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CN-121995535-A - Modeling method for carbonate fracture based on digital outcrop and geomechanical simulation

CN121995535ACN 121995535 ACN121995535 ACN 121995535ACN-121995535-A

Abstract

The invention discloses a modeling method of carbonate cracks based on digital outcrop and geomechanical simulation. The method comprises the steps of constructing a high-precision digital outcrop model through unmanned aerial vehicle oblique photography, obtaining outcrop surface crack parameters, dividing a crack group system, and determining ancient stress field characteristics of a multi-period seam making period by combining a filler isotope test and an acoustic emission experiment. Further, geomechanical simulation is carried out based on the recovered paleo-structure, and density and opening parameters of cracks in each period are quantitatively calculated by utilizing a two-section fracture criterion and a strain energy density theory. And then, combining deterministic modeling and random modeling technologies, constructing a multi-period multi-scale discrete fracture network model, and performing fluid simulation based on the model to analyze the control effect of the fracture on the ancient karst. Finally, through comparison and verification with outcrop measured data, a corrected crack-matrix coupling prototype geological model is output, quantitative prediction of the crack in the outcrop is realized, and the precision and reliability of the crack prototype model are obviously improved.

Inventors

  • DU HE
  • Xing Huilin
  • YAN WEICHAO
  • TAN YUYANG
  • ZHANG JIANMING

Assignees

  • 中国海洋大学

Dates

Publication Date
20260508
Application Date
20260130

Claims (10)

  1. 1.A method for modeling carbonate fractures based on digital outcrop and geomechanical simulation, comprising the steps of: S1, constructing a digital outcrop model of a typical outcrop, namely, based on unmanned aerial vehicle oblique photography technology, scanning and three-dimensional reconstruction are carried out on a selected outcrop area to obtain the digital outcrop model, and geometrical information of stratum, fault and outcrop surface cracks is extracted from the digital outcrop model; s2, counting and analyzing outcrop crack parameters, namely counting the yield, length and opening parameters of outcrop surface cracks by combining a digital outcrop model with field identification, and dividing different crack groups according to the yield and mechanical characteristics; S3, determining a main joint making period of the outcrop crack, namely determining a filling period time and a crack forming sequence through isotope testing and structural shape trace analysis of a crack filling material, and acquiring the ancient stress direction and the ancient stress magnitude of each period time by combining an acoustic emission experiment; S4, simulating the paleo-stress field in the main joint making period, namely establishing a geomechanical model based on the recovered paleo-structure model and rock mechanical parameters, and simulating paleo-stress field distribution in each main joint making period by taking paleo-stress data obtained in the S3 as boundary conditions; s5, quantitatively representing the multi-period crack parameters, namely judging cracks by adopting a rock cracking criterion based on the stress field result of the S4, and calculating the density and the opening of each period of cracks according to a quantitative relation model of stress-strain and the crack parameters; s6, performing multi-period multi-scale discrete modeling on the large-scale cracks, namely performing deterministic modeling on the large-scale cracks based on digital outcrop data, performing random modeling on the medium-small-scale cracks by taking the crack density obtained in the S5 as a constraint, and finally superposing to form a multi-period multi-discrete network model; S7, performing fluid flow simulation based on the discrete fracture network model of S6, calculating the fracture permeability and analyzing the control effect of the multi-stage fracture on the development of the ancient karst; and S8, verifying and correcting the outcrop prototype model, namely comparing, verifying and correcting the predicted attribute of the crack model with the outcrop measured data, and outputting a verified crack-matrix coupling prototype geological model.
  2. 2. The method of claim 1, wherein in the step S1, the unmanned aerial vehicle oblique photography technology comprises fixed-height aerial photography and proximity aerial photography, wherein the resolution of a model constructed by the fixed-height aerial photography is 0.1-0.3 m for analyzing structural characteristics of a region, and the distance between the unmanned aerial vehicle and a geologic body during the proximity aerial photography is less than 15 m, and the resolution of the constructed model is 3-6 mm for counting fracture parameters.
  3. 3. The method according to claim 1, wherein in step S2, the stacking sequence of the multi-stage cracks is determined by analyzing the cut-off, dislocation, restriction and sliding relationships between the different sets of cracks.
  4. 4. The method according to claim 1, wherein in the step S3, the acoustic emission experiment is specifically that triaxial loading is carried out on directional rock plunger samples in multiple directions, kaiser effect points on an acoustic emission accumulation curve are identified to obtain memory stress, and the maximum horizontal main stress is calculated through a formula according to memory stress values obtained through sampling tests in horizontal directions of 0 DEG, 45 DEG and 90 DEG Minimum horizontal principal stress Direction angle of maximum principal stress 。
  5. 5. The method according to claim 1, wherein in step S5, the rock breaking criterion is that when the minimum principal stress sigma 3 is not less than 0, the shearing breaking is judged by adopting a two-stage Coulomb-Mohr criterion, and the breaking criterion is that Wherein, sigma 1 is the maximum main stress, sigma 3 is the minimum main stress, C is the cohesive force of the rock, phi is the internal friction angle of the rock, and when sigma 3 is less than 0, the method adopts the Griffins criterion to judge the tensile fracture.
  6. 6. The method of claim 5, wherein the value of the internal friction angle phi in the two-stage coulomb-moire criterion is determined based on the relationship between the confining pressure σ 3 and the critical confining pressure σ 0 , wherein phi takes a first internal friction angle phi 1 when 0< σ 3 <σ 0 and a second internal friction angle phi 2 when σ 3 ≥σ 0 .
  7. 7. The method according to claim 1, wherein in step S5, the quantitative relation model is constructed based on strain energy density theory, specifically by calculating the ratio of the energy released by the rock fracture to the energy required to form the fracture surface and to generate the fracture per unit area to determine the fracture volume density, and further calculating the fracture line density and the opening degree in combination with the fracture angle, the characterization unit volume scale and the strain state.
  8. 8. The method according to claim 1, wherein in step S7, the calculating the fracture permeability is based on the Oda method and cubic law, and specifically, the permeability tensor is calculated according to the fracture opening, the linear density and the normal vector information of the fracture surface.
  9. 9. A storage device having stored thereon a computer program which, when executed by a processor, implements the method of any of claims 1 to 8.
  10. 10. An arithmetic device, comprising: A memory for storing a computer program; A processor for executing a computer program in the memory to implement the method of any one of claims 1 to 8.

