The use of tracers to assess leakage from the sequestration of CO2 in a depleted oil reservoir,New Mexico,USA

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.     

River discharge controls phytoplankton dynamics in the northern San Francisco Bay estuary

Phytoplankton dynamics in the upper reach of the northern San Francisco Bay estuary are usually characterized by low biomass dominated by microflagellates or freshwater diatoms in winter, and high biomass dominated by neritic diatoms in summer. During two successive years of very low river discharge (the drought of 1976-77), the summer diatom bloom was absent. This is consistent with the hypothesis that formation of the diatom population maximum is a consequence of the same physical mechanisms that create local maxima of suspended sediments in partially-mixed estuaries: density-selective retention of particles within an estuarine circulation cell. Because the estuary is turbid, calculated phytoplankton growth rates are small in the central deep channel but are relatively large in lateral shallow embayments where light limination is less severe. When river discharge falls within a critical range (100–350 m³ s^?1) that positions the suspended particulate maximum adjacent to the productive shallow bays, the population of neritic diatoms increases. However, during periods of high discharge (winter) or during periods of very low discharge (drought), the suspended particulate maximum is less well-defined and is uncoupled (positioned downstream or upstream) from the shallow bays of the upper estuary, and the population of neritic diatoms declines. Hence, the biomass and community composition of phytoplankton in this estuary are controlled by river discharge.     

Effect of mining and related activities on the sediment trace element geochemistry of Lake Coeur D'Alene,Idaho, USA part II: Subsurface sediments

During the summer of 1990, 12 gravity cores were collected in Lake Coeur d'Alene, Idaho at various depths and in a variety of depositional environments. All core subsamples were analysed to determine the bulk sediment chemistry; selected subsamples were analysed for trace element partitioning and ¹³⁷Cs activity. The purpose of these analyses was to determine the trace element concentrations and distributions in the sediment column and to try to establish a trace element geochemical history of the lake in relation to mining and mining-related discharge operations in the area. Substantial portions of the near-surface sediments in Lake Coeur d'Alene are markedly enriched in Ag, As, Cd, Hg, Pb, Sb and Zn, and slightly enriched in Cu, Fe and Mn. Variations in the thickness of the trace element-rich sediments, which range from more than 119 cm to as little as 17 cm, indicate that the source of much of this material is the Coeur d'Alene River. An estimated 75 million tonnes of trace element-rich sediments have been deposited on or in the lake bed. Estimated trace element masses in excess of those considered representative of background conditions range from a high of 468 000 tonnes of Pb to a low of 260 tonnes of Hg. The similarity between the trace element-rich surface and subsurface sediments with respect to their location, their bulk chemistry, their interelement relations and their trace element partitioning indicate that the sources and/or concentrating mechanisms causing the trace element enrichment in the lake sediments have probably been the same through-out their depositional history. Based on a Mt St Helens'ash layer from the 1980 eruption, ages estimated from ¹³⁷Cs activity and the presence of 80 discernible and presumably annual layers in a core collected near the Coeur d'Alene River delta indicate that deposition rates for the trace element-rich sediments have ranges from 2.1 to 1.3 cm/year. These data also indicate that the deposition of trace element-rich sediments began, at least in the Coeur d'Alene River delta, some time between 1895 and 1910, dates consistent with the onset of mining and ore processing activities that began in the area in the 1880s.     

