硬脆性泥页岩渗流-应力耦合井壁坍塌压力计算方法

硬脆性泥页岩的井壁坍塌是制约我国油气资源战略向深部地层成功转移的重要技术瓶颈。建立了裂缝渗流-应力耦合作用下孔隙压力的计算模型,选用弱面破坏准则,综合考虑各向异性、裂缝产状、井眼轨迹、地应力、渗流应力的影响建立了硬脆性泥页岩井壁坍塌压力的计算方法,分析了裂缝渗流、井眼轨迹和裂缝产状对坍塌压力的影响规律。研究发现,钻井液沿裂缝渗流导致坍塌压力升高,渗流初期坍塌压力升高较快,随时间推移,升高量逐渐逐渐减小;在高倾角裂缝中沿裂缝倾向钻进水平井坍塌压力较低。改善钻井液的封堵性、流变性和润湿性,减缓钻井液沿裂缝面的渗流,避免在坍塌压力较高的区域钻井,是该类地层安全钻井的关键。

Calculating method of collapse pressure for hard brittle shale coupled seepage and stess

Borehole collapse of hard brittle shale is the important technical bottleneck of China's oil and gas resources strategy transfer to deep formation. The calculating modle of pore pressre coupled seepage and stess was established, and chosen weak plane failure criteria, the calculating method of collapse pressure for hard brittle shale was established, in which anisotropic, crack occurrence, borehole trajectory, in-situ stress and seeapage stress were comprehensive taken account, and th influence law of seepage, borehole trajectory and crack occurrence on collapse pressure were analyzed. The results show that, collapse pressure increases due to drilling mud seeage along crack, and quickly in early period, but incease slowly with time; collapse pressure is low when drilling horizontal well along the crack tendency in the high angle crack. Improve drilling fluid performance including sealing, rheology and wettability to slow down seepage and avoid drilling in the area of high collapse pressure are the key methods for safely driiling in hard brittle shale.