Estimating carbon dioxide residence time scales through noble gas and stable isotope diffusion profiles

The study of natural carbon dioxide reservoirs provides fundamental insight into processes involved in carbon capture and storage. However, the calculations of process rates such as dissolution of CO2 into formation water remain uncertain due to indirectly determined ages of the CO2 influx. The proposed ages for the Bravo Dome gas field in New Mexico, USA, vary from 56 ka to 1.5 Ma. Here we demonstrate that residence times can be estimated from simple modeling of noble gas and stable isotope diffusion profiles from the gas-water contact through the gas column. The Bravo Dome gas field shows a gradient in noble gas concentrations and isotopic ratios from east to west across the 70-km-wide field. A mantle-like end member with a 3He/4He (R/RA) ratio of up to 4.7 is found in the west in contrast to a groundwater end member with high concentrations of air- and crustal-derived noble gases in the east. The air- and crustal-derived noble gases decrease gradually toward the west. Stable isotope compositions (C and O) also vary across the field. Diffusion modeling of He, Ne, Ar, Kr, Xe, and δ13C data yield residence times for the CO2 between 14.1 ± 0.2 ka and 16.9 +1.1/–0.5 ka. This is far less than the previous estimates of 1.2–1.5 Ma based on apatite (U-Th)/He thermochronology, leading to a dissolution rate of 29,900 +11,800/–10,700 t/a to 35,900 ± 12,300 t/a, implying that 28% of the total emplaced CO2 dissolved. This new method can be applied to a wide variety of gas fields with variation in the concentration of groundwater-derived noble gases and allow a better assessment of the time scale of other diffusive fluid-fluid interactions

Constraining the fluid history of a CO2 -H2 S reservoir: insights from stable isotopes, REE and fluid inclusion microthermometry

Reservoirs that host CO2‐H2S‐bearing gases provide a key insight into crustal redox reactions such as thermochemical sulfate reduction (TSR). Despite this, there remains a poor understanding of the extent, duration, and the factors limiting this process on a reservoir scale. Here we show how a combination of petrography, fluid inclusion, rare earth element (REE), and carbon (δ13C), oxygen (δ18O), and sulfur (δ34S) stable isotope data can disentangle the fluid history of the world's largest CO2 accumulation, the LaBarge Field in Wyoming, USA. The carbonate‐hosted LaBarge Field was charged with oil around 80 Ma ago, which together with nodular anhydrite represent the reactants for TSR. The nodules exhibit two distinct trends of evolution in δ13C with both δ34S and δ18O that may be coupled to two different processes. The first trend was interpreted to reflect the coupled dissolution of anhydrite and reduction to elemental sulfur and the oxidation of organic compounds and associated precipitation of calcite during TSR. In contrast, the second trend was interpreted to be the result of the hydrothermal CO2 influx after the cessation of TSR. In addition, mass balance calculations were performed to estimate an approximate TSR reaction duration of 80 ka and to identify the availability of organic compounds as the limiting factor of the TSR process. Such an approach provides a tool for the prediction of TSR occurrence elsewhere and advancing our understanding of crustal fluid interactions

Treatment Response of Cystic Echinococcosis to Benzimidazoles: A Systematic Review

Over the past 30 years, benzimidazoles have increasingly been used to treat cystic echinococcosis (CE). The efficacy of benzimidazoles, however, remains unclear. We systematically searched MEDLINE, EMBASE, SIGLE, and CCTR to identify studies on benzimidazole treatment outcome. A large heterogeneity of methods in 23 reports precluded a meta-analysis of published results. Specialist centres were contacted to provide individual patient data. We conducted survival analyses for cyst response defined as inactive (CE4 or CE5 by the ultrasound-based World Health Organisation [WHO] classification scheme) or as disappeared. We collected data from 711 treated patients with 1,308 cysts from six centres (five countries). Analysis was restricted to 1,159 liver and peritoneal cysts. Overall, 1–2 y after initiation of benzimidazole treatment 50%–75% of active C1 cysts were classified as inactive/disappeared compared to 30%–55% of CE2 and CE3 cysts. Further in analyzing the rate of inactivation/disappearance with regard to cyst size, 50%–60% of cysts <6 cm responded to treatment after 1–2 y compared to 25%–50% of cysts >6 cm. However, 25% of cysts reverted to active status within 1.5 to 2 y after having initially responded and multiple relapses were observed; after the second and third treatment 60% of cysts relapsed within 2 y. We estimated that 2 y after treatment initiation 40% of cysts are still active or become active again. The overall efficacy of benzimidazoles has been overstated in the past. There is an urgent need for a pragmatic randomised controlled trial that compares standardized benzimidazole therapy on responsive cyst stages with the other treatment modalities

Geochemical and mineralogical aspects of acid mine drainage associated with 100 years of coal mining in the arctic, Svalbard (78°N)

