Horizontal stress anisotropy and effective stress as regulator of coal seam gas zonation in the Sydney Basin, Australia

Coal seam gas zonation in the Sydney Basin, NSW, Australia is related to basin hydrodynamics and hydrochemical facies evolution along the flow path from the subcrop to the basin center. Biogenic methane corresponds with meteoric water under hydrostatic pressure and persists down to the top of the geopressured zone (~800 to 1000m). Thermogenic gases, including wet hydrocarbons, can reach up to relatively shallow horizons of less than 500-600m depth. In the transition zone between the top of the geopressured and base of the hydrostatic zone, a mixed water and gas regime prevails, comprising brackish waters, and gases of mixed biogenic, thermogenic and inorganic origins, including CO. Mechanisms for and the role of stress in the development of this layered hydrogeological and gas environment are investigated in this paper.The inverse relationship between effective horizontal stress and permeability in coals through regulation of cleat volumes is well documented, and there is evidence of regionally compartmentalized stress regimes with depth within the Sydney and other eastern Australian coal basins. This regional stress regime can be overprinted by the effect of localized geological features. It is hypothesized that the in situ stress regime plays an important role in the regulation of groundwater flow regimes and extents, resulting in the development of the reported gas content and compositional zonation.Analysis of regional gas and stress data obtained from public and private databases, as well as literature, supports this hypothesis. Changes in gas concentration and composition with depth correspond with discernable variations in horizontal stress anisotropy. Gas contents generally increase with depth down to a 'peak gas' horizon, below which concentrations decrease. This 'peak gas' zone is coincident with a horizontal stress anisotropy change from moderately high to low levels, associated with reverse to strike-slip faulting conditions, respectively. The stress release zone also marks the top of the thermogenic gas zone, identified by the first appearance of ethane in the vertical profile. This zone also hosts gases of mixed origins: biogenic, thermogenic and inorganic (CO) and represents a mixed (transitional) groundwater flow environment. The base of the mixed gas zone is the top of the 'geopressured-only' flow associated with thermogenic gases and is signaled by the return to high stress reverse faulting conditions below 850-900m depth in the Sydney Basin

Methodology to determine the extent of anaerobic digestion, composting and CH4 oxidation in a landfill environment

Abstract: An examination of the processes contributing to the production of landfill greenhouse gas (GHG) emissions is required, as the actual level to which waste degrades anaerobically and aerobically beneath covers has not been differentiated. This paper presents a methodology to distinguish between the rate of anaerobic digestion (rAD), composting (rCOM) and CH4 oxidation (rOX) in a landfill environment, by means of a system of mass balances developed for molecular species (CH4, CO2) and stable carbon isotopes (δ13C-CO2 and δ13C-CH4). The technique was applied at two sampling locations on a sloped area of landfill. Four sampling rounds were performed over an 18 month period after a 1.0 m layer of fresh waste and 30-50 cm of silty clay loam had been placed over the area. Static chambers were used to measure the flux of the molecular and isotope species at the surface and soil gas probes were used to collect gas samples at depths of approximately 0.5, 1.0 and 1.5 m. Mass balances were based on the surface flux and the concentration of the molecular and isotopic species at the deepest sampling depth. The sensitivity of calculated rates was considered by randomly varying stoichiometric and isotopic parameters by ±5% to generate at least 500 calculations of rOX, rAD and rCOM for each location in each sampling round. The resulting average value of rAD and rCOM indicated anaerobic digestion and composting were equally dominant at both locations. Average values of rCOM: ranged from 9.8 to 44.5 g CO2 m-2 d-1 over the four sampling rounds, declining monotonically at one site and rising then falling at the other. Average values of rAD: ranged from 10.6 to 45.3 g CO2 m-2 d-1. Although the highest average rAD value occurred in the initial sampling round, all subsequent rAD values fell between 10 and 20 g CO2 m-2 d-1. rOX had the smallest activity contribution at both sites, with averages ranging from 1.6 to 8.6 g CO2 m-2 d-1. This study has demonstrated that for an interim cover, composting and anaerobic digestion of shallow landfill waste can occur simultaneously

Mineralogical controls on porosity and water chemistry during O2-SO2-CO2 reaction of CO2 storage reservoir and cap-rock core

