中牟页岩气区块泥页岩井壁稳定影响因素分析及技术对策

Analysis on the Influence Factors to Mud Shale Borehole Stability in Zhongmu Shale Gas Block and the Technical Countermeasures

井壁失稳是钻井过程中常常遇见的难题之一,尤其在钻遇泥页岩井段。针对河南中牟页岩气区块在山西组-太原组泥页岩钻进过程中发生井壁坍塌掉块、卡钻、井径扩大率大等复杂情况,利用MY1井钻井岩心从泥页岩类型划分、孔渗特征、微观结构、岩石力学以及地应力等方面开展井壁稳定性影响因素实验分析。通过分析可知,中牟区块泥页岩属硬脆性泥页岩,造成井壁失稳的主要因素为地层非均质性强,岩石脆性程度较高,微裂缝发育,易导致井壁机械剥落、坍塌掉块。通过合理控制钻井液密度、优化井身结构及钻井参数、研发低自由水强封堵钻井液提高井壁稳定性,在区块钻井实践中取得了较好的应用效果,基本解决了井壁失稳难题。

Borehole wall instability is one of the common difficulties in drilling process,especially in the mud shale interval drilling.In view of the complicated conditions of borehole collapse,block falling,drill pipe sticking and borehole diameter enlargement in Shanxi-Taiyuan formation mud shale drilling process in Henan Zhongmu shale gas block,the experimental analysis on the influence factors to borehole stability is carried out in the shale classification,pore permeability characteristics,microstructure,rock mechanics and in-situ stress by using the cores of well MY1.The analysis shows that the mud shale of Zhongmu block belongs to hard-brittle mud shale,the main factors that cause wellbore instability are strong heterogeneity,high rock brittleness and micro fracture development,which are easily lead to wellbore wall mechanical flaking,collapse and block falling.Through the reasonable control of drilling fluid density,optimization of the wellbore structure and drilling parameters and the development of low free water and strong plugging drilling fluid to improve the wellbore stability,good application effect is obtained.