A degradable clear drilling fluid has been developed with a gel enhancer BZ-2 and a film fixating agent GMJ to resolve the contradiction between the safety of drilling operation and the protection of coal beds in coal-bed methane drilling.Laboratory experiments were done to evaluate BZ-2 and GMJ for their inhibitive capacity,rheology,residue contents,and their influences on the strengths of formation cores.The experimental results showed that the clear drilling fluid had percent shale recovery of 93.5％,YP/PV ratio of 0.93 Pa/mPa · s,gel strengths of 2.5 Pa/3.0 Pa,yield point of 20.5 Pa,API filter loss of less than 12 mL,and residue content of 4.5 mg/L.The strength of the cores tested increased by 16.7％.This drilling fluid has been tested on 4 wells in the Zhengzhuang block,south of Qinshui basin in Shanxi Province.The test has successfully resolved the problems of drilling safety and coalbed protection in multilateral well drilling.Daily gas production rate has been increased by 2 times more than that of the wells nearby,and the calculated constant rate of gas production was between 3,000-5,000 m3/d,suggesting a good prospect of promotion.%针对煤层气井钻井过程中钻井安全和煤层保护之间的矛盾问题,研制了钻井液用提切剂BZ-2和固膜剂GMJ,并以此为核心开发了可降解清洁钻井液体系.对BZ-2和GMJ的抑制性、流变性、残渣量及对岩心强度的影响等性能进行了评价.实验结果表明,该体系的页岩回收率为93.5％;流变性好,动望比达到0.93 Pa/mPa·s,初切、终切、动切力分别为2.5、3.0、20.5 Pa;API滤失量控制在12 mL以内,残渣量为4.5 mg/L,岩心强度增加了16.7％.该体系已在山西沁水盆地南部晋城斜坡带郑庄区块4口井进行试验.试验效果表明,其解决了该区块多分支水平井的钻井安全和煤层保护问题,日产气量较邻井提高了2倍以上,测算稳定产气量在3 000～5 000 m3/d,具有较好的推广应用前景.
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