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Stratigraphic and Petrophysical Analysis of the Three Forks Formation-Charlson Field, North Dakota


Although recent advancements in hydraulic fracturing and horizontal drilling technology have led to an increase in the production of hydrocarbons from the Three Forks Formation, the 2013 United States Geological Survey analysis indicates that the Three Forks still has a potential of 3.7 billion barrels of unrecoverable oil in the Williston Basin. This increase in the production has brought a major interest in the overall geological and petrophysical assessments of this formation. This analysis includes more accurate evaluations of porosity, oil saturation, and volumetric calculations which will enhance our knowledge to find prolific regions. The Devonian Three Forks Formation is unconformably overlain by the Bakken Formation and is stratigraphically divided into five members. In order to identify different units within the formation two approaches were utilized: 1) Different facies within the formation were identified thus four benches were determined from log and core analysis 2) Systems tracts were recognized after correlating the logs and a sequence stratigraphic model was built. As a major contribution to the geological study of the Three Forks Formation, the two models were compared and their connectivity was characterized. Charlson Field in McKenzie County is where this study was conducted. Ninety-nine wells with available resistivity, neutron density and gamma ray logs were used. The older logs had to be digitized and corrected. The tops for each member were picked and then petrophysical values such as, oil saturation and porosity were calculated and input into the 3D geological model for the purpose of property modeling. The next step was to preform volumetric calculations in order to find the most prolific regions in the field. Finally the relationship between the depositional environment and the variation of the facies was evaluated to realize how it governs on the productivity of hydrocarbons in this field. It was found that petrophysical properties vary significantly with sea level rise which has caused the existence of dolomitic facies in a fining upward sequence thus creating the producing units within the Three Forks Formation.