Abstract for SGA Townsville 2009

Like many of the basins along Australia's eastern seaboard, there is currently only a limited understanding of the geothermal energy potential of the New South Wales extent of the Clarence-Moreton Basin. To date, no study has examined the existing geological information available to produce an estimate of subsurface temperatures throughout the region. Forward modelling of basin structure using its expected thermal properties is the process generally used in geothermal studies to estimate temperatures at depth in the Earth's crust. The process has seen increasing use in complex three-dimensional (3D) models, including in areas of sparse data. The overall uncertainties of 3D models, including the influence of the broad assumptions required to undertake them, are generally only poorly examined by their authors and sometimes completely ignored. New methods are presented in this study which will allow estimates and uncertainties to be addressed in a quantitative and justifiable way. Specifically, this study applies Monte Carlo Analysis to constrain uncertainties through random sampling of statistically congruent populations. Particular focus has been placed on the uncertainty in assigning thermal conductivity values to complex and spatially extensive geological formations using only limited data. As a case study these new methods are then applied to the New South Wales extent of the Clarence-Moreton Basin. The geological structure of the basin has been modelled using data from existing petroleum drill holes, surface mapping and information derived from previous studies. A range of possible lithological compositions was determined for each of the major geological layers through application of compositional data analysis. In turn, a range of possible thermal conductivity values was determined for the major lithology groups using rock samples held by the NSW Department of Primary Industries (DPI). These two populations of values were then randomly sampled to establish 120 different forward models, the results of which have been interpreted to present the best estimate of expected subsurface temperatures, and their uncertainties. These results suggest that the Clarence-Moreton Basin has a moderate geothermal energy potential within an economic drilling depth. This potential however, displays significant variability between different modelling runs, which is likely due to the limited data available for the region. While further work could improve these methods, it can be seen from this study that uncertainties can provide a means by which to add confidence to results, rather than undermine it.

This is a 3 minute movie (with production music), to be played in the background during the October 28th 2010 Geoscience Australia Parlimentary Breakfast. The video shows a wide range of the types of activities that GA is involved in. These images include GA people doing GA activities as well as some of the results of offshore surveys; continental mapping; eath monitoring etc. The movie will be played as a background before and after GA's CEO (Chris Pigram) presentation.

Abstract # : 1479734 Paper # : GP43B-1142 Session : GP43B Potential-field and EM methods for geologic problems of the mid and upper crust Developments for 3D gravity and magnetic modeling in spherical coordinates Richard Lane - Geoscience Australia - rjllane@gmail.com Qing Liang - China University of Geosciences (Wuhan) - qingliang.cug@gmail.com Chao Chen - China University of Geosciences (Wuhan) - chenchao@cug.edu.cn Yaoguo Li - Colorado School of Mines - ygli@mines.edu At Geoscience Australia (GA), Australia's Commonwealth Government geoscientific agency, we perform gravity and magnetic modeling at a range of scales, from broad regional crustal studies with thousands of kilometer lateral extent and tens of kilometer vertical extent, to detailed local studies with kilometer or less lateral extent and meters to hundreds of meters vertical extent. To achieve greater integration and coherence, and to better understand the geological significance of this work, we are investing in a number of development projects; * Spherical coordinate gravity and magnetic modeling, * Modeling using High Performance Computing facilities, * Utilizing rock property data as an input into the modeling and interpretation of gravity and magnetic data, * Better management of geoscience data and models, and * Visualization of spatial data in a Virtual Globe format. In collaboration with the Colorado School of Mines (CSM) and the China University of Geosciences (CUG), we are developing a capability to model gravity and magnetic data in a spherical coordinate framework. This will provide more accurate calculations and permit us to integrate the results into a single framework that more realistically reflects the shape of the Earth. Modeling gravity and magnetic data in a spherical coordinate framework is far more compute intensive than is the case when performing the corresponding calculations in a Cartesian (rectangular) coordinate framework. To reduce the time required to perform the calculations in a spherical coordinate framework, we will be deploying the modeling software on the National Computational Infrastructure (NCI) High Performance Computing (HPC) facility at the Australian National University (ANU). This will also streamline the management of these software relative to the other main option of establishing and maintaining HPC facilities in-house. We are a participant in the Deep Exploration Technologies Cooperative Research Centre (DET CRC). In combination with this involvement, we are expanding our support for systematic management of rock property data, and developing a better understanding of how these data can be used to provide constraints for the modeling work. We are also using the opportunities afforded through the DET CRC to make progress with documentation and standardization of data storage and transfer formats so that the tasks of management, discovery and delivery of this information to users are simplified and made more efficient. To provide the foundations of integration and analysis of information in a spatial context, we are utilizing and customizing 3D visualization software using a Virtual Globe application, NASA World Wind. This will permit us to view the full range of information types at global to local scales in a realistic coordinate framework. Together, these various development activities will play an important role in the on-going effort by Geoscience Australia to add value to the potential field, rock property, and geological information that we possess. We will then be better able to understand the geology of the Australian region and use this knowledge in a range of applications, including mineral and energy exploration, natural hazard mitigation, and groundwater management.

