钻井液活度对川滇页岩气地层水化膨胀与分散的影响

Effects of Drilling Fluid Activity on Hydration and Dispersion of Formation Rocks in Shale Gas Drilling in Chuan-Dian Area

降低水基钻井液活度是解决钻井过程中泥页岩井段井壁失稳的重要技术手段,川滇地区页岩气地层泥质含量高、水敏性强,层理与微裂缝发育,井壁易失稳。以氯化钙等无机盐、甲酸钾等有机盐及丙三醇等有机化合物作为活度调节剂,通过线性膨胀实验、热滚回收实验研究了钻井液活度对宜宾龙马溪组、宜宾五峰组等页岩水化膨胀与分散的影响。结果发现,钻井液活度对页岩水化膨胀和水化分散影响小,泥页岩渗透水化不是上述地区页岩地层井壁失稳的主要原因。解决其井壁失稳问题,应从表面水化、毛管压力及微裂缝等其他机理入手。

Reducing the activity ofthe filtrate of drilling fluid is an important technology in mitigating shale problems during drilling. In shale gas drilling in the Chuan-Dian area, highly water sensitive clayey formations with fractures highly developed have been frequently encountered, necessitating the means of borehole wall stabilization. Linear swelling and hot rolling tests using a drilling fluid formulated with Ca Cl2, potassium formate and glyceryl alcohol as the activity agents, and shale samples from Longmaxi formation（Yibin, Sichuan） and Wufeng formation（Yibin, Sichuan） show that the activity of the drilling fluid has played a slight role in the hydration and dispersion of the shales, indicating that osmotic hydration of the shales is not the main cause for the shale formations to collapse. Surface hydration, capillary pressure as well as the micro fractures developed in the shale formations may have been causing the shale formation to collapse.