expansion encounters multiple activatable natural fractures at the same time.

[0099] When the hydraulic fractures extend and encounter multiple activatable natural fractures at the same time, it is necessary to determine the priority of the natural fractures to be opened. The present invention sets a natural fracture activation ability priority parameter, and its functional relationship is as follows (7)-(8). The greater the priority, the greater the possibility of the natural fracture opening.

[0100]

[0101]

[0102] Where P r is the injection priority, dimensionless; T r is the normalized fracture conductivity, dimensionless; O is the cosine of the angle between the normalized fracture direction and the minimum stress direction in the three-dimensional stress, dimensionless; C l is the normalized distance between the fracture unit and the perforation point, dimensionless; M, N, and L are the fracture conductivity T r , the cosine of the angle between the fracture direction and the direction of the minimum stress in the three-dimensional stress O, the distance between the fracture unit and the perforation point C l The coefficient of .

[0103] In step S1033, based on the Mohr-Coulomb criterion and taking into account the stress variation of natural fractures in the three-dimensional stress system, a shear analysis model is constructed to describe the shear failure of natural fractures during hydraulic fracturing.

[0104] The present invention judges the shear failure phenomenon of natural cracks based on the Mohr-Coulomb criterion. The rupture criterion takes into account the force changes of natural cracks in a three-dimensional stress system, that is, when the ratio of shear stress to normal stress on the shear plane reaches the maximum, the material yields to failure, that is, when the crack shear strength satisfies the following formula, the crack will undergo shear failure.

[0105] |τ|≥f(σ) (9)

[0106] Where f(σ) is a function of normal stress:

[0107] f(σ)=C+σtanφ (10)

[0108] Where C is the rock cohesion, MPa; φ is the internal friction angle, °.

[0109] In the Mohr-Coulomb theory, the shear stress τ and the normal stress σ are calculated as shown in the following equations (11)-(12). If the calculated (σ, τ) point is located within the Mohr-Coulomb circle shear line region, the crack will undergo shear failure. If it is located outside the region, the crack will not undergo shear failure.

[0110]

[0111]

[0112] Wherein, σ1 is the difference between the maximum principal stress and the pore pressure of the reservoir, MPa; σ3 is the difference between the minimum principal stress and the pore pressure, MPa.

[0113] In the actual fracturing process, the fracturing fluid will affect the connected natural fractures, which will cause the pressure inside the natural fracture to increase, thereby affecting the normal and tangential stress states of the natural fracture surface. The greater the pressure inside the natural fracture, the greater the stress state of the natural fracture (such as Fig.11 As shown) on the Mohr stress coordinate axis (as Fig.10 The point (σ, τ) on the graph (as shown) will move to the left, resulting in that when the pressure in the fracture reaches a certain value, the point will be outside the shear region of the Mohr circle, and the natural fracture will undergo shear failure.

[0114] In one embodiment, in step S103, the method further includes: considering the interaction between hydraulic fractures and natural fractures, simulating the initial fracturing fracture morphology through a three-dimensional hydraulic fracturing simulation model, and correcting the fracture size based on the fracturing fracture monitoring data and the production dynamic fitting results.

[0115] Specifically, based on the hydraulic fracturing fracture propagation theory and the current geological model, the initial fracturing simulation results are as follows: Fig.12 As shown in the figure, in the fault-fracture network reservoir model, the hydraulic fracturing network segments are quite different. The hydraulic fracturing in the well section far away from the fault (near target point B) is mainly the expansion of the hydraulic main fracture; the hydraulic fracturing in the well section near the fault (target point A) connects the natural fractures and is mainly the transformation of the fracture network.

[0116] In fractured clastic reservoirs, the fracture network formed by horizontal well fracturing is extremely complex. The present invention is based on finite element fracture network expansion, natural fracture and hydraulic fracture coupling simulation, etc., considering that the expansion of hydraulic fractures is affected by reservoir rock mechanics, reservoir stress field and natural fractures, etc., which may lead to asymmetry of fracture expansion and affect the formation effect of complex fracture network.

[0117] like Figure 1 As shown, in step S104, according to the production time of the horizontal well, combined with the three-dimensional hydraulic fracturing simulation model, the magnitude and direction distribution of the horizontal maximum principal stress and the horizontal minimum principal stress before repeated fracturing of the horizontal well are determined.

[0118] Specifically, according to the production time of the horizontal well, the pressure distribution during the reservoir production process and the dynamic change law of the ground stress are clarified, and the magnitude and direction distribution of the horizontal maximum principal stress and the horizontal minimum principal stress before repeated fracturing of the horizontal well are determined.

