页岩气水平井井壁稳定影响因素与技术对策

Influence Factors and Technical Countermeasures of Shale Gas Horizontal Well Stability

国内绝大多数页岩气水平井在页岩层段钻井过程都发生过坍塌,严重影响了钻井周期及后续压裂施工。由于页岩气井水平段一般较长,普遍在1 000 m以上;而且页岩地层层理发育,产状多变,岩石性质硬脆,水敏性矿物含量高,很容易发生井漏坍塌等问题。通过分析认为:影响页岩气水平井井壁失稳的因素主要包括页岩的综合特性、地质力学因素、钻井液的综合性质及其他工程因素。解决页岩气水平井井壁失稳的首要途径是认识层理页岩的特殊力学特性,重点研究不同钻井液体系对其力学特性的影响程度及影响规律(也是钻井液优选的重要依据之一)。再次,需要对地应力场进行综合研究。最后,通过采用合理的井壁稳定力学模型获得控制井壁失稳的钻井液密度范围,配合使用快速高效钻具,才能最大程度确保井壁稳定。

Wellbore collapse which has been found in most of the horizontal wells in shale gas reservoirs inland affects drilling cycle and subsequent fracturing. Since shale gas wells have horizontal section as long as 1 000 m or more in general, and shale has properties such as rich bedding planes, occurrence varied, hard and brittle, high water sensitive mineral content, wellbore collapse or leakage often happens. Influence factors of shale gas horizontal well stability include shale integrated features, geomechanical factors, the integrated nature of the drilling fluid and other engineering factors. The primary pathway to alleviate wellbore collapse is to recognize the special mechanical properties of shale, focusing on the impact of different drilling fluids on shale mechanical properties. This under- standing could be one of the most important bases for drilling fluid optimization. The next work is compressive study of earth stress. Finally, getting drilling fluid density range calculated by reasonable mechanical model and using of fast and efficient drilling tools could ensure shale gas horizontal well stability most effectively.