Reservoir characterization and origin of tight gas sandstones in the Upper Triassic Xujiahe formation, Western Sichuan Basin, China

The Western Sichuan Basin, which is located at the front of Longmen Mountain in the western Sichuan Province, China, is a foreland basin formed in the Late Triassic. The Upper Triassic Xujiahe formation in the Basin includes several tight gas sandstone reservoirs, whose porosity is less than 6.0 % and permeability less than 0.1 md. According to data of cores, thin sections, FMI, SEM and experiments, we summarize the reservoir characteristics, analyze the origin of these tight gas sandstones, and discuss the factors controlling the formation of relatively high-quality reservoirs. Xujiahe Formation is a set of terrestrial clastic rocks with low compositional maturity, low cement content, and medium textural maturity. Secondary dissolution pores are abundant, but pore spaces are small with narrow pore throats and high capillary pressures. Due to the existence of abundant fractures and intense diagenesis, these tight gas reservoirs are characterized by high reservoir heterogeneity, complex seepage system, and strong stress sensitivity. The original sedimentary facies belt and later tectonism co-control the distribution of favorable reservoirs. The intense compaction and cementation are the main factors making the Xujiahe formation to be tight. © 2015, The Author(s).