Big Stick/Four Eyes Fields: Structural, Stratigraphic, and Hydrodynamic Trapping Within Mission Canyon Formation, Williston Basin

John J. Breig

The Mississippian Mission Canyon formation of the Williston basin is the region's most prolific oil producing horizon. Big Stick/Four Eyes is among the most prolific of the Mission Canyon fields. Primary production from 87 wells is projected to reach 47 million bbl of oil. An additional 10-20 million bbl may be recovered through waterflooding.

The complex was discovered in 1977 by the Tenneco 1-29 BN, a wildcat with primary objectives in the Devonian Duperow and Ordovician Red River Formations. A series of Mission Canyon discoveries followed in the Big Stick, Treetop, T-R, and Mystery Creek fields. Early pressure studies showed that these fields were part of an extensive common reservoir covering 44.75 mi² (115.91 km²).

The reservoir matrix is formed from restricted marine dolostones deposited on a low-relief ramp. Landward are algal-laminated peritidal limestones and salina and supratidal evaporites of a sabkhalike shoreline system. Open-marine limestones, rich in crinoids, brachiopods, and corals, mark the seaward limit of reservoir facies. Regressive deposition placed a blanket of anhydrite over the carbonate sequence providing a seal for the reservoir.

Lateral trapping is accomplished through a combination of processes. Upper reservoir zones form belts of porosity that parallel the northeasterly trending shoreline. The trend is cut by the northward plunging Billings anticline, which provides structural closure to the north. Facies changes pinch out porosity to the south and east. Trapping along depositional strike to the southwest is only partially controlled by stratigraphic or structural factors. A gentle tilt of 25 ft per mi (5 m per km) occurs in the oil-water contact to the east-northeast, due to freshwater influx from Mississippian outcrop on the southern and southwestern basin margins. The front has advanced to the Big Stick/Four Eyes area. Formation waters grade in salinity from 18,000 to 260,000 ppm across the producing com lex.

AAPG Search and Discovery Article #91033©1988 AAPG Rocky Mountain Section, Bismarck, North Dakota, 21-24 August 1988