Quantitative analysis of pore evolution and its application to basin simulation: A case from Chang 8 reservoir in Heshui Area, Ordos Basin, NW China

Taking the Chang 8 Member of Upper Triassic Yanchang Formation in Heshui Area of Ordos Basin as the research object, the petrological, porosity, permeability characteristics, diagenesis and diagenetic sequence were researched; through core observation and thin section identification, combined with physical properties analysis and other methods. Furthermore, the quantitative analysis of reservoir pore evolution was carried out. Finally, the quantitative pore evolution results were used to simulate the recovery of hydrocarbon migration and accumulation. The result shows that the lithology of reservoir in the study area was siltstone with mudstone or argillaceous siltstone, which has typical characteristics of low porosity and low permeability. Based on the study of diagenetic characteristics and diagenetic history, and taking the present porosity as the constraint condition, the pore evolution process of diagenetic period was quantitatively recovered, the quantitative simulation results of pore evolution in diagenetic period were consistent with the actual geological situation. Using the quantified pore evolution results, PetroMod software was used to simulate the recovery of hydrocarbon migration. The results show that the oil charging in the basin began at the end of Late jurassic (J₃), the peak of hydrocarbon generation and expulsion and accumulation appeared at the end of Early cretaceous (K₁), to the late cretaceous which still had high aggregation, and the accumulation was significantly reduced to the present stage. Meanwhile, the model is superimposed with the actual drilling results to test the simulation results. The results proved reasonable, and it can be applied to other oilfields of the same type, providing some reference for further exploration and development.