The Powder River basin, in southeast Montana and northeast Wyoming, comprises several major oil fields in the US, including the Teapot Dome. Marine to Fluvial Upper Cretaceous faulted sandstone from the Shanon and Wall Creek formations serve as primary hydrocarbon-producing units. Geochemical studies within the basin reveal Lower Cretaceous Mowry shale as a primary source rock.
One-dimensional (1D) and three-dimensional (3D) basin modeling evaluation techniques of the Powder River basin petroleum system, in terms of burial, thermal, and basin evolution history, were attempted. The timing, maturity, and generation of hydrocarbon in the basin source rock were determined using these models. Basic inputs for the analyses were derived from integrated sequence stratigraphy-based geological studies performed using seismic and well log data. The 1D thermal and burial history model, based on a uniform 75 to 80 mW/m2 heat flux on selected wells, revealed that source rock maturation and transformation initiated approximately 100 million years ago. The calibrated 1D model confirmed that the Mowry formation reached the hydrocarbon-generation window with the level of maturity (LOM) index, indicating it was sufficiently mature to generate oil and gas.
The result of 3D petroleum system modeling provided a better understanding of source maturity, expulsion, and migration of the basin's hydrocarbon. The hydrocarbon expulsion and transformation ratio model indicated that hydrocarbon is still being generated from the Mowry formation. The model results were further integrated with the total organic carbon (TOC) model, which revealed a high TOC value (>6%) associated with regions having a hydrocarbon transformation ratio below 1.0. The current study illustrates that the Mowry formation, with highly matured organic material content, represents an active hydrocarbon-generation system in the basin. The Mowry formation is a good candidate for unconventional shale gas plays in the basin, with much of the organic matter having not yet transformed into hydrocarbon.
The Powder River basin is a geologic structure controlled basin located in southeast Montana and northeast Wyoming (Fig. 1). This basin is mostly known for its giant coal deposits. In addition to coal, the Powder River basin also contains major deposits of petroleum-saturated reservoir, including the giant Salt Creek oilfield. The present study area, Teapot Dome, comprises the southern part of the Salt Creek oilfield. Teapot Dome is one of the important fields, with almost 100 years of production history. In its peak time, Teapot Dome produced at the rate of 6,000 BOPD from approximately 1,300 wells drilled in the field (Anderson 2013). Marine to Fluvial Upper Cretaceous faulted sandstone from the Shanon and Wall Creek formations serve as primary hydrocarbon-producing units in Teapot Dome. To understand the geochemical characteristics of the source of oil and the origin of hydrocarbon in Teapot Dome, several studies have been conducted. These geochemical studies within the basin reveal Lower Cretaceous Mowry shale as a primary source rock responsible for the generation of hydrocarbon in the area (Hunt 1953; Burtner and Warner 1984).