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Abstract: Intensive carbonate and clay mineral authigenesis took place throughout the Late Permian Bowen–Gunnedah–Sydney basin system in eastern Australia. We conducted isotopic and trace element analyses of carbonate and clay minerals from clastic sedimentary rocks of the Gunnedah Basin and the Denison Trough in the Bowen Basin. Rb–Sr isochron age data of the illitic clays are consistent with episodic hydrothermal fluid flow events that occurred in association with Gondwana rifting accompanied by alkaline magmatism at ∼85Ma and ∼95Ma. Stable isotope data of carbonate and clay minerals from the Gunnedah Basin are indicative of meteoric waters from a high-latitude environment as the main fluid source, whereas trace element, Sr and Nd isotope data highlight mixing of meteoric fluids with magmatic and/or crustal components, with a possible input from marine carbonates for some samples. Trace metals, oxygen and strontium isotopes of dawsonites from the Denison Trough are interpreted to have been mobilised by fluids that interacted with evolved clastic sedimentary and marine carbonate end members. According to the carbon isotope data, CO2 for calcite and ankerite precipitation was sourced mainly from thermal degradation of organic matter and magmatism, whereas the CO2 used for dawsonite formation is inferred to have been derived from magmatic and marine sources. In the low permeability environments (particularly in coal seams), the increasing accumulation and oversaturation of CO2 particularly promote the precipitation of dawsonite. [Copyright &y& Elsevier]

Abstract: High- CO2 gas fields serve as important analogues for understanding various processes related to CO2 injection and storage. The chemical signatures, both within the fluids and the solid phases, are especially useful for elucidating preferred gas migration pathways and also for assessing the relative importance of mineral precipitation and/or solution trapping efficiency. In this paper, we present a high resolution study focused on the Gorgon gas field and associated Rankin Trend gases on Australia’s North West Shelf. The gas data we present here display clear trends for CO2 abundance (mole %) and δ13C CO2 both areally and vertically. The strong spatial variation of CO2 content and δ13C and the interrelationship between the two suggests that processes were active to alter the two in tandem. We propose that these variations were driven by the precipitation of a carbonate phase, namely siderite, which is observed as a common late stage mineral. This conclusion is based on Rayleigh distillation modeling together with bulk rock isotopic analyses of core, which indicates that the late stage carbonate cements are related to the CO2 in the natural gases. The results suggest that a certain amount of CO2 may be sequestered in mineral form over short migration distances of the plume. [Copyright &y& Elsevier]

