Evaluation of undiscovered oil and gas resources in Oriente basin, Ecuador

Abstract The Oriente basin is one of the important petrol-bearing basins in South America, and more than 250 oil and gas fields have been discovered within the basin. Since 1965, 7.6 billion barrels of petroleum have been produced from the basin, remaining 2.6 billion barrels of recoverable reserves. However, most of these fields are mainly distributed in the northern part of the basin, controlled by faults related to oil and gas charging, and have the main Cretaceous reservoirs. It is necessary to evaluate the resources to be discovered for unexplored areas and potential reservoirs. In the Late Cretaceous, the Pacific plate subducted towards the South American Plate, resulting in the formation of a series of foreland basins, including the Oriente basin. The thickness of the sedimentary strata in the basin is between 4000 and 9200 meters, with local areas exceeding 10,000 meters. The hydrocarbon sourced mainly from the Cretaceous Chonta Group in the north and the Triassic-Jurassic Pucara Group marine shales. Both Hollin Formation and Napo Formation sandstones are proved reservoirs with faulted anticlinal traps. According to the available drilling and seismic data, the favorable traps are proposed and the parameters of undiscovered reservoirs are deduced reasonably. The amount of undiscovered resources in each trap is calculated, and by adding these data together, the amount of undiscovered resources in the basin is obtained. According to the analysis, there are at least 75 prospective exploration traps for known and potential Cretaceous reservoirs, distributed in the northern and western regions of forethrust tectonic belt. Finally, the Oriente basin is presumed to have a good exploration prospect, with 1.26 Bboe of undiscovered recoverable resources.