渤海油田渤中区域中深部泥页岩地层井壁稳定性

渤中区域资源潜力巨大,是目前渤海油田勘探开发的重点区块.前期探井钻井过程中中深部东营组、沙河街组泥岩地层井壁坍塌失稳现象频发,出现蹩压、阻卡等复杂事故.为揭示渤中区域中深部泥页岩井壁失稳机理,指导开发井钻井设计,对取自渤中区域东营组泥岩岩心开展了电镜扫描、矿物组分测试、泥浆浸泡以及岩石力学等系列实验,定量刻画了该地层的理化特性、岩石力学特性以及钻井液对力学性质的影响规律.实验结果表明,该区块中深部泥页岩处于由水化膨胀性泥页岩向硬脆性泥页岩转化的过程,既具有硬脆性泥页岩层理、裂隙发育的特征,又仍表现出一定的水化膨胀和分散特征.在实验结果的基础上,利用线弹性理论和单一弱面准则,建立了考虑弱面结构和水化作用的井壁稳定模型,对渤中区域定向开发井坍塌压力及其随井斜角和井斜方位角的变化规律进行了分析,揭示了钻井液作用对坍塌压力的影响.研究结果对于渤中区域开发井安全钻井具有一定的指导意义.

Study on wellbore stability of shale formation in Bozhong Area of Bohai Oil Field

BZ area has great potential in oil/gas resources and is the key block for exploration and development of Bohai Oilfield. During the drilling process of exploratory Wells, wellbore instability issues in the shales located in the Dongying formation and Shahejie formation occurred frequently. To reveal the borehole instability mechanism of shale in the middle and deep part of BZ area, and to guide the development well drilling design, a series of experiments including electronic microscope scanning, mineral composition testing, mud soaking and rock mechanics tests were carried out on the shale cores from the Dongying formation of BZ area. The physical and chemical properties, rock mechanical properties and the effect of drilling fluid on mechanical properties of the formation were quantitatively described. The experimental results show that the shale in this block is in the process of transformation from hydrating and expanding shale to hard and brittle shale, which not only has the characteristics of hard and brittle mud shale, fracture development, but also has the characteristics of hydration and expansion and dispersion. Based on the experimental results, a borehole wall stability model considering the weak surface and hydration was established by using the linear elasticity theory and the single weak surface strength criterion. The collapse pressure in the directional development wells of BZ area and its variation with the well angle and azimuth angle were analyzed, and the influence of drilling fluid on the collapse pressure was revealed. The results of this paper are helpful for the safe drilling of development wells in BZ area.