应用CT技术研究钻井液污染三维空间分布特征

常规液相钻井技术对油气藏储层污染空间分布特征的认识是许多学者关心问题。采用高能、高精度CT仪探索研究了钻井液污染后全直径岩心3D空间分布特征,建立了相应测试方法及定量判断钻井液滤失深度手段,获取了不同条件下钻井液污染三维空间分布图形;并结合电镜扫描及能谱分析,分析孔隙型及裂缝型储层钻井液污染微观特征。研究表明,钻井液滤失深度主要集中在离岩心端面11~24 mm;钻井液污染后孔隙型、裂缝型储层岩心污染空间呈"锅底状"特征,裂缝型储层岩心还可观察到钻井液贯穿整个裂缝;压差及裂缝导流能力是制约钻井液侵入基质孔隙深度的重要因素;裂缝中侵入颗粒以重晶石颗粒、盐类结晶为主,以区域性滤饼、团聚状颗粒形态分布;基质孔隙储层侵入颗粒以盐类结晶为主,以孔隙表面沉淀、孔隙充填、孔喉堵塞分布。研究成果为深入认识孔隙型、裂缝型储层钻井液污染特征提供重要机理认识,为室内实验评价技术提供了新的研究技术方法。

Research on 3D spatial distribution features of drilling lfuid pollution using CT technology

The understanding on spatial distribution features of oil/gas reservoir pollution by conventional liquid drilling technique is a concern of many scholars. The authors used high-energy, high-precision CT instrument to explore the 3D spatial distribution features of full-diameter core after being polluted by drilling fluid, established the corresponding test method and the means of quantitatively determined the filtration depth of drilling fluid, and obtained the 3D spatial distribution diagram of drilling fluid pollution under various conditions. Besides, the authors analyzed the microscopic features of porous and fractured reservoir drilling fluid pollution with the help of scanning electron microscope and energy spectrum. The research shows that the drilling fluid filtration depth mainly occurs at 11 mm to 24 mm from the core end face. After being polluted by drilling fluid, the core from porous and fractured reservoirs shows ‘pot-bottom’ feature of polluted space. And from fractured reservoir cores, it can be observed that drilling fluid has penetrated the whole fracture. Pressure difference and fracture conductivity are the main factors restricting drilling fluid from invading the matrix pore depth. The introduced particles in fractures are mainly barite grains and salt crystals and distributed in regional filter cake and aggregated grains. The introduced particles in matrix porous reservoirs are mainly salt crystals and distributed in the forms of settlement on pore faces, pore filling and throat plugging. The research findings provide an essential understanding on the mechanism of drilling fluid pollution features in porous and fractured reservoirs and provide a new research method for indoor experimental evaluation.