顺北油气田深部破碎性地层井壁失稳机理及对策研究

顺北油气田多口探井在奥陶系碳酸盐岩地层钻遇破碎带，井壁失稳严重，已成为制约顺北油气田安全建井的突出问题。文章在综合分析顺北奥陶系破碎性碳酸盐岩地层井壁失稳类型及理化特性、裂缝面物理—力学特性和岩石力学实验的基础上，提出了井壁稳定钻井液技术对策。研究发现，区域断裂带附近地应力方向复杂，地应力差大；地层天然多尺度裂缝发育、破碎程度大、岩体等效强度较低；钻井液易沿天然裂缝侵入地层，钻井液-裂缝面水岩作用造成缝面粗糙度减小、摩擦系数降低，易诱发地层沿裂缝面失稳，是深部破碎性地层井壁失稳的主要机理。明确“合理密度支撑+钻井液刚柔并济多级配封堵”,配合使用“耐高温随钻/段塞固壁剂”是顺北油气田深部破碎性地层稳定的井壁钻井液技术对策。研究成果对促进深部破碎性地层安全高效钻井具有重要借鉴意义。

Study on the Wellbore Instability Mechanisms and Drilling Fluid Countermeasures of Deep Fractured Formation in Shunbei Oil and Gas Field

There are many exploratory wells in the Shunbei oil and gas field encountering fractured formations in the Ordovician carbonate formation, and the problem of wellbore instability was serious, which has become a prominent problem restricting the safe construction of the wells in the Shunbei oil and gas field. In this paper, the types of the wellbore instability in the deep fractured formations in the Shunbei Ordovician were analyzed. Then, a series of experiments in the physical and chemical properties, the physical and mechanical properties of fracture surfaces, and the rock mechanics experiments was carried out. In the end, a drilling fluid strategy for wellbore stability was proposed. The results indicated that the mechanism of wellbore instability mainly included three aspects. Firstly, the direction of in-situ stress near the regional fault zone was complex and the difference of in-situ stress was large. Secondly, the natural multi-scale fractures in the formation was developed, the degree of fragmentation was larger, and the equivalent strength of the rock mass was lower. Thirdly, the drilling fluid easily invaded the formation along the natural fractures, and the interaction between the drilling fluid and the fracture surface decreased the fracture surface roughness and friction coefficient at the same time. With the coefficient decreased, it was easy to induce formation instability along the fracture surface. As a result,reasonable density support and enhanced drilling fluid multi-scale plugging were thought as the effective wellbore stabilization drilling fluid technology, which also required the enhancement of both wellbore strengthening drilling fluid technology while drilling and Slug Wellbore strengthening drilling fluid technology. The research results have important reference significance for promoting safe and efficient drilling in deep fractured formation.