Quick-look assessments to identify optimal CO2 EOR storage sites

A newly developed, multistage quick-look methodology allows for the efficient screening of an unmanageably large number of reservoirs to generate a workable set of sites that closely match the requirements for optimal CO₂ enhanced oil recovery (EOR) storage. The objective of the study is to quickly identify miscible CO₂ EOR candidates in areas that contain thousands of reservoirs and to estimate additional oil recovery and sequestration capacities of selected top options through dimensionless modeling and reservoir characterization. Quick-look assessments indicate that the CO₂ EOR resource potential along the US Gulf Coast is 4.7 billion barrels, and CO₂ sequestration capacity is 2.6 billion metric tons. In the first stage, oil reservoirs are screened and ranked in terms of technical and practical feasibility for miscible CO₂ EOR. The second stage provides quick estimates of CO₂ EOR potential and sequestration capacities. In the third stage, a dimensionless group model is applied to a selected set of sites to improve the estimates of oil recovery and storage potential using appropriate inputs for rock and fluid properties, disregarding reservoir architecture and sweep design. The fourth stage validates and refines the results by simulating flow in a model that describes the internal architecture and fluid distribution in the reservoir. The stated approach both saves time and allows more resources to be applied to the best candidate sites.     

Mineralogy and geochemistry of the Texeo Cu–Co mine site (NW Spain): screening tools for environmental assessment

The Cu–Co–Ni Texeo mine has been the most important source of Cu in NW Spain since Roman times and now, approximately 40,000 m³ of wastes from mine and metallurgical operations, containing average concentrations of 9,263 mg kg⁻¹ Cu, 1,100 mg kg⁻¹ As, 549 mg kg⁻¹ Co, and 840 mg kg⁻¹ Ni, remain on-site. Since the cessation of the activity, the abandoned works, facilities and waste piles have been posing a threat to the environment, derived from the release of toxic elements. In order to assess the potential environmental pollution caused by the mining operations, a sequential sampling strategy was undertaken in wastes, soil, surface and groundwater, and sediments. First, screening field tools were used to identify hotspots, before defining formal sampling strategies; so, in the areas where anomalies were detected in a first sampling stage, a second detailed sampling campaign was undertaken. Metal concentrations in the soils are highly above the local background, reaching up to 9,921 mg kg⁻¹ Cu, 1,373 mg kg⁻¹ As, 685 mg kg⁻¹ Co, and 1,040 mg kg⁻¹ Ni, among others. Copper concentrations downstream of the mine works reach values up to 1,869 μg l⁻¹ and 240 mg kg⁻¹ in surface water and stream sediments, respectively. Computer-based risk assessment for the site gives a carcinogenic risk associated with the presence of As in surface waters and soils, and a health risk for long exposures; so, trigger levels of these elements are high enough to warrant further investigation.     

Environmental risk evaluation of the use of mine spoils and treated sewage sludge in the ecological restoration of limestone quarries

The ecologic restoration criteria in areas degraded from extraction activities require making use of their mine spoils. These materials do not meet fertility conditions to guarantee restoration success and therefore, need the incorporation of organic amendments to obtain efficient substratum. Reducing the deficiencies in the organic material and restoration material nutrients with the contribution of treated sewage sludge is proposed in this work. This experiment was based on a controlled study using columns. The work was conducted with two mine spoils, both very rich in calcium carbonate. The first mineral, of poor quality, came from the formation of aggregates of crushed limestone (Z). The other residual material examined originated in limestone extraction, formed by the levels of interspersed non-limestone materials and the remains of stripped soils (D). Two treatments were undertaken (30,000 and 90,000 kg/ha of sewage sludge), in addition to a control treatment. The water contribution was carried out with a device that simulated either short-duration rain or a flooding irrigation system in order to cover the surface and then percolate through the soil. The collection of leached water took place 24 h after the applications. Different parameters of the leached water were determined, including pH, electrical conductivity, nitrate anions, ammonium, phosphates, sulphates and chlorides. The values obtained for each irrigation application are discussed, and the nitrate values obtained were very elevated.     