[0119] In one embodiment, in step S104, the magnitude and directional distribution of the maximum horizontal principal stress and the minimum horizontal principal stress before repeated fracturing of the horizontal well are determined by the following steps: based on the geological model, the three-dimensional hydraulic fracturing simulation model, according to the mass conservation equation, the Darcy flow equation and the fluid state equation, combined with the natural fracture model, the flow of the fluid in the reservoir is simulated, the production history of the oil well is fitted, and the pressure distribution and ground stress changes during the reservoir production process are clarified by using the production curve characteristics and the reservoir distribution characteristics, and the reservoir utilization degree is clarified, and the magnitude and directional distribution of the maximum horizontal principal stress and the minimum horizontal principal stress before repeated fracturing of the current horizontal well are obtained.

[0120] Furthermore, based on the established geological model, hydraulic fracturing multi-field coupling model (three-dimensional hydraulic fracturing simulation model), based on the mass conservation equation, Darcy flow equation and fluid state equation, with the help of discrete fracture network model, the flow of fluid in the reservoir is simulated, the production history of oil wells is fitted using production curve characteristics and reservoir distribution characteristics, the pressure distribution in the reservoir production process and the law of ground stress change are clarified, the reservoir production degree is clarified, and the current formation pressure distribution (such as Figure 13-Figure 16 ). It can be seen from the figure that the stress field around the fracture decreases with production and development, and the horizontal maximum principal stress vector deflects to the low stress area (around the fracture network).

[0121] In summary, the current state of the geostress field must be clarified before the implementation of repeated fracturing of horizontal wells, which is the basis and key for selecting wells and sections for repeated fracturing, optimizing the parameters of repeated fracturing cracks and construction parameters. The present invention establishes a geological model along the trajectory of the horizontal well, and assigns corresponding physical parameters such as porosity, permeability, pore pressure, Young's modulus, and Poisson's ratio, then constructs a natural fracture model that meets the geological characteristics of the target area, combines the regional stress background and the rock mechanics physical property field, and uses the finite element method to calculate and obtain the regional three-dimensional geostress field distribution, and then according to the initial fracturing construction parameters, considers the interaction between hydraulic fractures and natural fractures, simulates the initial fracturing fracture morphology, and at the same time, based on the monitoring data of the fracturing fracture and the production dynamic fitting results, the fracture size is corrected, and finally, according to the production time of the horizontal well, the pressure distribution in the reservoir production process and the dynamic change law of geostress are clarified, and the geostress field state analysis before the geology-reservoir-engineering integrated horizontal well repeated fracturing is realized, and guidance is provided for the subsequent optimization design of fracturing parameters.

[0122] The method for analyzing dynamic changes in the geostress field of a repeatedly fractured horizontal well provided by the present invention can also be used in conjunction with a computer-readable storage medium, on which a computer program is stored, and the computer program is executed to run the method for analyzing dynamic changes in the geostress field of a repeatedly fractured horizontal well.

[0123] A computer program can run computer instructions, which include computer program code. The computer program code may be in source code form, object code form, executable file, or some intermediate form.

[0124] Computer-readable storage media may include: any entity or device that can carry computer program code, recording media, USB flash drives, mobile hard disks, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc.

[0125] It should be noted that the content contained in computer-readable storage media can be appropriately increased or decreased based on the requirements of legislation and patent practices in the jurisdiction. For example, in some jurisdictions, based on legislation and patent practices, computer-readable storage media do not include electrical carrier signals and telecommunications signals.

[0126] According to another aspect of the present invention, a device for analyzing dynamic changes in the geostress field of a repeatedly fractured horizontal well is provided, which executes a method for analyzing dynamic changes in the geostress field of a repeatedly fractured horizontal well. The device comprises: a geological model module, a fracture model module, and a fracturing model module.

[0127] The geological model module establishes a geological model along the horizontal well trajectory based on the geological data of the target area where the horizontal well is located, and assigns the corresponding rock mechanics parameters to the geological model. The fracture model module is used to construct a natural fracture model that conforms to the geological characteristics of the target area according to the development law of natural fractures in the reservoir, and calculate the three-dimensional geostress field distribution of the target area. The fracturing model module is used to construct a three-dimensional hydraulic fracturing simulation model based on the geological model and the natural fracture model through the initial fracturing construction parameters to simulate the initial fracturing fracture morphology. The stress distribution module is used to determine the maximum horizontal principal stress and the minimum horizontal principal stress before repeated fracturing of the horizontal well according to the production time of the horizontal well, combined with the three-dimensional hydraulic fracturing simulation model.

