顺北油气田奥陶系破碎性地层井壁失稳影响因素分析

Analysis on influencing factors of wellbore instability of Ordovician fractured formation in Shunbei Oil and Gas Field

张亚云,李大奇,高书阳,林永学,曾义金

页岩油气富集机理与有效开发国家重点实验室，北京 100101 中国石化石油工程技术研究院，北京 100101

State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Beijing 100101, China Research Institute of Petroleum Engineering, SINOPEC, Beijing 100101, China)

针对顺北油气田奥陶系破碎性地层井壁失稳频发的技术难题，通过开展X射线衍射、扫描电子显微镜和滚动回收率等室内实验，建立了考虑多弱面效应和力化耦合作用的井壁失稳模型，分析了井壁失稳机理及影响因素。研究表明：奥陶系破碎性地层以方解石为主，黏土矿物质量分数低，水化分散能力弱，多尺度非连续破碎结构和非黏土水化型水岩损伤作用是井壁失稳的关键因素；随弱面组数的增加，岩石强度的各向异性愈发显著，坍塌压力增大，安全钻井的优势方位角与倾角选择减少；随着弱面倾角由0°增大到90°，坍塌压力呈现先增加、后平稳、再逐渐减小的趋势；坍塌压力随弱面内聚力、内摩擦角的增大而显著降低，且内摩擦角的影响更显著，但随弱面胶结强度的升高，坍塌压力的降低率具有一定的极限。

Aiming at the technical problem of frequent wellbore instability of the Ordovician fractured formation in Shunbei Oil and Gas Field, based on basic physical and chemical tests such as XRD, SEM and rolling recovery, the mechanism and main controlling factors of wellbore instability in the fractured formation are analyzed combined with the study of wellbore instability model considering multiple weak planes and mechanochemical coupling effect. The research shows that the Ordovician fractured formation is mainly composed of calcite, with low clay content, weak hydration and dispersion ability. The multi-scale discontinuous fracture structure and non-hydrated water-rock damage are the main control factors of wellbore instability; with the increase of weak plane group, the strength anisotropy of rock becomes more obvious, the collapse pressure increases, and the selection range of dominant azimuth and dip angle of safe drilling is reduced. When the weak plane dip angle increases from 0° to 90°, the collapse pressure first increases, then becomes stable, and then decreases gradually; the collapse pressure decreases significantly with the increase of weak plane cohesion and internal friction angle, and the influence of internal friction angle is more significant, but the decrease of collapse pressure has a certain limit with the increase of weak plane cementation strength.

10.6056/dkyqt202202020