MOORE, W. RICHARD, NeedleRock Exploration Co., Crawford, CO

ABSTRACT: Distribution Of Hydrocarbons In The Williston Basin

The distribution of trapped hydrocarbons in the Williston Basin is aerially skewed. Two examples include Mississippian and Ordovician trends. Almost four billion barrels of recoverable oil exist in Mississippian reservoirs in the Canadian portion of the basin, but as producing trends enter North Dakota, the number of fields decreases dramatically. Another example includes Ordovician Red Riverfields on the west flank of the basin. Numerous petroleum traps in the Red River occur between the Canadian border and the Mondak field area along the Montana- North Dakota state line. However, farther south along the depositional trend of the Red River very few of these types of fields occur.

To study these changes in field density several data sets were collected and analyzed. These include Bouguer gravity, geothermal gradient, surface linear patterns, and fluid flow data. In the case of gravity, fluid flow, and linear data, published information was used. For analysis of geothermal gradient a new data set using both bottom hole log temperatures and DST temperatures was constructed.

Analysis of these data sets show a strong correlation between areas of hydrocarbon production, high geothermal gradient, high intensity of linear surface trends, and negative Bouguer gravity anomalies. It is believed that these areas reflect areas of high fracture intensity in the basement which controls trap formation and fluid flow patterns. Flow patterns in turn are responsible for areas of high geothermal gradients and migration of hydrocarbons.

AAPG Search and Discovery Article #90915©2000 AAPG Rocky Mountain Section, Albuquerque, New Mexico