Hydrocarbon accumulation in the third member of the Qingshankou Formation in the Wukeshu region,western Songliao Basin

The braided delta front deposits are accentuated in the third member of the Qingshankou Formation in the Wukeshu region,western Songliao Basin.The subaqueous distributary channel and channel-mouth bar sandstones as the bulk of the sandstones in this region are characterized by wide-spread occurrence,tremendous thickness,higher ratios of total sandstone thickness/stratigraphic thickness,and higher porosity and permeability.The prolific hydrocarbons in the study area are mainly derived from the I-type kerogen-dominated source rocks in the Qingshankou Formation in the Da’an-Gulong depression.The dark mudstones with higher organic matter contents in the Nenjiang Formation overlain upon the third member of the Qingshankou Formation may serve as the valid regional cap rocks.The two major faults in the northwestern and southeastern parts,respectively have a destructive effect on the hydrocarbon accumulation.The results of research in this study show that the third member of the Qingshankou Formation is highly prospective for oil and gas resources.The low-amplitude anticline model is proposed here as a main model for the hydrocarbon accumulation in the slope environment.