AN INTEGRATION OF SEQUENCE STRATIGRAPHIC AND PETROPHYSICAL ANALYSIS IN THE BAKKEN FORMATION, NORTH DAKOTA

A decrease in the discovery of reserves in conventional reservoirs has led to a focus on unconventional reservoirs. New techniques, such as hydraulic fracturing, provide better production conditions and allow the development of new reservoirs. The Bakken unconventional play is one of the most important oil plays since it has the largest crude oil accumulation in the United States.

During the study, 86 wells with the digitized format (log ASCII standard) were used for depositional environment analysis and petrophysical interpretation of the Bakken Formation in the northwest part of North Dakota. The Bakken Formation is subdivided into six facies which show diversity in thicknesses over the study area. The thicker parts of the Bakken Formation correlate to higher oil production.

Petrophysical and elastic properties of the Bakken Formation was examined in terms of their effects on productivity. The best calculation methods for these properties such as water saturation, effective porosity, brittleness, were tested according to the best match of log data calculations and core data results. Log data calculations show a harmonious trend with the core data.

It has been questioned as to whether brittleness can, in and of itself, be a key indicator of the productivity of a well. Brittleness, an important factor in hydraulic fracturing, was calculated by using log and mineralogy data. These results were used to estimate how the facies would respond to hydraulic fracturing, and were compared with petrophysical calculations for the determination of possible horizontal targets. High brittle conditions allow the rock to be fractured resulting in a smoother production process.

The brittleness analysis shows that an increase in brittleness also results in an increase of productivity. Even though there were some areas with high resistivity and low water saturation conditions, which are key points for oil production, due to unsufficient brittleness, these areas are not ideal for drilling. Therefore, the brittleness has been concluded to be a key factor of how productive a well can and will be.