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Hydrogen has attracted attention worldwide with its favourable inherent properties to contribute towards a carbon-free green energy future. Australia aims to make hydrogen as its next major export component to economize the growing global demand for hydrogen. Cost-effective and safe large-scale hydrogen storage in subsurface geology can assist Australia in meeting the projected domestic and export targets. This article discusses the available subsurface storage options in detail by first presenting the projected demand for hydrogen storage. Australia has many subsurface formations, such as depleted gas fields, salt caverns, aquifers, coal seams and abandoned underground mines, which can contribute to underground hydrogen storage. The article presents basin-wide geological information on the storage structures, the technical challenges, and the factors to consider during site selection. With the experience and knowledge Australia has in utilizing depleted reservoirs for gas storage and carbon capture and sequestration, Australia can benefit from the depleted gas reservoirs in developing hydrogen energy infrastructure. The lack of experience and knowledge associated with other geostructures favours the utilization of underground gas storage sites for the storage of hydrogen during the initial stages of the shift towards hydrogen energy. The article also provides future directions to address the identified important knowledge gaps to utilize the subsurface geology for hydrogen storage successfully. • Australia's hydrogen storage demand is discussed. • Different underground hydrogen storage options and their geologic information are provided. • Technical challenges associated with underground hydrogen storage are discussed. • Factors to consider during storage site selection are presented. [ABSTRACT FROM AUTHOR]

In-flight measurements of atmospheric methane (CH 4(a)) and mass balance flux quantification studies can assist with verification and improvement in the UNFCCC National Inventory reported CH 4 emissions. In the Surat Basin gas fields, Queensland, Australia, coal seam gas (CSG) production and cattle farming are two of the major sources of CH 4 emissions into the atmosphere. Because of the rapid mixing of adjacent plumes within the convective boundary layer, spatially attributing CH 4(a) mole fraction readings to one or more emission sources is difficult. The primary aims of this study were to use the CH 4(a) isotopic composition (δ13 C CH4(a)) of in-flight atmospheric air (IFAA) samples to assess where the bottom–up (BU) inventory developed specifically for the region was well characterised and to identify gaps in the BU inventory (missing sources or over- and underestimated source categories). Secondary aims were to investigate whether IFAA samples collected downwind of predominantly similar inventory sources were useable for characterising the isotopic signature of CH 4 sources (δ13 C CH4(s)) and to identify mitigation opportunities. IFAA samples were collected between 100–350 m above ground level (m a.g.l.) over a 2-week period in September 2018. For each IFAA sample the 2 h back-trajectory footprint area was determined using the NOAA HYSPLIT atmospheric trajectory modelling application. IFAA samples were gathered into sets, where the 2 h upwind BU inventory had > 50 % attributable to a single predominant CH 4 source (CSG, grazing cattle, or cattle feedlots). Keeling models were globally fitted to these sets using multiple regression with shared parameters (background-air CH 4(b) and δ13 C CH4(b)). For IFAA samples collected from 250–350 m a.g.l. altitude, the best-fit δ13 C CH4(s) signatures compare well with the ground observation: CSG δ13 C CH4(s) of -55.4 ‰ (confidence interval (CI) 95 % ± 13.7 ‰) versus δ13 C CH4(s) of -56.7 ‰ to - 45.6 ‰; grazing cattle δ13 C CH4(s) of -60.5 ‰ (CI 95 % ± 15.6 ‰) versus - 61.7 ‰ to - 57.5 ‰. For cattle feedlots, the derived δ13 C CH4(s) (- 69.6 ‰, CI 95 % ± 22.6 ‰), was isotopically lighter than the ground-based study (δ13 C CH4(s) from -65.2 ‰ to -60.3 ‰) but within agreement given the large uncertainty for this source. For IFAA samples collected between 100–200 m a.g.l. the δ13 C CH4(s) signature for the CSG set (- 65.4 ‰, CI 95 % ± 13.3 ‰) was isotopically lighter than expected, suggesting a BU inventory knowledge gap or the need to extend the population statistics for CSG δ13 C CH4(s) signatures. For the 100–200 m a.g.l. set collected over grazing cattle districts the δ13 C CH4(s) signature (- 53.8 ‰, CI 95 % ± 17.4 ‰) was heavier than expected from the BU inventory. An isotopically light set had a low δ13 C CH4(s) signature of - 80.2 ‰ (CI 95 % ± 4.7 ‰). A CH 4 source with this low δ13 C CH4(s) signature has not been incorporated into existing BU inventories for the region. Possible sources include termites and CSG brine ponds. If the excess emissions are from the brine ponds, they can potentially be mitigated. It is concluded that in-flight atmospheric δ13 C CH4(a) measurements used in conjunction with endmember mixing modelling of CH 4 sources are powerful tools for BU inventory verification. [ABSTRACT FROM AUTHOR]