Exploration models for Rot Rock geothermal energy plays in Australia are based primarily on high-heat producing granites (HHPG) in combination with overlying low-conductivity sedimentary rocks providing the insulator necessary to accumulate elevated temperatures at unusually shallow (therefore accessible) depths. Unknowns in this style of geothermal play include the composition and geometry of the HHPG and thermal properties, and the thickness of the overlying sediments. A series of 3D geological models have been constructed to investigate the range of geometries and compositions that may give rise to prospective Hot Rock geothermal energy plays. A 3D geological map of the Cooper Basin region which contains known HHPG beneath thick sedimentary sequences, has been constructed from gravity inversions and constrained by geological data. The inversion models delineate regions of low density within the basement that are inferred to be granitic bodies. Thermal forward modelling was carried out by incorporating measured and estimated thermal properties to the mapped lithologies. An enhancement of the GeoModeller software is to allow the input thermal properties to be specified as distribution functions. Multiple thermal simulations using Monte-Carlo methods would be carried out from the supplied distributions. Statistical methods will be used to yield the probability estimates of the in-situ heat resource, reducing the risk of exploring for heat. The two thermal modelling techniques can be used as a predictive tool in regions where little or no temperature and geological data are available.

Broken Hill Managed Aquifer recharge Projects 3D models and Fly-through

SGA 2009 abstract

The lower Darling Valley contains Cenozoic shallow marine, fluvial, lacustrine and aeolian sediments including a number of previously poorly dated Quaternary fluvial units associated with the Darling River and its anabranches. New geomorphic mapping of the Darling floodplain that utilises a high resolution LiDAR dataset and SPOT imagery, has revealed that the Late Quaternary sequence consists of scroll-plain tracts of different ages incised into a higher more featureless mud-dominated floodplain. Samples for OSL (Optically-Stimulated Luminescence) and radiocarbon dating were taken in tractor-excavated pits, from sonic drill cores and from hand-auger holes from a number of scroll-plain and older floodplain sediments in the Menindee region. The youngest, now inactive, scroll-plain phase, associated with the modern Darling River, was active in the period 5-2 ka. A previous anabranch scroll-plain phase has dates around 20ka. Indistinct scroll-plain tracts older than the anabranch system, are evident both upstream and downstream of Menindee and have ages around 30ka. These three scroll-plain tracts intersect just south of Menindee but are mostly separated upstream and downstream of that point. Older dates of 50 ka, 85 ka and >150 ka have been obtained from lateral-migration sediments present beneath the higher mud-dominated floodplain. Establishing a chronology for the Quaternary fluvial landscape has been important for groundwater investigations in the Darling River floodplain area. More specifically, this has assisted in constraining the 3D mapping of floodplain units, helped constrain conceptual models of surface-groundwater interaction, and aided in the assessment of managed aquifer recharge options.

Three-dimensional gravity models are a useful part of improving the geological understanding of large areas in various geological settings. Such models can assist seismic interpretation, particularly in areas of poor seismic coverage. In general, forward modelling and inversion are conducted until a single model is derived that fits well to the observed gravity field. However, the value of such a model is limited because it shows only one possible solution that depends on a fixed set of underlying assumptions. These underlying assumptions are not always clear to the interpreter and an arguably more useful approach is to prepare multiple models that test various scenarios under a range of different assumptions. The misfit between observed and calculated gravity for these various models helps to highlight flaws in the assumptions behind a particular choice of physical parameters or model geometry. Identifying these flaws helps to guide improvements in the geological understanding of the area. We present case studies for sedimentary basins off western Africa and western Australia. The flawed models have been used to rethink assumptions related to the geology, crustal structure and isostatic state associated with the basins, and also to identify areas where seismic interpretation might need to be revised. The result is a more reliable interpretation in which key uncertainties are more clearly evident.

There is growing awareness of the scientific and intrinsic value of Antarctic geological features, including sites containing rare, and in some cases, globally unique mineral occurrences, mineral assemblages, and unusual rocks features (e.g. ventifacts) and rare fossils. However, the global economic value of the mineral and fossil trade is also considerable and growing, with prized specimens being sold for prices per gram equivalent to that of gold. Locations of geological value, once considered 'protected' by virtue of the logistical complexity and prohibitive cost involved in collection, are becoming increasingly vulnerable as the interest of collectors grows and the inaccessibility of Antarctica diminishes with more frequent visits by private and adventure travellers. Thus the need for proactive intervention, protection and management of 'geo-heritage' sites is becoming increasingly urgent. Wider recognition of the geological values of sites achieved by invoking the provisions for area management of the Madrid Protocol will also help mitigate casual souveniring and accidental or deliberate damage caused by ill-advised construction or other human activity, such as use of heavy machinery.