An artificial fracture evaluation method based on geological engineering integration

Abstract

The application discloses a kind of artificial fracture evaluation methods based on geotechnical engineering integration, belong to petroleum reservoir field.The application comprehensively uses geological model and one-dimensional rock profile to establish regional geostress field model, and the establishment of geostress model is different from the modeling method of transmission geological attribute body, and the effect of its geostress field is more real through the whole rock mass loading regional stress and the deformation generated by rock mass stress.The fracture network is divided into the fracture part formed by artificial fracture main fracture and the damage area composed of natural fracture and artificial microfracture, and the factors considered are more comprehensive by comprehensively using geological model, geomechanical model and damage coupling theory.The corresponding characteristics of fracturing operation curve are used for interpretation, and the complexity of fracture network of reformed fracture is identified according to the peak value change of interpretation characteristic curve.Compared with microseismic monitoring, millions of test interpretation costs are saved, and the artificial fracture supported can be well explained by combining damage coupling prediction model.

Description

Technical Field

[0001] This invention belongs to the field of petroleum reservoirs, and in particular, it is a method for assessing artificial fractures based on integrated geological and engineering approaches. Background Technology

[0002] From the perspective of current international research, geostress field simulation is still based on ideal models, without much consideration for actual geological and rock mechanics parameter variations, nor for fitting with actual test data and fracturing construction data. In fracture morphology simulation, it is difficult to simultaneously consider the combined effects of production / injection, fluid flow caused by dynamic initiation of multi-stage fractures, rock deformation, and temperature changes on stress disturbance. The methods for identifying and predicting the morphology and complexity of volumetric fracturing fractures are relatively limited; there is no comprehensive fracturing construction data-driven post-fracturing fracture evaluation method that, based on this, analyzes influencing factors to establish a fracture prediction method. The current research status is as follows.

