Analysis and Application of Continental Shale Time-varying Character in Yanchang Group Chang 7 Segment Reservoir

Horizontal well is one of the key technologies to achieve shale gas economical,large-scale development. In shale formations,the safety and efficiency in drilling horizontal wells is subject by the time-varying character of formation collapse pressure and the wellbore collapsed instability under influence of drilling fluid. For Yanchang Group Chang 7 segment shale reservoir of Ordos Basin shale,based on poroelasticity and porous media percolation theory,the horizontal wells circumferential mathematical model is determined to descript the additional stress field with drilling fluid penetration. The shale mechanical strength and collapse pressure time-varying character is revealed under the drilling fluid effect via experimental. The drilling fluid density range of horizontal wellsu0027 safe drilling is quantitative studied,which has a positive influence on the economical and efficient drilling of shale formations.