Sunil Varma

Impact of multi-purpose aquifer utilisation on a variable-density groundwater flow system in the Gippsland Basin, Australia

The Latrobe aquifer in the Gippsland Basin in southeastern Australia is a prime example for emerging resource conflicts in Australian sedimentary basins. The Latrobe Group forms a major freshwater aquifer in the onshore Gippsland Basin, and is an important reservoir for oil and gas in both onshore and offshore parts of the basin. The Latrobe Group and overlying formations contain substantial coal resources that are being mined in the onshore part of the basin. These may have coal-seam-gas potential and, in addition, the basin is considered prospective for its geothermal energy and CO2 storage potential. The impacts of groundwater extraction related to coal-mine dewatering, public water supply, and petroleum production on the flow of variable-density formation water has been assessed using freshwater hydraulic heads and impelling force vectors. Groundwater flows from the northern and western edges towards the central part of the basin. Groundwater discharge occurs mainly offshore along the southern margin. Post-stress hydraulic heads show significant declines near the petroleum fields and in the coal mining areas. A hydrodynamic model of the Latrobe aquifer was used to simulate groundwater recovery in the Latrobe aquifer from different scenarios of cessation of groundwater and other fluid extractions.RésuméLe Latrobe aquifer dans le Gippsland Basin, Sud de l’Australie, est un exemple de premier ordre des conflits émergeants relatifs à une ressource. Le Latrobe Group forme un aquifère d’eau douce côtier majeur du Gippsland Basin, lequel est aussi un important réservoir d’huile et de gaz, à fois terrestre et marin. Le Latrobe Group et les formations sus-jacentes contiennent de substantielles ressources de charbon, qui sont en cours d’exploitation dans la partie terrestre du bassin. Celles-ci peuvent avoir un potentiel en gaz de houille et, de plus, le bassin est considéré comme future source d’énergie géothermique et réservoir potentiel de stockage de CO2. Les impacts du pompage de l’eau de nappe en relation avec l’exhaure de la mine de charbon, l’alimentation du réseau de distribution public, et la production de pétrole sur le flux d’eau de densité variable de la formation ont été estimés en utilisant potentiels hydrauliques eau douce et vecteurs force motrice. L’eau de nappe s’écoule des bordures Nord et Ouest vers la partie centrale du bassin. La décharge a principalement lieu en mer, le long de la bordure Sud. Les potentiels hydrauliques post-stress montrent des diminutions significatives près des champs pétroliers et dans les zones d’extraction houillère. Un modèle hydrodynamique du Latrobe aquifer a été utilisé pour simuler la remontée de la nappe suivant différents scénarios d’arrêt d’extraction de l’eau et autres fluides.ResumenEl acuífero Latrobe en la cuenca de Gippsland en el sudeste de Australia es un excelente ejemplo del surgimiento de conflictos en los recursos en cuenca sedimentarias australianas. El Grupo Latrobe forma un gran acuífero de agua dulce en la zona costera terrestre de la cuenca Gippsland, y es un reservorio importante de petróleo y gas tanto costa adentro como como costa afuera de la cuenca. El Grupo Latrobe y las formaciones suprayacentes contienen sustanciales recursos de carbón que están siendo explotados en la parte continental de la cuenca. Estos pueden tener vetas potenciales gas de carbón y, en adición, la cuenca es considerada como prospectiva por su energía geotermal y potencial almacenamiento de CO2. Los impactos de la extracción de agua subterránea relacionados con el drenaje de la mina de carbón, abastecimiento de agua potable, y la producción de petróleo sobre el flujo de agua de formación de densidad variable han sido evaluados usando las cargas hidráulicas del agua dulce y los vectores de las fuerzas impulsantes. El agua subterránea fluye desde los límites norte y oeste hacia la parte central de la cuenca. La descarga de agua subterránea ocurre principalmente costa afuera a lo largo del margen sur. Las cargas hidráulicas post stress muestran una disminución significativa cerca de los campos de petróleo y en el área de minas de carbón. Se usó un modelo hidrodinámico del acuífero Latrobe para simular la recuperación del agua subterránea a partir de diferentes escenarios de cesación de las extracciones de agua subterránea y otros fluidos.摘要澳大利亚东南部Gippsland盆地Latrobe含水层是澳大利亚沉积盆地新兴资源争论的首要例子。Latrobe Group在岸上的Gippsland盆地内形成了一个较大的淡水含水层,对盆地岸上和近海部分的油气是重要的储库。Latrobe Group以及上覆的地层包含大量的煤炭资源,盆地岸上部分的煤炭正在开采。此处还有煤层天然气的潜力,此外,盆地也被认为具有未来的地热能开采和CO2封存的潜力。抽取地下水对变密度地层水的水流的影响与煤矿脱水、公共给水和采油相关,并利用淡水水头和驱动力矢量进行估算。地下水从北侧和西侧边缘朝盆地中心运移。地下水排泄主要发生在沿南部边缘的近海。靠近采油和采矿点的应激后水头显著下降。Latrobe含水层的水动力模型是用于模拟Latrobe含水层从停止地下水和其它液体抽取的不同场景中的地下水恢复。ResumoO aquífero Latrobe, na Bacia de Gippsland, sudeste da Austrália, é um excelente exemplo de conflitos na gestão dos recursos hídricos em bacias sedimentares australianas. O Grupo Latrobe forma um importante aquífero de água doce na parte terrestre da Bacia Gippsland e é um importante reservatório de petróleo e gás em partes terrestres e submarinas da bacia. O Grupo Latrobe e as formações sobrejacentes contêm substanciais recursos de carvão, os quais se encontram em exploração na parte terrestre da bacia. Estes podem ter potencialmente gás de hulha. Além disso, a bacia é considerada uma reserva potencial de energia geotérmica e tem potencial para armazenamento de CO2. Os impactes da extração de águas subterrâneas relacionados com a drenagem na mineração de carvão, com o abastecimento público de água e com a produção de petróleo no fluxo de água subterrânea de formação com densidade variável foram avaliados usando potenciais de água doce e respectivos gradientes (forças impulsionadoras). A água subterrânea flui a partir das fronteiras norte e oeste em direcção à parte central da bacia. A descarga das águas subterrâneas ocorre principalmente no mar, ao longo da margem sul. Os gradientes pós-extração indicam rebaixamentos significativos perto dos campos de petróleo e nas áreas de mineração de carvão. Foi utilizado um modelo hidrodinâmico do aquífero Latrobe para simular a recuperação das águas subterrâneas nesse aquífero a partir de diferentes cenários de cessação da exploração das águas subterrâneas e de outros fluidos.

