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Exploration Frontiers in the Bakken Formation, Montana and North Dakota

LeFever, Julie A.
North Dakota Geological Survey, Grand Forks, ND

     Early exploration provides the framework for the current Bakken play. Numerous studies assessed optimum shale thickness, TOC, and wireline log resistivity relationship to thermal maturation. Maps were constructed showing the aerial distribution of the onset of hydrocarbon generation and areas of intense hydrocarbon generation in the Upper and Lower Bakken shales. Results show the shales range from 28 to 55 ft and are predominantly illite (up to 42%), organic material, silt-and clay-sized quartz, calcite, feldspar, and pyrite. No discernable trends in the major and heavy element geochemistry are observed. TOCs of up to 30% suggests large in place reserves remain ranging from 200 to 415 billion barrels. Bakken exploration has relied heavily on available technology. Formation damage was minimized using slightly under-balanced inverted mud systems. Vertical wells were fracture stimulated, whereas horizontal wells relied on naturally occurring fractures. Horizontal wells in the Upper Bakken Shale wells met with moderate success as the combination of low oil price, improper spacing, and poor EUR's ended the first phase of horizontal Bakken exploration.
     Current horizontal wells target the middle member, consisting of a sequence of low porosity, low permeability dolomite, silty dolomite, sandstone, and shale. Wells in the silty dolomite facies in Elm Coulee Field, Montana averaged 500,000 BOPW. The average pay thickness is 10 ft. To date, North Dakota well results are highly variable as drilling and completion practices adjust to account for lithologic variability in the Middle Bakken Member.


AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah