Mechanics Mechanism And Countermeasure Analysis Of Shaft Wall Collapse Mechanics

The main problems of horizontal drilling in shale are certainly borehole instability which lower significantly efficiency of drilling and raises cost. The research on borehole instability has become the highlight because primarily reasons for borehole instability are still unknown.This research is based on shale section W which has high degrees of dip angle and many leakage layers. It threatens the safety of drilling and lowers the economical benefit due to borehole collapse and stick pipe that occurred on horizontal section. In order to solve the problem on drilling, this paper studied on below aspects.(1) With analyzing the data on exploration and exploitation, it shows that reservoir bedding, cracks have a variety of change, which means mechanics is the primarily reason of borehole instability in this section.(2) This research established mechanical parameters profile with logging data and elastic modulus and Poisson’s ratio tested by rocks of section W.(3) This paper calculated maximum and minimum principal stress, law on distribution of vertical stress with stress model and logging data.(4) This paper analyzed law about crack stress distribution and mechanical stability with three-dimensional finite element model. Meanwhile, the cloud map about stress and displacement built with rocks physical parameters.(5) On the basis of analysis of the stress state of rock wall and the strength of the rock failure criteria, this paper established formation collapse pressure and fracture pressure calculation model. In considering the weak side angle, the analysis of horizontal drilling in shale researched the relationship between different directions, inclinations and borehole stability.(6) Based on borehole stability, this paper calculated safety fluid density and optimum drilling direction in horizontal wells in section W.