Date of Award

January 2016

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

Richard D. LeFever

Abstract

The Birdbear Formation in Williston Basin of western North Dakota is a carbonate-evaporite sequence that has been the subject of much research over the past decades. This study looks at the depositional environment and the diagenetic characteristics of the formation, and their relation to production characteristics. Much has been done over the years on the Birdbear Formation, but most of these studies were restricted to eastern Montana (USA), southern Manitoba and south western Saskatchewan (Canadian province). The approach of integrating the role and effects of deposition, diagenesis, and porosity of the Birdbear Formation (Upper Devonian) Williston Basin in McKenzie County, North Dakota was the main purpose for this research. A detailed study was carried out through physical core descriptions, thin section analysis, wireline log correlations, and nuclear magnetic resonance (NMR) spectroscopy measurements to determine if the effects of diagenesis have been critical enough to alter or create adequate porosity and permeability within rock fabrics for the migration of generated hydrocarbons. Results from core analysis showed that two units were recognized, first being a lower carbonate dolomite-limestone of uniform lithology (boundstone to wackestone classification) with abundant organic material that could have served as self-sourcing in production and the second, an upper anhydrite-carbonate lithology (packstone classification), that has the ability to entrap migrating fluids within the study area. Sediments of the upper section of the lower carbonate unit exhibited high diagenetic activities that enhanced porosity

and overall permeability through observed intra-crystalline, inter-granular, and moldic vuggy porosities that were confirmed by NMR analysis. These sediments also showed marked selective or partial dolomitization, micritization and dissolution of calcite cements from inclusion of brines that were effective in creating what could be excellent reservoir rock qualities in the potential for the Birdbear Formation as a hydrocarbon producer within the Williston Basin.

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