Sedimentary characteristics of the Lower Cretaceous strata and prediction of the favourable exploration areas in the Qingxi depression,Jiuxi Basin,Gansu

The exploration of several medium-to high-capacity industrial oil wells in the Lower Cretaceous strata indicates the favourable geological conditions for hydrocarbon accumulation in the Qingxi depression,Jiuxi Basin,Gansu.Controlled by the source areas in the western,northwestern,southern and eastern parts,the fan delta,lake and sublacustrine fan depositional systems are developed in the Lower Cretaceous strata in the Qingxi depression.A second-order fan model may be constructed displaying the distribution patterns of fan delta→lake→sublacustrine fan from the margin to the centre of the depression.The prediction and delineation of the favourable areas have been made on the basis of depositional system analysis,well logs,drilling cores and seismic data for further exploration,including four most favourable exploration areas,and one favourable exploration area.