Reservoir Characteristics And Petroleum Potential of the Bakken Formation, Southwestern Manitoba

Abstract

Abstract The Bakken Formation lies between the Upper Devonian Three Forks (Lyleton) Formation and the Mississippian Lodgepole Formation. The productive Middle Member of the Bakken Formation is a very fine- to fine-grained, argillaceous, dolomitic sandstone to siltstone. This paper outlines the geological setting in southwestern Manitoba and presents the general stratigraphy and lithology of the Bakken Formation. Conventional log analysis techniques result in erroneous calculations of porosity and water saturation for the litho-logically complex Middle Member. This paper illustrates the log analysis techniques developed to determine accurate porosity and water saturation for the Bakken Middle Member. Reservoir properties and production performance under both primary and secondary recovery for Bakken pools in Manitoba is also presented. Low drilling and completion costs; the province's drilling incentive program; high quality oil (over 40 ° API); and, original oil-in-place per pool of 500 × 103m3, make the Bakken an attractive exploration target in Manitoba. Bakken exploration and development prospects are discussed, including a brief overview of Bakken source rock and migration pathways and sample development drilling economics. Introduction The Bakken discovery well in Manitoba, 13-21-10-29(WPM) was drilled in the Daly Field in 1985. Production from the Bakken Formation in Manitoba is presently restricted to the Daly field (Figure 1), where it produces from the Middle Member. At year end 1992, there were 38 active Bakken producers in five pools in the Daly Field. Total oil production from the Bakken in Mamtoba in 1992 was 23.6 x. 103m3. As of December 31, 1992 cumulative Bakken oil production was 127.9 × 103m3 and remaining established Bakken reserves totalled 97.4 × 103m3. FIGURE 1: Manitoba oil fields and producing areas. (Available in full paper) Geological Setting The Williston Basin occupies portions of North Dakota, South Dakota, Montana, Saskatchewan and Manitoba (Figure 2). The productive areas of southwestern Manitoba are located on the northeastern flank of the Williston Basin. Paleozoic, Mesozoic and Cenozoic rocks form a basin ward-thickening wedge of sedimentary strata that reaches a thickness of 2,300 m in the extreme southwest corner of the province. The Mississippian stratigraphy in the Manitoba portion of the Williston Basin is shown in Table l. In southwestern Manitoba, Mississippian strata, divided into four formations, from the uppermost part of the Paleozoic sequence. These formations, in ascending order are: Bakken Formation, Lodgepole, Mission Canyon and Charles formations of the Madison Group. Approximately 70% of Manitoba's current oil production is from the Bakken, Lodgepole and Mission Canyon formations. The geological discussion in this paper focuses exclusively on the stratigraphy and lithology of the Bakken Formation. Stratigraphy The Bakken Formation is a thin, clastic unit that straddles the Devonian-Mississippian boundary. In southwestern Manitoba, the Bakken Formation uncomfortably overlies the Upper Devonian Three Forks (Lyleton) Formation and underlies the Mississippian Lodgepole Formation. The Bakken Formation is divided into three informal units: the Lower Member, Middle Member and Upper Member (Table 1). The three members exhibit an on-lapping relationship, each successively younger member extensively overlapping the older member(1). The Upper and Middle Members are present throughout southwestern Manitoba.