The oil-based drilling fluid is often used in shale gas horizontal well drilling for wellbore stability,but there are environmental protection concerns caused by the disposal of deserted oily wastes and drill debris.Therefore,it is desperately urgent to develop some anti-collapse water-based drilling fluid to replace the traditional oil-based drilling fluid.In this paper,the critical agents composing the anti-collapse water-based drilling fluid,such as blocking agent,inhibitors and lubricants were evaluated and optimized based on the mineral compositions and micro-structures of the Changning-Weiyuan shales.Then,the doses of each agent were determined to formulate the anti-collapse water-based drilling fluid,and its performances were evaluated.The results show that the so made water-based drilling fluid has better blocking,inhibiting and lubricating performances than the polysulfide drilling fluid and the polymer drilling fluid,and are almost comparable to those of the oil-based drilling fluid.Field tests in the Changning-Weiyuan National Shale Gas Demonstration Area indicate that the density of this drilling fluid can reach 2.31 g/cm3,its temperature resistance can reach 130 ℃,and it demonstrates a good blocking capacity and inhibiting ability both in the deflecting section and the horizontal section,thus having a good anti-collapse effect.This drilling fluid will definitely play a key role in efficient development and clean production of the shale gas in this demonstration area.%页岩气水平井钻进中常采用油基钻井液体系来解决页岩井壁失稳问题,但却面临废弃油基钻井液和油基后期岩屑处置的环保问题,因而迫切需要研制一种能防止页岩垮塌的水基钻井液来替代油基钻井液.为此,在分析四川盆地长宁—威远地区页岩矿物组分和微观结构的基础上,对构成防塌水基钻井液体系的关键处理剂,如封堵剂、抑制剂、润滑剂等进行了评价和优选,并确定了加量范围;然后通过室内配伍实验和复核,研制出防塌水基钻井液体系并对其性能进行了评价.结果表明,该钻井液的封堵性、抑制性、润滑性等性能均优于该区使用的聚磺钻井液、聚合物钻井液,接近或达到油基钻井液的水平.在长宁—威远国家级页岩气示范区进行的水平井钻进现场试验结果表明,该钻井液体系密度可达到2.31 g/cm3,抗温能力达到130℃,在造斜段和水平段表现出良好的封堵能力和抑制能力,具有很好地防塌效果.该钻井液体系对实现该区页岩气的清洁生产与效益开发将发挥重要作用.
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