Water Production from Unconventional Reservoirs: Example from NE Elm Coulee Field - Bakken Formation

Production wells within the northeast (NE) Elm Coulee experience significantly higher water cuts than wells within Elm Coulee Proper. The increased water production has a negative economic impact on Bakken operators seeking to maximize profitability within the area. A reservoir engineering-based research project has been conducted to determine the source of the increased water production within the NE Elm Coulee, and to identify recommendations for operators to mitigate the water production related expenses in the area. One option for the increased water production is from the water saturation within the matrix of the Middle Bakken Shale, and another possibility is from the Three Forks formation by vertical migration through natural fracture networks. Previous work has identified the presence of natural fracture systems within the Bakken that may be creating flow networks between stratigraphic layers. Numerous flow simulation models of the NE Elm Coulee were constructed to determine the source of the produced water. The reservoir models consist of three hydraulically fractured horizontal wells within the Middle Bakken Shale, and it incorporates the naturally fractured state of the Bakken through a discrete fracture network (DFN). Various reservoir parameters were altered within the envelope of uncertainty to obtain a history match for the reservoir model to both scenarios, and the resulting parameters from the Middle Bakken saturation case are more realistic and produce better history matching results than the Three Forks water migration case. The Three Forks fracture model produces an unrealistically high volume of water, and the breakthrough pattern is not consistent with field measurements. Thus, the source of the increased water production appears to come from matrix water saturation within the Middle Bakken Shale. Many relevant aspects of unconventional reservoir simulation are incorporated into the project; therefore, the methodology used in the research can help assist reservoir engineers that are modeling unconventional petroleum reservoir with stacked stratigraphic intervals. Modeling natural fractures and complex completion fracture networks using a DFN, pressure dependent permeability, and history matching in unconventional reservoirs are important topics that are discussed in the paper. Operators within the Bakken can use this information to better understand the geologic implications of producing in the area.