Analysis Of Sidewall Stability In Horizontal Well Drilling Based On ABAQUS

The exploration and development of shale gas and shale oil is another energy change after unconventional energy sources such as coalbed methane and tight sandstone gas.For this reason,countries around the world have carried out corresponding theoretical research and field applications.The instability of shale reservoirs in the drilling process mainly takes the form of borehole wall collapse,well leakage,shrinkage and stuck drilling,etc.The instability of reservoirs prolongs the drilling cycle and increases the cost of shale gas development.The main reason for the instability of the borehole wall is that the drilling process breaks the original in-situ stress balance of the borehole wall.Secondly,the strength of the reservoir rock in the borehole wall will soften after the drilling fluid and other intrusion,causing the redistribution of the stress field around the borehole.The formation of stress concentration makes the natural fractures and derivative fractures of the rock expand,extend,and penetrate,and finally leads to the instability of the well wall.In addition,due to the low permeability of shale reservoirs,the vertical well drilling method can no longer meet the productivity requirements.Therefore,the horizontal well can only be opened to increase the productivity.However,for horizontal wells encountered in wells with high inclination and horizontal wells During the period,the formation is extremely prone to collapse,stuck pipe and other instability of the borehole wall.Especially for the development of rational formations such as shale,the requirements for the stability of the borehole wall become greater and the horizontal well drilling process is challenged.Therefore,analyzing the stability mechanism of shale gas horizontal wellbore is particularly important for shale gas exploration and development.This article analyzes and understands the wall stability of shale horizontal wells from the following four aspects:(1)The seepage problem in geotechnical engineering belongs to unsteady state seepage.During the drilling process,the change of formation pore pressure first brings changes to the effective stress in the framework,which causes changes in porosity and permeability Secondly,the above changes will bring about changes in pore pressure,so the fluid-solid coupling effect cannot be completely ignored in the analysis of geotechnical engineering seepage field.The dynamic evolution models of parameters such as porosity and permeability are established.At the same time,the related commands of ABAQUS seepage-stress coupling are introduced,which provides a theoretical basis for the following ABAQUS numerical simulation.(2)From the point of view of mechanics,the plane stress state of surrounding rock of horizontal well is analyzed,and the stress distribution of surrounding rock of horizontal well is calculated by percolation mechanics theory.According to the characteristics of porous media,the failure pressure and failure pressure of surrounding rock can be obtained by selecting Mohr-Coulomb failure criterion and combining with the calculation model of surrounding rock stress.According to plastic theory,the range of plastic zone can be obtained.(3)Rock mass is a typical porous medium,and its loading method and boundary conditions are relatively complex.As a result,the borehole wall stability problem usually needs to be solved with the help of finite element method.With the powerful analytical capability of ABAQUS finite element software,the influence of ground stress difference,pore pressure,formation strength,drilling azimuth and drilling fluid density on sidewall stability of horizontal shale Wells is analyzed.(4)According to the mechanical model of wellbore stability and the ABAQUS finite element analysis software,the three-dimensional numerical simulation of the WW formation of well XX in yanchang group was carried out,and the distribution rules of stress,displacement,pore pressure and plastic zone of the rock mass near the wellbore under different drilling times were obtained.The mechanism of wall rock stability in horizontal Wells is correctly understood,and the corresponding countermeasures are put forward to control the wall rock instability in horizontal Wells effectively.