[0128] The present invention uses an integrated geological and engineering method. First, according to the fault data, lithofacies data, and structural layer data around the initial fracturing horizontal well, a geological model along the horizontal well trajectory is established, and the corresponding porosity, permeability, pore pressure, Young's modulus, Poisson's ratio and other physical parameters are given to the geological model in combination with the logging data. Then, according to the results of the natural fracture development law analysis, a natural fracture model that meets the geological characteristics of the target area is constructed using the three-dimensional discrete fracture geological modeling technology. Combined with the regional stress background and the rock mechanics physical property field, the finite element method is used to calculate the regional three-dimensional ground stress field model, and then the initial fracturing is input into the initial fracturing. The construction parameters are determined by the geological model, and a three-dimensional hydraulic fracturing simulation model is constructed based on the geological model. The interaction between hydraulic fractures and natural fractures is considered to simulate the fracture morphology of the initial fracturing. At the same time, the fracture size is corrected based on the fracturing fracture monitoring data and the production dynamic fitting results. Finally, according to the production time of the horizontal well, the pressure distribution in the reservoir production process and the dynamic change law of the maximum horizontal and minimum horizontal stresses and directions with the production time are clarified, which lays the foundation for the subsequent horizontal well repeated fracturing section selection and fracture morphology simulation, and finally realizes the geology-reservoir-engineering integrated horizontal well repeated fracturing state analysis.

[0129] The total length of the horizontal section of a well in southern Hubei is 1200m, and 840.14m of sandstone was encountered, accounting for 69.9% of the total length of the horizontal section. The comprehensive interpretation of well logging showed 21 oil layers with a cumulative apparent thickness of 124.2m; 10 oil-water layers with a cumulative apparent thickness of 49.5m; 26 poor oil layers with a cumulative apparent thickness of 225.5m; 33 dry layers with a cumulative apparent thickness of 298.9m. According to the regional tectonic evolution and regional geological research, the horizontal section crosses the NWW fault, and the fracture development area is mainly distributed near the fault zone. The fracture development is mainly high-angle fractures, with a fracture density of 4.8 / m; the fracture length is concentrated in 10-20cm and 20-30cm; the fracture width distribution is mainly in the range of less than 0.3mm, 0.4-0.5mm, 0.7-0.8mm, and 0.9-1mm; the crack opening degree of mudstone is low, the crack opening degree of sandstone is high, and semi-filled and filled fractures are the main ones.

[0130] The well was fractured from October 2 to October 9, 2013. The first fracturing used coiled tubing hydraulic jet fracturing. The design fracturing 12 sections, the actual fracturing 9 sections, the section spacing 73-131.5m; the average scale of single section fracturing 297.3m 3 The average reconstruction scale in the section is 2.25~5.12m 3 / m; average sand addition in a single stage: 31m 3 , the sand adding strength in the section is 0.23~0.49m 3 / m. The well was put into production in October 2013, shut down in January 2016, and resumed production in May 2017. It is currently producing in an intermittent manner. The cumulative oil production is 7288t, with a comprehensive water content of 35.7%. The current daily oil production is about 1.3t, with a water content of 67.8%. When it resumed production in May 2017, the static pressure was 11.1MPa, which was 50.4% of the initial formation pressure.

[0131] By applying the method provided by the present invention, the characteristics of horizontal well reservoirs, natural fractures and geostress fields are integrated to construct heterogeneous geological models, natural fracture models and geostress field models, conduct full three-dimensional hydraulic fracturing simulations, and further establish a post-fracturing numerical model of horizontal wells to fit the development history. Based on the reservoir geological model and the initial pressure simulation results, numerical simulation software is used to perform production dynamic simulations. From the perspective of reserve utilization, the distribution of natural fractures plays a decisive role in the utilization of reserves, and the production of fracture zones accounts for 79% of the total production. After the initial fracturing was put into production, the low-pressure area of ​​the reservoir was 0.201km 2 ; After the pressure is restored, it is currently about 0.15km 2 , indicating that the formation pressure recovers slowly, which is consistent with the low formation pressure coefficient. The dynamic changes of the geostress field during the production process are shown in Fig.17 shown.

