涪陵破碎性地层井壁失稳影响因素分析及技术对策

Borehole instability in broken formations of Fuling Block: Influence factors and countermeasures

柴油基钻井液体系具有良好的井壁稳定能力、低摩阻、低失水等特性,并在涪陵页岩气水平段得到广泛应用,但是随着涪陵二期垂深大于3 500 m的深层页岩气开发,采用油基钻井液体系钻进,出现一系列井下复杂情况,如掉块、起下钻通井遇阻卡,电测遇阻,甚至埋钻具填井事故,因此,有必要对油基钻井液环境下的页岩井壁失稳问题进行研究分析。以焦页XX井为例,从地质、钻井液、工程三方面进行综合研究分析,认为破碎性页岩地层本身的力学不稳定性是造成井壁失稳的主要因素,并提出一些建议性措施:钻井液的密度要保持高位,同时提高油基钻井液的封堵能力,保持高油水比例,工程和地质相结合,尽可能减少穿越该复杂地层。

Featured by better borehole-stabilizing capacity, and low friction resistance and fluid loss, the diesel-based drilling-fluid system has been widely applied to horizontal sections of shale-gas wells, Fuling Block. As Phase 2 development moved to some deeper layers with vertical depth over 3 500 m, however, several downhole complexities had occurred when oil-based drilling fluid was used, such as block falling, sticking in wiper trip, obstruction during electric logging, drilling-tool buried bringing about plug-back accidents. So, it＇s necessary to analyze these instability of shale-gas wells in which oil-based drilling fluid is used. Jiaoye XX well was taken as an example for analysis from three aspects of geology, drilling fluid, and engineering. It is indicated that the mechanical instability of broken formations is the main factor leading to borehole instability. And some constructive countermeasures are made, including to keep drilling-fluid density at a high level, to increase oil-based drilling-fluid plugging capacity, to maintain a high oil-water ratio, and to integrate engineering and geology factors in order to avoid drilling through certain complicated formations.