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Collaborating Authors
Formation Evaluation & Management
The Bakken formation in the Williston Basin has been rapidly developing since 1980s; however, the recent advancements in horizontal well completion and stimulation technology play a key role in the success of today's Bakken production. Pressure buildup tests, mini-DSTs and mini-frac tests are valuable sources of information for determining key reservoir properties, such as permeability. The Bakken formation is comprised of an upper and a lower organic-rich black shale and a middle silty dolostone or dolomitic siltstone, and sandstone member. The Bakken is overlain by the Lodgepole formation which consists of a dense, dark gray to brownish gray limestone and a gray calcareous shale and underlain by the Three Forks formation which is composed of thinly interbedded greenish gray and reddish brown shale, light brown to yellow gray dolostone, gray to brown siltstone, quartzite sandstone and minor occurrences of anhydrite (Kume, 1963). Historically, horizontal wells in the Bakken were drilled in the Upper Bakken formation while the recent developments have changed the focus to the Middle Bakken and Three Forks formations. Historically, when a reservoir interval has been productive it has been attributed to natural fractures (Murray, 1968). Natural fractures include regional fractures, local stress fractures and local micro-fractures resulting from pore fluid over-pressuring. Although fractures are typically determined by examining cores, image logs, and structural curvature, pressure transient tests could provide additional insight in deciphering the presence of fractures and their flow contribution.
- North America > United States > North Dakota (1.00)
- North America > Canada (1.00)
- Well Drilling > Drilling Operations > Directional drilling (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Pressure transient analysis (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Drillstem/well testing (1.00)
Abstract The success of oil production in North Dakota Bakken should be credited to advanced completion and stimulation techniques. The abundance of data on well production, core analyses and flooding, geologic reservoir characterization, and pressure transient testing has enhanced reservoir evaluation. Understanding matrix and fracture contribution to daily oil production is the key to identifying reservoir drivers affecting the lifelong well productivity. In this paper, we will present an application of core flooding, mini-frac and pressure build-up tests, decline curve analysis and reservoir simulation history matching to achieve reliable long-term reservoir performance predictions. This approach could lead to developing an integrated workflow for determining the performance drivers in the greater Bakken. Information presented in this paper includes well performance data from several Bakken fields, displacement results on selected cores, mini-frac and pressure transient analyses, and history matching using decline curve analysis and numerical simulation. Specifically, the matrix permeability from core measurements is on the order of 10 md while the permeability from well testing is on the order of 10 md. The latter represents the combined contributions of micro-fractures and matrix permeability. Reservoir simulation also shows that a single-porosity system, using only the matrix permeability from the core analysis, is not sufficient for matching well production performance without having a secondary permeability and porosity (micro-fractures). The dual-porosity nature of the reservoir was confirmed by a long-term pressure build-up test.
- North America > United States > South Dakota (1.00)
- North America > United States > North Dakota (1.00)
- North America > United States > Montana (1.00)
- North America > Canada > Saskatchewan (0.98)
- Geology > Geological Subdiscipline (0.68)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (0.31)
- Reservoir Description and Dynamics > Reservoir Simulation (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Drillstem/well testing (1.00)