Discussion of Reservoir Characteristics, Cedar Creek Anticline Fields, Montana

Abstract

Abstract At the present time, over one-half the total oil production in Montana originates from Williston Basin fields in Eastern Montana. Six of the seven foremost producing fields in this area are located along the Cedar Creek anticline. The characteristics of the reservoir rocks which constitute these fields, the characteristics of the reservoir fluids and the behavior of the fluids in the rocks are discussed. The conclusions drawn from the data available are that the carbonate reservoirs of the Cedar Creek anticline are under-saturated, of poor-to-fair permeability and of fair-to-good porosity with some localized fracturing. By comparison of various fields on the anticline, a general improvement in reservoir rock and fluid properties is shown to exist in a south-to-north direction. The valuable aid to reservoir interpretation and operation which can be obtained through a systematic gathering of data and modern mechanical methods of statistical analysis is emphasized. Introduction The nation's attention was focused on the Williston Basin potential in early 1951 by significant discoveries in Manitoba, Canada, and on the Nesson anticline in North Dakota. Later during the same year discoveries were made on the Cedar Creek anticline of Eastern Montana; namely, the Glendive and Pine fields. Rapid developments along the Cedar Creek anticline led to the discovery of 12 oil fields by 1955, one of which is located on the southern end in South Dakota (Fig. 1). Production from the Montana portion of the Cedar Creek anticline currently amounts to 34,000 BOPD which represents 44 per cent of the total Montana oil production. The first and third largest oil fields in Montana from the standpoint of production are found here, respectively, Pine and Cabin Creek. The purpose of this paper is to discuss the different reservoir characteristics in those fields where Shell is operating, e.g., those from Glendive to Buffalo. The discussion will not deal with stratigraphic detail but is limited to those aspects which are of practical value to the reservoir engineer, and are presented in the following order:reservoir rocks,reservoir contents, andreservoir pressures.