涪陵页岩气水平井油基钻井液技术

涪陵焦石坝区块采用水平井开发方式，水平段长1 500 m以上，水平井段为龙马溪组下泥岩段，页岩黏土矿物含量高，脆性强、微裂缝发育，易发生垮塌掉块造成井下事故；井底垂深大于3 500 m，深层页岩气开发，面临着井温升高、携岩带砂要求越来越高、部分井发生垮塌掉块、起下钻遇阻卡的问题，部分井发生失返性漏失，消耗了大量的人力、物力。对柴油基钻井液体系进行了研究，结果表明该体系具有良好的抗温性、在低油水比（70:30）下仍然具有稳定的性能，随钻堵漏材料（粒径级配的高纯超细碳酸钙+有机胶凝漏失控制材料）能够封堵2 mm的裂缝，承压强度达7 MPa，纳米封堵剂（纳米石墨粉和超细海泡石纤维组成的混合物）能够封堵0.1 mm裂缝，承压达到20 MPa。现场应用结果表明，该体系具有良好的井壁稳定能力，井径扩大率低，平均小于3%，润滑性好，起下钻摩阻低，钻井液性能稳定，易于维护处理，能够解决井漏、井垮等复杂情况。柴油基钻井液完全适用于涪陵区块的页岩气水平井钻井施工。 

Oil Base Drilling Fluid for Drilling Shale Gas Wells in Fuling

Horizontal drilling has been used in developing the block Jiaoshiba in Fuling, Chongqing. The horizontal section, more than 1,500 m in length, penetrated the lower Longmaxi mudstone formation, which has high clay contents, and is brittle and full of micro fractures. The vertical depths of the wells drilled in this area were deeper than 3,500 m. Deep well shale gas development in this area has been faced with difficulties such as high well temperature, cutting carrying, borehole wall collapse in some wells, over-pulls during tripping, and lost returns of muds in some wells, all of these have caused waste of manpower and material resources. To solve these problems, a diesel oil base drilling fluid has been studied for use in shale gas drilling. The diesel oil base drilling fluid formulated had good high temperature stability; at low oil/water ratio (70:30) the fluid was still stable. Two LCMs, were added in the oil base drilling fluid; one was a high purity ultra-fine CaCO3 mixed with an organic gel LCM which can plug fractures of 2 mm in width, and can stand pressure of 7 MPa. The other LCM, a nano graphite powder mixed with ultra-fine sepiolite fibers, can be used to plug micro fractures of 0.1 mm in width, and can stand pressure of 20 MPa. Field application demonstrated that this oil base mud greatly stabilized the borehole wall in easy-to-collapse hole sections, and reduced the average rate of hole diameter enlargement to less than 3%. Good lubricity of the mud made trip very smooth. The property of the mud was stable during the whole drilling period and was easy to maintain. Downhole problems previously encountered such as lost circulation and borehole wall instability were mitigated to acceptable levels. Field application proved the suitability of diesel oil base drilling fluid in shale gas horizontal drilling in Fuling area.