ABSTRACT The subsurface clastic deposits of the Borden Island gas zone constitute the major reservoir in the two largest gas fields yet discovered in the Sverdrup Basin. These gas fields (Drake Point and Hecla) lie on and adfacent to the Sabine Peninsula, Melville Island. The interval has been previously assigned in part to the Lower Jurassic Borden Island Formation and in part to the Wilkie Point Formation. The relationship of the rocks in the study area to those of the type locality of the Borden Island Formation is, however, uncertain. On the basis of colour, lithology, mechanical-log character and position in sequence, three units are recognized in the sediments of the gas zone and are correlated through 15 wells on northern Melville Island. Each unit appears as a basinward thickening wedge of sediment, the combined thickness of which ranges from 20 to 108 m (65 to 354 ft). Cores from 5 wells, when combined, provide an almost complete lithological record of the interval in the subsurface. The three units are informally labelled Units A, B and C in ascending order. Unit A is an oolitic ironstone lithofacies; Unit B, the major reservoir unit, is a cyclic sandstone-siltstone lithofacies, and Unit C is a mud-rich, glauconitic sandstone, siltstone and oolitic ironstone lithofacies. Based on sedimentary structures and textures, granulometric analyses, unit geometry, lithology, mineralogy and palaeontology, the over-all environmental model suggested is that of an interdistributary beach/offshore transition developed in a series of semirestricted, shallow-water coastal embayments. Units A and C represent deposition in a transition subenvironment between sand-silt and clay deposition. The glauconitic sandstones and siltstones of these units are interpreted as normal sediments of the transition zone and the oolitic ironstones are interpreted as high-energy storm deposits. Unit B cyclic sandstones and siltstones represent deposition in the dune, beach and shoreface subenvironments. Maximum porosity and permeability in the Borden Island gas zone is developed in sandstones attributed to deposition in the dune and beach/upper shoreface subenvironments. Porosity and permeability reduction is ascribed mainly to the presence of detrital and authigenic clay minerals.
Abstract The base of the ‘Fish Scale Sandstone’ or ‘Fish Scale Zone’ is used as a stratigraphic marker throughout a large area of the western Canadian plains. It occurs within the Colorado Group, and has been commonly used in the subsurface to mark the base of the Upper Cretaceous. Locally developed lenses, informally called the Barons Sandstone, occur about 12 metres above the base of the Fish Scale Zone. These oil-bearing pods, of small areal extent, occur within the unit. A typical sequence of Barons Sandstone has at the base a black silty shale with lenticular sandstones exhibiting starved ripple cross-lamination. Overlying these rocks, and in sharp contact with them, is a medium to coarse-grained sandstone which exhibits high angle crossbedding, and contains shale rip-up clasts. This sandstone becomes finer grained upwards, grading into interbedded fine-grained sandstone and shale, and then into typical dark grey Colorado shale. The section is wholly marine, implying shelf or basin deposition in water of unknown depth. Deposition is postulated to be related to storm action in an anaerobic environment, at an unknown distance from shoreline. The sandstones are made up of chert, quartz, and abundant fish scales. In non-productive zones, poikilotopic calcite is the dominant cement, whereas in productive zones quartz overgrowths are the main cementing agents. A typical pay zone in the Barons Sandstone is about 1 metre thick, has porosity of up to 22 per cent, and permeability of several hundred millidarcies.
Abstract Digital stratigraphy was applied to the Mannville Group in the Edam area of west-central Saskatchewan. Stratigraphic cross-sections were constructed using well logs, and markers that could be carried with confidence throughout the study area were chosen. There are nine markers within the Mannville sediments, five markers above the Mannville and one for the top of the Paleozoic unconformity that received numeric codes. All available well logs were examined in order to determine lithology, but only electric logs were used to give lithological subdivisions a numeric code, based on relative S.P. deflections. The Edam area lies near the receding edge of thick beds of halite which comprise the Middle Devonian Prairie Formation. Significant variations in the thickness of the salt beds can be attributed to the solution of the Prairie evaporites. Computer generated structure, isopach and facies maps of different marker horizons have been used to determine the relationship of the solution of the Prairie evaporites to the deposition of the Mannville. Mappable structural and stratigraphic features, resulting from collapse of strata after localized solution of evaporites, include: (1) isolated prominences of salt; (2) subcircular or elongate sinks which appear as anomalies on structure maps for post-evaporite strata; (3) anomalous antiformal and synformal features; (4) anomalous thicks in post-evaporite strata; (5) dependence of ancient drainage patterns on antecedent trends in post-evaporite strata. The above features can be given a geologic age based on the reasoning that structural trends will generally be younger than the affected salt beds.
