Upper and Lower Bakken shale production contribution to the Middle Bakken reservoir

Abstract

There is an uncertainty over the Upper and Lower (U&L) Bakken Shale production contribution to the Middle Bakken reservoir. For the Bakken system, a reliable degree of accuracy in the reservoir studies involving the fluid flow and recovery mechanism cannot be achieved without resolving this uncertainty. Performance anomalies in the gas-oil ratio (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 primary 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 for shale gas systems. These equations are incorporated in Computer Modeling Group's (CMG[trademark]) compositional simulator GEM[trademark] 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 surveyed numerical value-ranges of these parameters, the U&L Shale layers are found to contribute in the range of 12 to 52% of the cumulative production from a Middle Bakken well. Whereas, utilizing the mean numerical values of the parameters, the contribution is quantified as 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.