--> --> Importance of regional geological and petrophysical analysis of the Bakken/Three Forks formations of the Williston basin, North Dakota and Montana

AAPG Pacific Section and Rocky Mountain Section Joint Meeting

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Importance of regional geological and petrophysical analysis of the Bakken/Three Forks formations of the Williston basin, North Dakota and Montana

Abstract

The Bakken and Three Forks formations of the Williston Basin are prolific hydrocarbon producing units. The tack that operators take in resource development in these plays is largely an assembly-line approach, where closely spaced wells are drilled with factory-like efficiency. While that factory-style approach has been successful in developing these resources, we believe that geological and petrophysical variation is of greater importance for long-range planning, lease acquisition and high-grading available opportunities. To better understand and characterize some of the geological and petrophysical variation on a regional scale, we used almost a thousand wells with digital and/or raster logs to build a detailed stratigraphic framework of the Three Forks and Bakken systems and to develop a core-calibrated petrophysical model. Over the entire North Dakota and Montana play area, we correlated the standard lithostratigraphic units (e.g. Bakken shales, Three Forks benches), subdivided the Middle Bakken into detailed subunits, and differentiated the Lower Bakken Silt from the Pronghorn units and subunits. The core-calibrated petrophysical model was built on standard triple combo input. Our lithologic model solved for six lithologic components (anhydrite, calcite, dolomite, clay, quartz + feldspar, and total organic carbon) and was built with a combination of modified Umaa-Rhomaa and multi-variate linear regression solutions. A constant-salinity/variable-temperature Archie water saturation model was also applied to this large digital log dataset. Many interesting trends can be seen in the resulting maps of the entire North Dakota play fairway.