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B. E. Law

Publications and source records attributed to B. E. Law.

At least 19 recordsLinked to original sources
USGS2004

Sembar Goru/Ghazij Composite Total Petroleum System, Indus and Sulaiman-Kirthar Geologic Provinces, Pakistan and India

Geochemical analyses of rock samples and produced oil and gas in the Indus Basin have shown that the bulk of the hydrocarbons produced in the Indus Basin are derived from the Lower Cretaceous Sembar Formation and equivalent rocks. The source rocks of the Sembar are composed of shales that were deposited in shallow marine environments, are of mixed type-II and type-III kerogen, with total organic carbon (TOC) content ranging from less than 0.5 percent to more than 3.5 percent; the average TOC of the Sembar is about 1.4 percent. Vitrinite reflectance (Ro) values range from immature (< 0.6 percent Ro) to over mature (>1.35 percent Ro). Thermal generation of hydrocarbons in the Sembar Formation began 65 to 40 million years ago, (Mya) during Paleocene to Oligocene time. Hydrocarbon expulsion, migration, and entrapment are interpreted to have occurred mainly 50 to 15 Mya, during Eocene to Miocene time, prior to and contemporaneously with the development of structural traps in Upper Cretaceous and Tertiary reservoirs. The principal reservoirs in the Sembar-Goru/Ghazij Composite Total Petroleum System are Upper Cretaceous through Eocene sandstones and limestones.

Bulletin↗
USGS1998

Abnormal pressure in hydrocarbon environments

Abnormal pressures, pressures above or below hydrostatic pressures, occur on all continents in a wide range of geological conditions. According to a survey of published literature on abnormal pressures, compaction disequilibrium and hydrocarbon generation are the two most commonly cited causes of abnormally high pressure in petroleum provinces. In young (Tertiary) deltaic sequences, compaction disequilibrium is the dominant cause of abnormal pressure. In older (pre-Tertiary) lithified rocks, hydrocarbon generation, aquathermal expansion, and tectonics are most often cited as the causes of abnormal pressure. The association of abnormal pressures with hydrocarbon accumulations is statistically significant. Within abnormally pressured reservoirs, empirical evidence indicates that the bulk of economically recoverable oil and gas occurs in reservoirs with pressure gradients less than 0.75 psi/ft (17.4 kPa/m) and there is very little production potential from reservoirs that exceed 0.85 psi/ft (19.6 kPa/m). Abnormally pressured rocks are also commonly associated with unconventional gas accumulations where the pressuring phase is gas of either a thermal or microbial origin. In underpressured, thermally mature rocks, the affected reservoirs have most often experienced a significant cooling history and probably evolved from an originally overpressured system.

AAPG Memoir↗
USGS1993

Geochemical evaluation of upper cretaceous fruitland formation coals, San Juan Basin, New Mexico and Colorado

Geochemical analyses of coal samples from the Upper Cretaceous Fruitland Formation in the San Juan Basin of New Mexico and Colorado were used to determine thermal maturity, type of kerogen, and hydrocarbon generation potential. Mean random vitrinite reflectance (% R m ) of the Fruitland coal ranges from 0.42 to 1.54%. Rock-Eval pyrolysis data and saturated to aromatic hydrocarbon ratio indicate that the onset of thermal hydrocarbon generation begins at about 0.60% R m and peak generation occurs at about 0.85% R m . Several samples have hydrogen index values between 200 and 400, indicating some potential for liquid hydrocarbon generation and a mixed Type III and II kerogen. Pentacyclic and tricyclic terpanes, steranes, aromatic steroids and methylphenanthrene maturity parameters were observed through the complete range of thermal maturity in the Fruitland coals. Aromatic pentacyclic terpanes, similar to those found in brown coals of Australia, were observed in low maturity samples, but not found above 0.80% R m . N -alkane depleted coal samples, which occur at a thermal maturity of approx. 0.90% R m , paralleling peak hydrocarbon generation, are fairly widespread throughout the basin. Depletion of n -alkanes in these samples may be due to gas solution stripping and migration fromthe coal seams coincident with the development of pressure induced fracturing due to hydrocarbon generation; however, biodegradation may also effect these samples.

Colorado, New Mexico↗
USGS1992

Thermal maturity patterns of Cretaceous and Tertiary rocks, San Juan Basin, Colorado and New Mexico

Horizontal and vertical thermal maturity patterns and time-temperature modeling of Cretaceous and Tertiary rocks in the San Juan Basin of southwestern Colorado and northwestern New Mexico indicate that the high levels of thermal maturity in the northern part of the basin are due to either (1) convective heat transfer associated with a deeply buried heat source located directly below the northern part of the basin or (2) the circulation of relatively hot fluids into the basin from a heat source north of the basin located near the San Juan Mountains. Vitrinite-reflectance (R m ) well profiles through Cretaceous and Tertiary rocks in the basin are commonly nonlinear, with two to four segments having different gradients. The different gradients most likely represent the combined effects of contrasting thermal conductivities associated with lithologic variations and differences in heat transfer processes (conductive versus convective). Time-temperature and kinetic modeling of nonlinear R m profiles indicates that present-day heat flow is insufficient to account for the measured levels of thermal maturity. Furthermore, in order to match the nonlinear R m profiles, it is necessary to assign artificially high thermal-conductivity values to some of the stratigraphic units. These unrealistically high thermal conductivities are interpreted as evidence of convective heat transfer.

