Tectono-sedimentary differentiation of lower Palaeozoic carbonate rock in Ordos basin, NW China and its implications for hydrocarbon-play generation

The Lower Paleozoic carbonate rock in Ordos Basin is a major target of oil and gas exploration. At present, the potential reservoirs and traps of this rock in different tectonic units of Ordos Basin remain not well understood, which hinders prediction of preferable exploration targets. To solve this problem, based on the analysis of sedimentary and tectonic features, this paper reveals the sedimentary evolution and structural transformation of early Paleozoic carbonate rocks in the Ordos Basin. The results show that controlled by the Central ancient uplift and the epeiric sea environment, the southern margin of the basin is characterized by the development of rimmed reef-shoal facies association, the western margin is characterized by the development of bedded reef-shoal facies association, and the intracratonic basin is characterized by tidal flat of limited platform.The carbonate formations in the three different facies belts have favorable conditions for hydrocarbon-play generation, but their tectonic transformations are significantly different, which can be divided into a compressive tectonic unit in the west margin, extensional tectonic unit in the south margin and stable tectonic unit in the inner craton. Favorable traps in the broken fold belt of the western intracontinental foreland basin include overthrust faulting traps and secondary anticlinal traps in syncline. Traps related to buried hills developed in the south extensional tectonic unit affected by the Weibei graben. The Yishan slope of inner craton is a large monoclinal structure with weak reformation and lots of lithologic traps, and the macroscopic distribution of those lithologic traps are mainly controlled by rotary tidal current of the epeiric sea.