An analysis of hydrocarbon pooling conditions of the Quaternary lithologic gas reservoirs in Qaidam Basin

The Quaternary in Sanhu area of the Qaidam Basin consists of unconsolidated sandstones experienced with weak diagenesis.So exploration of structural traps in the study area has not been successful in recent years.In contrast,lithologic gas reservoirs will be a new source of gas reserve growth.Based on an analysis of sequence stratigraphy,we studied the unique depositional conditions and hydrocarbon accumulation conditions of lithologic gas reservoirs in the Quaternary.The following results were obtained.①The slope break zones in the periphery of the basin are favorable for the development of lithologic traps;②The slope zones have well-developed lithologic gas reservoirs;③The weak diagenesis of the deep rocks is favorable for the formation of lithologic traps.Based on a comprehensive analysis of the structural settings,distribution characteristics of the depositional systems and the conditions of lithologic trap development of the Quaternary in the Sanhu area,we identified several types of lithologic traps in the Qigequan Formation,including lithologic pinch-out zones,low uplift or nose-like uplift zones within the basin,slope zones and lenses.Specific technical proposals for exploration of lithologic gas reservoirs in Sanhu area were presented,including the enhancement of low-frequency-and amplitude-preservation seismic processing and comprehensive interpretation,the establishment of high-resolution outcrop sequences,and the detailed correlation of log data.