Micro-Pore Characteristics and Control Factors for Compact Silurian Sandstone Reservoirs in Sichuan Basin, Western Hubei, and Eastern Chongqing Areas

摘要

Silurian sandstone reservoirs in Western Hubei and Eastern Chongqing areas typically have low porosity and permeability. It serves as a guide for identifying similar reservoirs, mainly by analyzing reservoir micro-pore types and control factors thereof. Thorough research is conducted on micro-pore structure of the compact sandstone reservoir in the study area, primarily through pore casting slice analysis and several advanced unconventional reservoir testing methods, such as field emission scanning electron microscopy (FE-SEM), automatic mineral identification system (QEMSCAN), back-scattered electron image stitching (BSE), Modular Automated Processing System (MAPS). It is believed that Sandstone in the study area has fine granularity, large burial depth, strong diagenesis, undeveloped primary pores, but has developed secondary pores. The structural components of sandstone resulted due to the combined action of deposition and diagenesis. A new method for classifying secondary pores has been proposed, based on structural components and genesis of the compact sandstone, and influences of these elements on reservoir pore have also been discussed. The main micro-pore types described are intergranular dissolution pores formed by feldspar dissolution in particles, micro/nanoscale intercrystalline pores and dissolved pores of clay minerals in the matrix and cement, cement dissolution pores, as well as fractures formed by early siderite cement dissolution. Micro/nanopore contributions in clay matrix and cement are important factors that add considerable value to future research of compact sandstone reservoirs.