Acid mine drainage (AMD) is a pressing issue due to increasing mining activities in arctic climate zones. Over 100 years of coal mining in Svalbard presents an ideal study case for the development of AMD in arctic regions. The mined coal (low liptinite type oil prone coal) has less than 1.1 wt% sulphur with micro inclusions of pyrite but the contacting silt and sandstones contain pyrite nodules of centimeter size. These forms of pyrite are left to oxidize on multiple large waste rock piles. Simple accounting of the acid producing and neutralizing potential reveals that all studied lithologies are prone to produce acid waters despite a relatively low pyrite content but with an almost absent neutralization potential. During spring and summer, there are small streams draining the waste rock piles with a pH of 2.5 to 3.7, buffered by an iron hydroxide assemblage. The sulphate concentration of the water samples correlates well with the sum of the cations, indicating that pyrite oxidation is the dominant weathering process. There is no correlation between the age of the waste rock piles and the acidity of the effluents and the system might be controlled by the geometry of the waste rock piles combined with the local hydrology. Mass balance calculations for one of the mine sites estimates that AMD will continue for another 150 years. The sole operating mine site to date is likely to face a similar prospect once lime buffering measures seize.Validerad;2023;Nivå 2;2023-08-10 (joosat);Licens fulltext: CC BY License</p

Reaction path modelling illustrating the fluid history of a natural CO2-H2S reservoir

Despite the increasing interest in geologic co-sequestration of CO2 and H2S, the long-term consequences of the chemical interactions involved in this process remain largely unknown on a reservoir scale. A Mississippian aged CO2-H2S reservoir in LaBarge Field, Wyoming, USA is an ideal study site to investigate mineral and fluid reactions related to gaseous H2S and CO2. We conducted two reaction path models based on mineralogical, fluid, gas, and stable isotope compositional data to discern the role of CO2 influx upon the generation of H2S through thermochemical sulphate reduction (TSR). We discriminate between two models-one in which TSR is triggered by temperature at a given burial depth and one where TSR is triggered by ingress of CO2. The reaction path model based upon burial-controlled TSR and later CO2 influx is consistent with mineralogical observations and stable isotope measurements from drill cores. The models show that CO2 influx leads to calcite precipitation which is only limited by the calcium concentration in the fluid. This modelling approach is useful in constraining the timing of fluid flux in the reservoir and gives further insight into the mineralogical consequences of the gas, water, and rock interactions occurring in the reservoir. In terms of geologic co-sequestration this implies that the addition of CO2 into a reducing carbonate system can result in calcite precipitation, instead of anhydrite as previously thought. Furthermore, it is only limited by the availability of Ca2+ and will therefore not diminish the amount of H2S in the system

Porewater profiles of Cl and Br in boreholes penetrating the Mesozoic sequence in northern Switzerland

The analysis of tracer profiles of porewaters is a valuable tool to understand transport processes in argillaceous rocks and to unravel the paleo-hydrogeology of a site. In this contribution, anionic tracers (Cl, Br) from eight boreholes located in three study areas (∼20 km apart) penetrating the ∼800 m thick Mesozoic sequence in northern Switzerland, were analysed. A specific focus was on the Opalinus Clay, a ∼100 m thick homogeneous claystone formation, foreseen as host rock for radioactive waste disposal in Switzerland, as well as its mostly clay-rich confining units. Using porewater extraction methods, such as high-pressure squeezing, advective displacement and aqueous extraction, a unique dataset of spatially highly resolved Cl and Br profiles could be obtained. These show systematic and comparable patterns suggesting common paleo-hydrogeological evolution paths for all three study areas. The scatter in the tracer profiles based on the aqueous extraction data are mostly related to the uncertainty in the estimation of the anion-accessible porosity fraction on one hand and in the water content data in the case of low-porosity calcareous rocks on the other. Differences between the study areas are in line with differences in aquifer characteristics. The current shape of the anion profiles is dominated by diffusive exchange with the bounding aquifers over the last several ten thousands to millions of years, as supported by numerical modelling. The Br/Cl signals also suggest the preservation of older signals related to halite dissolution and highly evolved evaporitic porewaters occurring in evaporite-bearing units of the Triassic. Overall, the adopted methodology has enabled to obtain a unique dataset of anionic tracers at regional scale providing a solid basis for understanding the regional paleo-hydrogeology of siting areas for a potential nuclear waste repository

Mannose-binding lectin cord blood levels and respiratory symptoms during infancy: a prospective birth cohort study

Respiratory infections cause considerable morbidity during infancy. The impact of innate immunity mechanisms, such as mannose-binding lectin (MBL), on respiratory symptoms remains unclear. The aims of this study were to investigate whether cord blood MBL levels are associated with respiratory symptoms during infancy and to determine the relative contribution of MBL when compared with known risk factors. This is a prospective birth cohort study including 185 healthy term infants. MBL was measured in cord blood and categorized into tertiles. Frequency and severity of respiratory symptoms were assessed weekly until age one. Association with MBL levels was analysed using multivariable random effects Poisson regression. We observed a trend towards an increased incidence rate of severe respiratory symptoms in infants in the low MBL tertile when compared with infants in the middle MBL tertile [incidence rate ratio (IRR) = 1.59; 95% confidence interval (CI): 0.95-2.66; p = 0.076]. Surprisingly, infants in the high MBL tertile suffered significantly more from severe and total respiratory symptoms than infants in the middle MBL tertile (IRR = 1.97; 95% CI: 1.20-3.25; p = 0.008). This association was pronounced in infants of parents with asthma (IRR = 3.64; 95% CI: 1.47-9.02; p = 0.005). The relative risk associated with high MBL was similar to the risk associated with well-known risk factors such as maternal smoking or childcare. In conclusion the association between low MBL levels and increased susceptibility to common respiratory infections during infancy was weaker than that previously reported. Instead, high cord blood MBL levels may represent a so far unrecognized risk factor for respiratory morbidity in infants of asthmatic parents