Abstract

Charlson field is located on two south-plunging anticlines developed upon the Nesson anticline in the North Dakota portion of the Williston basin. The field was discovered in 1952 with the completion of a Madison Group well. Subsequent deeper drilling has established reserves in the Bakken, Nisku-Duperow, Interlake and Red River Formations. The Interlake is the most prolific deeper horizon and is the primary subject of this paper, with reviews of the other reservoirs included. Three separate pools producing from the upper 200 ft of the Interlake comprise the overall reservoir. The initial Interlake discovery in 1977 was the state's best producer, and subsequent wells have attained that status over the years. Flowing initial potentials of over 1000 bbls of oil per day are not uncommon, and per-well primary reserves range up to and may even exceed 606,000 bbls of oil and 1303 mmcf of gas. One such well could easily have been plugged had it not been located offsetting three producers. Sample and mud-log shows were characteristically weak and log evaluation showed water saturations as high as 85%. This problem in evaluating the dolomitized algal reservoirs suggests that passed-up producers could exist throughout the basin and especially along the Nesson anticline. Salt plugging of porosity and permeability renders otherwise promising wells non-productive, and its occurrence appears unpredictable. Entrained salt in the produced fluids along with a high pour point of the oil require special production procedures which can substantially increase operating costs.