The power of Machine Learning is demonstrated for automatic interpretation of well logs and determining reservoir properties for volume of shale, porosity, and water saturation respectively for tight clastic sequences. Random Forest algorithms are reputed for their efficiency as they belong to a class of algorithms called ensemble methods, which are traditionally seen as weak learners, but can be transformed into strong performers and they promise to deliver highly accurate results. The study area is located offshore Australia in the Poseidon and Crown fields situated in the Browse Basin, which are gas fields in tight complex clastic reservoirs. There are 5 wells used in this study with one well manually interpreted which is subsequently used in developing a machine learning model which predicts the output for the other 4 wells. The basic open hole logs namely Natural gamma ray, Resistivity, Neutron Porosity, Bulk Density, P-wave and S-wave sonic travel-time, are used in interpretation. One of the wells has a missing S-wave travel-time log which was also predicted by developing a Random Forest Machine Learning model. The results indicate a very robust improvement in performance when Random Forest algorithm was combined with Adaptive Boosting when interpreting the well logs. The training accuracy using Random Forest alone was 98.21%, but testing was 77.62% which suggested over-fitting by the Random Forest model. The Adaptive Boosting of the Random Forest algorithm resulted in the overall training accuracy of 99.40% and an overall testing accuracy of 97.03%, indicating a drastic improvement in performance. S-wave travel-time log was predicted by preparing a training set consisting of Natural gamma ray, Resistivity, Neutron Porosity, Bulk Density, and P-wave travel-time logs for the 4 wells using Random Forest which gave a training accuracy of 99.79% and a testing accuracy of 98.54%. Machine learning algorithms can be successfully applied for interpreting well log data in complex sedimentary environment and their performance can be drastically improved using Adaptive Boosting. [ABSTRACT FROM AUTHOR]

Coal seam gas (CSG) accounts for about one-quarter of natural gas production in Australia and rapidly increasing amounts globally. This is the first study worldwide using airborne measurement techniques to quantify methane (CH4) emissions from a producing CSG field: the Surat Basin, Queensland, Australia. Spatially resolved CH4 emissions were quantified from all major sources based on top-down (TD) and bottom-up (BU) approaches, the latter using Australia's UNFCCC reporting workflow. Based on our TD-validated BU inventory, CSG sources emit about 0.4% of the produced gas, comparable to onshore dry gas fields in the USA and The Netherlands, but substantially smaller than in other onshore regions, especially those where oil is co-produced (wet gas). The CSG CH4 emission per unit of gas production determined in this study is two to three times higher than existing inventories for the region. Our results indicate that the BU emission factors for feedlots and grazing cattle need review, possibly requiring an increase for Queensland's conditions. In some subregions, the BU estimate for gathering and boosting stations is potentially too high. The results from our iterative BU inventory process, which feeds into TD data, illustrate how global characterization of CH4 emissions could be improved by incorporating empirical TD verification surveys into national reporting. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 1)'. [ABSTRACT FROM AUTHOR]

Subsea flowlines are flexible or rigid pipelines that are used in oil and gas fields commonly for transporting production fluids from wells. The majority of the flowlines operating in basins across the world (including e.g. Australia's 1700 km infield flowlines) are approaching the end of their productive life, and will need to be decommissioned over the next 5 decades. This paper, for the first time, investigates the potential of repurposing decommissioned flowlines to dynamically installed anchors for mooring floating facilities. Five shapes of anchor have been developed using segments of flowline. Two series of tests were subsequently carried out on models of those shapes. The first series of tests involved releasing the models in still water to assess free-fall trajectory (i.e. verticality), terminal velocity, and anchor drag coefficient. The second series of tests were carried out at 50 g in clay to investigate the performance of the anchors in terms of tip embedment depth during dynamic installation and capacity under vertical loading. The results confirmed performance similar to conventional dynamically installed anchors, suggesting that there is potential to fabricate offshore anchors using segments of flowline. • Decommissioned flowlines. • Repurposing decommissioned flowlines to dynamically installed anchors. • Verticality, terminal velocity, and drag coefficient in water. • Tip embedment depth during dynamic installation in clay. • Capacity under monotonic vertical loading in clay. [ABSTRACT FROM AUTHOR]

