砂砾岩储层孔隙结构复杂模态差异机制

针对砂砾岩储层孔隙结构复杂、模态成因机制不明的情况,以325块岩芯分析化验数据为基础,利用压汞、铸体薄片、扫描电镜及X射线-CT扫描等方法,开展了岩石相分类、孔隙结构模态和驱油效率差异机制的研究,从油田开发与实用相结合的方式考虑,将砂砾岩储层岩相分为3大类、7亚类、13细类。研究表明：不同孔隙结构模态特征及注水驱替效率差异较大。单模态岩石颗粒以粗砂岩为主,孔隙发育程度高,孔隙呈网络状结构,相互连通性较好,注水驱替模式以网络状连通驱替为主,效率较高。双模态岩石颗粒由砾岩和中-粗砂岩两级颗粒组成,孔隙较发育,孔隙呈疏网状结构,相互连通性一般,注水驱替模式以星点状连通驱替为主,效率一般。复模态岩石颗粒由砾石、中-粗砂岩、粉砂或泥质三级颗粒组成,孔隙发育一般,孔隙呈星点状结构,相互连通较差,注水驱替模式以零星散乱状驱替为主,局部存在高渗带,效率整体较差。相同岩相呈不同孔隙结构模态和不同的岩相呈相同的结构模态的情况普遍存在。颗粒排列方式及成岩作用差异改造导致了同相异态,而颗粒分选、磨圆、排列方式等因素形成了异相同态。

Mechanism of Complex Modes of the Pore Structure of Sandstone/Conglomerate Reservoirs

The formation mechanism of complex modes of the pore structure of sandstone/conglomerate reservoirs is still unclear. Thus, this study investigated the difference mechanisms of lithofacies classification, pore structure modes, and displacement efficiencies based on experimental data of 325 core examples through mercury intrusion porosimetry, cast thin sections, scanning electron microscopy, and X-ray computed tomography. The results reveal that, taking both oil field exploitation and utility into consideration, lithofacies of sandstone/conglomerate reservoirs can be classified to 3 primary categories, 7 secondary categories, and 13 tertiary categories. They have different pore structure modal characteristics and relatively great variance in their efficiency of displacement by water injection. Single-mode rock particles are mostly coarse sandstones with highly developed and relatively well inter-connected pores in a network structure. The displacement by water injection is mainly via connected networks, resulting in higher efficiency. Dual-mode rock particles are composed of two classes of particles:conglomerates and medium-coarse sandstones. They have relatively developed and moderately inter-connected pores in a sparse network structure. The displacement, here, is mainly via star-shaped connected networks, with ordinary efficiency. Complexmode rock particles consist of three types of particles:conglomerates, medium-coarse sandstones, and silt or mud. Their pores are moderately developed and relatively poorly inter-connected with a star-shaped networking structure. The water injectiondriven displacement is mostly scattered over local high-permeability zones, resulting in poor overall efficiency. The same lithofacies typically show different pore structure modes while different lithofacies can have identical structure modes. Differential transformation due to particle configuration and diagenesis leads to different pore structure modes for identical lithofacies; while sorting, rounding, and arrangement of particles result in identical pore structure modes for different lithofacies.