Characteristics of hydrocarbon enrichment in lithologic reservoirs in the southwestern Qaidam basin

Lithologic reservoir,a special type of subtle reservoir,has become in recent years and will remain in the future one of the important exploration domains.The southwestern Qaidam basin has relatively high exploration maturity and large resource potentials,thus is a favorable area for exploration of lithologic reservoirs.However,the failure of some exploratory wells in recent years indicates that the pattern of hydrocarbon accumulation in lithologic reservoirs has become the key factor restricting the exploration.The source rocks,the major hydrocarbon kitchens,palaeogeomorphology and the sedimentary system under its control,and palaeo-structures in critical hydrocarbon pooling stages are reviewed,a comparative study is performed on the palaeo-structures and modern structures,and the typical discovery wells are analyzed in detail.Lithologic reservoirs in the southwestern Qaidam basin shows that,as a whole,the feature of near-sag and circum-sag,and are mainly distributed in delta front and shoal bar sandbodies under the control of distal sedimentary system,long-term stable slope zones,and transport zones where the structural highs of palaeo-structures and modern structures were transported and the modern structures contain oil.Favorable areas for exploration of lithologic reservoirs are recognized and hydrocarbon-pooling models are established for some key exploration areas.