Geological Effects and Petrophysical Flow Unit Model for the Middle Bakken Member, South-East Saskatchewan

Abstract

The Devonian-Mississippian Bakken formation is a relatively thin heterogeneous unit that stretches across the subsurface of the Williston Basin in North Dakota, Montana, Saskatchewan, and Manitoba. In terms of oil and gas exploration, the unit is undoubtedly one of the most important and ranks high on the scale as compared to other oil producing fields. It represents a single petroleum system that consists of a heterogeneous Middle Siltstone and Sandstone Member layered between two black organic rich shale members. The Sandstone Member represents the major potential reservoir while the black carbonaceous shale acts as the source and the cap rock of the Bakken petroleum system. These shale rocks have also generated an enormous volume of oil probably located some distance above and below the unit. Although these shales are undoubtedly productive in hydrocarbon generation, the problem remains that the Bakken formation is a tight system with very low reservoir qualities (permeability and porosity), which makes it difficult to allow reservoir fluid flow without introduction of a modern recovery technique to the natural reservoir drive energy. The relatively low permeability of these petroleum systems indicates that they might give better recovery if drilled using advanced technology combined with accurate reservoir evaluation measures. Oil production in the Bakken petroleum system (US and Canada) has increased over the years, mainly from fractured reservoirs in thermally mature, overpressured areas in the US and Middle Member Siltstone and Sandstone of Viewfield, Hummingbird, Roncott, and Rocanville pools, Court area and minor Torquay-Rocanville Trend in Saskatchewan, Canada. A cross examination of the Bakken core samples, geophysical logs/production history from south-eastern Saskatchewan certifies the prolific nature and hydrocarbon potential of the Bakken sand/shale members but encourages further research and better explanation, such as the introduction of a geological/petrophysical flow unit in the Middle Member zone. In the US, 87 wells in 35 fields currently produce at a combined rate of 2930 BOPD and 144 BWPD. The focus of this study is to introduce and characterize the use of a geological and petrophysical flow unit model in the Middle Member Siltstone and Sandstone of the Bakken formation in south-eastern Saskatchewan. The Middle Bakken is endowed with poor primary reservoir quality and secondary intergranular porosity and permeability. Due to the low cost effectiveness and ambiguous nature of the reservoir, production has been limited to certain modern technologies and stimulation/completion practices, including the use of horizontal and multilateral wells, hydraulic/multi-stage fracturing, pre-frac acidization, water flooding, caustic flooding with water, CO2 flooding, WAG processes, and a combination of the above processes with special treatments such as breakdown treatment, use of swellable packers, and well spacing techniques necessary for hydraulic fracturing. This study intends to incorporate the effect of these production techniques in combination with the flow unit model designed for the Middle Bakken reservoir. The ultimate goal of the research is to better characterize the Bakken reservoir to help identify ideal approaches for improving production in tight formations.