Relationship between resource-rich regions and sweet spots for tight oils: A case study of the Williston Basin in the USA

Tight oils from the Bakken Formation in the Williston Basin in the USA were studied to find out the relationship between the resource-rich regions and sweet spots for tight oils.Some maps with multiple parameters were drawn based on drilling and logging data from 948 wells.Genetic method, volume method and decline curves were used to evaluate the abundance of tight oils in the study area.The distribution of sweet spots was studied by comparing differences in abundance combined with geological data.The results show that high-quality hydrocarbon source rocks of the Bakken Formation were a prerequisite for the generation of tight oils.The resource-rich regions predicted by the genetic and volume methods clearly varied with the occurrences of tight oils, and could not be used individually in the prediction of sweet spots.The transitional region adjacent to the resource-rich regions had some favorable conditions for tight gas development, such as closeness to the hydrocarbon generation center, formation overpressure, high gas-oil ratio and tectonic setting.These transitional regions often developed in the slope zone of the basin or on positive structures such as anticlines.