[0003] In 2009, JEOlson and A.D. Taleghani considered the interaction between fractures and established a simplified numerical model to simulate the simultaneous extension of multiple fractures. Simulations of multiple horizontal well sections showed that the complexity of fracture extension is mainly influenced by the relative relationship between net pressure and horizontal stress difference, as well as the geometry of natural fractures. Stress analysis at the fracture tip indicated that the induced stress at the fracture tip is sufficient to open closed natural fractures before the arrival of hydraulic fractures. In 2011, Arash Dahi-Taleghani and Jon E. Olson argued that the influence relationship between natural and artificial fractures is a key factor affecting complex fracture morphology. They also pointed out that the crossing or blockage of hydraulic fracturing fractures in areas with naturally developed fractures is controlled not only by shear stress and slippage on the fracture surface but also by the influence of naturally closed fractures located at the tips of hydraulic fractures. Based on this, Arash and Jon developed a complex hydraulic fracture propagation model based on the finite element method. Their conclusions showed that the complexity of fracture morphology is jointly influenced by factors such as the heterogeneity of the in-situ stress field, rock toughness, the cementation strength of natural fractures, and the angle between natural and artificial fractures. In 2011, C. Cipolla and X. Weng et al. argued that existing models were insufficient for assessing and predicting fracture propagation. Combining this with recent advancements in fracture propagation modeling, they proposed a new approach to address this challenge. Their study used two different fracture models, combined with microseismic mapping, to describe fracture complexity and evaluate fracturing effectiveness. The conclusions demonstrated how fracture complexity varies with fracturing design parameters under different morphological conditions. In 2012, R. Wu, OKresse et al. first elucidated the impact of stress shadowing on fracture propagation and fracture network development. They then developed a method for calculating stress shadowing in complex fracture networks. This method, based on a two-dimensional discontinuous displacement method corrected for finite fracture height, was compared with a three-dimensional numerical model, yielding satisfactory results. The conclusions indicated that regardless of geostress anisotropy, the stress shadowing effect influences the injection volume of each segment and cluster in multi-point fracturing operations, thereby affecting the fracture network morphology. In 2012, Roger Yuan and Liang Jian et al., based on the problems encountered during fracturing operations in the main reservoirs of the Upper Triassic Xujiahe Formation in the Sichuan Basin in central and western China, studied the main influencing factors of complex fracture geometry and limiting fracture height. To quantitatively evaluate the effectiveness and strategies of hydraulic fracturing, the study presented two numerical models of hydraulic fractures. In addition to a model based on linear elastic fracture mechanics, a fully coupled finite element model was also used. This model considered the geological characteristics of sandstone-shale formations, which may limit or promote fracture development. The model results showed that, in addition to typical stress effects, mechanical properties and parallel layered geological features may also inhibit vertical fracture development while promoting the formation of horizontal fractures.In 2012, R. Keshavarzi and S. Mohammadi established an extended finite element model that incorporated fracture deflection criteria. Furthermore, this study considered a phenomenon rarely addressed in other studies: near the tip of an extended fracture, before the artificial fracture extends into the previously cemented natural fracture, the natural fracture may loosen. This loosening is crucial for the secondary deflection of hydraulic fractures, thus explaining the interaction between hydraulic and natural fractures under different conditions. The effects of approach angle and stress difference on the opening and penetration of natural fractures were also observed and compared with numerical models, showing a high degree of agreement. In 2013, Kan Wu and Jon E. Olson established a fully fluid-structure interaction model to study the geostress and construction parameters affecting fracture morphology in multi-stage fracturing of horizontal wells. Subsequently, sensitivity analyses were conducted on factors such as ground stress difference, pumping rate, and fluid viscosity. The results showed that the width development of adjacent fractures was limited, and phenomena similar to early desanding occurred. It was also pointed out that the synchronous propagation model for multi-point fracturing in slickwater, due to neglecting the integration of mechanical factors, led to an overestimation of the construction effect. Eric C. Bryant (2015) established a model based on the finite volume element method capable of simulating arbitrary fracture propagation. This model couples single-phase hydrodynamics, original ground stress, and pore elastic displacement, using a fixed strain slip assumption for model construction. Simultaneously, the established cohesive model (CZM) can be used to simulate the propagation of non-parallel fractures in heterogeneous media. Finally, this model was used to simulate microseismic events, yielding a series of related conclusions. Zongyu Zhai (2015) proposed a method for predicting multi-fracture propagation. This method is based on an integrated 3D hydraulic fracturing software package. It conducts simulation studies on fracture propagation for both single-well multi-stage fracturing and multi-well multi-stage fracturing. In addition, the simulation results of fracture morphology and pressure are matched with the interpretation results of field microseismic monitoring and construction pressure data, and the degree of agreement is high.

[0004] Domestic research on volumetric fracturing started relatively late. In 2009, the "fracture network fracturing" technology suitable for reservoirs with low porosity, low permeability and no natural fractures was proposed. The applicable conditions, process design ideas and application methods of the "fracture network fracturing" technology were discussed, and the implementation path of "fracture network fracturing" was explored.

[0005] With continuous technological advancements, scholars have gradually shifted their focus from the formation of complex fracture networks to the study of the interactions of various mechanical properties within existing fracture networks. In 2015, researchers established a complex fracture network model coupling rock mechanics and fluid mechanics to investigate the relationship between parameters such as perforation cluster spacing, stress difference, natural fracture morphology, and injection flow pressure. The conclusion suggests that the pursuit of a single-stage fracturing operation should not be blindly prioritized; rather, there exists an optimal balance between the number of fractures and the effective fracture coverage area. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide an artificial crack assessment method based on integrated geological engineering.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] An artificial fracture assessment method based on integrated geological and engineering methods includes the following steps:

[0009] (1) Coarsen the rock mechanics parameter model generated by Petrel, convert the Petrel and Flac3D attribute bodies after coarsening, and then transfer it into Flac3D. Based on the reservoir geological structure characteristics and attributes of the Flac3D model, and combined with the regional tectonic stress, load the triaxial stress environment to simulate the diagenesis process of the block rock mass, complete the three-dimensional rock mechanics simulation of the well area reservoir, and obtain the regional three-dimensional geomechanics model.

