长宁地区页岩气水平井防塌钻井液体系设计

Design of Anti-collapse Drilling Fluid System for Shale Gas Horizontal Wells in Changning Area

长宁地区页岩气膨胀性好、层理发育、胶结性差,易引起井壁失稳问题,针对上述问题本文提出页岩气水平井钻井液防塌技术。对长宁地区岩石的矿物组分和微观结构迚行分析,结果表明矿物组分以石英、长石等脆性矿物为主,含量主要分布在36.85%~49.42%,压实程度高,结构紧密,微裂缝发育。脆性矿物含量高及微裂缝发育是引起井壁失稳问题的原因所在,故从抑制页岩黏土矿物水化和封堵微裂缝两个角度出发来解决该地区井壁失稳问题。本文将上述两种关键处理剂与其他处理剂迚行合理复配,形成了一套防塌钻井液体系。实验结果表明,该体系可有效抑制黏土表面水化,滚动回收率高达97%,并对该地区微裂缝迚行有效封堵,防止钻井液固相颗粒和滤液侵入地层,降低钻井液动滤矢量,体系抗温能力可达120℃,满足长宁地区安全、高效、经济钻井的需求。

In Changning area,shale gas reservoir has good expansibility,bedding development and poor cementing property,which can easily cause wellbore instability.In view of the above problems,a drilling fluid anti-collapse technology for horizontal shale gas wells was proposed.The mineral compositions and microstructures of rocks in Changning area were analyzed.The results show that the mineral compositions are mainly brittle minerals,such as quartz and feldspar.The content of mineral compositions is mainly distributed in 36.85%~49.42%.The rocks have high compaction degree,compact structure and developed micro-cracks.The high content of brittle minerals and the development of micro-cracks are the causes of wellbore instability.Therefore,the problem of wellbore instability in this area can be solved from the two aspects of inhibiting the hydration of shale clay minerals and blocking micro-cracks.In this paper,a set of anti-collapse drilling fluid system was formed by mixing the two key additives and other additives reasonably.The experimental results show that the system can effectively inhibit the surface hydration of clay,and the rolling recovery rate is as high as 97%.It can effectively plug the micro-cracks in the area,prevent the solid particles and filtrate of drilling fluid from intruding into the formation,reduce the dynamic filtration vector of drilling fluid,and the temperature resistance of the system can reach 120℃,which can meet the requirements of safe,efficient and economical drilling in Changning area.