Differential Oil Gravity Enrichment Mechanism of the J Reservoir in Oriente Basin and Favorable Area Prediction

Based on the analysis of reservoir characteristics and crude oil geochemistry, the formation mechanism of differential oil gravity enrichment in the J oilfield in the slope zone of the Oriente basin is revealed, and it is pointed out that the structural down-dip area of the structural-lithologic reservoir in the slope zone is a favorable area for medium oil, which providing a solution for the exploration and development of structural-lithologic traps in the slope zone of the oriente basin. The results show that the J reservoir is a structural-lithological reservoir with a southwest dipping monoclinic structure in general, and a NW-SE trending mudstone belt developed in northeastern structural high to provide structural up dip sealing condition for the reservoir; The oil-source correlation analysis confirms that the crude oil in the reservoir is related to the marls of the Cretaceous Napo Formation; The dating of fluid inclusions reveals that the Cretaceous reservoir in the slope zone was formed in Miocene and experienced multiple stages of hydrocarbon charging. The results of geochemical analysis verify that the crude oil in the J reservoir is a mixture of the degraded oil filled at the early stage and the conventional oil charged at the late stage. Differential mixture of hydrocarbon accumulation is the main reason for differential oil gravity (API) distribution in the J reservoir. Comprehensive analysis predicts that the low part of the structural-lithologic trap in the slope zone is a favorable area for the enrichment of medium quality oil.