Reservoir Characterization of the Bakken Formation, Elm Coulee Field, Williston Basin, Montana

Aris Pramudito and Stephen Sonnenberg
Department of Geology, Colorado School of Mines, Golden, CO

Elm Coulee Field is one of the 20 largest oil fields in the United States and the highest producing onshore field found in the lower 48 states in the past 56 years. US Geological Survey estimates the resource for the Bakken formation to be 413 billion barrels (mean estimate). The Elm Coulee field, discovered in 2000, produced 15 mm bbl of oil through 2005 and is yielding nearly 50,000 BOPD. This production is about half Montana’s crude oil production.

The Bakken Formation consists of three members: upper, middle, and lower. The field produces from the middle dolomite member and is sourced from the upper and lower organic rich shale members. The three members onlap and pinch out towards the south-southwest in the field area. The thickness of middle Bakken ranges from 8 to 20 feet, with average porosity of 8 - 10% and average permeability of 0.05 md. The vertical depth of the middle Bakken ranges from 8,500’ - 10,500’.

Horizontal drilling and fracturing stimulation of the horizontal legs are the main technologies in the Elm Coulee Field development. Currently there are approximately 350 horizontal development wells that have been drilled in the field.

An integrated reservoir characterization study by performing petrophysical analyses, petrography, and subsurface geological mapping, is being conducted in the Elm Coulee Field. Creating correlations between petrophysical properties and lithofacies is an essential product for future Elm Coulee development. The main deliverables will be a paleoenvironmental setting interpretation, reservoir connectivity, and reservoir quality determination, which lead to the creation of geologic models that will be applicable for the field in specific, Williston Basin in general, and also as an analog for other tight dolomite and shale reservoirs.

AAPG Search and Discovery Article #90092©2009 AAPG Rocky Mountain Section, July 9-11, 2008, Denver, Colorado