[0010] (2) Based on the three-dimensional geomechanical model, obtain the configuration features, attribute parameters (including porosity, permeability, saturation, etc.) and rock mechanical parameters (Poisson's ratio, Young's modulus, horizontal stress, etc.). Combined with the construction parameters in the hydraulic fracturing design, use the finite element method of the continuous medium damage mechanics model to establish a global continuous medium damage mechanics model for the study area. For the damage mechanics model of rock microcracks, adopt the rock statistical damage constitutive model in which the micro-element strength follows the Weibull distribution. For the simulation of the fracture process of the main fracture during hydraulic fracturing, adopt the discrete element method. During the calculation process, update the range of the discrete element simulation area according to the range of the rock mass fracturing area, thereby establishing a fracture-damage coupling model.

[0011] (3) Based on the fracturing construction curve obtained from the on-site fracturing construction, the artificial fracture morphology is identified by using Meyer combined with the filtration coefficient, and the corresponding characteristics of the fracturing construction curve are interpreted.

[0012] Furthermore, the attribute parameters include porosity, permeability, and saturation;

[0013] The rock mechanics parameters include Poisson's ratio, Young's modulus, and horizontal stress.

[0014] Furthermore, in step (2), if the finite element damage variable D ≥ D c Then, the finite element domain is divided into the fracture calculation region, and the particle discrete element method is used for simulation, D c This is a critical damage variable.

[0015] Furthermore, in step two, the damage constitutive model is based on the rock element strength theory. The element strength follows a Weibull distribution. If rock failure follows an elastoplastic yield criterion, then the ratio of the number of failed elements to the total number of elements is used as the damage variable, expressed as:

[0016]

[0017] Where A is the total area, A* is the effective bearing area, and N is the total number of infinitesimal elements. f Let be the number of fracture elements; further, the intensity of each element follows a Weibull distribution, and the probability density function of the element is:

[0018]

[0019] P(F) is the probability distribution function, F is a random variable, F0 is the scaling parameter, and m is the shape parameter.

[0020] Furthermore, in step two, the specific process of establishing the fracture-loss coupling model is as follows:

[0021] The entire domain is initialized. After initialization, incremental loads are applied to initialize the DEM. The boundary conditions and particle kinematics of the DEM region are updated, and the particle forces are calculated. Before the time step ends, the finite element nodal mechanics is calculated and the finite element nodal kinematics are updated. At this time, the damage variables of the elements are judged, the discrete element region is expanded, and after the calculation is completed, the calculation of the next time step is carried out until the end. Under the simulation of the complete time step, the discrete element region of the elements is simulated according to the stress and kinematics, and natural crack shielding is added to obtain the extension direction and extension range of artificial cracks.

[0022] Furthermore, in step three, based on the construction curve data, the G-function response curve in the formation where micro-fractures are not well developed is obtained.

[0023] Furthermore, microcracks and main fractures were identified based on the trajectory of the G-function response curve.

[0024] Furthermore, after the closing time, if the superimposed derivative curve of the G function response curve is a straight line, it is determined that a single crack has been formed.

[0025] If the superimposed derivative curve shows a concave segment, it is determined that a multi-level main seam has been formed.

[0026] If the superimposed derivative curve shows an upward convex segment, it is determined that a multi-branch seam has been formed.

[0027] Furthermore, if the G function response curve is linear, the upward convexity on the G function response curve is used as the identification feature of the microcracks, and the development degree of the microcracks is judged according to the magnitude of the vertical axis corresponding to the G function response curve.

