Provenance types and controlling factors of the 4th member of the Xujiahe Formation in the Yuanba-Tongnanba area, northeastern Sichuan

The industrial gas flows have been explored recently in the 4th member of the Xujiahe Formation in the Yuanba-Tongnanba area, northeastern Sichuan. Judged from drill cores and thin section examination, the sediments in the 4th member of the Xujiahe Formation may emanate from several structural belts in the Longmen, Micang and Daba Mountain areas. The reservoir rocks contain three types:calcium-rich sandstones and conglomerates, quartz-rich sandstones and conglomerates and feldspar-rich sandstones. The controlling factors include provenance types, diagenesis and fissure development. The types and spatial distribution of the reservoir rocks are constrained by the provenance systems. The dissolution facilitates the improvement of the porosity and permeability of the reservoir rocks. The fissures may contribute to the improvement of the permeability of the dense sandstones. The fissure development in feldspar-rich sandstones in eastern Yuanba and calcium-rich sandstones and conglomerates in western Yuanba is believed to be most favourable exploration conditions in the 4th member of the Xujiahe Formation.