Analysis And Numerical Simulation Of Stress And Strain Field In Shale Horizontal Well

When the horizontal well is used in shale reservoir development,the phenomenon of wellbore instability occurs frequently,which seriously affects the drilling cycle and increases the drilling cost.The root cause of instability is the redistribution of borehole stress during drilling.Therefore,the study on the stress field of shale gas well is the key to solve the problem of wellbore instability.In this paper,a shale gas block as the research object for the following research:(1)Comprehensive analysis of geological data,well logging data and field drilling data.The results show that the hardness of the reservoir area of rock drillability and low,relatively complex geological structure;Wufeng-Longmaxi formation fractures,and tensional fracture;shale reservoir permeability,low porosity,is a typical low porosity and low permeability reservoir.(2)Carry out indoor rock mechanics experiment and logging interpretation,get the reservoir rock parameters and geostress profile and analyze the geostress distribution law.The results show that the rock mechanics parameters of the target layer have obvious anisotropy.The stress difference in the work area is large,and the tectonic movement is strong,and the leading cause of shroud wall instability is stress collapse.(3)Based on the extended finite element theory,the ABAQUS software is used to simulate the crack propagation process of the wall rock.The results show that the crack initiation,propagation,and fracture length and width are affected by the horizontal stress difference,drilling fluid properties and pore pressure.(4)Based on the analysis of the stress state of the wall of the borehole wall,the corresponding geometric analysis model of the straight and horizontal well sections is established.The drilling condition of the work area is simulated by ABAQUS finite element software,Stress and strain distribution law.The relationship between well angle,azimuth angle,fracture occurrence and ground stress and collapse pressure is analyzed,and effective measures are put forward to stabilize the work area.The results show that the horizontal section of the working area is drilled along the minimum geo-stress direction,and the collapse pressure is the lowest.It is preferable to select the high viscosity oil-based drilling fluid and adopt the drilling tool with simple structure and small size.