Study On The Fracture Prediction In Shale Gas Reservoir Based On Tectonic Stress Field

The production capacity of shale gas in the tight reservoir of shale is closely related to the degree of fracture development,and the tectonic stress field is the key factor to restrict the development of complex structural fractures.Therefore,in this paper,DingShan region Longmaxi layer was taken as an example to study the simulation of tectonic stress field,and on this basis,the fracture prediction based on the tectonic stress field is carried out.Firstly,according to the geological tectonic evolution process and the geodynamic setting of the corresponding block of the target layer,the main geological structural setting period of the target stratum was determined.And,the three-dimensional geological model of the target layer was established by using the 3DMove software.Secondly,the rock three axial compression test and Kaiser stress test about the core sample were carried out,and combining with the corresponded logging data,the dynamic and static rock mechanical parameters of transformation were established.The rock mechanics parameters of the target layer were calculated by using the velocity data of the 3D seismic data in the target layer,and spread them to the three dimensional space.Then,the point cloud data of the geological structure model was fitted to the CAD construction surface by using the reverse engineering software imageware,and import it into the finite element software ANSYS to establish three-dimensional finite element model of the target layer,combined with the 3D distribution data of rock mechanics parameters,the 3D finite element model of the target layer was established.Taking the experimental analysis results about the core sample and the logging data as the constraint,the real boundary conditions of the model were determined through the calculation method.On this basis,the three-dimensional paleotectonic stress field distribution characteristics of the target layer were calculated and analyzed.Finally,according to the differences in the causes of fracture and the differences in the fracture development characteristics,and according to the fracture of different rock mechanics properties,different rock failure criteria were adopted to calculate the rock failure rate in different failure forms and the corresponding fracture development orientation of rock.Based on the rock failure rate in different failure forms calculation results,combined with the factors of brittle mineral group in the shale and the organic carbon content in the shale influencing on the degree of fracture development,the parameter that determines the degree of fracture development——“comprehensive fracture development coefficient of rock” were introduced.And based on the value of “comprehensive fracture development coefficient of rock”,the fracture development degree of the target layer were divided into different grades.And finally,the prediction distribution map of the fracture development degree and the fracture development direction were calculated and plotted in this paper.