Procedia Earth and Planetary Science最新文献

Water-quality and isotopic data were collected in central Nevada, USA in an exploration hydraulic fracturing area with no previous oil or gas production. The target shales of the Elko Formation are unique fresh-water hydrocarbon reservoirs with relatively dilute source water (8.5 g/L total dissolved solids [TDS]). Additionally, the Elko Formation is underlain by a fresh-water carbonate aquifer (0.2-0.3 g/L TDS) that outcrops downgradient of the exploration area. The water quality and isotopic data were used to evaluate pre-hydraulic fracturing conditions in this undeveloped area. The same data were also collected for groundwater and surface-water sites about two months and one year after exploration hydraulic fracturing. No systematic differences in water chemistry were observed between pre- and post-hydraulic fracturing samples. Based on water chemistry of shallow groundwater, surface water, and from the production zone, the most useful constituents identified for monitoring for potential future incursion of reservoir-associated fluids into the near-surface environment are TDS (or electrical conductivity), chloride, propane, methanol, ethanol, and 2-butoxyethanol. Groundwater flow and transport models were developed to evaluate the potential movement of hydrocarbons and hydraulic fracturing fluids from the targeted zones, which are about 1800 to 3600 m beneath the land surface, to shallow groundwater (<300 m below land surface). Model simulations indicate that hydraulic fracturing fluid remains contained within the target shales for at least 1,000 years for most development scenarios.

The reservoir temperature of the waters in the low temperature carbonate-evaporitic geothermal system of Arnedillo has been estimated by using two different techniques: 1) chemical geothermometers and 2) geothermometrical modelling. By combining the results of both techniques a reliable range of temperature of 90 ± 20°C has been proposed for the waters in the reservoir. Despite being a carbonate-evaporitic system, the cationic geothermometers have provided good results, which, together with the geothermometrical modelling, indicate that the waters have reached equilibrium with anhydrite, quartz, calcite, dolomite, albite and K-feldspar in the reservoir.

In order to identify the effects of groundwater colloids on iodine mobilization in aquifer system, nine groundwater samples were in-situ filtered through successive pore-sized membranes (0.45 μm, 30 kDa and 5 kDa) using filtration technique under N₂ atmosphere. Obvious decrease in groundwater iodine, Fe, Al and DOC was observed in the larger pore-sized fractions, indicating that groundwater iodine is closely associated with larger Fe-Al colloids. The analysis result of sample DT15-27 suggests that the extremely reducing condition could promote iodine dissolved in the truly dissolved phase. For low iodine groundwater, no good correlation between iodine and Fe, Al, DOC was observed for all sequential filtration steps, suggesting that groundwater iodine is trapped in the truly dissolved phase because of competitive adsorption of iron/aluminum.

After mine closure and subsequent shutdown of the dewatering system, groundwater rebound led to drainage outflow from the Casargiu gallery (Montevecchio mine, SW Sardinia, Italy) since 1997. As compared with the first discharge, a very high contamination level still persists after almost 20 years of flushing. Mine drainage (20-70 L s^-1; pH 6.0±0.2; Zn-Mg-Ca-SO₄ composition) flows into the Rio Irvi. Abundant precipitation of amorphous Fe(III)-(oxy)hydroxides occurs. Moreover, sulfate-bearing green rust is observed to flocculate in the reach of the Rio Irvi where pH is still circumneutral. Water sampling along this stream shows a pH decrease from 6.0 to 4.0 and a significant removal of Fe (46%) and As (96%), while sulfate, Zn, Mn, Co, Ni and Cd show small variations downstream. Lead is initially adsorbed onto Fe(III)-(oxy)hydroxides, then desorbed as pH drops below 5.4. A conservative estimation of dissolved metals discharged into the Mediterranean Sea is significant (e.g. 900 kg day^-1 Zn, 1.4 kg day^-1 Cd, 5 kg day^-1 Ni).