JN1H井煤岩气长水平段钻井井壁稳定技术

Borehole Wall Stabilization Technology for Drilling the Long Horizontal Section Coal Rock Gas Well JN1H

针对鄂尔多斯东缘本溪组8#煤层长水平段钻完井过程中井壁易失稳、井眼延伸难度大的问题,开展了煤岩气钻井井壁稳定技术研究。对可能钻遇的顶板碳质泥岩、夹矸、上部煤层和下部煤层等岩心,开展了X-衍射、电镜扫描、CT扫描、三轴力学等相关实验。实验表明,非煤层黏土矿物含量在35%以上,主要由高岭石和伊利石组成,只含不到5%的伊蒙混层,煤层的黏土矿物含量在10%~18%之间,以高岭石为主,含25%左右的伊蒙混层;岩心裂缝宽度范围在25~1000 μm之间,主要分布在25、40、64、100、160、250、400 μm几个数值附近;最大坍塌压力当量密度是1.36g/cm^(3),在中下部煤层位置;从“封堵防塌、井眼清洁、润滑防卡”三个方面设计了钻井液配方,评价结果表明,中压滤失量为1.6 mL,高温高压(70℃)滤失量为4.4 mL,400 mD、100 D砂盘PPT滤失量小于15 mL,表明配方具有良好的封堵性能。井壁稳定技术在JN1H井进行了现场应用,完成2019 m水平段施工,钻完井周期为28.25 d,钻完井过程顺利,实现了煤岩气长水平段钻井井壁稳定。

Wells with long horizontal sections were drilled in the eastern margin of Ordos basin and penetrated the 8#coalbed of the Benxi formation.Borehole stability problems during drilling and completion of the wells made it difficult to drill these extended reach wells.Studies were conducted on the borehole stability of the coalbed methane production wells.X-ray diffraction,SEM,CT and triaxial stress test were conducted on the rock cores taken from the carbonaceous mudstones,the intercalated gangues,and the upper and lower coalbeds that are possibly penetrated by the wells.Analyses of these core samples show that the minimum amount of clay minerals of the cores taken from formations outside the coalbeds is 35%,and the clays are mainly kaolinite and illite.The content of mixed layer illite-montmorillonite is less than 5%.Cores taken from the coalbeds have clay content between 10%and 18%,and is mainly kaolinite,and the content of the mixed layer illite-montmorillonite is about 25%.The widths of the fractures in the cores are generally 25-1,000μm,mainly around those widths such as 25μm,40μm,64μm,100μm,250μm and 400μm.The maximum equivalent collapse pressure of the formations is 1.36 g/cm^(3) and is located in the middle and the lower coalbeds.A drilling fluid was formulated to drill these formations based on three policies,which were“prevent collapse by plugging,ensure the hole is as clean as possible,and prevent pipe sticking with good lubricity of the drilling fluid”.The drilling fluid formulated had these properties in laboratory evaluation:API filter loss of 1.6 mL,HTHP(70℃)filter loss of 4.4 mL,and sand bed(400 mD,100 D)PPT filter loss of less than 15 mL,indicating that it had excellent plugging capacity.This drilling fluid was used to drill the well JN1H whose horizontal section is 2,019 m in length.Drilling and completion This well was successfully drilled and completed in 28.25 days, and stabilization of the long horizontal section of a coal rock gas well was reached.