Porosity Formation and Evolution of the Deeply Buried Lower Triassic Feixianguan Formation, Puguang Gas Field, NE Sichuan Basin, China

Abstract

The deeply buried shoal dolomite reservoirs of the Lower Triassic Feixianguan Formation, giant Puguang Gas Field, NE Sichuan Basin, are exceptionally porous. The influences of diageneses on pore evolution are studied. Through pet-rologic investigation, diagenetic phases are divided into four stages, i.e., near-surface, pre-oil window, oil window, and gas window. The Adobe Photoshop system is used to quantify the rock texture components, porosity constitutions and the influences of diageneses on reservoir porosity. Porosity evolution curves are quantitatively recovered. The Feixian-guan reservoir porosities are mainly created by early meteoric dissolution, dolomitization, and organic acids dissolution. Dissolution during deep burial is insignificant. Pores are formed in near-surface and pre-oil window stages and effec-tively preserved till present. This result may be of great significance to the further exploration of deeply buried carbon-ate reservoirs not only in NE Sichuan Basin, but also around the world.