The use of principle component analyses in characterising trace and major elemental distribution in a 55 kyr peat deposit in tropical Australia: Implications to paleoclimate

The Lynch’s Crater peat deposit in NE-Australia is a sensitive environmental archive located in the tropical Southern Hemisphere. This unique deposit illustrates that local and regional changes had a profound effect on the local Australian ecosystem over the past 55 kyr. To obtain a proxy of past climate changes, trace and major element geochemistry analyses were applied to a 13 m peat core from the crater. Principle component analysis (PCA) was used to identify the main factors that control elemental distribution in the peat and to add interpretative strength to the geochemical behavior of selected major and trace elements. For example, Sc, Al, Cu, and Pb were found to be related to increased erosion of the basin soils, and from this, several periods of significant flux from atmospheric input and/or terrigenous run-off were identified. Geochemically mobile elements during rock weathering and pedogenesis, such as Mg, Ca, and Sr helped to identify the peat ombrotrophic-minerotrophic boundary at ∼1.5 m depth and offered important information about fluxes of these nutrients to the mire and their dynamics within the deposit. Arsenic and V comparisons between the peat record (high concentrations in some peat sections) and in local basin rocks (very low concentrations), suggested the presence of a long range, atmospheric dust source early in the formation of the mire. The Lynch’s Crater peat record presents a continuous record of environmental change in tropical Australia and contributes new understanding to geochemical processes in peatlands.     

Determination of fluid/melt partition coefficients by LA-ICPMS analysis of co-existing fluid and silicate melt inclusions: Controls on element partitioning

Analyses of co-existing silicate melt and fluid inclusions, entrapped in quartz crystals in volatile saturated magmatic systems, allowed direct quantitative determination of fluid/melt partition coefficients. Investigations of various granitic systems (peralkaline to peraluminous in composition, log fO₂ = NNO−1.7 to NNO+4.5) exsolving fluids with various chlorinities (1-14 mol/kg) allowed us to assess the effect of these variables on the fluid/melt partition coefficients (D). Partition coefficients for Pb, Zn, Ag and Fe show a nearly linear increase with the chlorinity of these fluid (D_Pb ∼ 6 ∗ m_Cl, D_Zn ∼ 8 ∗ m_Cl, D_Ag ∼ 4 ∗ m_Cl, D_Fe ∼ 1.4 ∗ m_Cl, where m_Cl is the molinity of Cl). This suggests that these metals are dissolved primarily as Cl-complexes and neither oxygen fugacity nor the composition of the melt affects significantly their fluid/melt partitioning. By contrast, partition coefficients for Mo, B, As, Sb and Bi are highest in low salinity (1-2 mol/kg Cl) fluids with maximum values of D_Mo ∼ 20, D_B ∼ 15, D_As ∼ 13, D_Sb ∼ 8, D_Bi ∼ 15 indicating dissolution as non-chloride (e.g., hydroxy) complexes. Fluid/melt partition coefficients of copper are highly variable, but highest between vapor like fluids and silicate melt (D_Cu ? 2700), indicating an important role for ligands other than Cl. Partition coefficients for W generally increase with increasing chlorinity, but are exceptionally low in some of the studied brines which may indicate an effect of other parameters. Fluid/melt partition coefficients of Sn show a high variability but likely increase with the chlorinity of the fluid (D_Sn = 0.3-42, D_W = 0.8-60), and decrease with decreasing oxygen fugacity or melt peraluminosity.     

Sedimentary petrology and geochemistry of siliciclastic rocks from the upper Jurassic Tordillo Formation (Neuquén Basin, western Argentina): Implications for provenance and tectonic setting

The Upper Jurassic Tordillo Formation is exposed along the western edge of the Neuquén Basin (west central Argentina) and consists of fluvial strata deposited under arid/semiarid conditions. The pebble composition of conglomerates, mineralogical composition of sandstones and pelitic rocks, and major- and trace-element geochemistry of sandstones, mudstones, and primary pyroclastic deposits are evaluated to determine the provenance and tectonic setting of the sedimentary basin. Conglomerates and sandstones derived almost exclusively from volcanic sources. The stratigraphic sections to the south show a clast population of conglomerates dominated by silicic volcanic fragments and a predominance of feldspathic litharenites. This framework composition records erosion of Triassic–Jurassic synrift volcaniclastic rocks and basement rocks from the Huincul arch, which was exhumed as a result of Late Jurassic inversion. In the northwestern part of the study area, conglomerates show a large proportion of mafic and acidic volcanic rock fragments, and sandstones are characterised by a high content of mafic volcanic rock fragments and plagioclase. These data suggest that the source of the sandstones and conglomerates was primarily the Andean magmatic arc, located west of the Neuquén Basin. The clay mineral assemblage is interpreted as the result of a complex set of factors, including source rock, climate, transport, and diagenesis. Postdepositional processes produced significant variations in the original compositions, especially the fine-grained deposits. The Tordillo sediments are characterised by moderate SiO₂ contents, variable abundances of K₂O and Na₂O, and a relatively high proportion of ferromagnesian elements. The degree of chemical weathering in the source area, expressed as the chemical index of alteration, is low to moderate. The major element geochemistry and Th/Sc, K/Rb, Co/Th, La/Sc, and Cr/Th values point to a significant input of detrital volcanic material of calcalkaline felsic and intermediate composition. However, major element geochemistry is not useful for interpreting the tectonic setting. Discrimination plots based on immobile trace elements, such as Ti, Zr, La, Sc, and Th, show that most data lie in the active continental margin field. Geochemical information is not sufficiently sensitive to differentiate the two different source areas recognized by petrographic and modal analyses of conglomerates and sandstones.     

