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321.
Grant Ferguson 《Ground water》2015,53(2):187-194
Injection of wastes into the deep subsurface has become a contentious issue, particularly in emerging regions of oil and gas production. Experience in other regions suggests that injection is an effective waste management practice and that widespread environmental damage is unlikely. Over the past several decades, 23 km3 of water has been injected into the Western Canada Sedimentary Basin (WCSB). The oil and gas industry has injected most of this water but large amounts of injection are associated with mining activities. The amount of water injected into this basin during the past century is 2 to 3 orders magnitude greater than natural recharge to deep formations in the WCSB. Despite this large‐scale disturbance to the hydrogeological system, there have been few documented cases of environmental problems related to injection wells. Deep injection of waste appears to be a low risk activity based on this experience but monitoring efforts are insufficient to make definitive statements. Serious uncharacterized legacy issues could be present. Initiating more comprehensive monitoring and research programs on the effects of injection in the WCSB could provide insight into the risks associated with injection in less developed sedimentary basins. 相似文献
322.
Dolerite sills, at times transgressive, and dykes are common at Majuba Colliery. Their behaviour within the Karoo stratigraphic pile limits and controls the effectiveness of extracting the deep-seated Gus coal seam. Due to the intrusion of dolerites, the coal seam elevation can vary by as much as 70 m. Data from 452 boreholes, 88 of which were drilled to granitic gneiss basement and data from the underground development were used to construct cross-sections through the colliery. Based on texture, geochemistry and mode of emplacement, there exist four different dolerite types (T1 to T4) at Majuba. These are intruded into sedimentary rocks of the Karoo Supergroup although one, the T3 dolerite, has been found intruded into basement gneiss. In the east, an ultramafic intrusion of pre-Karoo Supergroup age created a basement high. By far, the greatest number of dolerite sills intruded within a sandstone unit, and have identical sandstones in the footwall and hangingwall, rather than intruding along lithological boundaries. 相似文献
323.
Marian?B.?HolnessEmail author R.?Grant?Cawthorn James?Roberts 《Contributions to Mineralogy and Petrology》2017,172(11-12):102
The thickness of the crystal mush on magma chamber floors can be constrained using the offset between the step-change in the median value of dihedral angles formed at the junctions between two grains of plagioclase and a grain of another phase (typically clinopyroxene, but also orthopyroxene and olivine) and the first appearance or disappearance of the liquidus phase associated with the step-change in median dihedral angle. We determined the mush thickness in the Rustenburg Layered Suite of the Bushveld Complex at clinopyroxene-in (in Lower Main Zone) and magnetite-in (in Upper Zone). We also examined an intermittent appearance of cumulus apatite in Upper Zone, using both the appearance and disappearance of cumulus apatite. In all cases, the mush thickness does not exceed 4 m. These values are consistent with field observations of a mechanically rigid mush at the bases of both magnetitite and chromitite layers overlying anorthosite. Mush thickness of the order of a few metres suggests that neither gravitationally-driven compaction nor compositional convection within the mush layer is likely to have been important processes during solidification: adcumulates in the Bushveld are most likely to have formed at the top of the mush during primary crystallisation. Similarly, it is unlikely either that migration of reactive liquids occurs through large stretches of stratigraphy, or that layering is formed by mechanisms other than primary accumulation. 相似文献
324.
This research is supported by the Research Grants Council of the University Grants Committee of Hong Kong Grant . C. H. So Johnny C. L. Chan Department of Physics Materials Science City University of Hong Kong 《大气科学进展》1997,(2)
RegionalandSynoptic-scaleFeaturesAsociatedwithInactivePeriodsoftheSummerMonsoonoverSouthChina①C.H.SoandJohnnyC.L.ChanDepartme... 相似文献
325.