[0132] In summary, the present invention provides a method for analyzing dynamic changes in the geostress field of a repeated fracturing horizontal well, which has the following advantages over the prior art:

[0133] The present invention establishes a geological model along the trajectory of a horizontal well, a three-dimensional discrete natural fracture model, and combines logging data to give the geological model corresponding attribute parameters such as porosity, permeability, pore pressure, Young's modulus, Poisson's ratio, and far-field three-dimensional geostress. The finite element method is used to calculate the regional three-dimensional geostress field distribution. Then, according to the initial fracturing construction parameters, a three-dimensional hydraulic fracturing simulation model based on the geological model is constructed. The interaction between hydraulic fractures and natural fractures is considered to simulate the initial fracturing fracture morphology. At the same time, based on the fracturing fracture monitoring data and the production dynamic fitting results, the fracture size is corrected. Finally, according to the production time of the horizontal well, the pressure distribution in the reservoir production process and the dynamic change law of geostress are clarified, and the size and direction distribution of the maximum horizontal principal stress and the minimum horizontal principal stress before repeated fracturing of the horizontal well are determined, laying a foundation for the subsequent repeated fracturing optimization design.

[0134] It should be understood that the embodiments disclosed in the present invention are not limited to the specific structures, processing steps or materials disclosed herein, but should be extended to equivalent substitutions of these features understood by ordinary technicians in the relevant field. It should also be understood that the terms used herein are only used for the purpose of describing specific embodiments and are not meant to be limiting.

[0135] In the description of the present invention, unless otherwise specified, "plurality" means two or more than two; the orientations or positional relationships indicated by the terms "upper", "lower", "left", "right", "inner", "outer", "front end", "rear end", "head", "tail", etc. are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0136] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0137] Certain terms are used throughout this application document to indicate specific system components. As those skilled in the art will recognize, different names can usually be used to indicate the same components, so this application document is not intended to distinguish those components that are only different in name but not in function. In this application document, the terms "comprise", "include" and "have" are used in an open form, and therefore should be interpreted as meaning "including but not limited to...". In addition, the terms "substantially", "substantially" or "approximately" that may be used in this article relate to the tolerances of the corresponding terms accepted by the industry. The term "coupling" as may be used in this article includes direct coupling and indirect coupling via other components, elements, circuits, or modules, wherein for indirect coupling, the components, elements, circuits, or modules between them do not change the information of the signal but can adjust its current level, voltage level, and / or power level. Inferred coupling (for example, one of the elements is coupled to another element by inference) includes direct and indirect coupling between two elements in the same way as "coupling".

[0138] The "one embodiment" or "embodiment" mentioned in the specification means that the specific features, structures or characteristics described in conjunction with the embodiment are included in at least one embodiment of the present invention. Therefore, the phrases "one embodiment" or "embodiment" appearing in various places throughout the specification do not necessarily refer to the same embodiment.

[0139] The embodiments of the present invention are given for the purpose of illustration and description, and are not intended to be exhaustive or to limit the invention to the disclosed forms. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are selected and described in order to better illustrate the principles and practical applications of the present invention and to enable those of ordinary skill in the art to understand the present invention and thereby design various embodiments with various modifications suitable for specific uses.

[0140] Although the embodiments disclosed in the present invention are as above, the contents described are only embodiments adopted for facilitating the understanding of the present invention and are not intended to limit the present invention. Any technician in the technical field to which the present invention belongs can make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in the present invention, but the patent protection scope of the present invention shall still be subject to the scope defined in the attached claims.

Claims

1. A method for analyzing dynamic changes in the geostress field of a repeated fracturing horizontal well, characterized in that: The method comprises: Based on the geological data of the target area where the horizontal well is located, a geological model along the horizontal well trajectory is established, and corresponding rock mechanics parameters are assigned to the geological model; According to the development law of natural fractures in the reservoir, a natural fracture model that conforms to the geological characteristics of the target area is constructed, and the three-dimensional distribution of the geostress field in the target area is calculated; By using the initial fracturing construction parameters, a three-dimensional hydraulic fracturing simulation model based on the geological model and the natural fracture model is constructed to simulate the initial fracturing fracture morphology; According to the production time of the horizontal well, combined with the three-dimensional hydraulic fracturing simulation model, the magnitude and direction distribution of the horizontal maximum principal stress and the horizontal minimum principal stress before repeated fracturing of the horizontal well are determined.

2. A method for analyzing dynamic changes in the geostress field of a repeated fracturing horizontal well according to claim 1, characterized in that: The geological model is established by the following steps: Import the actual horizontal well trajectory, determine the position, size, shape, truncation relationship, and other fault parameter layers of the fault according to the fault data interpreted by seismic, and establish a structural model that conforms to the actual stratigraphic conditions of the fracturing horizontal well by combining well logging and structural layer data; Based on the structural model, the reservoir phase boundary is determined and the distribution range of physical properties is clarified by using fine layer division and comparative data combined with the distribution of sand bodies along the horizontal well trajectory; Data analysis is performed on the physical property parameters of the well points to determine the distribution characteristics of the rock mechanical parameters around the horizontal wellbore and between wells, and the results are compared with the logging data to correct the geological model.

