Reservoir Properties and Effect Factors on Volcanic Rocks of Basement beneath Wucaiwan Depression, Junggar Basin

The researches on oil- and gas-bearing volcanic rocks have largely developed the foreground of oil exploration. Types, facies distribution and physical properties (mainly porosity and permeability) of volcanic rock of the basement beneath the Wucaiwan depression, the eastern part of Junggar basin, are studied, based on the data of petrography and FMI. Oil- and gas-bearing volcanic rocks in this area belong to the Bashan group (C₂b). The rocks are mainly lava (including andesites and basalts) and pyroclastic ones. The average porosity and permeability are 7.42% and 0.82×10^-3 μm² in lavas, and are 9.84% and 0.33×10^-3 μm² in volcanic breccias respectively. The reservoir-spaces of the rocks are mainly composed of secondary pores and fissures. The reservoir property in the Wucaiwan area is slightly poorer than that of the basement beneath the Shixi oilfield, the center part of the basin, where there is the best reservoir property in volcanic rocks. The environment during the volcanic eruption, types and facies of the rocks, and subsequent modification play important roles on the reservoir properties of the basement rocks.