裂缝性致密储层工作液损害机理及防治方法

裂缝性致密储层裂缝发育，易发生工作液漏失，严重损害储层。为探究不同工作液漏失损害机理，形成高效
防治方法，以川西北九龙山构造须家河组、珍珠冲组裂缝性致密储层为研究对象，开展了钻井完井液储层损害实验及
工作液顺序接触损害实验。结果表明：钻井完井液滤液、体系和固相对基块岩样的损害程度介于中偏强强，且逐个
减弱；裂缝岩样渗透率动态损害程度为强；工作液顺序接触后损害程度加剧。分析认为，水相圈闭、固相堵塞是裂缝性
致密储层工作液漏失损害储层的主要机理。不同工作液漏失引起储层损害程度叠加、损害范围扩大。根据分析结果，
构建了工作液漏失损害模式，并提出相应损害防治方法。使用改性屏蔽暂堵钻井完井液提高封堵能力，改变岩石表面
润湿性，可有效预防工作液漏失损害；利用工作液漏失数据，确定漏失损害带范围，可为酸化作业提供指导。

Mechanism and Control Methods of the Working Fluid Damages inFractured Tight Reservoirs

Fractured tight gas reservoirs is characteristic of developed natural fractures which lead to lost circulation of working
fluid and induce formation damage. In order to study the damage mechanism of working fluids indifferent operations and to find
out prevention strategies，based on the Xujiahe formation and Zhenzhuchong formation in the Jiulongshan Structure in western
Sichuan Basin which is a fractured tight gas reservoir，we carried out the damage evaluation experiments of drill-in fluid and
the working fluids order contact. The experimental results show that the damage grades of blocks induced by the filtrate of
drill-in fluid，the drill-in fluid and the drill-in fluid solids range from medium to intensely and reduce gradually；the average
permeability dynamic damage grade of the fractured samples is intense；the working fluid order contact would strengthen the
damage degree. The analysis of the damage mechanism of different operations shows that water phase trapping，solid plugging
are the major mechanism of working fluids damage；the damage induced by different working fluid would be superimposed，
and increased the damage range. Based on the results，we constructed the damage patterns of lost circulation，and suggest using
the modified shielding plugging drill-in fluid to improve sealing ability and change the rock wettability can prevent the working
fluid damage effectively. Identification of damage range with lost circulation data can provide guidance for acidizing.