煤层气水平井井壁失稳和储层损害机理耦合研究

To improve the CBM well productivity,Increasingly widespread use of horizontal wells are widely used increasingly,Based on CBM "low cost" strategy,more water is used in horizontal wells drilling,which has a low cost,wide source and good reservoir protection effect,But coal borehole stability is poor,easily lead to wall collapse and other complex issues underground;If using conventional polymer drilling fluid,It has stable coal borehole ability,But coal pollution is very serious.the contradictions between wellbore stability and reservoir protection of CBM become more prominent,which is currently a major bottleneck and efficient development.Researchs on wellbore instability and reservoir damage mechanism domestic are relatively simple and lack of communication between each other,both as a whole did not interrelated research.This topic will be wellbore stability and reservoir damage mechanism are coupled study this topic will be the mechanism of coal and rock and reservoir damage coupled wellbore instability studies,By studying the different fluid types, performance to strength and influence of the coal seam coal seam permeability,explore the intrinsic link between coal borehole instability and reservoir permeability,find out the countermeasures which can stabilize coal borehole and protect reservoir,provide a scientific basis for the development of coal-bed methane in horizontal wells drilling.

为提高煤层气单井产能，采用水平井开发越来越普遍，基于煤层气“低成本”战略，水平井钻井液多采用清水，清水具有成本低，来源广和储层保护效果好的特点，但稳定煤层井壁能力差，易造成井壁垮塌等井下复杂问题；若采用常规聚合物钻井液，其稳定煤层井壁能力强，但煤层污染很严重。煤层气井壁稳定和储层保护之间矛盾比较突出，成为目前煤层气高效开发的主要技术瓶颈。国内对煤层气井壁失稳和储层损害机理研究比较单一，且相互之间缺乏联系，没有将两者做为一个相互关联的整体进行研究。本课题将煤岩的井壁失稳和储层损害机理进行耦合研究，通过研究不同流体种类、性能对煤层强度和煤层渗透率的影响规律，探索煤层井壁失稳和储层渗透性之间的内在联系，找出既能稳定煤层井壁又能保护煤层的对策，为研制煤层气水平井钻井液提供科学依据。

水平井在煤层气开发中应用广泛，但煤层气井壁稳定和储层保护之间矛盾比较突出，成为目前煤层气高效开发的主要技术瓶颈。目前对煤层气井壁失稳和储层损害机理研究比较单一，且相互之间缺乏联系，没有将两者做为一个相互关联的整体进行研究。本课题从目标区块煤岩特性研究入手，分析了煤岩井壁失稳和储层损害机理，并将两者进行耦合研究，通过研究不同种类流体和性能对煤岩强度和煤层渗透率的影响规律，探索煤层井壁失稳和储层渗透性之间的内在联系。结果表明，聚合物胶液能有效稳定煤岩强度，而且主要取决于聚合物胶液粘度而非种类，当漏斗粘度FV在35-38s时可以有效稳定煤岩强度；同时聚合物胶液也会严重损害煤层，损害程度与压差直接相关；“先稳定井壁后解除污染”是目前煤层气水平井钻井过程中解决井壁稳定和煤层保护之间矛盾突出的有效措施，这就要求所采用钻井液体系必须具有可降解性。这些研究结果和结论对于指导我国煤层气水平井安全钻井和保护煤层、释放低渗煤层产能具有重要现实意义。