Evidence for the existence of groups of meteorite-producing asteroidal fragments

Abstract— The MORP camera network in western Canada observed 56 events which we associate with meteorites larger than 0.1 kg. An additional 33 Prairie Network (central USA) fireballs with published orbits were previously identified as the sources of meteorites of at least 0.25 kg. A comparison of the MORP orbits with each other and with the PN orbits, using the D′ criterion of orbital similarity, exhibits a surprising number of small values. This suggests there are groups of related objects among the 89 events. We evaluate the probability of small values of D′ arising by chance from a group of random orbits that has the distribution of orbital elements expected for meteorites. There is an excess of small values of D′ among the 89 meteoritic objects over the expectation for random orbits and a marked excess of very small values. Four groups comprising a total of 16 objects account for this excess. These groups exhibit a preference for the larger masses of the population and a very strong concentration of perihelia just slightly inside the Earth's orbit. Although it has been shown by others that gravitational perturbations will disperse Earth-crossing streams in times that are much less than cosmic-ray exposure ages, the properties of the four groups suggest they may be streams of fragments that crossed the Earth's orbit only recently. Such streams may include a considerable fraction of meteorites falling at a given time. Orbital evolution of these streams could alter the sample of meteorites arriving on Earth over time intervals that are less than the accumulation time of the Antarctic collections.     

On the penetration of a hot diapir through a strongly temperature-dependent viscosity medium

Summary. The ascent of a hot spherical body through a fluid with a strongly temperature-dependent viscosity has been studied using an axisymmetric finite element method. Numerical solutions range over Peclet numbers of 10⁻¹– 10³ from constant viscosity up to viscosity variations of 10⁵. Both rigid and stress-free boundary conditions were applied at the surface of the sphere. The dependence of drag on viscosity variation was shown to have no dependence on the stress boundary condition except for a Stokes flow scaling factor. A Nusselt number parameterization based on the stress-free constant viscosity functional dependence on the Peclet number scaled by a parameter depending on the viscosity structure fits both stress-free and rigid boundary condition data above viscosity variations of 100. The temperature scale height was determined as a function of sphere radius. For the simple physical model studied in this paper pre-heating is required to reduce the ambient viscosity of the country rock to less than 10²² cm² s⁻¹ in order for a 10 km diapir to penetrate a distance of several radii.     

GEOGRAPHERS' RANKINGS OF FOREIGN GEOGRAPHY AND NON-GEOGRAPHY JOURNALS

Questionnaires sent to 500 geographers randomly selected from U.S. graduate departments solicited opinions on the quality of scholarship of articles in 65 journals: 33 foreign geography journals and 32 non-geography journals. The five highest ranked were Science, Geological Society Bulletin, Journal of Atmospheric Sciences, Journal of Sedimentary Petrology, and Journal of Ecology. When familiarity and quality were considered together, the top five were Science, Canadian Geographer, Progress in Human Geography, Geographical Journal, and Transactions of the IBG. Specialty of respondent proved most significant in explaining ranking variations.     

Observations and comments for the solar event of 24 October, 1969

Observations of the flare of October 24, 1969 by Zirin et al. (1971) Solar Phys. 19, 463, are given with accompanying graphs of XUV emissions from satellites and four microwave radio emissions from Sagamore Hill Observatory. This event provides an excellent example of the development of two types of radio spectra within the same center and similar profiles for the hard X-ray burst and the 8800 MHz radio profile. The examination of the 2700 MHz burst from the Dominion Radio Astrophysical Observatory provides a clarification of the radio profile and shows the existence of a long enduring burst not previously considered. This event parallels a similar variation of intensity in the soft X-ray burst.     

The typical meteorite event,based on photographic records of 44 fireballs

Abstract— We study the observational data relating to 44 events recorded by the Canadian fireball camera network between 1971 and 1984. Each event is believed to have dropped meteorites, with main masses in the range from 0.1 to 11 kg. Median values are given for 20 parameters describing the atmospheric behavior and orbital elements. A typical duration for a meteoritic fireball is 4 seconds, reaching an end height of 31 km and a velocity of 8 km s^?1 at the end of the luminous path. The peak brightness is typically ?9 magnitude but varies from ?7 to ?15. Meteorites may survive from relatively unspectacular fireballs. Numerous correlations among parameters are investigated. The strong correlations of brightness with initial mass and of duration with slope of the trajectory could be anticipated. Moderate correlations also exist between: (1) initial mass and end height; (2) initial mass and duration of luminosity; (3) initial velocity and beginning height; (4) initial velocity and the fraction of the mass that survives as the largest fragment; (5) initial velocity and the perihelion distance of the orbit. Ablation limits the survival of small masses while fragmentation is usually severe for masses larger than 10 kg. The fractional survival may peak for entry masses between 1 and 10 kg.     

