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The New Bakken Play in Eastern Montana

Sonnenberg, Stephen A.*1
(1) Geology, Colorado School of Mines, Golden, CO.

New exploration drilling northeast of Elm Coulee Field and southeast of the Brockton-Froid Fault System (BFFS) in eastern Montana (eastern Roosevelt and northeast Richland counties) is targeting the middle Bakken. Active companies in the area include EOG, Brigham, Whiting, XTO, Continental, Oasis Petroleum and others. Operators report initial production ranging from 369 Boepd to 2962 Boepd. The area is characterized by higher water cuts than other Bakken producing areas. The source of the water may be the middle Bakken. The majority of wells are being drilled on 1280 spacing units and the orientation of the laterals is north-south.

The middle Bakken is 30 to 40 ft thick in the new area and both the upper and lower Bakken shales are present. The middle Bakken thickens to over 50 ft northwest of the BFFS and thins to a wedge-edge southwest of Elm Coulee Field.

Other potential horizons within the Bakken petroleum system in the new area include the upper and middle Three Forks. To date, these intervals have not been tested. Oil saturation throughout the Three Forks interval in a core at Poplar Dome suggests these intervals will be targets for exploration in the future.

High heat flow characterizes the new area and typical bottom-hole temperatures at the Bakken level are in excess of 225oF. Pressure gradients for the Bakken appear to be slightly over 0.5 psi/ft in the area. The upper and lower Bakken shales are thermally mature in the area based on source rock analysis (SRA data), bottom-hole temperatures, and high resistivity.

The new play area is an exciting development for the Bakken Petroleum System of the Williston Basin. Initial well results are encouraging. Shallower and deeper production also occurs in the new play area (i.e., Madison, Red River, Nisku, etc.).

Several operators consider the area northwest of the BFFS to be a more conventional play area. Both temperature and pressure gradients decrease northwest of the BFFS. In addition, the middle Bakken ‘D’ facies thickens in this area and generally has better reservoir properties than other areas of the basin. The continuity of the Bakken ‘D’ facies along with better reservoir properties may enable the unit to behave like a traditional carrier bed. Structures in this area may be needed for trapping. Source beds still appear to be mature based on resistivity, however. This area northwest of the BFFS has Three Forks potential.


AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California