Reservoir and cap-rock core samples with variable lithology's representative of siliciclastic reservoirs used for CO storage have been characterized and reacted at reservoir conditions with an impure CO stream and low salinity brine. Cores from a target CO storage site in Queensland, Australia were tested. Mineralogical controls on the resulting changes to porosity and water chemistry have been identified. The tested siliciclastic reservoir core samples can be grouped generally into three responses to impure CO-brine reaction, dependent on mineralogy. The mineralogically clean quartzose reservoir cores had high porosities, with negligible change after reaction, in resolvable porosity or mineralogy, calculated using X-ray micro computed tomography and QEMSCAN. However, strong brine acidification and a high concentration of dissolved sulphate were generated in experiments owing to minimal mineral buffering. Also, the movement of kaolin has the potential to block pore throats and reduce permeability. The reaction of the impure CO-brine with calcite-cemented cap-rock core samples caused the largest porosity changes after reaction through calcite dissolution; to the extent that one sample developed a connection of open pores that extended into the core sub-plug. This has the potential to both favor injectivity but also affect CO migration. The dissolution of calcite caused the buffering of acidity resulting in no significant observable silicate dissolution. Clay-rich cap-rock core samples with minor amounts of carbonate minerals had only small changes after reaction. Created porosity appeared mainly disconnected. Changes were instead associated with decreases in density from Fe-leaching of chlorite or dissolution of minor amounts of carbonates and plagioclase. The interbedded sandstone and shale core also developed increased porosity parallel to bedding through dissolution of carbonates and reactive silicates in the sandy layers. Tight interbedded cap-rocks could be expected to act as baffles to fluids preventing vertical fluid migration. Concentrations of dissolved elements including Ca, Fe, Mn, and Ni increased during reactions of several core samples, with Mn, Mg, Co, and Zn correlated with Ca from cap-rock cores. Precipitation of gypsum, Fe-oxides and clays on seal core samples sequestered dissolved elements including Fe through co-precipitation or adsorption. A conceptual model of impure CO-water-rock interactions for a siliciclastic reservoir is discussed

Biogenic methane production from Bowen Basin coal waste materials

A microbial consortium derived from sewage sludge from the treatment of wastewater (Luggage Point Wastewater Treatment Plant, Brisbane, Australia) has been applied to Jameson Cell (J-cell) rejects (R\ua0=\ua00.96\ua0±\ua00.008) of a Bowen Basin coal preparation plant to assess the potential for biogenic methane production. A maximum methane yield of 26.20\ua0μmol/g J-cell rejects (0.64\ua0m\ua0CH/ton) was observed, suggesting biogenic methane production from coal waste materials is a feasible process if yields can be improved. Molecular analysis performed on the microbial consortium showed similar microbial community compositions to those observed in natural coal bed environments. The study demonstrates that Australian coal waste materials can be used as a viable feedstock for biogenic methane production using microorganisms that are not native within the coal beds

Chemical and mineralogical characterisation of illite-smectite: implications for episodic tectonism and associated fluid flow, central Australia

The Warburton-Cooper-Eromanga basins of central-eastern Australia contain a number of reactivated fracture-fault networks that relate to a complex and poorly understood thermal and tectonic evolution. Authigenic illite was sampled from two prominent features of the Warburton-Cooper basins: the Gidgealpa-Merrimelia-Innamincka Ridge, composed of anticlinal imbricate thrust fault blocks, and the synclinal Nappamerri Trough. These sample sets were investigated using a combination of clay mineralogical, trace element and stable isotope analyses to deduce the palaeofluid chemistry associated with past tectonothermal perturbations. The Nappamerri Trough hosts the highly radiogenic Big Lake Suite granite and part of one of Australia's larger on-shore oil and gas reserves. Calculated fluid stable isotope values from the trough, in conjunction with calculated palaeotemperatures, indicate an influx of evolved high-latitudinal meteoric waters under an extremely high geothermal gradient (~100°Ckm) and high water/rock ratios consistent with an extensional environment. Such high water/rock ratios resulted in intense alteration of the granite during which it underwent substantial enrichment in the heat-producing elements (HPE), particularly Th. This hydrothermal system is interpreted to result from continent-wide transmission of tensional stress originating from episodic rifting of the eastern Australian margin in the mid Cretaceous, as dated by Sm-Nd, Rb-Sr and Ar-Ar. The Gidgealpa-Merrimelia-Innamincka Ridge, by contrast, is marked by a lower, but still elevated, palaeogeothermal gradient (~42°Ckm) and calculated fluid isotopic values compatible with evolved basinal fluids of meteoric origin under low water/rock ratio conditions. Distinct trace element compositions of residue and leachate aliquots further indicate two periods of fluid flow with unique chemical compositions. In light of previous geochronology, these events are interpreted as westward extensions of widespread crustal tensional stress that affected much of central and eastern Queensland in the Carboniferous and Late Triassic. Integrated analyses of authigenic illite provide evidence for three periods of fluid flow and elevated thermal regime associated with regional tectonism during the Carboniferous, Late Triassic and Cretaceous. Our data further show that due to the extremely high geothermal gradient and water/rock ratios, Cretaceous fluid flow had profound effects on the surrounding geology, which may have formed/enhanced two of Australia's most significant energy resources

