Reservoir Characterization of the Niobrara Formation, Southern Powder River Basin, Wyoming

Abstract The Niobrara Formation is emerging as an attractive target for horizontal drilling in the southern Powder River Basin. Although production has previously been established in the Niobrara Formation in this area, advancements in drilling and completion technology have made it a more economically attractive target throughout a greater part of the southern Powder River Basin. In the southern Powder River Basin the Niobrara Formation is made up of three argillaceous chalk intervals separated by more siliciclastic-rich marls and mudstones. The middle chalk bench, informally designated the B bench, demonstrates the most promising reservoir potential based on encouraging petrophysical characteristics, regional extent, and previous production. The basal chalk, informally named the C bench, also appears to be prospective, but in a smaller area confined to a north-south trending erosional scour that has formed an up-dip stratigraphic trap in the eastern part of the study area. Analysis of the source rock properties of the Niobrara Formation from cuttings data demonstrate that this formation in the southern Powder River Basin is sufficiently organic-rich (TOC 0.90 to 3.24 wt. %) and thermally mature enough to be considered an effective source rock (Tmax 426 to 456°C). Through analysis of distinct facies, it is evident that the marls are on average the most organic-rich facies with TOC values as high as 3.24 wt. %. Through an integrated research approach utilizing a number of data sources, this study demonstrates that the Niobrara Formation is a very prospective hydrocarbon resource in the southern Powder River Basin. While previous petroleum system studies of the Niobrara Formation have primarily been focused in adjacent basins, this study provides an in-depth analysis of the petroleum system characteristics of the Niobrara Formation in the Powder River Basin where little petroleum system-related research has been published.