The stratiform Century Zn-Pb deposit and the discordant Zn-Pb lode deposits of the Burketown mineral field, northern Australia, host ore and gangue minerals with primary fluid inclusions that have not been affected by the Isan orogeny, thus providing a unique opportunity to investigate the nature of the ore-forming brines. All of the deposits are hosted in shales and siltstones belonging to the Isa superbasin and comprise sphalerite, pyrite, carbonate, quartz, galena, minor chalcopyrite, and minor illite. According to Pb model ages, the main ore stage of mineralization at Century formed at 1575 Ma, some 20 m.y. after deposition of the host shale sequence. Microthermometry on undeformed, primary fluid inclusions hosted in porous sphalerite shows that the Zn at Century was transported to the deposit by a homogeneous, Ca2+- and Na+-bearing brine with a salinity of 21.6 wt percent NaCl equiv. δDfluid of the fluid inclusion water ranges from -89 to -83 per mil, consistent with a basinal brine that evolved from meteoric water. Fluid inclusion homogenization temperatures range between 74° and 125°C, which are lower than the 120° to 160°C range calculated from vitrinite reflectance and illite crystallinity data from the deposit. This discrepancy indicates that mineralization likely formed at 50 to 85 Mpa, corresponding to a depth of 1,900 to 3,100 m. Transgressive galena-sphalerite veins that cut stratiform mineralization at Century and breccia-filled quartz-dolomite-sphalerite-galena veins in the discordant Zn-Pb lodes have Pb model ages between 1575 and 1485 Ma. Raman spectroscopy and microthermometry reveal that the primary fluid inclusions in these veins contain Ca2+, Na+, but they have lower salinities between 23 and 10 wt percent NaCl equiv and higher δ18Dfluid values ranging from -89 to -61 per mil than fluid inclusions in porous sphalerite from Century. Fluid inclusion water from sphalerite in one of the lode deposits has δ18Ofluid values of 1.6 and 2.4 per mil, indistinguishable from δ18Ofluid values between -0.3 to +7.4 per mil calculated from the isotopic composition of coexisting quartz, dolomite, and illite. The trend toward lower salinities and higher δDfluid values relative to the earlier mineralizing fluids is attributed to mixing between the fluid that formed Century and a seawater-derived fluid from a different source. Based on seismic data from the Lawn Hill platform and paragenetic and geochemical results from the Leichhardt River fault trough to the south, diagenetic aquifers in the underlying Calvert superbasin appear to have been the most likely sources for the fluids that formed Century and the discordant lode deposits. Paragenetically late sphalerite and calcite cut sphalerite, quartz, and dolomite in the lode deposits and contain Na+-dominated fluid inclusions with much lower salinities than their older counterparts. The isotopic composition of calcite also indicates δ18Ofluid from 3.3 to 10.7 per mil, which is larger than the range obtained from symmineralization minerals, supporting the idea that a unique fluid source was involved. The absolute timing of this event is unclear, but a plethora of Pb model, K-Ar, and 40Ar/39Ar ages between 1440 and 1300 Ma indicate that a significant volume of fluid was mobilized at this time. The deposition of the Roper superbasin from ca. 1492 ± 4 Ma suggests that these late veins formed from fluids that may have been derived from aquifers in overlying sediments of the Roper superbasin.… [ABSTRACT FROM AUTHOR]

Mudrocks and carbonates of the Isa superbasin in the Lawn Hill platform in northern Australia host major base metal sulfide mineralization, including the giant strata-bound Century Zn-Pb deposit. Mineral paragenesis, stable isotope, and K-Ar dating studies demonstrate that long-lived structures such as the Termite Range fault acted as hot fluid conduits several times during the Paleoproterozoic and Mesoproterozoic in response to major tectonic events. Illite and chlorite crystallinity studies suggest the southern part of the platform has experienced higher temperatures (up to 300°C) than similar stratigraphic horizons in the north. The irregular downhole variation of illite crystallinity values provides further information on the thermal regime in the basin and shows that clay formation was controlled not only by temperature increase with depth but also by high water/rock ratios along relatively permeable zones. K-Ar dating of illite, in combination with other data, may indicate three major thermal events in the central and northern Lawn Hill platform at 1500, 1440 to 1400, and 1250 to 1150 Ma. This study did not detect the earlier Century base metal mineralizing event at 1575 Ma. 1500 Ma ages are recorded only in the south and correspond to the age of the Late Isan orogeny and deposition of the Lower Roper superbasin. They may reflect exhumation of a provenance region. The 1440 to 1300 Ma ages are related to fault reactivation and a thermal pulse at ∼1440 to 1400 Ma possibly accompanied by fluid flow, with subsequent enhanced cooling possibly due to thermal relaxation or further crustal exhumation. The youngest thermal and/or fluid-flow event at 1250 to 1150 Ma is recorded mainly to the east of the Termite Range fault and may be related to the assembly of the Rodinian supercontinent. Fluids in equilibrium with illite that formed over a range of temperatures, at different times in different parts of the platform, have relatively uniform oxygen isotope compositions and more variable hydrogen isotope compositions (δ18O = 3.5-9.7‰ V-SMOW; δD = -94 to -36‰ V-SMOW). The extent of the 18O enrichment and the variably depleted hydrogen isotope compositions suggest the illite interacted with deep-basin hypersaline brines that were composed of evaporated seawater and/or highly evolved meteoric water. Siderite is the most abundant iron-rich gangue phase in the Century Zn-Pb deposit, which is surrounded by an extensive ferroan carbonate alteration halo. Modeling suggests that the ore siderite formed at temperatures of 120° to 150°C, whereas siderite and ankerite in the alteration halo formed at temperatures of 150° to 180°C. The calculated isotopic compositions of the fluids are consistent with 18O-rich basinal brines and mixed inorganic and organic carbon sources (δ18O = 3-10‰ V-SMOW; δ18C = -7 to -3‰ V-PDB). In the northeast Lawn Hill platform carbonate-rich rocks preserve marine to early diagenetic carbon and oxygen isotope compositions, whereas ferroan carbonate cements in siltstones and shales in the Desert Creek borehole are 18O and 13C depleted relative to the sedimentary carbonates. The good agreement between temperature estimates from illite crystallinity and organic reflectance (160°-270°C) and inverse correlation with carbonate δ18O values indicates that organic maturation and carbonate precipitation in the northeast Lawn Hill platform resulted from interaction with the 1250 to 1150 Ma fluids.… [ABSTRACT FROM AUTHOR]