Description

Modeling method for carbonate fracture based on digital outcrop and geomechanical simulation Technical Field The invention belongs to the field of petroleum development, and particularly relates to a method for constructing a carbonate fracture prototype model driven by digital outcrop and geomechanical simulation. Background The carbonate reservoir of the Tarim basin is currently a hot spot area for oil and gas exploration and development, accounting for about 38% of the total oil and gas resources of the basin. The construction of the fracture and karst fracture-cave system as an important construction part of a carbonate reservoir can not only provide migration channels for oil and gas, but also serve as an important reservoir space. Therefore, defining the development mode and distribution law of fracture-karst evolution is important for oil and gas exploration of carbonate reservoirs. With the continuous advancement of carbonate hydrocarbon reservoir development process, the requirements of oilfield exploration and development operations on the accuracy of geological models are increasing. However, due to the heterogeneous nature of the reservoir, it is difficult to accurately delineate the reservoir fracture solely by the characterization of the seismic data and interpretation of the well log data. In order to break through the limitation of underground data on the fine description of the reservoir fracture, geologists have tried to provide reasonable parameters for reservoir fracture modeling by adopting methods such as outcrop observation, test assay, prototype model construction and the like in recent years. Prototype models refer to fine reservoir models that resemble outcrop, close-well patterns of developing mature fields, or modern depositional environments that simulate target zone reservoir characteristics. Practice proves that outcrop is the most true and direct data source, and based on the outcrop data, the establishment of a prototype model and a geological knowledge base is the most suitable choice for modeling the assisted reservoir fracture. However, conventional outcrop prototype models generally employ means such as measurement descriptions, sampling analysis, and geological radar. These methods are mostly characterizations at a two-dimensional level, with limited help to model reservoir fractures. With the development of mapping technology, three-dimensional digital outcrop technology based on unmanned aerial vehicle scanning appears, and the three-dimensional digital outcrop technology can effectively help to identify and count crack parameters of the outcrop surface. However, the digital outcrop model cannot reflect the characteristics of cracks in the rock mass, and the existing methods such as geological radar and the like have low detection precision and limited use conditions, so that the cracks in the whole area of the outcrop rock mass are difficult to detect and identify. Therefore, research is needed from the aspects of geological analysis, geomechanics, structural stress field and the like, the cracks inside the outcrop rock mass are predicted and characterized, and the construction of a carbonate prototype model is constrained and guided by combining digital outcrop modeling. Disclosure of Invention Aiming at the problems, the invention provides a method for constructing a carbonate fracture prototype model driven by digital outcrop and geomechanical simulation, and develops a three-dimensional fracture modeling method driven by the digital outcrop model and the geomechanical theory together. And measuring crack data of the outcrop surface through a digital outcrop model, and predicting the crack data in the outcrop by adopting a geomechanical theory. Based on the three-dimensional digital model of the typical outcrop, modeling data, crack parameters and the like are extracted. And analyzing the geometric distribution and the secondary characteristics of the development period of the crack by comprehensive geological analysis and test assay. And (3) adopting a numerical simulation method to simulate the multi-stage stress field of the research area and further calculate the crack parameters. Under the data support of a digital outcrop model and the guidance of a geomechanical theory, adopting a multi-period and multi-scale crack discrete model construction technology, carrying out multi-period seepage simulation on the basis, reconstructing the erosion and seepage characteristics of the ancient fluid, recovering the development distribution mode of cracks and ancient karst cave, establishing a prototype geological model of the outcrop crack, The invention adopts the following technical scheme: A method for modeling carbonate fractures based on digital outcrop and geomechanical simulation, as shown in fig. 1, comprising the steps of: S1, constructing a digital outcrop model of a typical outcrop, namely, based on unmanned aerial vehicle oblique photography technology, scan