高庙子气田井壁稳定性研究及钻井技术对策

STUDY ON WELLBORE STABLILITY AT GMZ GASFIELD AND TECHNICAL COUNTERMEASURES

通过运用伊顿法建立了地层孔隙压力剖面,采用库仑—摩尔强度准则建立了地层坍塌压力剖面,根据岩石最大拉应力理论建立地层破裂压力剖面。综合应力、掉块形态、裂缝发育、井斜等多因素分析,高庙地区地层裂缝发育,钻井液密度过小引发力学原因垮塌,密度过高滤液易进入地层造成缝隙中地层压力的增大并降低地层强度,从而增大坍塌压力加剧井壁失稳;同时井斜角在30°~40°之间的定向井坍塌压力最高,斜井段掉块最严重,是造成地区地层失稳的主要原因。通过设计合理钻井液密度、优化钻井液性能、增加其封堵性和润滑性,基本解决了钻井过程地层掉块,有效减少工程复杂情况,实现气田高效开发。

The formation pore pressure profile was established by applying the method of Eaton,the formation collapse pressure profile was set up based on Mohr-Coulomb strength criterion,and the formation fracture pressure profile was established on the theory of maximum pulling stress of rock. By comprehensive analysis of combined stresses,falling debris shape,fracture development and well deviation,it was found that at Gaomiaozi area formation fracture was developed,drilling fluid density was so small that mechanical collapse was produced. And high density filtrate invaded into formation to generate greater formation pressure in interstices and lower formation strength,which resulted in greater collapse pressure and intensified sidewall instability. And the highest collapse pressure existed in directional wells with angles between 30° ~ 40°,leading to the most serious sidewall chunking. it was the main cause of wellbore instability in this region. Through setting reasonable drilling fluid density,optimizing drilling fluid performance,increasing its blocking behavior and lubricity, wellbore chunking problem was nearly avoided,the engineering events effectively reduced and efficient development of gas fields realized.