Analysis on forming conditions of deep marine reservoirs and their concentration belts in superimposed basins in China

By taking the Tarim Basin, Sichuan Basin and Ordos Basin as examples, the conditions for deep marine reservoir formation were illustrated in three aspects listed below： late-stage superimposition style, burial history and structural deformation of the marine stratigraphic system. The burial history of marine source rocks can be divided into three types, i.e., type I, type II and type III, which are obviously different from the case with present hydrocarbon phases in terms of hydrocarbon generation and pe- troleum-reservoir formation. Based on evolution history, the structural belts in the marine stratigraphic sequence can also be divided into four types, i.e. earlier normal fault-later fault-fold type, earlier uplift-later fault-fold type, earlier uplift-later flattened slope type, and earlier depression-later thrust type. In this paper, a successive gas generation model was proposed, and it was particularly pointed out that coupling of geothermal field annealing evolution and tectonic subsidence and late gas generation from dispersed liquid hydrocarbon in highly matured to over-matured source rocks are key factors for formation of marine petroleum reservoirs. The geological conditions for formation of high-grade reservoirs in deep marine system, covering early hydrocarbon injection, deep denudation and buried dolo- mitization, were summarized. It was finally concluded that three major structural belts, i.e. paleo-uplift belt characterized by composite hydrocarbon accumulation, paleo-fault belt and high-energy sedimentary facies belt, were involved in marine hydrocarbon accumulation.

Analysis on forming conditions of deep marine reservoirs and their concentration belts in superimposed basins in China