Dr Geoffrey O’Brien
Manager Energy Geoscience
GeoScience Victoria

Introduction

Victoria’s energy sector progressed and evolved rapidly during 2005-06. The more traditional petroleum activities, such as exploration for oil and gas, remained strong with the drilling of numerous exploration and appraisal wells. Significant amongst these were the discovery of the Henry gas field in the eastern Otway Basin (Santos Limited) and the drilling of the Basker-2 and Manta-2A wells by Anzon Australia in the Gippsland Basin. Nexus Energy Ltd engineered the highly innovative Longtom-3 well within VIC/P54 in the Gippsland Basin. The Longtom-3H extended reach sinusoidal/horizontal production well bore successfully tested four gas-bearing zones within the Late Cretaceous Emperor Subgroup’s Admiral Formation, further highlighting the untapped hydrocarbon potential of the “older and deeper” section within flanking platform and terrace areas along the northern margin of the Gippsland Basin.

Exploration for hydrocarbons is only one aspect of energy activity in the State, as both industry and government face a number of emerging issues and opportunities.

DPI’s “Action Agenda on Climate Change and Greenhouse” was presented in 2006. A key goal of this was to provide the framework for cleaner and more secure energy for the State. Specific aspects of direct relevance to the Energy Geoscience Group included:

1. Facilitate development of Victoria’s natural gas reserves, including those in Commonwealth waters.

2. Encourage industry to explore all possible uses for Victoria’s energy resources, whilst meeting greenhouse targets.

3. Establish capture/storage of CO₂ for Victoria’s brown coal.

Point 1 has long been facilitated by research undertaken as part of GeoScience Victoria’s basin studies programme. However, points 2 and 3 represent a partial change of direction, with a greater emphasis on the related issues of greenhouse abatement and CO2 geosequestration. New policy and/or geotechnical initiatives related specifically or generally to points 2 and 3 are discussed below.

Geothermal Energy Activity Heats Up in Victoria

The Victorian Government held the Geothermal Energy Acreage Release Forum on 11th April 2006, with the Hon. Theo Theophanous, Minister for Energy Industries and Resources, inviting applicants to explore for geothermal energy. 31 geothermal exploration areas, covering the entire State of Victoria, were gazetted [Figure 1]. The bidding process was open for six months; 20 received bids were assessed against several criteria, including the proposed work program and associated expenditure. Successful applicants are expected to be announced in April 2007. If no bids are successful for a given area, then this acreage will be able to be applied for on a “first-come, first-served” basis.

A report - VIMP 85 (J.Driscoll, 2006) - representing a preliminary assessment of the geothermal prospectivity of onshore Victoria, was released in April 2006. The quality of temperature data derived from a number of sources, which included groundwater bores, oil and gas exploration wells, mineral wells, stratigraphic wells and coal bores were critically assessed and a robust temperature database developed. GeoScience Victoria also commissioned new temperature profiles from eleven boreholes of the State Water Observation Network in both the Gippsland and Otway basins. In order to eliminate potentially erroneous temperatures in shallow bores, only data from wells and groundwater bores which were drilled to a depth in excess of 300 m were included in the database.

There are over 630 datasets in the temperature database, derived from 353 wells and boreholes. A ‘depth-to-150°C’ temperature distribution map for onshore Victoria [Figure 2] shows that the areas with the greatest potential for hydrothermal energy tend to be associated intimately with structural grain. This relationship will be further constrained over time, as new data are received and geothermal exploration in Victoria moves from its infancy to a more mature phase.

Several vintage radiometric surveys have recognised radiogenic granites within Victoria. Only limited data are available and thus the Hot Dry Rock (HDR) potential in Victoria remains speculative. It is worth noting, however, that in South Australia several companies are actively investigating HDR targets in the Murray Basin and onshore Otway Basin.

In addition, a number of small-scale geothermal projects, including district heating and aquaculture using lower water temperatures, are either in the planning or building phases within both the Gippsland and Otway basins of Victoria.

New Studies into Basin Architecture & Geological Carbon Dioxide Storage Potential

The Energy Geoscience Group within GeoScience Victoria is currently planning a series of major studies which will better constrain the potential of Victoria’s basins for geological carbon dioxide storage (GeoCO₂St) as well as dramatically improving our understanding of the State’s hydrocarbon potential.

These studies will commence in the 2007-08 financial year, as part of GeoScience Victoria’s 4 year, ‘Rediscover Victoria in 3D’ initiative. The core of these studies will be the construction of a series of robust, fully attributed 3D models of Victoria’s sedimentary basins, both onshore and offshore. The key sedimentary horizons and surfaces in all of the sedimentary basins will be included in these models. The major sedimentary basins will be evaluated sequentially, in the following order: the Gippsland Basin, the Otway Basin and the Murray Basin.

Detailed investigations will be undertaken into factors such as top seal integrity, reservoir and source rock quality and distribution and fault geometries. Integration of these data with the constructed 3D surfaces will ultimately allow the development of high-resolution, 3D fluid flow models for both CO₂ and hydrocarbons. A simple visualisation of several regional surfaces in the Gippsland Basin is shown in Figure 3.

This initiative will provide GeoScience Victoria with a very substantially improved understanding of both the critical success factors which control the distribution of hydrocarbon accumulations in Victoria’s sedimentary basins as well as their potential for geological CO₂ storage. In this way, it is hoped that Victoria’s vibrant gas industry can be expanded further, while at the same time facilitating the sustainable exploitation of Victoria’s enormous brown coal reserves.

For more information on the Energy Geoscience programme at GeoScience Victoria, please contact Dr Geoffrey O’Brien (email: geoff.o’brien@dpi.vic.gov.au; phone: +61 3 9658 4537).