The article offers information on the formation of basin system and fluid-flow models of the mineral deposits in Northern Australia. The origin and evolution of gold, zinc and lead deposits in the McArthur-Mount Isa-Cloncurry mineral belt is discussed. The formation of four types of mineral deposits, including the Mount Isa type, the Broken Hill type, volcanic hosted massive sulfide deposits and the Mississippi Valley type deposits, are discussed.

Alteration zones at the gold-rich Bajo de la Alumbrera porphyry copper deposit in northwestern Argentina are centered on several porphyritic intrusions. They are zoned from a central copper-iron sulfide and gold-mineralized potassic (biotite-K-feldspar ± quartz) core outward to propylitic (chlorite-illite-epidote-calcite) assemblages. A mineralized intermediate argillic alteration assemblage (chlorite-illite ± pyrite) has overprinted the potassic alteration zone across the top and sides of the deposit and is itself zoned outward into phyllic (quartz-muscovite-illite ± pyrite) alteration. This study contributes now data to previously reported δ18O and δD compositions of fluids responsible for the alteration at Bajo de la Alumbrera, and the data are used to infer likely ore-forming processes. Measured and calculated δ18O and δD values of fluids (+8.3 to +10.2 and -33 to -81‰, respectively) confirm A primary magmatic origin for the earliest potassic alteration phase. Lower temperature potassic alteration formed from magmatic fluids with lower δD values (down to -123‰). These depleted compositions are distinct from meteoric water and consistent with degassing and volatile exsolution of magmatic fluids derived from an underlying magma. Variability in the calculated composition of fluid associated with potassic alteration is explained in terms of phase separation (or boiling). If copper-iron sulfide deposition occurred during cooling (as proposed elsewhere), this cooling was largely a result of phase separation. Magmatic water was directly involved in the formation of overprinting intermediate argillic alteration assemblages at Bajo de la Alumbrera. Calculated δ18O and δD values of fluids associated with this alteration range from +4.8 to +8.1 and -31 to -71 per mil, respectively. Compositions determined for fluids associated with phyllic alteration (-0.8 to +10.2 and -31 to -119‰) overlap with the values determined for the intermediate argillic alteration. We infer that phyllic alteration assemblages developed during two stages; the first was a high-temperature (400°-300°C) stage with D-depleted water (δD = -66 to -119‰). This compositional range may have resulted from magma degassing and/or the injection of new magmatic water into a compositionally evolved hydrothermal system. The isotopic variations also can be explained by increased fluid-rock interaction. The second stage of phyllic alteration occurred at a lower temperature (∼200°C), and variations in the modeled isotopic compositions imply mixing of magmatic and meteoric waters. Ore deposition that occurred late in the evolution of the hydrothermal system was probably associated with further cooling of the magmatic fluid, in part caused by fluid-rock interaction and phase separation. Changing pH and/or oxygen fugacity may have caused additional ore deposition. The ingress of meteoric water appears to postdate the bulk of mineralization and occurred as the system at Bajo de la Alumbrera waned. [ABSTRACT FROM AUTHOR]

