高密度油基钻井液在长宁——威远区块页岩气水平井中的应用

Application of high density oil-based drilling fluid in shale gas horizontal wells of Changning-Weiyuan Bolck

四川盆地长宁—威远国家级页岩气示范区下志留统龙马溪组黑色页岩层具有较强的层理结构,微裂缝和裂缝发育。钻进过程中钻井液沿微裂缝和裂缝侵入地层,使井壁易发生层间剥落,造成井壁失稳。针对该区龙马溪组页岩层的地质特点,分析使用油基钻井液钻井的技术难点,提出了相应的技术对策。在自主研发出三合一乳化剂CQMO的基础上,通过实验优选出高密度油基钻井液配方,并对其性能进行实验分析评价。实验结果表明,该高密度油基钻井液体系具有好的高温沉降稳定性、抑制性、封堵性和抗污染性。该高密度油基钻井液体系已成功应用于长宁—威远国家级页岩气示范区36口水平井钻井,解决了钻进页岩气水平井摩阻大、井眼净化难和井壁失稳等难题,能满足页岩气水平井技术需要;钻进过程中,钻井液性能稳定,井壁稳定,携砂良好,井下安全。该高密度油基钻井液可在其他页岩气区块推广应用。

In the Changning-Weiyuan National Shale Gas Demonstration Area of Sichuan Basin, Lwer Silurian the Longmaxi Forma- tion shale is characterized by strong bedding structures and existence of microfractures and fractures. In the process of drilling, drill- ing fluids flow into the strata along microfractures and fractures. As a result, sidewalls are prone to interlayer scaling and instability. In this paper, the technical difficulties of oil-based drilling fluids were analyzed based on geological characteristics of Longmaxi For- mation shale, and then the technical solutions were proposed. Based on the independently developed three-in-one emulsifier CQMO, the formula of high density oil-based drilling fluid was experimentally optimized, and its properties were analyzed and evaluated. It is shown that this high density oil-based drilling fluid system is advantageous with high-temperature settlement stability, inhibition, plugging and pollution resistance. It has been successfully applied to the drilling of 36 wells in the Changning-Weiyuan National Shale Gas Demonstration Area, with the drilling difficulties of shale gas horizontal wells solved, such as high friction, difficult hole cleaning and wellbore instability. It is indicated that this high density oil-based drilling fluid system can satisfy the technical requirements of shale gas horizontal wells. In the process of drilling, the drilling fluid presents stable performance with good proppant carrying capac- ity, and the downhole is safe with stable sidewalls. This high density oil-based drilling fluid is worthy of popularization in other shale gas blocks.