In regions where there are multiple sources of methane (CH4) in close proximity, it can be difficult to apportion the CH4 measured in the atmosphere to the appropriate sources. In the Surat Basin, Queensland, Australia, coal seam gas (CSG) developments are surrounded by cattle feedlots, grazing cattle, piggeries, coal mines, urban centres and natural sources of CH4. The characterization of carbon (δ13C) and hydrogen (δD) stable isotopic composition of CH4 can help distinguish between specific emitters of CH4. However, in Australia there is a paucity of data on the various isotopic signatures of the different source types. This research examines whether dual isotopic signatures of CH4 can be used to distinguish between sources of CH4 in the Surat Basin. We also highlight the benefits of sampling at nighttime. During two campaigns in 2018 and 2019, a mobile CH4 monitoring system was used to detect CH4 plumes. Sixteen plumes immediately downwind from known CH4 sources (or individual facilities) were sampled and analysed for their CH4 mole fraction and δ13CCH4 and δDCH4 signatures. The isotopic signatures of the CH4 sources were determined using the Keeling plot method. These new source signatures were then compared to values documented in reports and peer-reviewed journal articles. In the Surat Basin, CSG sources have δ13CCH4 signatures between -55.6 ‰ and -50.9 ‰ and δDCH4 signatures between -207.1 ‰ and -193.8 ‰. Emissions from an open-cut coal mine have δ13CCH4 and δDCH4 signatures of -60.0±0.6 ‰ and -209.7±1.8 ‰ respectively. Emissions from two ground seeps (abandoned coal exploration wells) have δ13CCH4 signatures of -59.9±0.3 ‰ and -60.5±0.2 ‰ and δDCH4 signatures of -185.0±3.1 ‰ and -190.2±1.4 ‰. A river seep had a δ13CCH4 signature of -61.2±1.4 ‰ and a δDCH4 signature of -225.1±2.9 ‰. Three dominant agricultural sources were analysed. The δ13CCH4 and δDCH4 signatures of a cattle feedlot are -62.9±1.3 ‰ and -310.5±4.6 ‰ respectively, grazing (pasture) cattle have δ13CCH4 and δDCH4 signatures of -59.7±1.0 ‰ and -290.5±3.1 ‰ respectively, and a piggery sampled had δ13CCH4 and δDCH4 signatures of -47.6±0.2 ‰ and -300.1±2.6 ‰ respectively, which reflects emissions from animal waste. An export abattoir (meat works and processing) had δ13CCH4 and δDCH4 signatures of -44.5±0.2 ‰ and -314.6±1.8 ‰ respectively. A plume from a wastewater treatment plant had δ13CCH4 and δDCH4 signatures of -47.6±0.2 ‰ and -177.3±2.3 ‰ respectively. In the Surat Basin, source attribution is possible when both δ13CCH4 and δDCH4 are measured for the key categories of CSG, cattle, waste from feedlots and piggeries, and water treatment plants. Under most field situations using δ13CCH4 alone will not enable clear source attribution. It is common in the Surat Basin for CSG and feedlot facilities to be co-located. Measurement of both δ13CCH4 and δDCH4 will assist in source apportionment where the plumes from two such sources are mixed. [ABSTRACT FROM AUTHOR]

With the presence of highly permeable pathways, such as faults and fractures zones, coal seam gases, particularly CO2, could potentially migrate upwardly from the coal deposits into the shallow subsurface and then to the atmosphere. This letter reports soil gas mapping and gamma ray survey in coal basin of Hunter River Valley, Australia. The survey facilitated the delineation of fault structures across the sampling regions, where the identified faults were confirmed by an independent drilling investigation later. Furthermore, to evaluate the gas emission fluxes from coalbeds through fault zones, the measured CO2 concentrations, coupled with an inverse modeling, enable the estimation of the width of the fault zone and associated CO2 emission flux in the range of 2 × 10−5–6 × 10−5 mol/m2/s at the study site. Our new approach provides a way to determine emissions of gases from deep formations, which may contribute considerably to the greenhouse gases cycles. Plain Language Summary: Australia is one of the world's biggest coal exporters. Total fugitive emissions in Australia have increased in line with the expanding coal and gas production sector. CO2 emissions may occur during the operation and following the closure of coal mines and coal seam gas fields. Leakage of gases to the atmosphere may be induced through fractured gas‐bearing strata and open vents. Hence, the emissions of CO2 from coal basins should be counted toward the overall emissions budget. The new approach proposed by the current study can be applied to estimate emissions of CO2 from fracture and fault zones, which have not been well quantified and yet can be potentially an important source of greenhouse gases contributing to the overall budget at a global scale. So this work could provide a better track progress on international emission commitments. Key Points: Field assessments on gas emission fluxes from coal basin at fault zones in the Hunter River Valley, AustraliaSoil gas mapping and gamma ray survey delineated several fault structures across the sampling transects, which were later confirmed by an independent borehole drilling investigationAn inverse modeling is applied to determine the width of the fault zone and its CO2 emission flux at the study site [ABSTRACT FROM AUTHOR]