Carbon dioxide geological storage involves injecting captured CO2 streams into a suitable reservoir. Subsequent mineral trapping of the CO2 as carbonate minerals is one of the most secure forms of trapping. Injection of CO2 dissolved in water or co-injection of CO2 with water may enhance trapping mechanisms. Produced waters are already re-injected into reservoirs worldwide, and their co-injection with CO2 could enhance mineral trapping in low reactivity rock by providing a source of cations. Sandstone drill core from a reservoir proposed for CO2 storage was experimentally reacted with supercritical CO2 and a synthetic produced water. Micro computed tomography (CT), QEMSCAN, and SEM were performed before and after the reaction. The sandstone sample was predominantly quartz with minor illite/muscovite and kaolinite. The sandstone sub-plug micro-CT porosity was 11.1% and 11.4% after the reaction. Dissolved Ca, Mg, and Sr decreased during the reaction. After the reaction with CO2 and synthetic produced water, precipitation of crystalline carbonate minerals calcite and dolomite was observed in the pore space and on the rock surface. In addition, the movement of pore filling and bridging clays, as well as grains was observed. Co-injection of CO2 with produced waters into suitable reservoirs has the potential to encourage CO2 mineral trapping. [ABSTRACT FROM AUTHOR]

The Toolebuc Formation of Australia, a potential unconventional hydrocarbon resource, has limited studies on its pore structure and sorption characteristics. In this study, shale samples covering the lower mixed argillaceous mudstone (MAM) lithofacies, the middle interbedded calcareous mudstone and shelly thin beds (CM-STB) lithofacies, and the upper interbedded calcareous mudstone and shelly horizons (CM-SH) lithofacies of the Toolebuc Formation were collected. These samples were analysed for pore structure using a combination of scanning electron microscopy, X-ray diffraction, helium pycnometry, mercury intrusion porosimetry, and N 2 physisorption techniques. Additionally, methane sorption isotherms were measured under in-situ conditions. The results reveal that most pores are mineral-related intraparticle (intraP) and interparticle pores, with slit, equant and elongated shapes. Organic matter (OM) pores are rare. Porosity, total pore volume and BET specific surface area (SSA) are 3.25–8.26%, 1.32–3.55 cm3/100 g, and 1.26–9.65 m2/g, respectively. Pore volume is dominated by mesopores and macropores while specific surface area is dominated by fine mesopores and micropores. The porosity of the organic matter is significantly low due to the rarity of OM pores in the stage of early oil-window thermal maturity; organic matter consequently occludes pore space and also negatively impacts the average porosity. Clay by contrast is positively correlated to the average porosity. Carbonate provides intraP pores in fecal pellets, but also fills in other pore spaces as occlusion. Methane isotherms exhibit linear shapes, suggesting that a portion of the gas is stored in solution. The lower MAM lithofacies, characterised by rich clay, high porosity and BET SSA, was measured to have an in-situ methane sorption capacity of 4.32 cm3/g; the middle CM-STB lithofacies has intermediate porosity, but exhibits excellent gas generation potential and high in-situ methane sorption capacity (4.12–5.5 cm3/g). Within the CM-STB lithofacies, porosity declines with depth. The upper CM-SH lithofacies is carbonate-rich, exhibiting the lowest porosity and in-situ methane sorption capacity (2.56 cm3/g), but may act as an intraformational seal. The combination and vertical stacking pattern of the three lithofacies provided a favourable setting for gas storage. • Most observed pores are intraparticle and interparticle pores related to minerals. • Mesopores (2–50 nm) and macropores (>50 nm) contribute significantly to the total pore volume. • Clays and organic matter are the main influences on porosity and methane sorption capacity. • The combination of the three lithofacies provides a favourable setting for gas storage. [ABSTRACT FROM AUTHOR]

