Genesis of Carboniferous volcanic reservoirs in Chepaizi salient in western margin of Junggar Basin

Key words:  Junggar Basin  Chepaizi salient  Carboniferous  volcanic reservoirs  reservoirs evolution

Abstract:

Carboniferous volcanic rock is an important reservoir type in Chepaizi salient, western margin of Junggar Basin. Based on the results of core observation, thin section identification, element test and physical property analysis, this study analyzed the lithology, lithofacies, reservoir space types, physical property and genesis of the Carboniferous volcanic rocks. The results reveal that Carboniferous volcanic rocks are dominated by volcanic lava (including basalt, andesite, and basaltic andesite) and pyroclastic rocks (including intermediate-basic volcanic breccias and tuff).The volcanic rocks are low porosity and ultra-low permeability reservoirs, with main reservoir space of secondary dissolved pore and fracture. The Carboniferous volcanic rocks have undergone intense reformation at late stage, including condensation consolidation, tectonic uplifting, weathering leaching, and cavity filling and dissolution. The quality of volcanic reservoirs is changed accordingly:first improved by tectonic uplifting or weathering leaching, then deteriorated by cavity filling, and finally improved by dissolution.