Coalbed damage mechanism,borehole instability mechanism and safety drilling technologies of multi-lateral horizontal wells in coalbed were proposed,which studied by coalbed geology,drilling engineering characteristics and field practices.The research show that stress sensitivity,fluid and solid phase intrusive,water phase trap are main types of coalbed damage.Controlling drilling fluid filtration,enhancing compatibility of filtrate and coalbed,improving coalbed energy and damage relieve means are the effective measures of controling formation damage.Geological conditions complex,coal rock of low intensity,water inflatable uneven,drilling fluids properties instability,and drilling fluids density unreasonable are main reasons of coalbed damage and wellbore stability,during drilling in coalbed by multi-lateral well.Conducting studies,which on three-dimensional seismic optimization disposing wells,drilling technology,water modification and temporary shielding-flowback drilling fluids system,are useful to realize coalbed multi-lateral horizontal safety drilling.%通过对煤层地质特征、钻井工程特点以及现场实践分析,归纳了煤层损害与井壁失稳机理,提出了煤层多分支水平井安全钻井策略。研究表明：应力敏感、流体及固相侵入、水相圈闭是煤层损害的主要类型;控制钻井液滤失量,增强滤液与煤层配伍性,提高煤层能量,完善煤层损害解除方法是保护煤层的有效手段;地质情况复杂,煤岩强度低,钻进液性能不稳、密度不合理,清水充气不均是清水充气欠平衡钻进多分支井水平井煤层损害和井壁失稳的主要机理;开展三维地震优选布井,钻井工艺,清水改性及暂堵-返排钻井液体系等配套技术研究有利于煤层多分支水平井钻井安全。
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