深层脆性页岩水平井井壁崩落失稳研究

Study on wellbore caving and instability of horizontal well in deep brittle shale

刘厚彬 崔帅 孟英峰 周彦行 罗益3

西南石油大学油气藏地质及开发工程国家重点实验室，四川 成都 610500 西南石油大学保卫处安全消防科，四川 成都 610500 中国石油西南油气田分公司通信与信息技术中心，四川 遂宁 629000

State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China Fire Saefty Division of Security Department, Southwest Petroleum University, Chengdu 610500, China Communication and Information Technology Center, Southwest Oil & Gas Field Company, PetroChina, Suining 629000, China

随着钻井深度的不断加深，页岩地层的井下复杂情况增加，通常表现为井壁崩落掉块。针对泸州区块龙马溪组深层页岩开展了水平井井壁崩落失稳研究，制定了井下工况下力学加卸载模拟实验方案，分析了围压加卸载速度对岩石力学性能的影响，建立了深层脆性页岩水平井井壁崩落失稳模型。研究表明：龙马溪组深层页岩脆性矿物质量分数高，脆性强，但层理缝较为发育，井底压力环境下容易沿层理缝发生脆性劈裂破坏；不同工况下井底有效液柱压力变化明显，井底激动压力变化越迅速，越容易引起井壁岩石沿层理缝发生崩落掉块；根据理论模拟结果，起钻、停钻停泵后，水平井段上、下井壁的页岩受拉应力，将会发生小范围拉伸崩落。研究结果对深层脆性页岩水平井安全钻进具有一定的指导意义。

With the increasing drilling depth of shale formation, downhole complexity occurs frequently, which is often manifested as borehole wall caving and falling. Aiming at the deep shale of Longmaxi Formation in Luzhou block, the wellbore caving and instability study was carried out, a simulation experiment scheme of mechanical loading and unloading under downhole working conditions was developed, the influence of confining pressure loading and unloading speed on the mechanical property parameters of rock was analyzed, and the evaluation method of wellbore caving and instability of deep brittle shale in horizontal well was established. The study shows that the deep shale of Longmaxi Formation has high content of brittle mineral and strong brittleness, but the bedding fractures are relatively developed. It is easy to cause brittle splitting failures along bedding fractures under the environment of bottomhole pressure. Under different working conditions, the pressure of effective fluid column at the bottom of the well changes obviously. The faster the bottom hole surge pressure changes, the more likely it is to cause the wellbore rock break down and falling along the bedding fractures. The results of theoretical simulation show that, after the tripping out and pump off, the tensile stress of shale in the upper and lower sidewalls of horizontal well section will cause a small range of tensile caving. The results provide some guiding significance for safe drilling of horizontal well in deep brittle shale.

10.6056/dkyqt202103007