Geochemical monitoring of CO 2 storage requires understanding of both innate and introduced fluids in the crust as well as the subsurface processes that can change the geochemical fingerprint of CO 2 during injection, storage and any subsequent migration. Here, we analyse a natural analogue of CO 2 storage, migration and leakage to the atmosphere, using noble gas and stable isotopes to constrain the effect of these processes on the geochemical fingerprint of the CO 2. We present the most comprehensive evidence to date for mantle-sourced CO 2 in south-east Australia, including well gas and CO 2 -rich mineral spring samples from the Otway Basin and Central Victorian Highlands (CVH). 3He/4He ratios in well gases and CO 2 springs range from 1.21 to 3.07 R A and 1.23–3.65 R C /R A , respectively. We present chemical fractionation models to explain the observed range of 3He/4He ratios, He, Ne, Ar, Kr, Xe concentrations and δ13C(CO 2) values in the springs and the well gases. The variability of 3He/4He in the well gases is controlled by the gas residence time in the reservoir and associated radiogenic 4He accumulation. 3He/4He in CO 2 springs decrease away from the main mantle fluid supply conduit. We identify one main pathway for CO 2 supply to the surface in the CVH, located near a major fault zone. Solubility fractionation during phase separation is proposed to explain the range in noble gas concentrations and δ13C(CO 2) values measured in the mineral spring samples. This process is also responsible for low 3He concentrations and associated high CO 2 /3He, which are commonly interpreted as evidence for mixing with crustal CO 2. The elevated CO 2 /3He can be explained solely by solubility fractionation without the need to invoke other CO 2 sources. The noble gases in the springs and well gases can be traced back to a single end-member which has suffered varying degrees of radiogenic helium accumulation and late stage degassing. This work shows that combined stable and noble gas isotopes in natural gases provide a robust tool for identifying the migration of injected CO 2 to the shallow subsurface. [ABSTRACT FROM AUTHOR]

Offshore faulted block oilfields with considerable technical development risks are frequently encountered in offshore oilfield exploitation. This paper proposes a two-level fuzzy hierarchy technique for an integrated evaluation of the technical development risk of offshore faulted block oilfields. The proposed technique can classify the technical recoverable volume quality according to the characteristics of offshore faulted block oilfields. It includes a two-level evaluation index and a two-level fuzzy hierarchy evaluation method. We conducted a thorough evaluation of the proposed technique, using actual offshore faulted block oilfields in Australia and China. The results verified the reliability and applicability of the proposed technique. •. Developed a technique for the quality evaluation of offshore block faulted gas field. •. Established the two-level evaluation index system of the technique. •. Established the two-level fuzzy hierarchy evaluation method of the technique. •. Two different offshore block faulted gas fields were evaluated by using the technique. [ABSTRACT FROM AUTHOR]

Abstract The Great Australian Bight is one of Australia's most valuable marine ecosystems supporting globally significant populations of marine mammals, seabirds, and diverse and highly endemic benthic assemblages, as well as important fishing, aquaculture and ecotourism industries. The region is also considered a significant frontier for potential offshore petroleum resources and is actively being explored for oil and gas. The Great Australian Bight Research Program (GABRP) was an innovative, multi-year, $20 million, inter-disciplinary research collaboration involving BP Developments Australia (BP), CSIRO, the South Australian Research and Development Institute (SARDI), the University of Adelaide and Flinders University, that was developed in response to exploration activities in the region. The Program was the first large-scale, integrated study of the Great Australian Bight that involved more than 100 of Australia's leading scientists to generate a whole-of-system understanding of the region's environmental, economic and social values. We outline the processes to establish this strategic research collaboration, identify the key areas for success, and critically the lessons learned in order to guide future initiatives in regions open to exploration and development. As a result of the GABRP, there is now a legacy of data, information and models to inform future sustainable development in the Great Australian Bight; leading to the region now being one of the better understood deep water Australian marine systems. [ABSTRACT FROM AUTHOR]

