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Janet K. Pitman

Publications and source records attributed to Janet K. Pitman.

At least 163 records · Page 9Linked to original sources
USGS1989

Diagenesis of hydrocarbon-bearing rocks in the Middle Ordovician Simpson Group, southeastern Anadarko Basin, Oklahoma

Quartzarenites and subarkoses in the Middle Ordovician Simpson Group in the Gulf Costello No. 1 and Sunray-DX Parker No. 1 Mazur wells, southeastern Anadarko basin, have undergone a complex diagenetic and petroleum-migration history. During early burial, petroleum migrated locally through sandstones; patches of bitumen in calcite and bitumen-lined quartz overgrowths containing oil-bearing inclusions reflect the introduction of petroleum-bearing fluids at shallow depths. Stable-isotope data reveal that early calcite precipitated at near-surface temperatures from fluids dominated by marine carbon. At moderate to deep burial, calcite dissolution, followed by ferroan-dolomite and clay-mineral precipitation, occurred at about the same time as the rocks reached levels of thermal maturity sufficient for the generation of hydrocarbons. Maximum paleotemperatures during deep burial are estimated from maturation models to have reached 250°F in the Costello well and 300°F in the Mazur well. Maturation-derived temperatures in the Costello well are consistent with preliminary homogenization temperatures (210-250°F) for oil inclusions along microscopic healed fractures that formed during deep burial, thus supporting an Early to Middle Pennsylvanian timing for the generation and migration of late-stage hydrocarbons. The early petroleum phase, emplaced while the rocks were at shallow burial depths, migrated from mature source rocks deeper in the basin.

Oklahoma↗
USGS1987

Pressure sensitivity of low permeability sandstones

Detailed core analysis has been carried out on 32 tight sandstones with permeabilities ranging over four orders of magnitude (0.0002 to 4.8 mD at 5000 psi confining pressure). Relationships between gas permeability and net confining pressure were measured for cycles of loading and unloading. For some samples, permeabilities were measured both along and across bedding planes. Large variations in stress sensitivity of permeability were observed from one sample to another. The ratio of permeability at a nominal confining pressure of 500 psi to that at 5000 psi was used to define a stress sensitivity ratio. For a given sample, confining pressure vs permeability followed a linear log-log relationship, the slope of which provided an index of pressure sensitivity. This index, as obtained for first unloading data, was used in testing relationships between stress sensitivity and other measured rock properties. Pressure sensitivity tended to increase with increase in carbonate content and depth, and with decrease in porosity, permeability and sodium feldspar. However, scatter in these relationships increased as permeability decreased. Tests for correlations between pressure sensitivity and various linear combinations of variables are reported. Details of pore structure related to diagenetic changes appears to be of much greater significance to pressure sensitivity than mineral composition.

Journal of Petroleum Science and Engineering↗
USGS1987

Marine and nonmarine gas-bearing rocks in Upper Cretaceous Blackhawk and Neslen Formations, eastern Uinta Basin, Utah: Sedimentology, diagenesis, and source rock potential

The Upper Cretaceous Blackhawk and Neslen Formations in the eastern Uinta basin contain large amounts of thermogenic gas that was generated from interbedded humic-rich source rocks. The geometry and distribution of hydrocarbon source and reservoir rocks are controlled by depositional environment. The Blackhawk, composed of laterally extensive sandstone and locally interbedded carbonaceous siltstone and minor coal, reflects deposition in nearshore marine and backshore environments. The Neslen contains organic-rich siltstone and mudstone with lesser amounts of carbonaceous shale, coal, and lenticular sandstone that formed in coastal and lower alluvial-plain depositional settings. Potential reservoir sandstones are composed dominantly of monocrystalline quartz grains and sedimentary lithic fragments. Mechanical compaction during early burial was followed by the precipitation of quartz, carbonate, and barite later in the burial history. Variations in porosity and permeability (2-10%; < 1 md) reflects the presence of authigenic clay, mineral cements, and dissolved lithic grains. Natural fractures, cemented with carbonate, barite, and kaolinite, occur locally. Active hydrocarbon generation occurred in the Neslen and Blackhawk during the Oligocene and Miocene when these units were near their maximum burial depth and temperature. The rate of hydrocarbon generation decreased from the late Miocene to the present, owing to widespread cooling that occurred in response to regional uplift and erosion associated with the development of the Colorado Plateau. Temporally equivalent rocks in other areas of the basin may have experienced similar diagenetic and hydrocarbon generation histories.

Colorado, Utah↗
USGS1982

Depositional setting and diagenetic evolution of some Tertiary unconventional reservoir rocks, Uinta Basin, Utah

