Spatial and temporal associations of traps and sources: Insights into exploration in the southern Junggar foreland basin, northwestern China

Several roughly east-west-trending fold-and-thrust belts in the southern Junggar basin constitute the largest anticlinal trap zones in the entire Junggar basin, and four sets of Paleozoic-Cenozoic organic-rich shale and coal-bearing strata make up the majority of the source rocks. However, only small amount of oil and gas has been obtained from this area. Key factors controlling petroleum accumulation and potential plays are not clear. Based on seismic, drilling, and geochemical data from petroleum industry along with plenty of published research results, we investigated the geometry and timing of traps of the three fold and thrust belts, the principal phases of hydrocarbon generation in the sources, and the origins of discovered petroleum. We propose that the spatial and temporal associations of traps and sources should be the key factors of controlling petroleum accumulation in the southern Junggar Basin. Jurassic petroleum system may be the primary petroleum system in this area. Then we established a five-stage accumulation model to reveal the accumulating processes of the multiple petroleum systems in the southern Junggar basin. Our results suggest that the lower reservoir-seal assemblage (sand reservoirs sealed by Lower Cretaceous Tugulu Group mudstone) anticlinal traps in fold and thrust belt II along with lithostratigraphic traps in the foreslope have favorable geological conditions for forming large petroleum fields. This assumption was testified by a major breakthrough (GT-1 well) in southern Junggar basin, in January 6, 2019.