--> Effects of Sedimentary Heterogeneity on Hydrocarbon Accumulations in the Permian Ordos Basin, China: Insight From Integrated 3-D Petroleum System and Forward Stratigraphic Modelling

AAPG Annual Convention and Exhibition

Datapages, Inc.Print this page

Effects of Sedimentary Heterogeneity on Hydrocarbon Accumulations in the Permian Ordos Basin, China: Insight From Integrated 3-D Petroleum System and Forward Stratigraphic Modelling

Abstract

The sedimentary heterogeneities of the Permian Shanxi Fm in the Ordos Basin, China were modelled using SEDSIM, a forward stratigraphic modelling program. The simulation results were then used to construct a 3D petroleum system model using PetroMod. The SEDSIM simulation result shows that considerable sedimentary heterogeneities are present in the Shanxi Fm, resulting from the interplay of initial topography, tectonic subsidence, base level change and sediment inputs. A variety of lithofacies were developed within the Shanxi Formation at meter scales, with mudstones mainly developed in the central area, while sandstone developed in the southern and northern areas. A base-case conventional 3D basin model was constructed to quantify the Permian petroleum system in the Ordos Basin. The geological and thermal models were calibrated using measured and field data. It shows that the source rocks of the Upper Paleozoic began to reach maturity (Ro > 0.5%) and high maturity (Ro > 1.2%) in the early Jurassic and early Cretaceous, respectively, in the central and southern areas. During the Early Cretaceous, a tectonically induced geothermal event occurred in the southern Ordos Basin. As a result, source rocks reached over maturity (Ro > 2.0%) quite rapidly in the early Late Cretaceous in the central and southern areas. Hydrocarbons began to charge into the Shanxi Formation in the Middle Jurassic and continued till the early Late Cretaceous. In the base-case model, a large amount of hydrocarbons had been expelled and migrated into the Shanxi Fm, but only a minor amount was accumulated to form reservoirs. In the model, the Shanxi Fm sandstone was set to be homogeneous and there was also lack of seal rocks at the top of the Shanxi Formation, thus hydrocarbons could not be trapped effectively with only minor accumulations in some local structural highs. In contrast, the coupled SEDSIM-PetroMod model took into account of the internal lithological heterogeneities within the Shanxi Formation, forming a complex contiguous sandstone-mudstone stacking patterns. Hydrocarbons were accumulated in multiple intervals of lithological traps within the Shanxi Fm. The calibration results indicate that the coupled SEDSIM-PetroMod model is much more reasonable compared with the base-case “layer-cake” model, showing that sedimentary heterogeneities can exert a significant influence on hydrocarbon accumulation especially for lithological reservoirs.