Ordovician Red River B": Horizontal Oil Play  in the Southern Williston Basin"

Abstract

Recent application of horizontal drilling technology to the Ordovician Red River B zone in the southern Williston basin has resulted in a successful oil play, with more than 100 wells drilled in 1995 and 1996. The Red River B reservoir is a dolomitized laminated carbonate with microsucrosic porosity of 8-25% and permeabilities in the range of 1-66 md. It occurs within the middle of three depositional cycles (A, B, and C) that form the upper Red River Formation. Each cycle consists of a lower burrowed limestone, middle laminated member, and capping anhydrite or lime mudstone. The B reservoir is confined to the B laminated member and consists of an upper portion, characterized by better reservoir quality, and a lower, less permeable portion. Horizontal drilling has the advantage of significantly increasing well-bore exposure to the upper, more permeable portion. Well data indicate the total Red River B porosity zone has remarkable extent over parts of southwestern North Dakota, southeastern Montana, and northwestern South Dakota. Productivity from horizontal wells displays considerable variation that can be correlated with structure/tectonic patterns and with reservoir petrophysical character.