ABSTRACT A subsurface study of the upper Mannville sub-group (Vigrass, 1977) of east-central Alberta was undertaken in order to determine the sand body geometry and depositional format of channel fills and associated sediments. These channel fills are narrow (300 m minimum), thick (16 to 35 m), anastomosing shoestring bodies which trend north-northwest by south-southeast. The channel fills are enclosed by siltstones, shales, coals, and thin (6 m) sheet-like sandstones. Some of the channel and off-channel sandstones form important hydrocarbon reservoirs. The upper Mannville sub-group can be divided into three facies: a) major channel facies; b) crevassesplay, levee, overbank flood, and minor channel sandstone facies; and c) interdistributary quiet-water facies. The upper Mannville channel system is interpreted to be representative of an anastomosed fluvial system. Deposition was dominantly by vertical aggradation. The extreme lateral variation in lithologies points to a stratigraphically controlled hydrocarbon trapping mechanism. As of December 1978, the rocks of the upper Mannville sub-group of the study area were thought to contain reserves of 18 million bbl (3 106 m3) of oil and 2.3 tcf (66 109 m3) of natural gas in both channel and off-channel sandstone bodies.
Ground water moving through permeable Paleozoic carbonate rocks represents the most likely pathway for migration of radioactive contaminants from nuclear weapons testing at the Nevada Test Site, Nye County, Nevada. The strontium isotopic composition (87Sr/86Sr) of ground water offers a useful means of testing hydrochemical models of regional flow involving advection and reaction. However, reaction models require knowledge of 87Sr/86Sr data for carbonate rock in the Nevada Test Site vicinity, which is scarce. To fill this data gap, samples of core or cuttings were selected from 22 boreholes at depth intervals from which water samples had been obtained previously around the Nevada Test Site at Yucca Flat, Frenchman Flat, Rainier Mesa, and Mercury Valley. Dilute acid leachates of these samples were analyzed for a suite of major- and trace-element concentrations (MgO, CaO, SiO2, Al2O3, MnO, Rb, Sr, Th, and U) as well as for 87Sr/86Sr. Also presented are unpublished analyses of 114 Paleozoic carbonate samples from outcrops, road cuts, or underground sites in the Funeral Mountains, Bare Mountain, Striped Hills, Specter Range, Spring Mountains, and ranges east of the Nevada Test Site measured in the early 1990's. These data originally were collected to evaluate the potential for economic mineral deposition at the potential high-level radioactive waste repository site at Yucca Mountain and adjacent areas (Peterman and others, 1994). Samples were analyzed for a suite of trace elements (Rb, Sr, Zr, Ba, La, and Ce) in bulk-rock powders, and 87Sr/86Sr in partial digestions of carbonate rock using dilute acid or total digestions of silicate-rich rocks. Pre-Tertiary core samples from two boreholes in the central or western part of the Nevada Test Site also were analyzed. Data are presented in tables and summarized in graphs; however, no attempt is made to interpret results with respect to ground-water flow paths in this report. Present-day 87Sr/86Sr values are compared to values for Paleozoic seawater present at the time of deposition. Many of the samples have 87Sr/86Sr compositions that remain relatively unmodified from expected seawater values. However, rocks underlying the northern Nevada Test Site as well as rocks exposed at Bare Mountain commonly have elevated 87Sr/86Sr values derived from post-depositional addition of radiogenic Sr most likely from fluids circulating through rubidium-rich Paleozoic strata or Precambrian basement rocks.
