考虑割理面时煤层造斜段坍塌压力变化规律研究

Variation Law of Collapse Pressure in Inclined Section of Coal Seam Considering Cleat Plane

在武威盆地太原组水平井钻进作业时,依据井史数据调研发现,煤层段卡钻、井径扩大、钻具掉落等井壁坍塌导致的井下复杂事故发生,严重制约了煤层气勘探开发的进程。由于煤岩交错割理性(面割理、端割理)弱结构面发育,使煤岩在造斜钻进时井壁破坏在力学上呈现为非连续性和非均质性。建立了考虑弱面的井壁坍塌数学模型。通过分析煤岩矿物成分、微宏观结构,确定煤岩井壁坍塌为力学机制占主导因素,得出割理导致的煤岩碎裂成块是井壁失稳的根本原因,建议在后续煤层钻井中优化井眼轨迹、优化钻井液性能进行井壁防塌,并引入煤岩井壁坍塌实时监测系统。

During the drilling operation of horizontal wells in Taiyuan Formation of Wuwei Basin,the investigation of well history data shows that downhole complex accidents caused by shaft wall collapse such as sticking of the drill in coal rock seam,expansion of well diameter and the falling of drilling tools have seriously restricted the process of coalbed methane exploration and development.Due to the development of weak structural planes of coal rock cross cutting(face cutting and end cutting),the shaft wall failure of coal rock during deviation drilling presents discontinuity and heterogeneity in mechanics.A mathematical model of shaft wall collapse considering weak planes is established in this paper.By analyzing the mineral composition and micro macro structure of coal and rock,it is determined that the collapse of coal and rock shaft wall is the dominant factor of mechanical mechanism,and it is concluded that the fragmentation of coal and rock caused by cleat is the root cause of shaft wall instability.It is suggested to optimize the well trajectory and the performance of drilling fluid in the subsequent coal seam drilling to prevent shaft wall collapse,and the real-time monitoring system of coal and rock shaft wall collapse is introduced.