Diagenesis and porosity evolution of sandstones in Xujiahe Formation, Yuanba area

The sandstones in the Triassic Xujiahe Formation in Yuanba area are typical low-porosity and low-permeability reservoirs. The diagenesis and porosity evolution of sandstones as well as their influences on reservoir physical properties were studied by means of ordinary and casting thin section microscopic identification, SEM and X-ray diffraction. The main diagenetic effects included compaction/pressolution, cementation, replacement, corrosion and cracking, among which the compaction/pressolution, siliceous and carbonate cementation effects greatly reduced native sandstone porosities and destructed sandstone reservoirs, while the chlorite rim cementation, corrosion and fracturing effects protected and improved reservoirs. At present, the sandstones in the Xujiahe Formation in Yuanba area have entered the middle diagenesis stage A, and partially in the middle diagenesis stage B.Most of the reservoir's primary porosities have been destroyed after severe diagenetic evolution, and the main pore types are secondary pores and associated cracks.