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P. H. Nelson

Publications and source records attributed to P. H. Nelson.

12 recordsLinked to original sources
USGS2004

Permeability-porosity data sets for sandstones

P ermeability-porosity relations vary from formation to formation, so it is desirable to obtain core and determine permeability ( k ) and porosity (φ) on core plugs in the laboratory for the formation of interest. If core data are not available, one might resort to data obtained in formations with similar properties. Analog data are not easy to find, however, and for this reason a catalog of k versus φ data sets has been compiled and made available on a Web site (see suggested reading). The catalog cites relevant observations such as depositional environment, depth, age of formation, field name, and petrographic description as well as complete references to data sources. Examples from the catalog are shown here to illustrate some aspects of k versus φ dependencies.

Leading Edge (Tulsa, OK)↗
USGS2002

Subsurface fluid pressures from drill-stem tests, Uinta Basin, Utah

High fluid pressures are known to be associated with oil and gas fields in the Uinta Basin, Utah. Shut-in pressure measurements from drill-stem tests show how pressure varies with depth and by area within the basin. The data base used in this report incorporates over 2,000 pressure measurements from drill-stem tests in wells completed prior to 1985. However, the number of useful pressure measurements is considerably less, because many drill-stem tests fail to stabilize at the actual formation pressure if the permeability is low. By extracting the maximum pressure measurements recorded in a collection of wells within an area, the trend of formation pressure within that area can be approximated. Areal compilations of pressures from drill-stem tests show that overpressured rock formations occur throughout much of the northern and eastern areas of the Uinta Basin. In particular, significant overpressuring (0.5 < pressure gradient < 0.8 psi/ft) is found throughout much of the Altamont-Bluebell field at depths ranging from 10,000 to 13,000 ft, equivalent to 5,000 to 8,000 ft below sea level. Limited data indicate that the pressure gradient declines at depths greater than 13,000 ft. An underpressured zone appears to exist in the Altamont-Bluebell field at depths shallower than 5,000 ft. Throughout the eastern Uinta Basin, moderately overpressured zones (0.46 < pressure gradient < 0.5 psi/ft) are common, with local evidence of significantly overpressured zones, but pressure gradients greater than 0.6 psi/ft are rare.

Mountain Geologist↗
USGS2002

A review of the multiwell experiment in tight gas sandstones of the Mesaverde Group, Piceance Basin, Colorado

The Cretaceous Iles and Williams Fork Formations of the Mesaverde Group contain important reservoir and source rocks for basin-centered gas accumulations in the Piceance Basin of northwestern Colorado. The sandstones in these formations have very low permeability, so low that successful production of gas requires the presence of fractures. To increase gas production, the natural fracture system of these "tight gas sandstones" must be augmented by inducing artificial fractures, while minimizing the amount of formation damage due to introduced fluids. The Multiwell Experiment was undertaken to provide geological characterization, obtain physical property data, and perform stimulation experiments in the Iles and Williams Fork Formations. Three vertical wells and one follow-up slant well were drilled, logged, partially cored, tested for gas production, stimulated in various manners, and tested again. Drawing from published reports and papers, this review paper presents well log, core, and test data from the Multiwell Experiment while emphasizing the geological controls on gas production at the site. Gas production is controlled primarily by a set of regional fractures trending west-northwest. The fractures are vertical, terminating at lithologic boundaries within and at the upper and lower boundaries of sandstone beds. Fractures formed preferentially in sandstones where in situ stress and fracture gradients are lower than in shales and mudstones. The fractures cannot be identified adequately in vertical wellbores; horizontal wells are required. Because present-day maximum horizontal stress is aligned with the regional fractures, artificial fractures induced by pressuring the wellbore form parallel to the regional fractures rather than linking them, with consequent limitations upon enhancement of gas production.

Mountain Geologist↗
USGS1998

An application of well data in oil and gas assessment-arctic national wildlife refuge

A current assessment of oil and gas resources in the Arctic National Wildlife Refuge (ANWR) 1002 Area by the U.S. Geological Survey relies upon seismic data, geological mapping of exposures south and west of the assessment area, and exploratory wells. Information obtained from wells up to 50 km west and north of ANWR is presented. It is emphasized that the synthesis of well data with other geological and geophysical data provides a quantitative foundation for resource estimates of ANWR.

Conference Paper↗