[0028] If the G-function curve shows a concave shape on a straight line segment, it can be used as an identification feature that connects to natural cracks.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] This invention presents an integrated geological and engineering method for assessing artificial fractures. It comprehensively utilizes geological models and one-dimensional rock profiles to establish a regional geostress field model. This geostress model differs from traditional methods that rely on transmitted geological attributes; it is not generated at the bottom of a single well or through inter-well interpolation, but rather generated based on the stress and deformation of the entire rock mass under load, resulting in a more realistic geostress field. The fracture network is divided into fracture zones formed by the main artificial fracture and damage areas composed of natural and artificial micro-fractures. By integrating geological models, geomechanical models, and fault-loss coupling theory, this integrated geological and engineering method for identifying artificial fracture networks considers more comprehensive factors compared to traditional methods. The method interprets the corresponding characteristics of fracturing operation curves, identifying the complexity of the fracture network based on the peak changes of the interpretation characteristic curves. Compared to microseismic monitoring, it saves millions in testing and interpretation costs. Combined with the fault-loss coupling prediction model, it can effectively interpret supporting artificial fractures, rather than dynamic fractures interpreted through microseismic means. Attached Figure Description

[0031] Figure 1 This is a diagram illustrating the geostress modeling effect of the present invention, wherein, Figure 1 (a) is the three-dimensional model of the minimum horizontal principal stress. Figure 1 (b) is the three-dimensional model of the maximum horizontal principal stress;

[0032] Figure 2 This is a schematic diagram illustrating the coupling analysis of fracture and damage mechanics during hydraulic fracturing.

[0033] Figure 3 A simplified flowchart of the adaptive multi-scale method for calculating rock mass fracture damage;

[0034] Figure 4 The effect of artificial crack identification in the fracture coupling model;

[0035] Figure 5 Artificial crack identification chart for fracturing operation curves;

[0036] Figure 6 An example of artificial seam mesh identification for the coupling model of geostress field and fracture loss. Detailed Implementation

[0037] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0038] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0039] The present invention will now be described in further detail with reference to the accompanying drawings:

[0040] 1. Regional reservoir geostress simulation

[0041] Numerical simulation calculations for geostress parameter inversion were performed using Flac3D software. During the model simulation process, the three-dimensional geomechanical model established by Petrel was exported and converted into a three-dimensional data volume of rock mechanics parameters, which was then organically integrated with Flac3D software. Since the three-dimensional data volume of rock mechanics parameters reached the level of tens of millions of grids, if the above model were used directly, the stability, reliability, and computational efficiency of the algorithm would be greatly reduced. Therefore, it was necessary to coarsen the three-dimensional data volume of rock mechanics parameters to meet the computational requirements of the finite difference software as much as possible while ensuring that the lithological data was not distorted.

[0042] Petrel's parametric model primarily uses a corner mesh model. The corner mesh data is mainly described by COORD and ZCORD data. COORD data describes the pillars of each row of meshes, specifying the top and bottom coordinates (x, y, z) of each row. ZCORD data describes the elevation of each corner point of the mesh, specifying the Z-value of each mesh. Flac3D mesh data, however, follows the right-hand rule. Therefore, this invention utilizes computer programming to convert Petrel's data volume into a Flac3D-recognizable data volume, achieving interoperability between Petrel and Flac3D software.

[0043] The 3D rock mechanics data volume generated by Petrel is coarsened, and the output data file is transferred into Flac3D to prepare for stress simulation calculations. Based on the structural and property Flac3D model, and considering the regional tectonic stress, a three-dimensional stress environment is applied to simulate the diagenetic process of the rock mass in the study block. When the maximum unbalanced force is 0, i.e., when there is no displacement of the rock mass in the study block, the 3D rock mechanics simulation of the well area reservoir is completed. See the simulation model example below. Figure 1 ,in, Figure 1 (a) is the three-dimensional model of the minimum horizontal principal stress. Figure 1 (b) is a three-dimensional model of the maximum horizontal principal stress. The stress trend and stress range of the entire reservoir can be seen from the figure. Different depths can be sliced ​​according to the needs to obtain stress attribute values ​​at different depths.

[0044] 2. Establishment and numerical simulation of the fracture-damage coupling model

[0045] Based on step 1, the reservoir has three-dimensional realistic diagenetic environment, stress environment and structural features, etc. The distribution range, morphology and important parameters (including fracture length, width, height, support volume, etc.) of artificial fractures in the reservoir are simulated. The artificial fractures are visualized in true three-dimensional simulation and the artificial fractures are evaluated intuitively.

