Detailed Analysis of the Nesson Antiform Williston Basin, ND
Dropkin, Michael, Krisitin Campbell, and Robert Ehrlich
Residuum Energy Inc, Salt Lake City, UT
The Nesson antiform is a composite feature composed of a chain of horsts and associated intra-horst simple folds. Faults are vertical and probably cut Precambrian basement. The Larimide was a period of major uplift; but the Nesson area had broken into discrete blocks by the Mesozoic—each block having a different subsidence history. Presence of these sharp-edged thickness domains can be detected as early as the Devonian. At least three families of faults occur: 1) northeast across the trend, 2) southeast oriented faults and 3) medial faults parallel to the Nesson trend. The Nesson is thus subdivided into discrete fault bonded rhombs. Within some rhombs, the strata are arched. These results corroborate earlier concepts that the Nesson complex is a bundle of wrench faults localized over an ancient zone of crustal weakness. As many as 20 tops (Cretaceous-Ordovician) and more than 25,000 wells were used in the analysis. Data was screened algorithmically, ~5% was in error (errors included input error, incorrect KB, no correction to true vertical depth, incompetence). More than 40 Swath sections-were derived, each swath containing 100-300 wells ranging in length from 30 to 100 miles. Screened data combined with computer-assisted graphical analysis resolves structures down to a vertical relief of about 10 feet, control permitting. . These same procedures easily resolve subtle stratigraphic and structural features basin-wide and at depths more sparsely penetrated. The ubiquity of vertical faults basin-wide can complicate interpretation of seismic data.
AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah