3D Stress Field Calculation And Fracture Simulation Of Shale Gas Reservoir

Ding mountain tectonic zone is located in the southeast of Sichuan area of Sichuan basin.Sichuan basin and its peripheral area is the earliest area of shale gas that be found in China.And this area is considered to be the most potential for shale gas exploration.Ding mountain tectonic zone of shale gas reservoirs have great developed faults and fractures and the area is a region of favorable reservoir.However the study of in-situ stress precision is relatively low,restricting the progress of exploitation of oil and gas exploration in the area of follow-up.In this paper,Ding mountain tectonic zone as an example,the first step is combined with the geological?geophysical logging and logging data,based on the regional geological tectonic features,determine the geological model of Silurian Longmaxi group objective layer.Establish the corresponding geometric model by three axis mechanical test,well logging data to determine study on Regional mechanical parameters.Then combined with logging and fracturing data,establish the boundary conditions.Using Ansys software to take geological model into finite element model,and get numerical simulation of the in-situ stress field in target layer.Through numerical simulation and analysis,the in-situ stress distribution of Ding mountain area Silurian Longmaxi group as follows.The range of Maximum horizontal principal compressive stress is from 35MPa to130MPa,the overall performance is from the southeast to the north gradually increasing,the maximum area is in the northern margin.The range of the minimum horizontal principal compressive stress is from 25MPa to 100MPa,the overall performance is from the southeast to the northwest gradually increasing trend,the maximum value appeared is in the northwest corner of the mountain area.The range of vertical principal stress is from 25MPa to 170MPa.Because the vertical compressive principal stress is mainly affected by the depth of strata,the vertical principal stress is larger in the deep buried area.The relative error of the simulation results of the maximum and minimum principal stress and vertical principal stress and measured results is 3.9%,and the coincidence rate reached 96.1%;the maximum horizontal principal compressive stress direction simulation error is 9.76%,the coincidence rate reached 90.24%.The error is in the allowable range,the results can be used for subsequent applications.Secondly,based on the results of analysis of in-situ stress field,distribution and structure in the area of horizontal principal stress has certain rules.So in the present ground stress field on the basis of the research of the Ding mountain area,designing a fold stress model.The results of the stress changes is with the increase of curvature change,and the main influence range is the radius of curvature of|K|>0.001(K is the curvature).The structure transition end curvature changes effected by curvature,the wings of the structure few effected by curvature.According to research presented stress relation model,reveal the non-uniformity of fold area stress distribution.Finally,the study based on the tectonic framework and combined with the results of rock mechanics parameters,to build the calculation model of the crustal stress fields.Combined with the Acoustic emission test?hydraulic fracturing and logging data to establish the boundary condition and the Ding mountain area present stress field distribution characteristics.On the basis of the above research,studying further analysis that the influence that different range of natural fractures on fracture orientation of in-situ stress field characteristics.When there is no natural fracture,wells surrounding tension and tensile strain characteristics is mainly affected by the characteristics of ground stress field,hydraulically created fracture parallel to the strike?_H direction and crack along?_h direction.When the natural fractures exist and natural fracture medium tensile strength is less than or equal to 2/3 tensile strength of rock,the angle of natural fracture trend and?_H is less than 30 degrees,the hydraulic fracturing will open along the direction of natural fractures.When the tensile strength is 3:1,the natural fracture angle less than 45 degrees,hydraulic fracturing may open.When the natural fracture angle exceeds 45degrees,hydraulic fracturing along?_H direction to produce new crack.