Samples of Bakken Formation core from the Fleckton 1-20 well in Ward County, North Dakota, were analyzed using the Strontium Residual Salt Analysis (SrRSA) method to assess pore-water communication among the upper, middle, and lower sections of the unit by analyzing 87Sr/86Sr in pore-water salts leached from the core. Major and trace element analyses were also conducted on bulk-rock samples and leachates (Elemental Residual Salt Analysis or ERSA). The middle part of the Bakken Formation, a calcareous and dolomitic siltstone to fine sandstone, is encased between two black shales—the upper and lower sections of the formation. These units are informal and herein named the upper, middle, and lower Bakken members. Strontium isotope measurements and concentration of some solutes in leachates indicate that pore water in the black shale of the upper Bakken member has remained isolated from pore water in the middle Bakken member except for within a few feet immediately near the contact where elemental profiles indicate diffusive mixing. The SrRSA 87Sr/86Sr values from the middle Bakken member are consistent with produced water collected from 28 wells in Montana and North Dakota. In contrast to the similarity in 87Sr/86Sr values, ratios of concentrations such as K/Rb, Ca/Sr, Ca/Mg, and Na/Cl are slightly different between the pore-water leachates and produced water values. The differences in K/Rb and Ca/Sr are probably due to selective adsorption of Rb leading to larger K/Rb ratios and minor dissolution of carbonate minerals leading to larger Ca/Sr ratios in the leachates.
ABSTRACT Samples from four cored wells in central Alberta were studied by X-ray fluorescence and diffraction methods in order to determine the chemical composition and mineralogy of the Upper Devonian Ireton and Duvernay Formations. The results are presented as both chemical and mineralogic logs of the cores. The dominant minerals throughout are illite, chlorite, quartz, dolomite and calcite. Vertical variations are extreme, with rocks ranging from pure carbonate to those with about 25 per cent carbonate and the remainder consisting of the silicates. Individual stratigraphic units show no significant lateral variations across the basin. Both local and regional implications of the data are discussed.
Ground water moving through permeable Paleozoic carbonate rocks represents the most likely pathway for migration of radioactive contaminants from nuclear weapons testing at the Nevada Test Site, Nye County, Nevada. The strontium isotopic composition (87Sr/86Sr) of ground water offers a useful means of testing hydrochemical models of regional flow involving advection and reaction. However, reaction models require knowledge of 87Sr/86Sr data for carbonate rock in the Nevada Test Site vicinity, which is scarce. To fill this data gap, samples of core or cuttings were selected from 22 boreholes at depth intervals from which water samples had been obtained previously around the Nevada Test Site at Yucca Flat, Frenchman Flat, Rainier Mesa, and Mercury Valley. Dilute acid leachates of these samples were analyzed for a suite of major- and trace-element concentrations (MgO, CaO, SiO2, Al2O3, MnO, Rb, Sr, Th, and U) as well as for 87Sr/86Sr. Also presented are unpublished analyses of 114 Paleozoic carbonate samples from outcrops, road cuts, or underground sites in the Funeral Mountains, Bare Mountain, Striped Hills, Specter Range, Spring Mountains, and ranges east of the Nevada Test Site measured in the early 1990's. These data originally were collected to evaluate the potential for economic mineral deposition at the potential high-level radioactive waste repository site at Yucca Mountain and adjacent areas (Peterman and others, 1994). Samples were analyzed for a suite of trace elements (Rb, Sr, Zr, Ba, La, and Ce) in bulk-rock powders, and 87Sr/86Sr in partial digestions of carbonate rock using dilute acid or total digestions of silicate-rich rocks. Pre-Tertiary core samples from two boreholes in the central or western part of the Nevada Test Site also were analyzed. Data are presented in tables and summarized in graphs; however, no attempt is made to interpret results with respect to ground-water flow paths in this report. Present-day 87Sr/86Sr values are compared to values for Paleozoic seawater present at the time of deposition. Many of the samples have 87Sr/86Sr compositions that remain relatively unmodified from expected seawater values. However, rocks underlying the northern Nevada Test Site as well as rocks exposed at Bare Mountain commonly have elevated 87Sr/86Sr values derived from post-depositional addition of radiogenic Sr most likely from fluids circulating through rubidium-rich Paleozoic strata or Precambrian basement rocks.