[0046] Hydraulic fracturing is a highly efficient and economical key technology for artificially increasing permeability. The water pressure load acting within the borehole triggers the initiation and propagation of fractures in the surrounding rock mass, leading to a denser and more developed fracture network around the borehole, thereby increasing the permeability of the surrounding rock mass. Hydraulic fracturing creates a network of main fractures and microfractures; large fractures and microfracture damage occur coupled and are interconnected during this process. From the initial damage accumulation and cracking to the formation of the main fracture and fracture network, both damage and fracture accumulate and develop simultaneously in the hydraulically fracturing rock mass. Damage continuously accumulates into more fractures, and the propagation of these fractures further damages the rock mass.

[0047] The finite element method (FEM) based on a continuous medium damage mechanics model is used to simulate the entire computational domain, while the granular discrete element method (DEM) is used to simulate localized areas with severe rock mass fracturing. During the calculation, the range of the DEM simulation domain is updated accordingly based on the location of the rock mass fracturing to ensure that the DEM calculation covers all areas of rock mass fracturing. This allows for accurate and efficient numerical simulation analysis of both the macroscopic fracturing process and the microscopic damage process of hydraulic fracturing. If the finite element damage variable D ≥ D... c This finite element domain is designated as the fracture calculation region and simulated using the particle discrete element method. Wherein, D c This is the critical damage variable. A schematic diagram of the fracture and damage areas is shown below. Figure 2 As shown in the figure, the stress damage and the extent of artificial crack propagation during fracturing can be observed.

[0048] For finite element method (FEM) simulation of rock damage mechanics, a statistical damage constitutive model of rock with micro-element strength following a Weibull distribution is adopted. Damage constitutive parameters are determined based on indoor rock mechanics tests. A discrete element method (DEM) simulation of rock fracture mechanics is developed, employing a bonded-particle contact model for fracture analysis to simulate the cracking and propagation process of large-scale rock fractures. Building upon this, an adaptive multi-scale numerical simulation of hydraulic fracturing fracture and damage coupling is finally developed. The DEM is used to simulate the cracking and propagation of large-scale hydraulic fracturing fractures, while the FEM is used to simulate the damage to the surrounding rock mass.

[0049] Damage mechanics simulation of rock microcracks employs a statistical damage constitutive model. This model is based on the rock element strength theory, assuming a given element strength follows a Weibull distribution and that rock failure follows an elastoplastic yield criterion. The damage variable is defined as the ratio of the number of damaged elements to the total number of elements, expressed as:

[0050]

[0051] Where A is the total area, A * The effective bearing area is N, where N is the total number of infinitesimal elements. f Let be the number of fracture elements. The strength of each element follows a Weibull distribution, with the following probability density function:

[0052]

[0053] The discrete element method (DEM) was used to simulate the fracture process of the main fracture during hydraulic fracturing. Rock masses exhibit a transformation from continuous to discontinuous media during fracture failure. Using only continuous medium damage mechanics numerical analysis methods for rock fracture analysis is insufficient. The DEM, as an important numerical analysis method for rock fracture problems, is receiving increasing attention. This method has a simple theoretical basis, can analyze the fracture failure process from microscopic to macroscopic levels, and can more accurately simulate the discontinuous fracture failure phenomenon of rocks. The commercial discrete element software PFC is widely used for simulating rock fracture failure. This project utilizes a rock fracture discrete element software developed by the research team using Fortran and Matlab to analyze rock fracture during hydraulic fracturing. The computational framework of the discrete element method for rock fracture mechanics simulation is as follows: Figure 3 As shown, the entire domain is initialized. After initialization, an incremental load is applied to initialize the DEM. The boundary conditions and particle kinematics of the DEM region are updated, and the particle forces are calculated. Before the time step ends, the finite element nodal mechanics is calculated and the finite element nodal kinematics are updated. At this time, the damage variables of the element are judged, the discrete element region is expanded, and after the calculation is completed, the next time step is calculated until the end. Under the simulation of the complete time step, the discrete element region of the element is calculated based on the stress and kinematics, and natural crack shielding is added to simulate the extension direction and extension range of artificial cracks.

