Upper and Lower Bakken Shale Production Contribution to the Middle Bakken Reservoir
Abstract There is an uncertainty over the production contribution from the Upper and Lower (U&L) Bakken Shale to the Middle Bakken reservoir. For the Bakken system, reservoir studies involving the fluid flow and recovery mechanism cannot be fully understood without resolving this uncertainty. Performance-anomalies in the GOR trends of the production-history of the Middle Bakken wells in the Reunion Bay, Sanish, Parshall and the Elkhorn-Ranch fields indicate the possibility of the anticipated contribution.
Quantifying the U&L Shale contribution requires knowledge of the mechanism of fluid storage and flow in the liquid rich shale systems. For the U&L Shale, adsorption is considered as the significant mode of fluid storage, and the process of diffusion is considered crucial for the matrix-to-fracture fluid transfer. The governing mathematical equations for desorption and diffusion was adopted from the shale gas systems. These equations are utilized in CMG™’s compositional simulator GEM™ to propose a reservoir simulation-based quantification scheme for the U&L Shale contribution.
Through the sensitivity analyses, the effect of variation in the parameters of the U&L Shale, the Middle Bakken layer and the hydraulic fracture is investigated. Utilizing the ranges of these parameters, the U&L Shale layers are found to contribute from 12% to 52% of the cumulative production from a Middle Bakken well, whereas, the mean contribution is 40%. Relative sensitivity study suggested that the U&L Shale production contribution is the most sensitive to the U&L Shale matrix parameters, such as total organic carbon (TOC, wt.%) and molecular diffusion coefficients. The TOC controls the desorption-parameters; therefore, the findings suggest that the phenomena of desorption and diffusion are expected to play a crucial role in the anticipated production-contribution.
