Evaluating hydrocarbon-in-place and recovery factor in a hybrid petroleum system: Case of Bakken and three forks in North Dakota

This paper presents an integrated workflow for hydrocarbon-in-place and recovery factor estimation in Bakken. Evaluating factors that control generation and storage of hydrocarbon such as total organic carbon (TOC), maturity of shale, thickness, porosity and permeability is a challenge in any shale play study. In addition, hybrid nature of the Bakken petroleum system where source and reservoir rock present within short depth interval adds complexity to the production interpretation and outlook of the play. One of the complexities is the contribution from the shaley Upper and Lower Bakken to the production of horizontal wells completed in the Middle Bakken. In addition, presence of local, structural and stratigraphic traps complicates mapping water saturation distribution in Middle Bakken that is mostly affected by hydrocarbon generation in the Upper and Lower Bakken. We address geological and petrophysical uncertainties and calculate and map hydrocarbon pore volume. For fluid characterization, we use three models in order to accurately cover a range of American Petroleum Institute (API) gravity and gas/oil ratio (GOR). We evaluate the contribution of Upper and Lower Bakken in production by constructing simulation models and used that knowledge to estimate recovery factor of the horizontal wells. Production depletes the Middle Bakken, creating a pressure difference between the Middle Bakken and the Upper/Lower Bakken, which in turn depletes the Upper/Lower Bakken. Vertical permeability controls production from the Upper and Lower Bakken, and higher vertical permeability increases the contribution of the two shale members. An understanding of maturity and trap mechanism can help to explain the water saturation distribution and understanding these factors is crucial to any future development of the play.