Colorado, New Mexico↗
USGS1989

Kinky vitrinite reflectance well profiles: Evidence of paleopore pressure in low-permeability, gas-bearing sequences in Rocky Mountain foreland basins

Vitrinite reflectance (R m ) profiles of wells drilled in abnormally pressured, low-permeability gas-bearing sequences in Rocky Mountain foreland basins are commonly nonlinear with two or more nonparallel segments. These kinky profiles are most likely due to perturbations of the thermal gradient caused by contrasting heat transfer processes associated with the development of abnormally high pressures. We interpret the intersection of the shallow and intermediate R m segments to mark the approximate original boundary between normal-pressured, water-bearing rocks and underlying overpressured gas- and water-bearing rocks. The intersection of the intermediate and deep R m segments marks the approximate original boundary between overpressured gas- nd water-bearing rocks and underlying overpressured gas-bearing rocks. However, because overpressuring is a transient condition that eventually evolves into normal pressuring or underpressuring, these intersections may not coincide with the present top of abnormal pressuring. These segmented R m profiles occur in several Rocky Mountain basins of the United States and Canada.

Alberta, Colorado, Wyoming↗
USGS1988

Structure contour map of the greater Green River basin, Wyoming, Colorado, and Utah

The Greater Green River basin of Wyoming, Colorado, and Utah contains five basins and associated major uplifts (fig. 1). Published structure maps of the region have commonly used the top of the Lower Cretaceous Dakota Sandstone as a structural datum (Petroleum Ownership Map Company (POMCO), 1984; Rocky Mountain Association of Geologists, 1972). However, because relatively few wells in this area penetrate the Dakota, the Dakota structural datum has to be constructed by projecting down from shallower wells. Extrapolating in this manner may produce errors in the map. The primary purpose of this report is to present a more reliable structure contour map of the Greater Green River basin based on datums that are penetrated by many wells. The final map shows the large- to small-scale structures present in the Greater Green River basin. The availability of subsurface control and the map scale determined whether or not a structural feature was included on the map. In general, large structures such as the Moxa arch, Pinedale anticline, and other large folds were placed on the map based solely on the structure contours. In comparison, smaller folds and some faults were placed on the map based on structure contours and other reports (Bader 1987; Bradley 1961; Love and Christiansen, 1985; McDonald, 1975; Roehler, 1979; Wyoming Geological Association Oil and Gas Symposium Committee, 1979). State geologic maps and other reports were used to position basin margin faults (Bryant, 1985; Gries, 1983a, b; Hansen 1986; Hintze, 1980; Love and Christiansen, 1985; Tweto, 1979, 1983). In addition, an interpreted east-west-trending regional seismic line by Garing and Tainter (1985), which shows the basin configuration in cross-section, was helpful in locating buried faults, such as the high-angle reverse or thrust fault along the west flank of the Rock Springs uplift.

Colorado, Utah, Wyoming↗
USGS1985

Conceptual model for origin of abnormally pressured gas accumulations in low-permeability reservoirs

The largest gas fields in the Rocky Mountain region occur in abnormally pressured reservoirs. These gas accumulations are different from more conventional gas accumulations in that they are commonly located in basin-center positions, they occur downdip from water-bearing rocks, and they are in overpressured or underpressured low-permeability reservoirs. We suggest that overpressured and underpressured gas accumulations of this type have a common origin. In basins containing overpressured gas accumulations, rates of thermogenic gas accumulation exceed gas loss, causing fluid (gas) pressure to rise above the regional hydrostatic pressure. Within the overpressured gas generation zone, free water in the larger pores is forced out of the gas generation zone into overlying and updip, normally pressured, water-bearing rocks. The remaining tightly bound water, at irreducible saturation levels, cannot remove dissolution products, precluding significant permeability and porosity enhancement. Thus, while other diagenetic processes continue, a pore network with very low permeability develops. As a result, gas accumulates in these low-permeability reservoirs at rates higher than it is lost. In basins containing underpressured gas accumulations, rates of gas generation and accumulation are less than gas loss. These basins have typically experienced significant uplift and erosion and/or temporal variations of paleotemperature. Despite these modifications, the basin-center gas accumulation persists, but because of changes in the basin dynamics, the overpressured accumulation evolves into an underpressured system.

American Association of Petroleum Geologists Bulle↗
USGS1983

Biostratigraphic correlation chart of some Upper Cretaceous rocks from the Lost Soldier area, Wyoming to west of Craig, Colorado

This chart depicts the time-stratigraphic relations of some Upper Cretaceous rocks along the eastern and southeastern margins of the Greater Green River Basin, south-central Wyoming and northwestern Colorado. The purpose of this report is to release a preferred set of correlations based upon marine mollusk biostratigraphy. The senior author, with the help of B. E. Law, has acquired, synthesized, compiled, and interpreted data from various sources. These include selected published documents (see "References Cited") and unpublished reports of fossil identifications by W. A. Cobban who examined collections made by the late J. R. Gill. Numerous measured sections of Gill's were also utilized. It must be emphasized that all interpretations on this chart are based on information obtained from these sources and the senior author has yet to substantiate these correlations in the field. Not all data from the area of this study is included herein because it is either repetitive in nature or its reliability is uncertain. This uncertainty is due to the ambiguity inherent in both fossil identification and stratigraphic interpretation. Questionable unpublished material has been omitted while published data which is inconsistent with the senior author's correlations may be found in the footnotes portion of this report. The rock units are assigned to a range of ammonites that have been related to an absolute time scale. The ammonite zonation and age boundaries are adapted from Obradovich and Cobban (1975). "D" numbers are provided for each geographic locality where fossils were collected and described by personnel of the U.S. Geological Survey. These fossils may be accessed at the offices of the Survey in Lakewood, Colorado.

Colorado, Wyoming↗