Approccio alla lingua italiana per allievi stranieri - ALIAS

Contiene, di P. E. Balboni, - "Approccio alla lingua italiana per allievi stranieri", pp. 55-71 - "Problemi interculturali nei rapporti con allievi stranieri e con le loro famiglie", pp. 73-90 - "La fomrazione dei docenti: i contenuti e gli strumenti di base", pp. 181-184

Experimental and modelled reactions of CO2 and SO2 with core from a low salinity aquifer overlying a target CO2 storage complex

CO2‐induced reactions in low salinity aquifers overlying CO2 storage sites are of interest to understand potential reactions or impacts in the possible case of a leak. Previous investigations of overlying aquifers in the context of CO2 storage have focused on pure CO2 streams, however captured industrial CO2 streams may contain ancillary gases, including SO2, O2, NOx, H2S, N2, etc., some of which may be more reactive than CO2 when dissolved in formation water. Eight drill cores from two wells in a low salinity sandstone aquifer that overlies a target CO2 storage complex are characterised for porosity (helium, mercury injection, or micro CT), permeability, and mineral content. The eight Hutton Sandstone cores are variable with porosities of 5.2–19.6%, including carbonaceous mudstones, calcite cemented sandstones, and quartz rich sandstones, common lithologies that may be found generally in overlying aquifers of CO2 storage sites. A chlorite rich sandstone was experimentally reacted with CO2 and low concentrations of SO2 to investigate the potential reactions and possible mineral trapping in the unlikely event of a leak. Micro CT characterisation before and after the reaction indicated no significant change in porosity, although some fines movement was observed that could affect permeability. Dissolved concentrations of Fe, Ca, Mn, Cr, Mg, Rb, Li, Zn, etc., increased during the reaction, including from dissolution of chlorite and trace amounts of ankerite. After ~40 days dissolved concentrations including Fe, Zn, Al, Ba, As and Cr decreased. Chlorite was corroded, and Fe‐rich precipitates mainly Fe‐Cr oxides were observed to be precipitated on rock surfaces after experimental reaction. Concentrations of Rb and Li increased steadily and deserve further investigation as potential monitoring indicators for a leak. The reaction of chlorite rich sandstone with CO2 and SO2 was geochemically modelled over 10 years, with mainly chlorite alteration to siderite mineral trapping 1.55 kg/m of CO2 and removing dissolved Fe from solution. Kaolinite and chalcedony precipitation was also predicted, with minor pyrite precipitation trapping SO2, however no changes to porosity were predicted

Methane metabolism in the archaeal phylum Bathyarchaeota revealed by genome-centric metagenomics

Methanogenic and methanotrophic archaea play important roles in the global flux of methane. Culture-independent approaches are providing deeper insight into the diversity and evolution of methane-metabolizing microorganisms, but, until now, no compelling evidence has existed for methane metabolism in archaea outside the phylum Euryarchaeota. We performed metagenomic sequencing of a deep aquifer, recovering two near-complete genomes belonging to the archaeal phylum Bathyarchaeota (formerly known as the Miscellaneous Crenarchaeotal Group). These genomes contain divergent homologs of the genes necessary for methane metabolism, including those that encode the methyl–coenzyme M reductase (MCR) complex. Additional non-euryarchaeotal MCR-encoding genes identified in a range of environments suggest that unrecognized archaeal lineages may also contribute to global methane cycling. These findings indicate that methane metabolism arose before the last common ancestor of the Euryarchaeota and Bathyarchaeota

