Defining the Updip Eastern Limit of Commercial Bakken Oil Production, McLean and Dunn Counties, North Dakota
With the high density of horizontal wells drilled in the Devonian-Mississippian middle member of the Bakken Formation in Parshall Field, the eastern updip limit of commercial oil production from the Bakken in this area is reasonably well defined and understood. Similar patterns governing the commercial limit of Bakken production in Parshall should hold true south of Parshall Field where exploitation of the Bakken reservoir currently is expanding on the Fort Berthold Reservation.
By evaluating mud-gas shows, utilizing water saturation calculations from vertical and horizontal wells, and integrating oil- and water-production data, a transitional zone of non-commercial oil production is identified on the eastern updip edge of the Bakken oil accumulation on the Fort Berthold Reservation similar to that observed at Parshall Field. Progressive updip decrease in Bakken oil production across this non-commercial zone is accompanied by a progressive increase in percent water produced, reflecting a west-to-east transition zone with water saturation progressively increasing updip.
Mudlogs from several updip laterals drilled roughly normal to the east-flank of the Bakken transition zone record strong oil and gas shows downdip reflecting commercial Bakken oil, deteriorating shows structurally updip through a transition zone (less than 1,000 feet wide in one well), and poor shows farther updip, reflecting non-commercial Bakken oil. Approximately four townships south of Parshall Field toward the southern boundary of the Fort Berthold Reservation, two horizontal wells drilled in opposite directions from the same pad exhibit mud-gas shows that reflect the updip transition from commercial to non-commercial oil production and clearly define these zones.
The observed progressive updip increase in the amount of water produced relative to oil on the east flank of Parshall Field is accompanied by increasingly higher calculated water saturations in the more limited suite of vertical wells and in the triple-combo logs run in the horizontal leg of a recent Bakken well. Increase in water saturation is associated with an updip decrease in porosity, which restricts updip movement of oil, and is controlled in part by depositional facies. Water saturations calculated along the length of the lateral increase updip to the east, suggesting that this wellbore likely spans part of the transition from commercial production to poorer, possibly non-commercial, Bakken production.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California