ABSTRACT: Criteria for Horizontal and Vertical Prospect Generation in the Bakken Formation, Williston Basin, Montana and North Dakota

William B. Hansen, George I. W. Long

A study of the Bakken Formation was begun in 1985 throughout the North Dakota/Montana portion of the Williston basin. A review of producing Bakken wells and failures along the northwest-southeast depositional pinchout "fairway" reveals three criteria that can be used to locate fractures and generate both vertical and horizontal prospects.

One of these criteria is the drillstem test (DST). The best vertical producers display a rapid rise in shut-in pressure. The second criterion is a wide separation between the Dual Laterolog (DLL)-Micro Spherically Focused log (MSFL) resistivity curves. This is felt to be in response to formation damage when drilling muds inject into open fracture systems. Numerous wells were discovered with these two criteria which did not attempt completion in the Bakken. In the absence of DSTs and logs, production information can be used to refine the location of fractures.

In areas with dense well control, such as Elkhorn Ranch field, these criteria can be used to define regional fracture trends and extrapolated into undrilled areas. A vertical well drilled along a regional fracture trend, when correctly stimulated, will yield similar results to some of the best horizontal producers. The best well in the "fairway" to date is from a vertical completion that has produced 300,000+ barrels of oil (BO) since 1985, and is currently flowing 200+ BOPD.

Well control in Richland County, Montana, is not sufficient to define fracture trends. However, DSTs and DLL-MSFL logs in the vicinity of Spring Lake field indicate similar potential exists for substantial Bakken production in the Montana portion of the "fairway."

AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990