In one of the South Pars projects barely six months after commissioning, 3 out of 4 operating MEG regenerators experienced severe scale deposition problems with extensive damages to the internals of the still columns that went out of service in quick succession. Several operators of gas-condensate fields in Bass strait, Australia also reported similar damages to MEG regenerators. This study compares the conditions in both cases and investigates the reasons for the same. Operators from Bass Strait noted that iron carbonate which was one of the two corrosion products deposited in their MEG regenerators. They observed regular carry under of condensate into the still columns that resulted in occasional column ‘burping’ leading to the collapse of the internals. In South Pars it was an unforeseen occurrence of calcite deposition and the only corrosion product was iron sulphide. On careful analysis of the solids and liquids from different locations of the facilities after ‘burping’, we established that a part of the CaCO 3 mud lost in the reservoir has returned causing the problems. Iron sulphide did not precipitate inside the columns in both cases. Preferentially oil wetting nature of iron sulphide is the likely reason of condensate carry under to the columns. [ABSTRACT FROM AUTHOR]

The Walloon Subgroup coal seam gas (CSG) play in the Surat Basin, Queensland, is Australia's pre-eminent onshore gas field. Concerted multi-disciplinary research is underway investigating the distribution, origin and composition of waters and gases in this dominantly microbial CSG reservoir, to guide both continued production and potential microbially enhanced coal bed methane (MECoM) applications. However, prior to the present research, a detailed study of co-produced waters and gases from across the Surat Basin was not available in the public domain. This study tested whether co-produced water compositional and stable isotopic data show relationships with production gas stable isotope compositions, to elucidate further evidence for microbial CO 2 reduction and explore the down-dip geochemical evolution of Walloon coal bed waters and gases. A total of 41 wells were sampled with 50 water and 25 gas samples spanning the 3 major production areas of the Surat Basin. Detailed isotopic and hydrochemical analysis of these samples revealed distinct spatial trends between the different production locales. Water compositions were distinct for each of the production regions reflecting the different lithologies of adjacent recharge zones, differing fluid–rock interactions, likely different microbial consortia, and the extent of methanogenesis. On the western side of the basin near Roma, waters were the ‘freshest’ with the lowest median values for alkalinity (861 mg/L), and Cl − (588 mg/L) and a δ 13 C DIC of 14.2‰. On the eastern side of the basin, the Kogan Nose waters were the most saline with the highest median values for Na + (1955 mg/L), Cl − (2280 mg/L) and δ 13 C DIC (20.0‰). Also in the east, in the present gas fairway, the Undulla Nose waters had the highest median alkalinity (1841 mg/L) and were found to have a Na + excess (median = 1050 mg/L) and a lower than expected median δ 13 C DIC (14.0‰). Co-mingled, produced methane carbon isotope values (δ 13 C − 57.0‰ to − 44.5‰) from both the upper (Juandah) and lower (Taroom) coal measures plot within the mixed ‘thermogenic/microbial’ genetic field. By contrast, deuterium isotopic difference [Δ 2 H(H 2 O–CH 4 )] values and cross-plots of δ 2 H–H 2 O and δ 18 O–H 2 O suggest that microbially mediated CO 2 reduction is the dominant methane generation process in situ. At a given depth, the Undulla Nose waters in the east are more depleted in 2 H and 18 O than elsewhere in the Surat Basin, which may suggest these samples have been more heavily impacted by water–rock–microbial reactions. 14 C values from the 3 production regions (0.115 to 1.769 pmC; age: 32,400 to > 50,000 years before present (B.P.)) suggest that Walloon coals likely recharged in the last ~ 50,000 years (limit of radiocarbon dating). Consistent with these dates, δ 2 H–H 2 O and δ 18 O–H 2 O values for the Surat Basin (δ 2 H − 32‰ to − 56‰, δ 18 O − 5.9‰ to − 9.0‰) echo the stable isotopic composition of meteoric waters during the initial part of the last glacial period in southeast Queensland. Based on a strong correlation between δ 2 H–CH 4 and δ 2 H–H 2 O, we suggest that methane was generated since the Late Pleistocene. PCA analysis showed a degree of positive correlation between total alkalinity and both the δ 13 C DIC (median 14.2‰) and δ 13 C–CH 4 (median − 52.1‰) vectors that is consistent with finite reservoir effects. The results inform ongoing studies of gas distribution and origins and MECoM potential in the Surat Basin, and underpin a broader study examining aquifer interactions. [ABSTRACT FROM AUTHOR]

