塔里木盆地顺北5号断裂带志留系碎屑岩地层漏失机理

LEAKAGE MECHANISM OF SILURIAN CLASTIC ROCK FORMATION IN SHUNBEI NO.5 FAULT BELT,TARIM BASIN

塔里木盆地顺北油气田5号断裂带志留系碎屑岩层段钻井液漏失严重。顺北5号断裂带SHB5-7井岩芯资料、岩芯样品10余块、20口漏失井的钻井、测井、FMI成像测井、地震资料(1562 km^(2))及岩石力学参数研究表明志留系碎屑岩地层的构造活动强度、裂缝和岩性控制了碎屑岩地层漏失。志留系塔塔埃尔塔格组和柯坪塔格组漏失特征差异较大,漏失层分布呈现“纵向分层、平面分段”的特点,塔塔埃尔塔格组上段漏失频次(57次)高于下段(31次),柯坪塔格组上段(11次)、下段(15次)漏失频次高于中段(9次),5号断裂带中段和南段漏失频率高。漏失点岩性多为(粉)砂质泥岩(测井解释泥质含量介于55%~80%),漏失点孔隙度普遍较低(孔隙度介于1%~5%),漏失点处多发育低角度裂缝,漏失点距断层面水平距离普遍小于150 m。根据漏失点处岩性、孔隙度、渗透率、漏失速率和距断层距离将漏失类型分为孔隙型、孔隙+裂缝型和裂缝型,其中裂缝型(诱导缝、天然裂缝)漏失最为普遍。顺北5号断裂带志留系碎屑岩段地层漏失机理为断层及其伴生裂缝系统在井筒—地层压力差的作用下开启,钻井液经裂缝渗入地层造成井漏。研究成果为科学认识志留系钻井液漏失机理、减低钻井成本提供了技术参考。

The Silurian clastic formation in the No.5 fault zone of Shunbei oil and gas field in Tarim Basin suffered serious fluid loss.The study of the core data,core samples,drilling,borehole logging,FMI imaging logging,seismic data and rock mechanical parameters in the ShB5-7 well shows that the loss of Silurian clastic formation is controlled by the intensity of tectonic activity,fractures and lithology.The leakage characteristics of the Silurian Tata Ertag Formation and the Kepintag Formation are quite different,featuring"longitudinal stratification and plane segmentation".The leakage frequency of the middle and southern parts of the No.5 fault is high.The leakage frequency of the upper part of the Tata Ertag Formation is higher than that of the lower part,the leakage frequency of the upper and lower parts of the Kalpintag Formation is higher than that of the middle part.Sandy mudstone with a shale content of 55%~80% has a high leakage frequency,and the porosity of the leakage point is mostly 1%~5%.Logging,mud logging and seismic information show that low-angle fractures are developed at the leakage point and the horizontal distance from the leakage point to the fault plane is generally less than 150 m.According to the lithology,porosity,permeability,loss rate and distance from the fault,the leakage loss types can be divided into pore type,pore+fracture type and fracture type,among which fracture type(induced fracture and natural fracture)is the most common one.The formation loss mechanism of Silurian clastic section in Shunbei No.5 fault zone is that the fault and its associated fracture system are opened under the action of borehole-formation pressure difference,and drilling fluid seeps into the formation through the fracture,resulting in well loss.The research results provide technical reference for scientific understanding of Silurian fluid loss mechanism and the drilling cost reduction.