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Dynamics of the Sub-Salt Structural Transitions in the Kuqa Foreland Basin and its Implication for Hydrocarbon Explorations


The Cenozoic Kuqa depression, south to the Chinese Tianshan Mountain, is a superimposed foreland basin. The imbricated wedges within the Mesozoic strata were developed between two sets of detachment layers, i.e., the upper Paleogene rock salt and the basal Triassic-Jurassic coal layers, respectively. The sub-salt sequences in the Kelasu structural belt has been targeted as main field for hydrocarbon explorations. Controlled by the differential distributions of detachments, the sub-salt structures change vastly along their strike. Previous studies considered these variations as the results of strike-slip faults between different segments. The anticline traps were mostly sabotaged near the strike-slip faults, which impeded the further hydrocarbon explorations. In this research, the latest 3-D seismic data, well drillings and magnetotelluric sections were integrated to investigate the deformation features and mechanics of the structural transition zones in the Kelasu structural belt. Results show that it could be subdivided into four sectors: Awate, Bozi, Dabei and Keshen sectors from east to west. More evidence also shows that the segmentation is in highly accordance with the detachment competence, and the Pliocene orogenesis caused uneven shortening between different sectors due to the differential decollement abilities. Furthermore, interpretations of high-resolution seismic data suggest that the transitions between different sectors are completed by the formation of oblique ramps, other than strike-slip faults. The development of oblique ramps have been proved as a common mechanism for foreland structural transitions with differential detachment competence. The development of oblique ramps generated brachyanticlines above them, and a series of trap swarms would form consequently. The dynamic mechanism of transition ramps and the prediction of relative sub-salt traps have been proved by recent well drillings, which tremendously promotes the hydrocarbon explorations in the Kuqa foreland basin.