Characterisation of bioavailability of Surat Basin Walloon coals for biogenic methane production using environmental microbial consortia

The study sets out to characterise the bioavailability of six Surat Basin Walloon coals from different stratigraphic layers in a single borehole to environmental methanogenic consortia. Factors that control bioavailability have also been investigated on grounds of coal petrographic composition and the organic composition of solvent-extractable matter. Finely crushed coal core samples were inoculated with digested sludge culture from domestic wastewater treatment in serum bottles kept anoxically before incubation at mesophilic temperature over 30 days for biomethane production. Degradation of coal compounds was demonstrated via GC–MS characterisation of methanol and dichloromethane (DCM) extracts, in combination with aqueous volatile fatty acids and alcohols and total organic carbon (TOC) analysis on fresh and microbially-digested coal samples. The resulting methane yields ranged from 14 to 33 μmol/g, with an average of 21 μmol/g (0.515 m/t), comparable to those previously reported for subbituminous coals. Organic solvent-extractable materials that accounted for 3.8 to 12% of coal weight were generally dominated by aliphatic compounds, composed of mainly medium-long-chain n-alkanes, n-alcohols and esters. Aromatics were detected up to three fused rings, and are rich in dibenzofuran, alkyl benzene, diphenyls and alkyl PAH (polymeric aromatic hydrocarbon). The abundance of solvent-extractable matter was found to be positively associated with liptinite content, particularly suberinite, sporinite and liptodetrinite. Preservation of these compounds was thought to rely on vitrinite, such as telinite and collotelinite that are rich in micropores, serving as storage for the hydrocarbons. Environmental factors, such as microbe-carrying groundwater might compromise coal extractability by converting coal hydrocarbons to biogas. Bioavailability of coal was shown to be controlled by three factors: 1) Water solubility - Bioassay eliminated an average 98% of aqueous compounds (based on TOC), which were dominated by volatile fatty acids and alcohols, and to a lesser degree, medium-chain (primarily C to C) n-alcohols, esters and aliphatic amine; 2) Solvent extractability – 34.5% of solvent-extractable compounds were shown to be biodegraded (based on peak intensity in GC–MS), with methanol extracts being more bioavailable than DCM's; 3) Heterogeneous moieties, particularly aliphatic hydroxyl group, ester bond, ether bond and C–N bond in aliphatic amine - These functional groups present heteroatoms that can lower the activation energy of nearby bonds, making them vulnerable for microbial cleavage. Compound degradation in bioassays was shown to be clearly associated with methane yield, but only a small proportion degraded was converted to methane. Further improvement may be achieved via proper adaptation of the current microbial community

Exploring the Contextual Sensitivity of Factors that Determine Cell-to-Cell Variability in Receptor-Mediated Apoptosis

Stochastic fluctuations in gene expression give rise to cell-to-cell variability in protein levels which can potentially cause variability in cellular phenotype. For TRAIL (TNF-related apoptosis-inducing ligand) variability manifests itself as dramatic differences in the time between ligand exposure and the sudden activation of the effector caspases that kill cells. However, the contribution of individual proteins to phenotypic variability has not been explored in detail. In this paper we use feature-based sensitivity analysis as a means to estimate the impact of variation in key apoptosis regulators on variability in the dynamics of cell death. We use Monte Carlo sampling from measured protein concentration distributions in combination with a previously validated ordinary differential equation model of apoptosis to simulate the dynamics of receptor-mediated apoptosis. We find that variation in the concentrations of some proteins matters much more than variation in others and that precisely which proteins matter depends both on the concentrations of other proteins and on whether correlations in protein levels are taken into account. A prediction from simulation that we confirm experimentally is that variability in fate is sensitive to even small increases in the levels of Bcl-2. We also show that sensitivity to Bcl-2 levels is itself sensitive to the levels of interacting proteins. The contextual dependency is implicit in the mathematical formulation of sensitivity, but our data show that it is also important for biologically relevant parameter values. Our work provides a conceptual and practical means to study and understand the impact of cell-to-cell variability in protein expression levels on cell fate using deterministic models and sampling from parameter distributions