3. A method for analyzing dynamic changes in the geostress field of a repeated fracturing horizontal well according to claim 1 or 2, characterized in that: The rock mechanical parameters are calculated by the following steps: the rock dynamic mechanical parameters are calculated by rock density and longitudinal wave time difference; the rock dynamic mechanical parameters are converted into rock static mechanical parameters as the rock mechanical parameters, wherein: Based on the rock density and the longitudinal wave time difference, the transverse wave time difference is calculated; Based on the shear wave time difference, the rock density, and the longitudinal wave time difference, Young's modulus is calculated; Based on the transverse wave time difference and the longitudinal wave time difference, the Poisson's ratio is calculated.

4. A method for analyzing dynamic changes in geostress field of a repeated fractured horizontal well according to any one of claims 1 to 3, characterized in that: The natural fracture model is constructed by the following steps: according to the target area faults and the core description of the natural fracture occurrence, combined with the natural fracture coherent volume data, the natural fracture model of the high-angle structure around the well is constructed.

5. A method for analyzing dynamic changes in geostress field of a repeated fractured horizontal well according to any one of claims 1 to 4, characterized in that: The three-dimensional geostress field distribution in the target area is calculated through the following steps: combining the stress background and the heterogeneous rock mechanics parameter field in the target area, the finite element method is used to calculate the stress and strain of each node, and the well point geostress test data is fitted to obtain the three-dimensional geostress field distribution in the target area.

6. A method for analyzing dynamic changes in geostress field of a repeated fractured horizontal well according to any one of claims 1 to 5, characterized in that: The three-dimensional hydraulic fracturing simulation model is constructed by the following steps: A computational model for calculating the aperture of natural fractures is constructed by integrating local rock elastic properties, fluid pressure, and the path distance from the fracture unit to the injection section location; Set the natural fracture activation capability priority parameter to characterize the priority of natural fracture opening when hydraulic fracture expansion encounters multiple activatable natural fractures at the same time; According to the Mohr-Coulomb criterion, the stress variation of natural fractures in the three-dimensional stress system is considered, and a shear analysis model is constructed to describe the shear failure of natural fractures during hydraulic fracturing.

7. A method for analyzing dynamic changes in geostress field of a refractured horizontal well according to any one of claims 1 to 6, characterized in that: The method further comprises: considering the interaction between hydraulic fractures and natural fractures, simulating the morphology of primary fractures through the three-dimensional hydraulic fracturing simulation model, and correcting the fracture size based on fracture monitoring data and production dynamic fitting results.

8. A method for analyzing dynamic changes in geostress field of a refractured horizontal well according to any one of claims 1 to 7, characterized in that: The magnitude and direction distribution of the maximum horizontal principal stress and the minimum horizontal principal stress before repeated fracturing of the horizontal well are determined by the following steps: Based on the geological model and the three-dimensional hydraulic fracturing simulation model, according to the mass conservation equation, Darcy flow equation and fluid state equation, combined with the natural fracture model, the flow of fluid in the reservoir is simulated, the production history of the oil well is fitted, and the pressure distribution and ground stress changes in the reservoir production process are clarified by using the production curve characteristics and reservoir distribution characteristics, and the reservoir utilization degree is clarified, and the magnitude and direction distribution of the horizontal maximum principal stress and the horizontal minimum principal stress before repeated fracturing of the current horizontal well are obtained.

9. A storage medium, characterized in that: It contains a series of instructions for executing the method steps as claimed in any one of claims 1 to 8.

10. A device for analyzing dynamic changes in the geostress field of a repeated fracturing horizontal well, characterized in that: The method according to any one of claims 1 to 8 is performed, wherein the device comprises: A geological model module, which establishes a geological model along the horizontal well trajectory based on the geological data of the target area where the horizontal well is located, and assigns corresponding rock mechanics parameters to the geological model; The fracture model module is used to construct a natural fracture model that conforms to the geological characteristics of the target area according to the development law of natural fractures in the reservoir, and calculate the three-dimensional distribution of the geostress field in the target area; A fracturing model module, which is used to construct a three-dimensional hydraulic fracturing simulation model based on the geological model and the natural fracture model through the initial fracturing construction parameters to simulate the initial fracturing fracture morphology; The stress distribution module is used to determine the magnitude and direction distribution of the maximum horizontal principal stress and the minimum horizontal principal stress before repeated fracturing of the horizontal well according to the production time of the horizontal well and in combination with the three-dimensional hydraulic fracturing simulation model.

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