Re-Evaluating Petroleum Potential of the Birdbear Formation, Williston Basin in McKenzie County, North Dakota

Abstract

The Birdbear Formation in Williston Basin is a carbonate-evaporite sequence that extends across Western North Dakota (USA), Eastern Montana (USA), Southern Manitoba and South Western Saskatchewan (Canadaian provience). Integrating the role and effects of diagenesis, porosity and pattern of depositional facies of this formation in McKenzie County, North Dakota was carried out in order to re-evaluate the petroleum potential through: 1) core and thin section examination, 2) geochemical analysis (TOC Rock-Eval pyrolysis), 3) wireline log correlations, and 4) nuclear magnetic resonance (NMR) spectroscopy measurments to determine the role of deposition and diagenesis with regards toward porosity types, lateral and vertical distribution of porosity/reservoir, lateral and vertical distribution of prospective source beds and anhydrite seals. Results showed two distinct units of 1) lower carbonatedolomite-limestone of uniform lithology (boundstone to wackestone classification) with abundant organic material that could have served as self-sourcing in production, and 2) 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 activites that enhanced porosity and overall permeability through observed intra-crystalline, inter-granular and moldic vuggy porosities that were confirmed by NMR analysis and porosity maps across McKenzie County (basin center). 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 (15-20% Φ, 20-85 md perm). TOC Rock-Eval pyrolysis data indicates fair to probable good distribution of prospective source beds (1-2% TOC), which further enhances the potential for the Birdbear Formation as a hydrocarbon producer within the Williston Basin.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018