The influence of the pre-existing topography on the depositionary systems, the development of the Lower Jurassic reservoirs and hydrocarbon accumulation in Central Western Ordos Basin

Pre-existing topography not only influenced the development of the Jurassic depositional systems and the reservoirs, but also controlled the hydrocarbon accumulation in Central Western Ordos Basin. Detailed re-construction of the paleotopography and mapping of the depositional systems and reservoir fairways reveal that the two are closely related. In order to better understand their relationships, detailed environmental facies, channel fairways, source directions of the sediment supplies, burial depth/history, and paleo-bathymetries have been rebuilt and mapped out using well, seismic and log data. The mapping results show that the pre-existing topography and paleogeography prior to the deposition of the Jurassic rocks have a clear influence on (1) a monadnock rising from a third-order valley; (2) sediment microfacies that result in primary distribution of the oil reservoir on the marginal bank region of a watercourse; and (3) factors such as current structural culmination on the top surface. These findings should provide useful guidance for the exploration and development of hydrocarbons from the Lower Jurassic formation in the region.