Abstract Strontium isotopes, water chemistry and whole rock chemistry have been used to investigate the evolution of water from its surface meteoric composition into methane-rich groundwater. Previous studies established that co-produced Surat Basin coal seam gas waters from the Walloon Subgroup (Queensland, Australia) are meteoric in origin and are distinct across the main production regions but the dominant hydrochemical processes have yet to be determined. In this study, strontium isotope ratios (87Sr/86Sr) were measured on production waters from 36 coal seam gas wells, 14 sequentially leached host rock samples and 6 whole rock samples to improve understanding of the water-rock reactions that control spatial variability in solute and isotope chemistry. Strontium isotope ratios of Walloon Subgroup production waters across all production areas are uniformly low in value, ranging from 0.70338 to 0.70456. The majority of values are significantly lower than shallow Walloon formation waters in the recharge zone and extend the lower range of 87Sr/86Sr ratios recorded for Surat Basin groundwaters. These very low 87Sr/86Sr ratios (0.70338) are reached early along the flow paths, within 10 km of the shallow recharge area waters, before then undergoing a gradual increase with flow distance. Mineralogical and geochemical analyses of whole rock samples representing each of the main lithologies across the Walloon Subgroup has identified that the low 87Sr/86Sr ratios are not derived from any one interval but rather the combination of the same few minerals that are present in every unit. The rapid accumulation of relatively non-radiogenic strontium early in the flow path across all three gas producing regions has been attributed to a combination of fluid-rock interactions occurring within the Walloon Subgroup itself. Initial surface 87Sr/86Sr ratio values are quickly dominated through a combination of processes whereby recharge waters with low Sr concentrations are absorbed onto montmorillonite clays via cation exchange and this combined with weathering of plagioclase causes a re-equilibration of the groundwater to lower 87Sr/86Sr ratios. Strontium ratios then start to slowly increase again with flow distance through silicate weathering of K-feldspars and muscovites, which are present at low levels across the basin. Local geological features such as the Hutton-Wallumbilla fault and the Kogan and Undulla anticlines appear to influence flow paths and consequently water and gas composition. Graphical abstract Image 1 Highlights • Investigation into hydrochemical processes occurring in a large sedimentary basin. • Hydrochemical controls on Walloon Subgroup groundwater, GAB identified. • Production waters have lower 87Sr/86Sr ratios (0.7034 - 0.7046) than recharge waters. • Low ratios not derived from any one interval but from every unit within subgroup. • Processes are a combination of cation exchange and silicate weathering. [ABSTRACT FROM AUTHOR]

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 ( r AD ), composting ( r COM ) and CH 4 oxidation ( r OX ) in a landfill environment, by means of a system of mass balances developed for molecular species (CH 4 , CO 2 ) and stable carbon isotopes (δ 13 C-CO 2 and δ 13 C-CH 4 ). 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 r OX , r AD and r COM for each location in each sampling round. The resulting average value of r AD and r COM indicated anaerobic digestion and composting were equally dominant at both locations. Average values of r COM : ranged from 9.8 to 44.5 g CO 2 m −2  d −1 over the four sampling rounds, declining monotonically at one site and rising then falling at the other. Average values of r AD: ranged from 10.6 to 45.3 g CO 2 m −2  d −1 . Although the highest average r AD value occurred in the initial sampling round, all subsequent r AD values fell between 10 and 20 g CO 2 m −2  d −1 . r OX had the smallest activity contribution at both sites, with averages ranging from 1.6 to 8.6 g CO 2 m −2  d −1 . This study has demonstrated that for an interim cover, composting and anaerobic digestion of shallow landfill waste can occur simultaneously. [ABSTRACT FROM AUTHOR]