Arthur W. Wells J. Rodney Diehl Grant Bromhal Brian R. Strazisar Thomas H. Wilson Curt M. White 《Applied Geochemistry》2007
Geological sequestration of CO2 in depleted oil reservoirs is a potentially useful strategy for greenhouse gas management and can be combined with enhanced oil recovery. Development of methods to estimate CO2 leakage rates is essential to assure that storage objectives are being met at sequestration facilities. Perfluorocarbon tracers (PFTs) were added as three 12 h slugs at about one week intervals during the injection of 2090 tons of CO2 into the West Pearl Queen (WPQ) depleted oil formation, sequestration pilot study site located in SE New Mexico. The CO2 was injected into the Permian Queen Formation. Leakage was monitored in soil–gas using a matrix of 40 capillary adsorbent tubes (CATs) left in the soil for periods ranging from days to months. The tracers, perfluoro-1,2-dimethylcyclohexane (PDCH), perfluorotrimethylcyclohexane (PTCH) and perfluorodimethylcyclobutane (PDCB), were analyzed using thermal desorption, and gas chromatography with electron capture detection. Monitoring was designed to look for immediate leakage, such as at the injection well bore and at nearby wells, and to develop the technology to estimate overall CO2 leak rates based on the use of PFTs. Tracers were detected in soil–gas at the monitoring sites 50 m from the injection well within days of injection. Tracers continued to escape over the following years. Leakage appears to have emanated from the vicinity of the injection well in a radial pattern to about 100 m and in directional patterns to 300 m. Leakage rates were estimated for the 3 tracers from each of the 4 sets of CATs in place following the start of CO2 injection. Leakage was fairly uniform during this period. As a first approximation, the CO2 leak rate was estimated at about 0.0085% of the total CO2 sequestered per annum. 相似文献
326.
Grant Heiken Napoleon Ramos Wendell Duffield John Musgrave Kenneth Wohletz Sue Priest James Aldrich Wilmer Flores Alexander Ritchie Fraser Goff Dean Eppler Carlos Escobar 《Journal of Volcanology and Geothermal Research》1991,45(1-2)
The Platanares geothermal area, Departamento de Copán, Honduras, is located within a graben that is complexly faulted. The graben is bounded on the north by a highland composed of Paleozoic (?) metamorphic rocks in contact with Cretaceous - Tertiary redbeds of unknown thickness. These are unconformably overlain by Tertiary andesitic lavas, rhyolitic ignimbrites, and associated sedimentary rocks. The volcanic rocks are mostly older than 14 Ma, and thus are too old to represent the surface expression of an active crustal magma body. Thermal fluids that discharge in the area are heated during deep circulation of meteoric water along faults in a region of somewhat elevated heat flow. Geothermometry based upon the chemical composition of thermal fluids from hot springs and from geothermal gradient coreholes suggests that the reservoir equilibrated at temperatures as high as 225 to 240°C, within the Cretaceous redbed sequence. Three continuously cored geothermal gradient holes have been drilled; fluids of about 165°C have been produced from two drilled along a NW-trending fault zone, from depths of 250 to 680 m. A conductive thermal gradient of 139°C/km, at a depth of 400 m, was determined from the third well, drilled 0.6 km west of that fault zone. These data indicate that the Platanares geothermal area holds considerable promise for electrical generation by moderate- to hightemperature geothermal fluids. 相似文献
327.
The concept of global warming potential was developed as a relative measure of the potential effects on climate of a greenhouse gas as compared to CO2. In this paper a series of sensitivity studies examines several uncertainties in determination of Global Warming Potentials (GWPs). For example, the original evaluation of GWPs for the Intergovernmental Panel on Climate Change (IPCC, 1990) did not attempt to account for the possible sinks of carbon dioxide (CO2) that could balance the carbon cycle and produce atmospheric concentrations of CO2 that match observations. In this study, a balanced carbon cycle model is applied in calculation of the radiative forcing from CO2. Use of the balanced model produces up to 21% enhancement of the GWPs for most trace gases compared with the IPCC (1990) values for time horizons up to 100 years, but a decreasing enhancement with longer time horizons. Uncertainty limits of the fertilization feedback parameter contribute a 20% range in GWP values. Another systematic uncertainty in GWPs is the assumption of an equilibrium atmosphere (one in which the concentration of trace gases remains constant) versus a disequilibrium atmosphere (one in which the concentration of trace gases varies with time). The latter gives GWPs that are 19 to 32% greater than the former for a 100 year time horizons, depending upon the carbon dioxide emission scenario chosen. Five scenarios are employed: constant-concentration, constant-emission past 1990 and the three IPCC (1992) emission scenarios. For the analysis of uncertainties in atmospheric lifetime (τ) the GWP changes in direct proportion toτ for short-lived gases, but to a lesser extent for gases withτ greater than the time horizontal for the GWP calculation. 相似文献
328.