Abstract: The CO2CRC Otway Project, located in south-eastern Australia, has demonstrated geological storage of CO2 in a depleted natural gas field. Prior to injection, a comprehensive site characterisation study established that the site should meet the requirements of safe and effective storage. In contrast to the conventional methods applied to characterising oil and gas reservoirs for production purposes, CO2 storage site assessments place greater emphasis on injectivity, capacity, and long-term containment. The site location was assessed in the context of accessibility for monitoring activities and impact on local communities and natural resources. Additional well-log data and cores were acquired from the gas field, in conjunction with the drilling of the CRC-1 injector well, in order to reduce the uncertainty surrounding the geological heterogeneity of the reservoir, capacity of the seal to retain CO2, fault seal geomechanics, and regional hydrodynamics. Specialised core analysis revealed that small scale sedimentary features, related to depositional environment impact reservoir quality, CO2 trapping and plume migration behaviour. Based on these effects, a depositional model was established to better understand storage potential away from well control. Finally, a nearby gas storage facility provided a valuable analogue for the project and added confidence that the CO2CRC Otway Project site would be suitable to inject, store and contain CO2 within the technological and economical limits of the project. Following the injection period, long term monitoring of the reservoir, as well as the overlying aquifers, soil, groundwater and the atmosphere above the site, have confirmed the storage concept is effective and that the CO2 is safely contained. As a result, the site characterisation methodology serves as an example for others contemplating CO2 storage into depleted gas fields. [Copyright &y& Elsevier]

Abstract: This paper presents a 3D geomechanical modelling study of the Iona gas storage facility in the state of Victoria, Australia. The results provide important information pertaining to gas storage, which can then be used to understand certain geomechanical aspects of CO2 storage. A key finding in this paper is that significant changes to the horizontal stress magnitudes are imparted by changes to the fluid pressure due to gas injection or withdrawal. This effect, known as the reservoir stress path, significantly influences fault stability by counteracting the changes to effective stress. In the case of Iona, pressurisation of the field results in a stress path which is parallel to the failure criterion rather than towards it, as would be expected in a classical treatment which does not incorporate complex poro-elastic effects. Another output of interest relates to reservoir deformation, which would be manifested at the ground surface as heave or subsidence. During periods of peak gas withdrawal and injection, surface ground movement is predicted to be on the order of −9mm and +2.5mm, respectively. These numbers are similar to the surface deformation observed at the In Salah CO2 injection project, but much smaller than the subsidence observed in some producing hydrocarbon fields. [Copyright &y& Elsevier]

The proposed Coolimba Power Plant will generate 400 megawatts of baseload power from coal resources near Eneabba in Western Australia and will require geological storage of CO2. Potential storage sites have been assessed for capacity and containment security in depleted oil and gas fields, deep saline aquifers, and the coal seams based on existing openfile data. A combination of some of these options in a hybrid solution will likely be sufficient to store the >80 megatonnes (Mt) of CO2emissions expected from the proposed power plant. The Dongara Field has the largest individual contingent storage capacity of all the onshore depleted hydrocarbon fields in the study area (13 to 30 Mt). Additional prospective storage capacity in deep saline aquifers adjacent to the field is between 12 and 46 Mt. Deep saline aquifers offer many CO2storage options with an estimated combined prospective storage capacity of 167 to 512 Mt of CO2. These include stacked reservoirs below the existing hydrocarbon fields. The highest uncertainty in containment security for the saline aquifer storage sites is ‘up fault leakage’ owing to a lack of high-quality seismic data needed to adequately characterise the architecture of faults and traps. Additional containment risk is related to uncertainty in the CO2migration direction after injection owing to poorly constrained structural geometry of the base-seal derived from seismic data with poorly constrained depth conversion. The highest uncertainty in containment security related to the depleted gas field storage is fault reactivation and well leakage. [ABSTRACT FROM PUBLISHER]

