ABSTRACT

The North Dakota part of the Williston Basin has produced more than 1.1 billion BOE, and has additional proven reserves of about 0.7 billion BOE. The purpose of this study is to estimate the undiscovered resources of the approximately 20,000 sq mi (52,000 sq km) in which oil is produced in western North Dakota.

Ultimate recoveries were estimated for 509 producing oil and gas pools; an additional 307 pools have already been abandoned, with known total production. These 816 pools formed the sample from which the characteristics of the total population of pools were estimated. Although 17 stratigraphic intervals produce hydrocarbons, only 3 intervals, the Madison, Devonian, and Ordovician, produce from enough fields to allow statistical characterization. Estimated resources remaining to be discovered for the three zones for class 8 or larger pools (>.128 MMBOE) are 157, 547, and 123 MMBOE for the Madison, Devonian, and Ordovician, respectively, for a total of 827 MMBOE.

A volumetric estimate of undiscovered resources was done for comparison with the statistical estimates. Known producing pools were categorized into 41 plays, and analog fields and areas were selected for each play. The undiscovered resource was estimated using the nonproductive volumes in each play, the recovery from the analog fields, and the historical wildcat success rate. This method yielded an estimate of the total remaining reserve of about 842 MMBOE.

The undiscovered resources of North Dakota are estimated to be more than 800 million BOE. Reservoirs most likely to contain these reserves are in Devonian and older strata, and most of the new pool discoveries will probably be in class 12 pools and smaller (< 4 MMBOE), but the discovery of larger pools cannot be ruled out.