Kevin J. Grant Simon C. Kohn Richard A. Brooker 《Contributions to Mineralogy and Petrology》2006,151(6):651-664
The solubility of water in coexisting enstatite and forsterite was investigated by simultaneously synthesizing the two phases in a series of high pressure and temperature piston cylinder experiments. Experiments were performed at 1.0 and 2.0 GPa at temperatures between 1,100 and 1,420°C. Integrated OH absorbances were determined using polarized infrared spectroscopy on orientated single crystals of each phase. Phase water contents were estimated using the calibration of Libowitzky and Rossman (Am Mineral 82:1111–1115, 1997). Enstatite crystals, synthesized in equilibrium with forsterite and an aqueous phase at 1,350°C and 2.0 GPa, contain 114 ppm H2O. This is reduced to 59 ppm at 1,100°C, under otherwise identical conditions, suggesting a strong temperature dependence. At 1,350°C and 1.0 GPa water solubility in enstatite is 89 ppm, significantly lower than that at 2.0 GPa. In contrast water solubility in forsterite is essentially constant, being in the range 36–41 ppm for all conditions studied. These data give partition coefficients
in the range 2.28–3.31 for all experiments at 1,350°C and 1.34 for one experiment at 1,100°C. The incorporation of Al2O3 in enstatite modifies the OH stretching spectrum in a systematic way, and slightly increases the water solubility. 相似文献
329.
Susan J. Webb Lewis D. Ashwal R. Grant Cawthorn 《Contributions to Mineralogy and Petrology》2011,162(1):101-107
The three-dimensional shapes of mafic layered intrusions have to be inferred from surface outcrops, in some cases aided by drilling and/or geophysical data. However, geophysical models are often equivocal. For the 2.06?Ga Bushveld Complex of South Africa, early geological models proposed a shape of a single, gently inward dipping lopolith. Subsequent resistivity and gravity data were interpreted to suggest that the eastern and western limbs were discrete, dipping wedge-shaped intrusions separated by ~150?km. A more recent gravity model that takes crustal flexure into account allows continuity and the reversal to the original model. Distinguishing between these possibilities is difficult from surface-based studies because the central regions of the Complex are obscured by large volumes of younger granites and sedimentary/volcanic cover rocks. Here, we describe xenoliths from the Cretaceous Palmietgat kimberlite pipe, located mid-way between the exposed western and eastern lobes of the Complex. They are chromite-bearing feldspathic pyroxenites considered equivalent to those of the typical outcropping Critical Zone of the Bushveld Complex. This result provides strong support for a regionally interconnected Bushveld Complex, implying its emplacement as a single sill-like body. Confirming the continuity of the Bushveld Complex greatly expands exploration opportunities and implies that other layered mafic intrusions could have similar geometry. 相似文献
330.
Pollen data indicate Tilia was an important component of the primary woodland cover of many lowland areas in northern and central Europe. High values recorded in mid-Holocene pollen diagrams are generally followed by well-defined declines. In this study the palynological, spatial and temporal trends associated with declines in Tilia pollen at sites from lowland Britain are assessed to evaluate the nature and relative importance of the processes responsible. Processes primarily related to the depositional environment (paludification, marine inundation, breaks in sedimentation) and percentage representation of pollen data play the dominant role in 44% of the 164 declines included in the study. Anthropogenic activity can account for the remainder. Tilia rarely recovers from low values after anthropogenic declines, suggesting such declines have the potential to elucidate patterns in the destruction of primary woodland across lowland Britain. Other than declines associated with the mid-Holocene Ulmus decline event, few anthropogenic Tilia declines have been reliably dated prior to c. 5000 cal. BP. Tilia largely disappeared from areas with calcareous and loamy soils as a result of clearance activity in the period 5000–3000 cal. BP (Late Neolithic to Late Bronze Age). Between 3000 and 2500 cal. BP few declines are recorded suggesting a link between clearance activity and climate change. Later declines are concentrated on the sandier lithologies and often associated with heathland formation. The scarcity of declines after 2000 cal. BP is likely to be related to the exhaustion of primary woodland. 相似文献