Abstract: The first stage of the CO2CRC Otway Project, located in south-eastern Australia, has stored 65,445 tonnes of CO2-rich gas in the depleted Naylor Gas Field. Comparisons have been made between simulations using the non-isothermal multi-phase flow simulator TOUGH2/EOS7C and the accumulated field data up to and beyond the end of injection. The geological models and the derived simulation models have been able to fit most of the key features of the field data, including the downhole pressure measurements and the arrival time at the observation well. When fitting to the downhole pressure only, the observed arrival time was in the range of uncertainty of the model predictions. The use of multiple geostatistical realisations of heterogeneity demonstrates the importance of capturing the range of uncertainty in the geology and the consequent scatter in forward predictions. Thus the storage of CO2 in the Naylor depleted gas field is shown to be adequately modelled by numerical simulation, and this increases confidence in the suitability of similar depleted gas fields for underground storage. [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]

Abstract: Thirty six onshore basins in Queensland, Australia, have been assessed for their CO2 geological storage prospectivity through injection into either: regional reservoir-seal intervals (‘saline reservoirs‘ and aquifers); depleted oil and gas fields; or deep unmineable coal seams. This comprehensive state wide regional assessment is based on the technical (geological) suitability for geological storage, and does not consider factors such as potential interference with other resources, distance from emissions nodes or absolute storage volumes. Basins were assessed by evaluating the potential reservoir-seal intervals for their effectiveness for injection, storage and containment of CO2. Methodologies have been developed that allow the estimation of storage capacity volumes within highly prospective reservoir-seal fairways at a regional scale. These estimates reflect conservative values that are more reliable than previous theoretical estimates, which relied upon access to pore space at the physical limit of the pore rock volume to accept fluids. Results show that the greatest potential to store the large quantities of CO2 required to make deep cuts in Queensland’s stationary emissions is to use deep, regional reservoir-seal intervals using structural traps or migration assisted storage (MAS) mechanisms. The Bowen, Cooper, Eromanga, Galilee and Surat basins contain Paleozoic–Mesozoic age fluvial reservoirs that have either produced hydrocarbons, and/or are major aquifers, and are evaluated as having the highest prospectivity for CO2 geological storage in Queensland. Other basins have either low prospectivity or are unsuitable for geological storage. Depleted oil and gas fields and deep unmineable coal seams provide only limited opportunities for geological storage of CO2 in Queensland. [Copyright &y& Elsevier]

Abstract: A geomechanical assessment of the Naylor Field, Otway Basin, Australia has been undertaken to investigate the possible geomechanical effects of CO2 injection and storage. The study aims to evaluate the geomechanical behaviour of the caprock/reservoir system and to estimate the risk of fault reactivation. The stress regime in the onshore Victorian Otway Basin is inferred to be strike–slip if the maximum horizontal stress is calculated using frictional limits and DITF (drilling induced tensile fracture) occurrence, or normal if maximum horizontal stress is based on analysis of dipole sonic log data. The NW–SE maximum horizontal stress orientation (142°N) determined from a resistivity image log is broadly consistent with previous estimates and confirms a NW–SE maximum horizontal stress orientation for the Otway Basin. An analytical geomechanical solution is used to describe stress changes in the subsurface of the Naylor Field. The computed reservoir stress path for the Naylor Field is then incorporated into fault reactivation analysis to estimate the minimum pore pressure increase required to cause fault reactivation (ΔP p). The highest reactivation propensity (for critically-oriented faults) ranges from an estimated pore pressure increase (ΔP p) of 1MPa to 15.7MPa (estimated pore pressure of 18.5–33.2MPa) depending on assumptions made about maximum horizontal stress magnitude, fault strength, reservoir stress path and Biot''s coefficient. The critical pore pressure changes for known faults at Naylor Field range from an estimated pore pressure increase (ΔP p) of 2MPa to 17MPa (estimated pore pressure of 19.5–34.5MPa). [Copyright &y& Elsevier]