South West Hub: a carbon capture and storage project

The South West CO2 Geosequestration Hub (the South West Hub) is located in South West Western Australia in proximity to industrialised regions around Kwinana, Kemerton, and coal mining and power production facilities around Collie. Recognition that there is a potentially suitable geosequestration site in the region near extensive emission sources led to the formation of the South West Hub and its submission as a potential Flagship under the Australian Federal Clean Energy Initiative (CEI). An area with geosequestration potential was identified based on data from years of active research in the region to investigate oil and gas potential, ground-water resources and more recently for geothermal energy potential and now carbon storage. Three interesting factors stand out regarding this site: (1) the storage site relies primarily on residual and dissolution trapping, (2) some of the CO2 will be sequestered by mineralisation during the amelioration of bauxite residue from some nearby alumina plants, and (3) the subsurface storage area can be tested at a relatively early stage by accessing significant pilot-scale quantities of high-purity CO2 from existing industry in the Kwinana area. CO2 is already being captured and vented at a site in Kwinana, and a proposed pipeline will transport the CO2 to the alumina plants with the remainder of the gas used for a pilot-scale test. The upfront capital costs are therefore reduced to the pipeline cost rather than for a full-scale capture-ready power plant. In preparation for an investment decision (to drill a new data well addressing the main criteria for characterising carbon storage potential of the proposed Lesueur site) a series of studies have increased the understanding of the geology of the area. Modelling studies suggest that up to 6.4 million tonnes per annum could be stored in the Triassic aged Lesueur Sandstone, with total capacity estimates of 200–260 million tonnes of CO2 over the lifetime of the project. This paper primarily discusses the evolution of the geological understanding of the Lesueur Sandstone and associated formations in and around the Harvey Ridge structure, which falls within the Lesueur study area, as well as how the Collie coal users and producers and other local industries and government have become engaged in the project. Recent activities in the project have included seismic data acquisition and the drilling, coring and logging of a data well that will allow significant reductions in geological uncertainties for the project.

CO2 geosequestration potential in the Northern Perth Basin, Western Australia

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 CO2 emissions 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 CO2 storage 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 CO2 migration 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.

Basin resources and carbon storage

Prospective sites for geological storage of carbon dioxide target sedimentary basins as these provide the most suitable geological settings for safe, long-term storage of greenhouse gases. Sedimentary basins can also host different natural resources including groundwater, oil and gas, unconventional gas, coal and geothermal energy.Understanding the nature of how these resources are distributed in the subsurface is fundamental to managing basin resource development and carbon dioxide storage. The underlying principal of the proposed workflow is to assess what basin resource – storage interactions are likely and to evaluate, at different scales, how they may be best managed. For regions having potential for resource conflicts a basin resource management plan may be required, and the appropriate regulator would need to decide on the priority of each resource and, if parallel development is not feasible, the order in which resources should be exploited.