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Researchers found that neptunium, which is a small but very significant element within nuclear waste, is more stable in the environment than previously thought, which will make designing appropriate disposal methods more problematic. Tables and figures accompany the article.

Researchers from the Los Alamos National Laboratory in New Mexico performed experiments from the Yucca Mountain Nuclear Waste Repository site, NV for the solubility of neptunium and plutonium.

Changes in pore (throat) size, surface roughness, and mineralogy induced by supercritical CO2‐water‐rock reactions impact petrophysical properties such as porosity, permeability, and especially wettability. Herein, we show that these changes directly impact relative permeability and capillary pressure curves, a fact rarely studied in the literature. In this work, we show that CO2 contact angle changes emerge after Madison Limestone samples were soaked for 400 hr in CO2‐enriched brine. Coreflooding results show that the water production rate and cumulative water production increased after the rock was exposed to carbonic acid. Moreover, the mercury capillary pressure decreased in mesopores and macropores, indicating the increase of size in these pores due to reactions. This compounded wettability and pore network alteration can directly affect CO2 injectivity, migration, and storage capacity. This fundamental insight into CO2 geological storage processes should aid practitioners to reduce uncertainties in forecasting CO2 distribution via injection simulation. Plain Language Summary: Emitting a large amount of greenhouse gases into the atmosphere has disrupted the global carbon cycle. CO2 captured from various sources could be transported to a close‐by site for injection into deep saline aquifers or oil/gas reservoirs for storage or/and enhanced oil recovery. Reactions between the rock and the carbonic acid can alter the rock fabric. These reactions can change rock properties, for example, pore structure, porosity, permeability, and wettability. These changes can affect capillary pressure and relative permeability. These rock alterations can significantly impact the fate of the injected CO2. Despite efforts made to determine changes in pore architecture or petrophysical properties, a few studies have investigated the impact of rock alteration on multiphase flow properties, namely, capillary pressure and relative permeability. Even less is understood on this subject when diffusion dominates over convective transport. Here we focused on changes in pore (throat) size distribution and wettability, and dynamic properties, as induced by geochemical reactions. We observed pore enlargement among the larger pores (mesopores to macropores) due to mineral dissolution, which contrasts with a decreased size in smaller pores (micropores), resulting from mineral precipitation. These processes lead to a more CO2 surface wetting and thereby capillary pressure and relative permeability. Key Points: CO2‐brine‐rock reactions at reservoir conditions improve CO2 wettabilityGeochemical reactions alter the rock pore architecture and multiphase flow responseMultiphase flow alterations correlate well with changes in wettability and pore structure [ABSTRACT FROM AUTHOR]

We present a reservoir geophysics study, including rock physics modeling and seismic inversion, of a carbon dioxide sequestration site in Southwestern Wyoming, namely the Rock Springs Uplift, and build a petrophysical model for the potential injection reservoirs for carbon dioxide sequestration. Our objectives include the facies classification and the estimation of the spatial model of porosity and permeability for two sequestration targets of interest, the Madison Limestone and the Weber Sandstone. The available dataset includes a complete set of well logs at the location of the borehole available in the area, a set of 110 core samples, and a seismic survey acquired in the area around the well. The proposed study includes a formation evaluation analysis and facies classification at the well location, the calibration of a rock physics model to link petrophysical properties and elastic attributes using well log data and core samples, the elastic inversion of the pre-stack seismic data, and the estimation of the reservoir model of facies, porosity and permeability conditioned by seismic inverted elastic attributes and well log data. In particular, the rock physics relations are facies-dependent and include granular media equations for clean and shaley sandstone, and inclusion models for the dolomitized limestone. The permeability model has been computed by applying a facies-dependent porosity-permeability relation calibrated using core sample measurements. The study shows that both formations show good storage capabilities. The Madison Limestone includes a homogeneous layer of high-porosity high-permeability dolomite; the Weber Sandstone is characterized by a lower average porosity but the layer is thicker than the Madison Limestone. [ABSTRACT FROM AUTHOR]

Magnesite (MgCO3) precipitation within the nanoconfined space of adsorbed H2O films (∼5 monolayers) was determined to have an apparent activation energy of only 36 ± 6 kJ mol−1, suggesting that Mg2+ under nanoconfinement adopts a hydration configuration that mimics that of aqueous Ca2+, at least energetically, if not also specifically in hydration structure. [ABSTRACT FROM AUTHOR]

