There’s large differences in oil bearing characteristics of Chang-8 reservoirs in different regions of southwestern Ordos Basin. The exploration potential is great. Studies on major control factors of oil accumulation and enrichment mode of Huanxi-Pengyang area have been carried out on the basis of fundamental oil formation condition analysis in southwestern margin of Ordos Basin to provide a theoretical support for the determination of oil exploratory potential and prediction of favorable zones. By the methods of formation test

logging and core analysis

organic geochemistry and thermodynamic simulations on the fluid inclusions

the migration and accumulation characteristics and major controlling factors of oil enrichment in Huanxi-Pengyang area is systematically analyzed based on the difference in sedimentary reservoir and reservoir characteristics of Chang-8 low-permeability tight reservoir. The results show that there is big difference exists in the features and formation conditions between north and south reservoir. As the source rock thickness is greater and hydrocarbon generation and expulsion conditions is better

and the overall physical property is good

it’s more favorable for oil charge and accumulation in Pengyang than that in Huanxi area. But structural adjustment influence secondary oil-gas migration or damage in southwestern margin contrast to basin center

resulting in more complex oil distribution. Thus

the oil-gas accumulation model of the Pengyang and Huanxi is further established while the former belongs to vertical hydrocarbon migration pattern and the latter lateral pattern. The research results provide significant guidance for next step of petroleum exploratory orientation evaluation and development for Chang-8 reservoirs in marginal areas of Ordos Basin.