The passivation of calcite by acid mine water. Column experiments with ferric sulfate and ferric chloride solutions at pH 2

Column experiments, simulating the behavior of passive treatment systems for acid mine drainage, have been performed. Acid solutions (HCl or H₂SO₄, pH 2), with initial concentrations of Fe(III) ranging from 250 to 1500 mg L⁻¹, were injected into column reactors packed with calcite grains at a constant flow rate. The composition of the solutions was monitored during the experiments. At the end of the experiments (passivation of the columns), the composition and structure of the solids were measured. The dissolution of calcite in the columns caused an increase in pH and the release of Ca into the solution, leading to the precipitation of gypsum and Fe–oxyhydroxysulfates (Fe(III)–SO₄–H⁺ solutions) or Fe–oxyhydroxychlorides (Fe(III)–Cl–H⁺ solutions). The columns worked as an efficient barrier for some time, increasing the pH of the circulating solutions from 2 to 6–7 and removing its metal content. However, after some time (several weeks, depending on the conditions), the columns became chemically inert. The results showed that passivation time increased with decreasing anion and metal content of the solutions. Gypsum was the phase responsible for the passivation of calcite in the experiments with Fe(III)–SO₄–H⁺ solutions. Schwertmannite and goethite appeared as the Fe(III) secondary phases in those experiments. Akaganeite was the phase responsible for the passivation of the system in the experiments with Fe(III)–Cl–H⁺ solutions.     

Impact of lightning on organic matter-rich soils: influence of soil grain size and organic matter content on underground fires

A detailed study was carried out on a piece of land that had been struck by lightning during the violent rainstorm that raged over the Island of S?o Miguel (Azores Archipelago) in late October 2006. Temperature and gas measurements (CO₂, CO, H₂S and CH₄) were performed in four study trenches, dug in an area of ∼3 m², where an underground fire had been initiated by the impact with a lightning stroke, followed by the emission of a column of gases and smoke. The soil under study was originally a well-pedogenized about 80 cm thick bed, made of volcanic clayey to silty tephra fallouts and contained 5.5–9.7% of organic matter. The underground fire was monitored for one week and revealed a peak release of 404 ppm CO and 3.4% CO₂ originating from a horizon located about 45 cm under the soil surface. Measurements of temperature, performed one week after the impact, indicated a maximum value of 326°C inside the soil, while 516.5°C were measured on the surface of a lava block interred about 20 cm under the surface. Subsequently, a stratigraphic and sedimentologic study proved the role of the grain-size of the soil and of the organic matter content of the different horizons of the impact area, in determining the ratio between anoxic/oxidised combustion conditions and in the progress of the process itself. It was also noticed that combustion was not total all over in the soil bed and that the process had slightly migrated toward SW during the observation period. The combustion process went on for about ten days, in spite of several other violent rainstorms, until it was artificially extinguished through the excavations made to obtain study trenches. This particular circumstance evidenced the potential natural hazard represented by this kind of atmospheric event, especially in a land where the volcanic nature of the soil may easily mislead inexperienced observers and, consequently, delay proper action.     

Rain-induced debris and mudflow triggering factors assessment in the Santiago cordilleran foothills,Central Chile

Debris and mudflows are some of the main geological hazards in the mountain foothills of the Chilean capital city of Santiago. There, the risk of flows triggered in the basins of ravines that drain the range into the city increases with time due to the city growth. A multivariate statistical study based on the logistic regression method is presented. The model provides equations that allow the computation of combined meteorological triggering factors associated with a probability of rain-induced flow occurrence. Daily rainfall, accumulated rainfall and the snowfall level, traditionally considered as the relevant factors, are analysed for a 25-year period. The results show a strong relevance of the rainfall on the day of the flow event over the other factors. However, the relatively low probabilities returned for some real flow events suggest that the model does not capture all the significant variables and the problem is more complex than as it has been traditionally assumed, and further investigations are needed to develop predictive models of flow triggering.