The Douglas Creek Member of the Tertiary Green River Formation underlies much of the Uinta basin, Utah, and contains large volumes of oil and gas trapped in a complex of fractured low-permeability sandstone reservoirs. In the southeastern part of the basin at Pariette Bench, the Eocene Douglas Creek Member is a thick sequence of fine-grained alluvial sandstone complexly intercalated with lacustrine claystone and carbonate rock. Sediments were deposited in a subsiding intermontane basin along the shallow fluctuating margin of ancient Lake Uinta. Although the Uinta basin has undergone postdepositional uplift and erosion, the deepest cored rocks at Pariette Bench have never been buried more than 9,800 ft (3,000 m). The sandstones, dominantly lithic arkoses and feldspathic litharenites, were derived from source terranes south of the Uinta basin. Secondary silica and several generations of authigenic calcite [Ca 1.8-1.9 (Mg 0.02-0.06 Fe 0.02-0.06 )(CO 3 ) 2 ], dolomite [Ca 1.3-1.4 (Mg 0.6-0.7 Fe 0.02-0.04 )(CO 3 ) 2 ], and ankerite [Ca 1.2-1.3 (Mg 0.2-0.3 Fe 0.4-0.6 )(CO 3 ) 2 ] form a replacive cement in the sandstones. Commonly, syntaxial overgrowths of late iron-bearing carbonate occur on detrital grains and preexisting relicts of iron-free carbonate cement. In sandstone where carbonate has been partly dissolved, abundant authigenic illite, partly ordered mixed- ayer illite-smectite, and small amounts of chlorite partly to completely fill secondary pores. Isotopic composition of carbonate cement and grain-supported rock range from -0.39 to -6.18 ^pmil for ^dgr 13 C and -7.80 to -13.98 ^pmil for ^dgr 18 O, indicating that authigenic carbonate formed at low temperatures in the presence of meteoric waters by a process of solution-precipitation. Enrichment of carbon and oxygen in early diagenetic calcite and fossiliferous rock relative to late diagenetic ankerite indicates a trend toward lighter isotopic carbonate compositions with increasing diagenesis. Kerogenous rocks at Pariette Bench are thermochemically immature and therefore are not the source of oil produced in the field. Hydrocarbons are compositionally similar to some of the oils produced from the Green River Formation in the Bluebell-Altamont field and are interpreted to have migrated from mature Green River source rocks through a network of open fractures. The occurrence of small amounts of hydrocarbon in secondary pores indicates that its emplacement postdated carbonate dissolution.

Utah↗
USGS1979

A study of reservoir characteristics of the Nanushuk and Colville groups, Umiat test well 11, National Petroleum Reserve in Alaska

Cretaceous sandstones in the Umiat Anticline contain the largest volume of oil discovered to date in the National Petroleum Reserve in Alaska. Umiat test well 11, although dry and abandoned, penetrated the most complete sequence of Cretaceous rocks in the Umiat area. Cretaceous formations cored (oldest to youngest) were the Grandstand, Chandler, and Ninuluk Formations of the Nanushuk Group and the Seabee and Prince Creek Formations of the Colville Group. Cores from sandstone beds in each of the formations penetrated were studied to identify the factors influencing porosity and permeability. Based on lithologic, textural, sedimentary-structural, faunal and floral, and regional paleogeographic evidence, the Cretaceous stratigraphic sequence in the Umiat area can be described as complexly interbedded delta-front and delta-plain facies (named the Umiat delta). The Grandstand Formation and Killik Tongue of the Chandler Formation represent one thick progradational sequence of delta-front and delta-plain facies, respectively. This sequence was followed by deposition of transgressive marine facies of the Ninuluk and Seabee Formations, which were in turn overlain by another progradational delta-plain facies, the Tuluvak Tongue of the Prince Creek Formation. The delta-front sandstone of the Grandstand Formation is well-sorted, fine-grained to very fine grained, angular to subangular chert arenite and phyllarenite. Authigenic cements include dolomite, calcite, siderite, quartz overgrowth, kaolinite, chert, pyrite, and possibly some small flakes of chlorite. The source terrane was southwest of Umiat and, on the basis of the aforementioned petrographic evidence, consisted of low-grade metamorphic rocks and possibly sandstone and cherty limestone. The weighted average porosity, based on well-log analyses, for the lower part of the Grandstand Formation is 15.1 percent and for the upper part is 15.6 percent; the weighted average permeability is 58.6 md for the lower part and 167 md for the upper part. The average size of visible pores is about 50 ?m. A linear relationship was established between permeability and porosity for sandstone samples from depths less than 405 m and greater than 644 m; the average permeability of these intervals can be estimated with reasonable accuracy not only for the Grandstand but also for the Tuluvak, Seabee, and Killik. The delta-front, delta-plain marginal facies of the Killik Tongue of the Chandler Formation includes sandstone, siltstone, shale, and coal. Sandstone samples studied petrographically are similar to those of the Grandstand Formation; the delta prograded northeasterly across the Umiat area and the source terrane for the sediments remained the same. Well-log analyses indicate that the weighted average porosity for the Killik Tongue is 16.4 percent and the weighted average permeability is 96.2 md. The delta-front sandstone of the Ninuluk Formation is similar to that of the Grandstand and Killik, but is moderately sorted and contains less detrital quartz and significantly more metamorphic rock fragments than chert fragments. Sandstone in the upper part of the formation contains a considerable amount of calcite. Visible pores average about 35 ?m in size. The weighted average porosity for the Ninuluk Formation, based on well-log analyses, is 12.6 percent; the weighted average permeability is 10.7 md. The Seabee Formation is primarily shale deposited in an open-marine environment; sandstone units in the Seabee overlie and are overlain by black marine shale. The mineralogy of these sandstone units differs markedly from that of the older formations. The sandstones are characterized by an abundance of volcanic rock fragments, high content of volcanic plagioclase feldspar, and low content of detrital quartz. Quartz, chert, phyllite, and metaquartzite all appear to be the same petrographically as in the Nanushuk Group. Abundant chlorite and smectite reduce permeability and make sandstones

Circular↗
USGS1976

Concentration and mineralogical residence of elements in rich oil shales of the Green River Formation, Piceance Creek basin, Colorado, and the Uinta Basin, Utah - A preliminary report

Ten samples from drillcore of two rich oil-shale beds from the Parachute Creek Member of the Eocene Green River Formation, Piceance Creek basin, Colorado, and Uinta Basin, Utah, were analyzed for 37 major, minor, and trace elements. For 23 of these elements, principal mineralogical residence is established or suggested and such studies may provide data which are useful for predicting the kinds and amounts of elements and compounds that might be released into the environment by oil-shale mining operations. ?? 1976.

Chemical Geology↗