Date of Award

1991

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

R.D. LeFever

Abstract

Billings and southern McKenzie Counties contain about 40 active oil and gas fields. In the same area, two major structural highs and several minor ones can be recognized. The first of these, the Billings anticline, extends approximately 60 km (18 mi.) along a north-south line in central Billings County, and is composed of two parallel folds. A second major structure, here termed the Rough Rider anticline, lies west of the Billings anticline, and also extends about 60 km (18 mi.) along a north-south line from north-central Billings County into southern McKenzie County. Both of these structures are fault-bounded on their eastern sides, and are sites of significant hydrocarbon accumulation.

Data were collected from the wireline logs of 931 oil wells within the study area. From these, a total of 45 log markers were picked from the Precambrian basement and the Pierre Formation (Cretaceous). Structural maps were used in conjunction with trend surface residuals to define structures. Isopach map patterns, along with subsidence analysis were used to identify episodes of tectonic activity within the area.

Although the subsidence of the Williston Basin was the principal regional tectonic activity, the structural features in Billings and McKenzie Counties were intermittently decoupled from the larger-scale basin movement, producing local highs. The two major positive features, as well as several minor ones, have behaved independently of each other through time. Most of the development of these structures took place during the Devonian and Mississippian.

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