This paper presents the results of a data-driven; field-modeling (DDFM) evaluation applied to a high-temperature reservoir in Australia for the purpose of determining the significance of chemistry, reservoir, well, and hydraulic-fracture characteristics on well production. The DDFM approach has identified key production drivers for a gas-well field in Australia. This information has been useful in explaining hydraulic-fracture well production and providing guidelines for future fracture stimulation success. A DDFM process is used to develop a model for 32 wells completed in a complex, 250 to 350°F gas reservoir in Australia. This type modeling technique uses data from the field, including chemical formulation, geology, reservoir, well, completion, hydraulic-fracture stimulation, and production results. The data is integrated into a common format and resolution, and then a visual and statistical evaluation is performed. Relevant correlations and useful trends are noted. Next, an effort is made to develop a predictive model that can be used to provide an overall explanation as to what parameters drive production in the well field. Or, in effect, derive a high-level understanding about the effect of the fracturing process on the reservoir. This is accomplished by the use of data modeling/optimization technologies, including artificial neural network (ANN) and genetic algorithms. The resulting ANN model can then be used to evaluate the production associated with various hydraulic-fracturing scenarios and/or characteristics. Validation of conclusions and/or resolution of difficult interpretation issues are done by detailed evaluation and modeling of key wells. Hydraulic-fracture stimulation scenario evaluations performed by the ANN model have yielded some expected as well as unexpected results. As expected, reservoir characteristics, such as pay thickness, porosity, and water saturation have a dominant effect on well production. What was unexpected is the significance of well operations and stimulation fluid chemistry on well production. The practice of killing the well after stimulation and using inappropriate perforation techniques can reduce gas production by as much as one-half, while the use of a high-temperature gel breaker in combination with a reduction in base-gel polymer load can provide a 67% increase in production. [ABSTRACT FROM AUTHOR]

Changes to benthic infauna caused by exploratory gas drilling operations in the Minerva field were examined experimentally using a BACI (before, after, control, impact) design. Analysis of 72 × 0.1 m2 Smith–McIntyre grab samples obtained from one pre-drilling and three post-drilling periods yielded a diverse fauna consisting of 196 invertebrate species and 5035 individuals. Changes to benthic community structure were assessed using ANOVA and nonmetric multidimensional scaling (MDS). The abundances of two common species (Apseudes sp. 1 and Prionospio coorilla) decreased significantly at the well-head site immediately after drilling. The size of these reductions in abundance ranged between 71% and 88%, and persisted for less than 4 months after drilling. A third common species (Katlysia sp. 1) increased in abundance 200 m east of the well-head following drilling. Most species occurred at densities too low to be analysed individually and so were pooled at higher taxonomic levels. Changes in the abundance of species aggregated by phylum varied, but significant declines in the most abundant phyla (Crustaceans and Polychaetes) of 45–73% were observed at all sites within a 100 m radius of the well-head following drilling. In most cases these changes became undetectable four months after drilling following species recruitments. MDS ordinations confirm that drilling related changes to benthic community structure are most pronounced at stations located closest to the well-head. Additionally, the ordinations indicate that modified communities persist at the well-head for more than 11 months following exploratory drilling. [Copyright &y& Elsevier]

• Modelling the impacts of coal mining and coal seam gas extraction on streamflow. • Reductions in annual streamflow are proportional to the area of coal mine coverage. • For coal seam gas, reductions in annual streamflow are proportional to well density. • A zone of potential hydrological change is identified, wherein impacts may be felt. This manuscript presents examples of the modelling of the impacts of coal mining and coal seam gas extraction on streamflow in five study catchments in Australia. The manuscript includes details on data preparation and model set-up and calibration. The modelling methodology enables the prediction of cumulative impacts from multiple future coal resource developments and distributes these predictions at multiple locations in the landscape. It is framed in terms of a structured uncertainty analysis to provide information on the likelihoods and potential ranges of various impacts. Also included is a qualitative uncertainty analysis which subjectively assesses the likely impact on model results of various assumptions made during the modelling procedure. Model results suggest that, in the Australian context, maximum percentage reductions in annual streamflow are approximately commensurate with the proportion of coal mine coverage. In coal seam gas fields, reductions in annual streamflow are proportional to well density. The manuscript goes on to demonstrate how these modelling results can be used to identify a zone of potential hydrological change within a catchment. This zone delineates those parts of the landscape where water-dependent landscape classes and assets may be vulnerable to change associated with changes in the streamflow regime. A corollary of this is that any parts of the landscape outside the zone of potential hydrological change are unlikely to be affected by coal resource development. [ABSTRACT FROM AUTHOR]

The article offers information on the Otway Project, located in Victoria in Australia. It mentions how the said project provides demonstrations on large-scale carbon capture and storage (CCS) in depleted gas field. Moreover, it features how public consent and risk assessment affects the demonstration of carbon storages.