During CO 2 geological storage, low porosity and permeability cap-rock can act as a structural trap, preventing CO 2 vertical migration to overlying fresh water aquifers or the surface. Clay and organic matter rich shales, fine-grained sandstones and mudstones often act as cap-rocks and may contain substantial sub-micron porosity. CO 2 -brine-rock interactions can open or close pore throats through dissolution, precipitation or migration of clay fines or grains. This could affect CO 2 migration if the porosity is accessible, with unchanging or decreasing accessible porosity favourable for trapping and integrity. Two cap-rock core samples, a clay and organic-rich mudstone and a more organic-lean feldspar-rich fine grained sandstone, from a well drilled for a CO 2 storage feasibility study in Australia were experimentally reacted with impure CO 2 (+ SO 2 , O 2 ) and low salinity brine at reservoir conditions. Mercury injection capillary pressure indicated that the majority of pores in both cores had pore throat radii ~ 5–150 nm with porosities of 5.5–8.4%. After reaction with impure CO 2 -brine the measured pore throats decreased in the clay-rich mudstone core. Dissolution and precipitation of carbonate and silicate minerals were observed during impure CO 2 reaction of both cores via changes in water chemistry. Scanning electron microscopy identified macroporosity in clays, mica and amorphous silica cements. After impure CO 2 -brine reaction, precipitation of barite, Fe-oxides, clays and gypsum was observed. Ion leaching from Fe-rich chlorite was also apparent, with clay structural collapse, and fines migration. Small-angle neutron scattering measured the fraction of total and non-accessible pores (~ 10–150 nm radii pores) before and after reaction. The fraction of pores that was accessible in both virgin cap-rocks had a decreasing trend to smaller pore size. The clay-rich cap-rock had a higher fraction of accessible pores (~ 0.9) at the smallest SANS measured pore size, than the feldspar rich fine-grained sandstone (~ 0.75). Both core samples showed a decrease in SANS accessible pores after impure CO 2 -water reaction at CO 2 storage conditions. The clay-rich cap-rock showed a more pronounced decrease. After impure CO 2 -brine reaction the fraction of accessible pores at the smallest pore size was ~ 0.85 in the clay-rich cap-rock and ~ 0.75 in the feldspar-rich fine-grained sandstone. Reactions during impure CO 2 -brine-rock reaction have the potential to close cap-rock pores, which is favourable for CO 2 storage integrity. [ABSTRACT FROM AUTHOR]

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 3 /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 10 to C 20 ) 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. [ABSTRACT FROM AUTHOR]

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 o,max = 0.96 ± 0.008) of a Bowen Basin coal preparation plant to assess the potential for biogenic methane production. A maximum methane yield of 26.20 μmol/g J-cell rejects (0.64 m 3 CH 4 /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. [ABSTRACT FROM AUTHOR]

Injection of CO 2 subsurface may lead to chemical reactivity of rock where CO 2 is dissolved in groundwater. This process can modify pore networks to increase or decrease porosity through mineral dissolution and precipitation. A lattice Boltzmann (LB) based computational model study on the pore scale reactive transport in three dimensional heterogeneous porous media (sandstone consisting of both reactive and non-reactive minerals) is described. This study examines how fluid transport in porous materials subject to reactive conditions is affected by unsteady state local reactions and unstable dissolution fronts. The reaction of a calcite cemented core sub-plug from the Hutton Sandstone of the Surat Basin, Australia, is used as a study case. In particular, the work studies the interaction of acidic fluid (an aqueous solution with an elevated concentration of carbonic acid) with reactive (e.g. calcite) and assumed non-reactive (e.g. quartz) mineral surfaces, mineral dissolution and mass transfer, and resultant porosity change. The proposed model is implemented in our custom LBM code and suitable for studies of multiple mineral reactions with disparate reaction rates. A model for carbonic acid reaction with calcite cemented sandstone in the CO 2 -water-rock system is verified through laboratory experimental data including micro-CT characterization before and after core reaction at reservoir conditions. The experimentally validated model shows: (1) the dissolution of calcite cement forms conductive channels at the pore scale, and enables the generation of pore throats and connectivity; (2) the model is able to simulate the reaction process until the reaction equilibrium status is achieved (around 1440 days); (3) calcite constituting a volume of around 9.6% of the whole core volume is dissolved and porosity is consequently increased from 1.1% to 10.7% on reaching equilibrium; (4) more than a third of the calcite (constituting 7.4% of the total core volume) is unaffected, which suggests that this calcite is not connected with open pores (at the resolution of the model) that the acidic fluid can access. The model enables exploration of the porosity change in systems as they react, which has applications for analysis of the induced permeability change at the macroscale. [ABSTRACT FROM AUTHOR]