[0054] The calculation process is as follows: Secondary development is performed using a subroutine of the Flac3D software. Figure 3 The simulation effect is as follows: Figure 4 As shown in the figure, the propagation pattern of artificial fractures encountering natural fractures in a reservoir with naturally developed fractures is illustrated. The figure shows the process from the initiation of artificial fractures to their final morphology after the completion of the overall fracturing operation.

[0055] 3. Identifying and modifying crack characteristics using fracturing construction curves

[0056] In formations with underdeveloped microfractures, the G-function response curve appears as a flat line because the overall matrix filtration is relatively uniform. However, due to differences in matrix permeability, the slope of the curve will vary, with a larger slope generally corresponding to higher matrix permeability. When microfractures are well-developed in the formation, the curve will show a distinct upward convexity, which can be used as an identification feature for connecting microfractures. Figure 5 As shown in (a). At the same time, the degree of microcrack development can be judged based on the magnitude of the corresponding vertical axis of the curve.

[0057] The main fracture is characterized by high pump shutdown pressure, high friction, and high filtration loss. The fracture propagation pressure increases continuously after rupture, caused by the simultaneous propagation of multiple hydraulic fractures. This is reflected in the G-function curve as a significant dip in the straight section, such as... Figure 5As shown in (b). The response of the G-function curve can be used to determine whether natural cracks were connected during the construction and renovation, thereby determining the degree of microcrack development in the renovated area.

[0058] Example

[0059] 1. Artificial seam mesh identification based on integrated geostress field and fracture-damage coupling model

[0060] Based on the true 3D geomechanical model of the study block, see Figure 1 As shown, a true three-dimensional artificial fracture model of the well group was established. Using an integrated geological and engineering approach, the identification of true three-dimensional hydraulic fractures in the well group was completed. The identification results are as follows: Figure 6 As shown in the figure, the 3D artificial fracture morphology and the 2D artificial fracture morphology are respectively displayed. They conform to the interaction criterion of artificial fractures and natural fractures, forming a large fracture network, and the effect of fracturing to expand the volume is obvious.

[0061] 2. Identifying and modifying crack characteristics using fracturing construction curves

[0062] The main fractures formed by hydraulic fracturing are characterized by high pump shutdown pressure, high friction, and high filtration loss. The fracture propagation pressure increases continuously after rock fracturing, resulting from the simultaneous propagation of multiple hydraulic fractures. This is reflected in the G-function curve as a significant dip in the straight section, such as... Figure 5 As shown:

[0063] The response of the G-function curve can be used to determine whether artificial cracks have connected with natural cracks during construction and renovation, and to assess the degree of microcrack development in the renovated area.

[0064] Because the overall reservoir matrix filtration is relatively uniform, the G-function response curve of formations without well-developed microfractures appears as a flat straight line. However, due to differences in matrix permeability, the slope of the curve will vary, with a larger slope generally corresponding to higher matrix permeability. When microfractures are developed in the formation, the curve will show a distinct upward convexity, which can be used as an identification feature for connecting microfractures, such as... Figure 5 As shown in the figure. The degree of microcrack development can also be determined by the magnitude of the vertical axis corresponding to the curve.

[0065] Taking well C as an example, from the perspective of the shape of the G function ( Figure 5 ), Figure 5 (a) shows that the natural cracks are well-developed and the pre-filled liquid is offset from a large number of micro-cracks. Figure 5 (b) shows that the fiber temporary plugging deflects and forms a new branch main fracture, but the microcrack characteristics are not obvious. The fracture deflects twice to form three main fractures. Local natural fractures are more developed, forming a large number of branch microcracks. The two deflecting main fractures are locally connected to a small number of microcracks. The overall complexity of the artificial fractures is relatively high.

