It is widely recognized that shale resource plays such as the Bakken Petroleum System, in the Williston Basin, North America, are significantly more spatially complex over nearly every geological parameter than previously understood. For example, closely spaced Bakken wells can have much different production rates over their lifetime, despite very similar completion strategies. In ultra-low porosity and permeability regimes typical of shale resources plays, the variations in rock characteristics from well to well may be below the resolvable scales of seismic reflection and well data. These undetectable variations can lead to variations in organic content or elasticity that in turn affect production. I attempt to address differences in first year cumulated production from wells in the Red Sky survey area of the Ross Field, North Dakota, using results from core studies on bulk mineralogy, clay content, thermal maturity, and in situ stress. These data allow me to make assessments of brittleness and ultimate fracability of wells having differing production histories of closely spaced wells within Ross Field.

Wide-azimuth, long-offset seismic data allow azimuthal anisotropy and direction resulting from the presence of natural fractures and anisotropic in situ stress to be estimated. This can be done by measuring how seismic velocities and amplitudes vary as a function of the acquisition azimuth. Rock intrinsic properties like anisotropy, azimuth of fast and slow directions, fracture density, and total porosity, as well as the in-situ principal stress components, can be inferred and used to help with well design, placement, and completion strategies. Recent advances in seismic azimuthal analysis of media having orthotropic symmetry (an orthotropic medium has three orthogonal planes of mirror symmetry), and quantitative interpretation work flows are illustrated using high resolution pre-stack seismic inversion in an unconventional play in the Williston basin in North America. The algorithm, valid for orthotropic symmetry, was first tested on synthetic data, and then applied to real wide-azimuth 3D data. Results indicate that AVAz (Amplitude Versus Azimuth) analysis of wide-azimuth seismic data for orthotropic media can be used to estimate anisotropy, azimuth, and to constrain the orientation and magnitude of the principal in situ stresses.

Over a century has passed since 1901 when W.T. Hornaday showed a fragment of a horn of Triceratops found in the valley of Hell Creek to H.F. Osborn at the American Museum of Natural History. The following year Osborn's assistant, Barnum Brown, was dispatched to eastern Montana and began investigations of its geology and paleontology. By 1929, Brown had published a geological analysis of the rocks exposed in the southern tributaries of the Missouri River, named the Hell Creek Formation, and published studies of some of the dinosaurs discovered there. Parts of his collections of fossil mollusks, plants, and vertebrates contributed to research by others, particularly members of the U.S. Geological Survey. From 1930 to 1959, fieldwork was slowed by the Great Depression and World War II, but both the continuing search for coal, oil, and gas as well as collections of fossils made during construction of Fort Peck Dam set the stage for later research. Field parties from several museums collected dinosaurian skeletons in the area between 1960 and 1971. In 1962, concentrations of microvertebrates were rediscovered in McCone County by field parties from the University of Minnesota. Ten years later, field parties from the University of California Museum of Paleontology began collecting microvertebrates from exposures in the valley of Hell Creek and its tributaries. The research based on this field research provided detailed geological and paleontological analyses of the Hell Creek Formation and its biota. In turn, these contributed to studies of evolutionary patterns and the processes that produced the changes in the terrestrial biota across the Cretaceous-Paleogene boundary.

In 1907, Barnum Brown named the Hell Creek beds (Formation) for the strata exposed in the Hell Creek Valley and other downstream tributaries of the Missouri River. In the absence of a stratotype section, a lectostratotype is herein proposed for the Hell Creek Formation based on 84.2-m-thick exposures at Flag Butte (local name) in Ried Coulee (archaic use; East Fork of Hell Creek) and East Ried Coulee, tributaries of Hell Creek, Garfield County, Montana (sec. 29, T. 21 N., R. 38 W., NAD27 CONUS; base 47.55931°N, 106.88111°W; top 47.55533°N, 106.86810°W). The formation is underlain with general conformity by sandstone beds of the Fox Hills Formation (as characteristically known, the Colgate Member is absent) and is for the most part conformably overlain locally by the Tullock Member of the Fort Union Formation. The upper contact at Flag Butte is demarcated at the base of the IrZ lignite bed (above an iridium anomaly). The boundary has been demonstrated to be somewhat unconformable in areas to the west. The IrZ bed is also missing at Bug Creek in McCone County. In its type section, the Hell Creek Formation is subdivided (simply and informally) into Ried Coulee (lower Hell Creek), East Ried Coulee (middle Hell Creek), and Flag Butte (upper Hell Creek) units, each containing a sandstone and a mudstone lithofacies. Formational thickness varies with local depositional and erosional history of various coastal-deltaic environments across the Williston Basin and a trend of overall thinning to the east and northeast.

The interval spanning the uppermost Hell Creek Formation to the overlying lowermost Fort Union Formation in north-central Montana encompasses a marked paleoenvironmental change (associated with the formational contact), the Chicxulub impact event, and the Cretaceous-Paleogene boundary. We have examined the record of this transition at the Hell Creek Formation lectostratotype to determine the placement of these events using a series of lithological, geochemical, palynological, and 40Ar/39Ar geochronological analyses. The claystone derived from the Chicxulub impact is identified based on lithological criteria, enrichment of iridium and osmium, and osmium isotope ratios. The impact claystone also contains a Cyathidites fern spike. The first continuous lignite horizon in the section immediately overlies this claystone and represents the Hell Creek–Fort Union formational contact. A tuff ~3 m above the impact layer is dated to 66.024 ± 0.059 Ma. Given this evidence, at the lectostratotype the Cretaceous-Paleogene boundary is coincident with the impact claystone and therefore with the formational contact. Due to poor preservation and apparent reworking of palynomorphs surrounding the formational contact, the Cretaceous-Paleogene boundary is difficult to identify based on biostratigraphically significant taxa. The presence of marine dinoflagellates is suggestive of reworking of older marine sediments during the deposition of the Cretaceous-Paleogene boundary interval.