The US shale revolution in the past decade has doubled the country's crude production, and tight clay-rich formations account for 60% of the US crude production. Nevertheless, our knowledge of petroleum system controls on the reservoir performance of these tight shale systems remains poor. We report on a methodology to utilize production data to compare and rank the US shale oil plays in conjunction with geologic descriptions of the plays.
For this study, we have used 36,642 horizontal oil wells from 12 tight shale formations in the Rockies and Midwest basins with vertical depths ranging from 5,000-15,000 feet and with at least 24 months of production to rank these plays based on their performance. These formations include: Wolfcamp (Delaware and Midland/Permian), Bone Spring (Delaware/Permian), Eagle Ford (Gulf Coast West and Central/ Cretaceous), Niobrara (Denver and Powder River/Cretaceous), Bakken (Williston/Devonian), Austin Chalk (Gulf Coast West/Cretaceous), Woodford (Anadarko/Devonian), Spraberry (Midland/Permian), and Barnett (Fort Worth/Mississippian). Their production data were normalized for cumulative oil (STB/ft/month), and the results were then analyzed in light of geologic and geochemical data from the formations.
Integrated production and geologic-geochemical data on the tight formations offer valuable insights into the control of petroleum system elements on production patterns. These comparative patterns were used for ranking the shale plays for various parameters. In terms of cumulative oil production (STB/ft/month), Wolfcamp (Delaware) ranks top (0.93 STB/ft/month) while Barnett (Fort Worth) has the lowest crude production (0.07 STB/ft/month). In terms of GOR changes during production, Wolfcamp (Delaware) shows the lowest change (1.38 times), while Barnet (Fort Worth) has the highest change (13.37 times). These may be related to the oil-prone nature of Wolfcamp and the gas-prone characteristics of Barnet. Overall, deeper shale plays yield more oil (per foot per month) than the shallower plays. Some plays exhibit intra-formational migration of hydrocarbons.
The results and the methodology of this study provide a multi-disciplinary geo-engineering to characterize shale oil plays in various basins. Variability in the performance of shale oil plays given by production data can be reverse engineered to petroleum systems.