[0066] Using the above method, the previously analyzed single wells were classified according to different construction methods. Then, the G function was used for feature identification, and the conclusions shown in Table 1 were obtained:

[0067] Table 1 Examples of Artificial Fracture Network Identification Based on Fracturing Construction Curves in Well Area A

[0068]

[0069]

[0070] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for assessing artificial fractures based on integrated geological and engineering methods, characterized in that, Includes the following steps: (1) Coarsen the rock mechanics parameter model generated by Petrel, convert the Petrel and Flac3D attribute bodies after coarsening, and then transfer it into Flac3D. Based on the reservoir geological structure characteristics and attributes of the Flac3D model, and combined with the regional tectonic stress, load the triaxial stress environment to simulate the diagenetic process of the block rock mass, complete the three-dimensional rock mechanics simulation of the well area reservoir, and obtain the regional three-dimensional geomechanical model. (2) Based on the three-dimensional geomechanical model, obtain the configuration features, attribute parameters and rock mechanical parameters. Combined with the construction parameters in the hydraulic fracturing design, use the finite element method of the continuous medium damage mechanics model to establish a global continuous medium damage mechanics model for the study area. For the damage mechanics model of rock microcracks, adopt the rock statistical damage constitutive model in which the micro-element strength follows the Weibull distribution. For the simulation of the fracture process of the main fracture during hydraulic fracturing, adopt the discrete element method. During the calculation process, update the range of the discrete element simulation area according to the range of the rock mass fracturing area, thereby establishing a fracture-damage coupling model. (3) Based on the fracturing construction curve obtained from the on-site fracturing construction, the artificial fracture morphology is identified by using Meyer's method combined with the filtration coefficient, and the corresponding characteristics of the fracturing construction curve are interpreted. The attribute parameters include porosity, permeability, and saturation; The rock mechanical parameters include Poisson's ratio, Young's modulus, and horizontal stress. In step (2), if the finite element damage variable Then, the finite element domain is divided into the fracture calculation region, and the particle discrete element method is used for simulation. For critical damage variables; In step two, the damage constitutive model is based on the rock element strength theory. The element strength follows a Weibull distribution. If rock failure follows an elastoplastic yield criterion, then the ratio of the number of failed elements to the total number of elements is used as the damage variable, expressed as: in, A For the total area, A* For effective bearing area, N The total number of infinitesimal elements, N f The number of fractured infinitesimal elements; The intensity of each infinitesimal element follows a Weibull distribution, and the probability density function of the infinitesimal element is: P(F) Let be the probability distribution function. F For random variables, F 0 is the proportional parameter. m For shape parameters; In step two, the specific process of establishing the fracture-loss coupling model is as follows: The entire domain is initialized. After initialization, incremental loads are applied to initialize the DEM. The boundary conditions and particle kinematics of the DEM region are updated, and the particle forces are calculated. Before the time step ends, the finite element nodal mechanics is calculated and the finite element nodal kinematics are updated. At this time, the damage variables of the elements are judged, the discrete element region is expanded, and after the calculation is completed, the calculation of the next time step is carried out until the end. Under the simulation of the complete time step, the discrete element region of the elements is simulated according to the stress and kinematics, and natural crack shielding is added to obtain the extension direction and extension range of artificial cracks.

2. The artificial fracture assessment method based on integrated geological and engineering methods according to claim 1, characterized in that, In step three, based on the construction curve data, the G-function response curve in the formation where micro-fractures are not well developed is obtained.

3. The artificial fracture assessment method based on integrated geological and engineering methods according to claim 2, characterized in that, Microcracks and main fractures were identified based on the trajectory of the G-function response curve.

4. The artificial fracture assessment method based on integrated geological and engineering methods according to claim 2, characterized in that, If the superimposed derivative curve of the G function response curve is a straight line after the closing time, it is determined that a single crack has been formed. If the superimposed derivative curve shows a concave segment, it is determined that a multi-level main seam has been formed. If the superimposed derivative curve shows an upward convex segment, it is determined that a multi-branched seam has been formed.

5. The artificial fracture assessment method based on integrated geological and engineering methods according to claim 2, characterized in that, If the G function response curve is linear, the upward convexity of the G function response curve is used as the identification feature of microcracks. At the same time, the degree of microcrack development is judged based on the magnitude of the vertical axis corresponding to the G function response curve. If the G-function curve shows a concave shape on the straight line segment, it serves as an identification feature that connects to natural cracks.

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