川西南玄武岩储层微观孔隙结构及岩石力学特征

Microscopic pore structure and rock mechanics characteristics of basalt reservoir in southwest Sichuan

四川盆地川西南乐山地区火山岩以溢流相玄武岩为主,储层厚度大、分布广、埋深浅,勘探开发潜力大。通过物性分析、扫描电镜、铸体薄片、高压压汞、三轴力学以及地应力测试等技术,研究了储层微观孔隙结构及岩石力学特征。研究结果表明:1)玄武岩储层致密,呈低孔低渗特征,储集空间以杏仁状残余气孔、基质溶蚀孔、收缩缝和构造缝为主,多被充填-半充填,且储层存在中等偏强水敏和中等酸敏特征;2)微观孔隙结构可划分为孔隙-裂缝型、孔隙型和致密孔隙型3类,其中主力孔隙型储层发育纳米级孔喉,喉道分布较为集中,退汞效率很低,小孔喉较多且连通性差;3)岩石力学实验表明,玄武岩储层呈现明显的轴向劈裂模式,表现出一定的脆性破坏,但抗压强度高,水平应力差异大,且垂向应力更接近于最小水平主应力。

The volcanic rocks in Leshan Area of southwest Sichuan Basin are mainly overflow basalt,the reservoir thickness is larges,wide distribution and shallow burial depth,indicating great potential for exploration and development.The microscopic pore structure and rock mechanical characteristics were studied in this paper according to physical property analysis,scanning electron microscopy,casting thin section,high pressure mercury injection,triaxial mechanics and in-situ stress test.The results show that:1)The basalt reservoir space is mainly composed of amygdaloid residual pores,matrix dissolution pores,shrinkage fractures and structural fractures,which are mostly filled-semi-filled,showing the characteristics of low porosity and low permeability,and the reservoir has medium to strong water sensitivity and medium acid sensitivity;2)The microscopic pore structure can be divided into three types:pore-fracture type,pore type,dense pore type.The main pore type reservoir develops nanometer pore throat and throat distribution is concentrated,the mercury removal efficiency is very low,which reflects that the small pore throat is more and the connectivity is poor.3)Rock mechanics experiments have shown that basalt fracture is axial splitting mode,showing a certain brittle failure,but the compressive strength is high,the horizontal stress difference is large,and the vertical stress is closer to the minimum horizontal principal stress.