Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Petroleum Potential of the Upper Three Forks Formation, Williston Basin, USA
(1) Colorado School of Mines, Golden, CO.
The upper Three Forks is evolving into a significant resource play in the Williston Basin. Although Three Forks production was established in Antelope Field in 1953, the play has re-emerged because of the horizontal drilling and multi-stage fracturing technologies. The upper Three Forks can be subdivided into three main facies: a) massive to chaotic bedded dolostone; b) interbedded dolostone with green mudstones; c) bioturbated dolostone to sandstone. The bioturbated sandstone and dolostone is referred to as the Sanish. The units represent an overall transgressive sequence ranging from upper intertidal/supratidal to subtidal.
The upper Three Forks has poor reservoir quality with low porosities (generally less than 8%) and low permeabilities (less than 0.1 md). The reservoirs require fracture stimulation to produce economically. Sweet spot areas are related to favorable facies development, natural fractures, and mature Bakken source rocks. The main source rock for the Three Forks is the lower Bakken shale. Where the lower and middle Bakken members thin in the southern part of the Williston basin, the primary source rock becomes the upper Bakken shale. The Three Forks is overpressured and overpressuring is related to hydrocarbon generation.
The upper Three Forks does not appear to be in communication with the overlying middle Bakken reservoirs where the lower Bakken shales are sufficiently thick to form a barrier between the producing units. The Three Forks resource potential is estimated to be 2 billion barrels of recoverable oil.