顺北油气田破碎性地层井壁稳定技术难题与对策

Technical Problems and Measures of Wellbore Stability of Broken Formation in Shunbei Oil and Gas Field

近年来,顺北油气田多口井因钻遇破碎性地层出现了严重的井壁坍塌掉块情况,导致阻卡频繁,多口井回填侧钻,已成为顺北油田勘探开发的重大技术难题之一。统计分析了顺北油气田奥陶系破碎性地层复杂现状,针对破碎性地层技术难点,研究分析了其坍塌失稳机理,提出了安全钻井技术对策。结果表明:失稳机理主要为受挤压构造影响,地层破碎,应力集中,加之地层高角度裂缝、层理等弱面发育,胶结性差,结构松散,极易发生剪切破坏,产生大面积坍塌失稳现象。钻井液应强化致密封堵、固结性能,提高地层完整性和岩石强度,适当提高钻井液密度,加强力学支撑作用,同时提高钻井液携带能力,保持井眼清洁。破碎性地层钻进时应尽量简化钻具,优化钻井参数,“少进多退”,保证井下安全。

In recent years,many wells in Shunbei oil and gas field have encountered serious wellbore collapse due to drilling in broken formation,resulting in frequent jamming and many wells backfill sidetracking,which has become one of the major technical problems in the exploration and development of Shunbei oil and gas field.Statistics and analysis on the complicated situation of Ordovician broken formation in Shunbei oil and gas field were made.In view of the technical difficulties in the broken formation,the collapse and instability mechanism were studied and analyzed,and the technical measures for safe drilling were put forward.The results show that the instability mechanism is mainly affected by the extrusion structure,the stratum is broken and the stress is concentrated.In addition,the weak planes such as high angle micro fractures and bedding are developed,and the cementation is poor and the structure is loose.It is easy to shear failure and cause large area collapse and instability.The drilling fluid should strengthen the sealing and consolidation properties,improve the formation integrity and rock strength,appropriately increase the drilling fluid density,strengthen the mechanical support,and improve the carrying capacity of drilling fluid to keep the borehole clean.In order to ensure downhole safety,when drilling in broken formation,drilling tools should be simplified as much as possible,drilling parameters should be optimized,drilling strategy should be“less advance,more retreat”.