Interactions between perched and saprolite aquifers on a small,salt-affected and deeply weathered hillslope

A small hillslope was chosen to investigate the role of throughflow as a mechanism responsible for the movement of soil water and solutes towards a saline seep and as a source of recharge to a permanent, regional aquifer at depth. The hydraulic properties, chemical characteristics and physical responses of both systems were studied on a deeply weathered, salt-affected hillslope. Additional data were also obtained from other sites in south-western Australia. Regional groundwater flow occurred in a variably textured, deeply weathered material in which the hydraulic conductivity varied from < 0·001 to 0·14m day^?1. Perched groundwater flow (throughflow) occurred in the higher permeability (? 1·5 m day^?1), near-surface soil materials. Throughflow occurred throughout winter, contributing approximately 530 m³ of fresh (? 160 mg l^?1 Cl) water to a saline seep. By contrast, the deep aquifer discharged approximately 1100 m³ of waters with salt concentrations of 2000–6000 mg l^?1 Cl. Recharge and discharge rates to and from the deep aquifer, were estimated to be of the order of 5–20 mm a^?1 and 50–300 mm a^?1 respectively. Saturated conditions existed throughout winter within the seep and the immediately adjacent non-saline area, with up to 60 per cent of the hillslope soils becoming saturated after major rainfall events ( > 20 mm day^?1). In the mid-slopes, in particular along a central depression, saturation of the shallow soils caused macropore channel recharge to take place through the clay-textured subsoils. Water-level responses suggest that approximately 25–30 per cent of annual recharge occurred from one storm studied in September 1984. Recharge through macropore channels is a significant mechanism in the concave slope areas on the hillslope. Throughflow was found to be a major source of water, but not salt, contributing to the saline seep. In general, the contribution of throughflow was found to decrease further inland at other sites studied. However, at inland sites where perennial, perched aquifers have developed in deep sands, saline areas have been caused by throughflow and not by deep aquifer discharge.     

The relationship between geology and landforms along a coastal mountain front,northern Calabria,Italy

The geomorphology of the central Coastal Range, a north-south trending horst along the west coast of northern Calabria, is governed largely by major faults, fault scarps and the distribution of principal rock types, as well as by a variety of slope processes operative in a Mediterranean climate. Segments of the major rivers and streams have three principal orientations parallel to major faults in the study area: northwest right-oblique slip faults (oldest); E-W oblique slip faults; NE left-oblique slip faults; and north-south right oblique normal faults (youngest), all of which cut pre-Tertiary metamorphic rocks, Mesozoic limestone, Miocene molasse and calcarenite. Small, underfit alluvial fans, composed chiefly of locally derived debris flow detritus, are present at the mouths of large, west-flowing canyons, some of which reach eastward to the crest of the mountain range. Not only do the north-south normal faults displace rocks and structures of all orientations, but they also make steep scarps in the small alluvial fans and in sediments of the coastal plain. Locally, some of the scarps are buried by recent debris flow deposits. Incipient young rivers utilized the weaknesses along the major faults and cracks as avenues of erosion. Smaller streams and gullies generally flowed westward downflank of the north-trending horst and incised, thereby, deep, V-shaped canyons; some of them have captured older, SW-flowing canyons. Locally, they were guided in other directions where they encountered faults or tectonic fractures. The rocks present a varied resistance to erosion, depending upon the degree of cementation by groundwater salts, upon the orientation of the foliation, and upon the rocks themselves. Thus, mica schist with a relatively flat foliation forms nearly vertical sea cliffs, but the sea cliffs are more gentle where the foliation is steep or dips towards the sea. Therefore, downslope movements are facilitated by seaward slip on foliation, schistosity, bedding and fault surfaces, and are evinced especially by large and deep pre-Holocene landslides (Sackung) in phyllite having areal dimensions up to 2 Km². Other downslope processes include surficial creep and soil slip, particularly of highly fractured phyllite and schist, block sliding and rock falls.