3d Gravity Modeling in the Williston Basin: from Effective Technique for Enhancement of Basement Structure and Fracturing

Von Lunen, Eric M.^1
1 Lunen & Associates, Austin, TX.

The Williston Basin is a mature hydrocarbon province, with nearly 4 billion barrels of oil production and 470 bcf of natural gas production. The basin has an extensive database of nearly 10,000 wells with accompanying log suites. It has been actively explored and produced for 50 years. Recent advances in unconventional production and reservoir stimulation techniques have led to a dramatic increase in exploration activity in the Bakken Formation within the basin. Fracture density, on a micro-scale and a macro-scale, appears to be a strongly influencing factor on the success of recent Bakken wells.

We have developed a new approach to the enhancement and mapping of basement-controlled fractures in the Williston Basin using 3D gravity forward modeling layer-stripping. Using well control we generate a constrained 3D volume of the density structure of the known sedimentary formations within the basin. The gravity response of this ‘known’ geology is computed and then subtracted from the observed Bouguer gravity field over the basin. The residual gravity field provides a higher resolution, more refined image of basement density contrasts and basement density structure.

The residual gravity field derived from the 3D gravity ayer stripping represents the ‘unknown’ geology of the basin. We interpret this dataset in tandem with public domain aeromagnetic data and DEM information to obtain an integrated map of likely macro-scale fracture network among the three datasets. We have successfully correlated some of these high-confidence fractures imaged in potential field data with seismic data character from 3D seismic surveys.

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009