Carbon capture, utilization, and storage, one proposed method of reducing anthropogenic emissions of CO2, relies on low permeability formations, such as shales, above injection formations to prevent upward migration of the injected CO2. Porosity in caprocks evaluated for sealing capacity before injection can be altered by geochemical reactions induced by dissolution of injected CO2 into pore fluids, impacting long-term sealing capacity. Therefore, long-term performance of CO2 sequestration sites may be dependent on both initial distribution and connectivity of pores in caprocks, and on changes induced by geochemical reaction after injection of CO2, which are currently poorly understood. This article presents results from an experimental study of changes to caprock porosity and pore network geometry in two caprock formations under conditions relevant to CO2 sequestration. Pore connectivity and total porosity increased in the Gothic Shale; while total porosity increased but pore connectivity decreased in the Marine Tuscaloosa. Gothic Shale is a carbonate mudstone that contains volumetrically more carbonate minerals than Marine Tuscaloosa. Carbonate minerals dissolved to a greater extent than silicate minerals in Gothic Shale under high CO2 conditions, leading to increased porosity at length scales <∼200 nm that contributed to increased pore connectivity. In contrast, silicate minerals dissolved to a greater extent than carbonate minerals in Marine Tuscaloosa leading to increased porosity at all length scales, and specifically an increase in the number of pores >∼1 μm. Mineral reactions also contributed to a decrease in pore connectivity, possibly as a result of precipitation in pore throats or hydration of the high percentage of clays. This study highlights the role that mineralogy of the caprock can play in geochemical response to CO2 injection and resulting changes in sealing capacity in long-term CO2 storage projects. [ABSTRACT FROM AUTHOR]

Subsurface injection of CO2 for enhanced hydrocarbon recovery, hydraulic fracturing of unconventional reservoirs, and geologic carbon sequestration produces a complex geochemical setting in which CO2-dominated fluids containing dissolved water and organic compounds interact with rocks and minerals. The details of these reactions are relatively unknown and benefit from additional experimentally derived data. In this study, we utilized an in situ X-ray diffraction technique to examine the carbonation reactions of forsterite (Mg2SiO4) during exposure to supercritical CO2 (scCO2) that had been equilibrated with aqueous solutions of acetate, oxalate, malonate, or citrate at 50 °C and 90 bar. The organics affected the relative abundances of the crystalline reaction products, nesquehonite (MgCO3·3H2O) and magnesite (MgCO3), likely due to enhanced dehydration of the Mg2+ cations by the organic ligands. These results also indicate that the scCO2 solvated and transported the organic ligands to the forsterite surface. This phenomenon has profound implications for mineral transformations and mass transfer in the upper crust. [ABSTRACT FROM AUTHOR]

The Thermopolis hydrothermal system is located in the southern portion of the Bighorn Basin, in and around the town of Thermopolis, in northwest Wyoming. It is the largest hydrothermal system in Wyoming outside of Yellowstone National Park. The system includes hot springs, travertine deposits, and thermal wells. Published models for the hydrothermal system propose the Owl Creek Mountains as the recharge zone, simple conductive heating at depth, and resurfacing of thermal waters up the Thermopolis Anticline. The geochemistry of the thermal waters of three active hot springs--Big Spring, White Sulphur Spring, and Teepee Fountain--is similar in composition and characteristic of carbonate or carbonate-bearing siliciclastic aquifers. Previous studies of the Thermopolis hydrothermal system postulate that the thermal waters are a mixture of waters from Paleozoic formations. Major element geochemical analyses available for waters from these formations are not of sufficient quality to determine whether the thermal waters are a mixture of the Paleozoic aquifers. In the time frame of this study (one year), the geochemistry of all three springs was constant through all four seasons, spanning spring snowmelt and recharge as well as latesummer and fall dryness. This relationship is consistent with a deep source not influenced by shallow, local hydrogeology. Anomalies are evident in the historic data set for the geochemistry of Big Spring. We speculate that anomalies occurring between 1906 and 1926 suggest mixing of source waters of Big Spring with waters from a siliciclastic formation, and that anomalies occurring between 1926 and 1933 suggest mixing with waters from a formation containing gypsum or anhydrite. Decreased concentrations measured in our study-- relative to concentrations measured between 1933 and 1976--may reflect mixing of thermal waters with more dilute waters. Current data are not sufficient to rigorously test these suggestions, and events of sufficient scale taking place in these timeframes have not been identified. [ABSTRACT FROM AUTHOR]