This paper describes the use of reservoir simulation to refine reservoir descriptions of the Bakken Shale for predictions of single well and multiple well performance. The descriptions were achieved by matching drawdown, buildup, and interference data from horizontal wells in the Buckhorn Field, McKenzie County, North Dakota, Figure 1.
Reservoir descriptions - matrix and fracture storativities, ϕCtH, and matrix and fracture permeability-thickness products, KmH and KfH -- were developed for both single well and multi-well interference data. More than one description could be found to match single well data; however, only one description was found which matched all the data. The best match of long term production interference data was obtained with a dual porosity description that included anisotropic, stress-sensitive permeability.
In the dual porosity model, both microgeneration fractures and enhanced or extension fractures were modeled with a lumped description. The permeability anisotropy for this lumped fracture system was approximately 4 to 1 with the maximum permeability direction in the northern Buckhorn area being east-to-west.
Bakken Shale porosity was determined to be 2 to 3 % with one-tenth of that volume or 0.2% being in microfractures. The ratio of fracture to matrix permeability was 100 to 1 with an effective permeability for the fracture system of 0.6 md at maximum net confining stress. It is believed that silt-stones and dolomites adjacent to the Bakken Shales make a significant contribution to the oil production through the extension fracture system.