Abstract:

Petroleum exploration of Xujiahe Formation in the western Sichuan depression has gradually integrated conventional and unconventional petroleum systems. Petroleum reservoirs accumulated within the source beds have been new fields of petroleum exploration. In this study, the principle of the petroleum geology, sedimentary petrology and analysis method were used to reveal the reservoir development characteristics and controlling factors of the Xujiahe Formation (5^th member) in the depression. The porosity of the reservoir in the Xujiahe Formation (5^th member) is of 1.371% to 8.000% (< 10%), and the permeability is 0.005×10^-3 to 0.701×10^-3μm² (< 1×10^-3μm²), which belongs to the tight reservoir category. Based on the sandstone grain size, the reservoir physical properties and gas-bearing properties, three types of high-quality reservoirs have been identified, i.e.coarse sand, medium sand, and fine sand. In the study area, the coarse sand is less developed, while thick medium sand and fine sand are better developed in the delta front of the upper, middle and lower subsegments. The reservoir space developed micro-pores and a few micro-cracks. Median granularity likely controlled the type of high-quality tight sandstone reservoirs, sedimentary-facies belts; the stratigraphic controlled the location of high-quality reservoirs; and the diagenesis controlled the formation of high-quality reservoirs.

Key words: in-source, tight sandstone, high quality reservoir, Xujiahe Formation (5^th member), western Sichuan depression