Numerical simulation of a hot dry rock geothermal reservoir in the Cooper Basin, South Australia

Bronwyn Muller (2009). Numerical simulation of a hot dry rock geothermal reservoir in the Cooper Basin, South Australia PhD Thesis, School of Earth Sciences, The University of Queensland.

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Author Bronwyn Muller
Thesis Title Numerical simulation of a hot dry rock geothermal reservoir in the Cooper Basin, South Australia
School, Centre or Institute School of Earth Sciences
Institution The University of Queensland
Publication date 2009-01-15
Thesis type PhD Thesis
Open Access Status Other
Supervisor Hans Muhlhaus
Peter Mora
Total pages 196
Total colour pages 42
Total black and white pages 154
Subjects 260000 Earth Sciences
Formatted abstract
 This thesis describes the development and production of numerical simulations of the creation of a Hot Dry Rock (HDR) geothermal reservoir. This geothermal reservoir that was simulated is owned by Geodynamics Limited and is located in the Cooper Basin, South Australia. The simulations show the geometry of the geothermal reservoir and predict the productive lifespan of the reservoir. Geothermal energy, which is the thermal energy that is stored in the interior of the earth, is an enormous energy source and as such there is great interest in technology that allows this energy to be harnessed.

The HDR process of extracting the geothermal energy from rock involves drilling a borehole to a suitable depth and injecting cold water into the rock via this well (known as the injection well) to create a reservoir by opening up fractures in the rock. As water is forced through the reservoir, heat is extracted from the rock via conduction and transferred to the water, creating an heat exchange. Warm water is brought to the surface via another well known as the extraction well. The heat from the water is used to generate electricity and then the water is fed back into the injection well, completing the cycle. The creation of a HDR geothermal reservoir comprises of many aspects: the injection of the fluid into the jointed rock system, the opening and shearing of the joints, the creation of the fluid reservoir in the rock and the temperature effects of the fluid flow through the joints. This work incorporates all of these aspects.

Due to the multi-physics nature of this process multiple computational modelling strategies were implemented to allow for authentic simulation of the entire process. The mechanical rock behaviour was primarily simulated the Distinct Element Method. This two dimensional Distinct Element Method program allowed for a realistically scaled model of the whole geothermal reservoir to be developed. This model was particularly useful for modelling the joint behaviour as the discrete nature of this method compares well with the joint system on such a scale.

A discrete particle based model was used to model the joint behaviour on a small scale. These models demonstrated the behaviour of joints under compressional strain, showing slip and the effects of joint dilatancy.

The productive lifespan of the geothermal reservoir was modelled using a Finite Element Method program based on Darcy's Law and an height-averaged heat equation. The aim of this model was to simulate the effects on the rock temperature of the fluid flow through the reservoir. The lifespan of the reservoir with differing well geometries was tested using this model to show which geometry would extend the productive lifetime of the geothermal reservoir.

The results produced from the DEM models showed that the reservoir geometry is very much dependent upon the joint angle, and under the Cooper Basin stress regime steeper joints will be more likely to open. Joint dilatancy also affects the fluid flow rates as the amount of joint opening is dependent upon the joint dilatancy angle. The modelling of the temperature drawdown of the rock due to the fluid flow showed that a square configuration of wells is the ideal configuration to prolong the productive lifespan of the HDR geothermal reservoir. Results produced with the modelling parameters provided by Geodynamics Limited indicate that the productive lifespan of the Cooper Basin HDR geothermal reservoir created is approximately 50 years. This reservoir is only one of many that can be created at the site to prolong the productivity of the energy plant.

The combined results of this modelling strategy give an overall image of the creation and lifetime of the HDR geothermal energy plant in the Cooper Basin.
Keyword HDR
Cooper Basin
Finite element
Distinct element

Document type: Thesis
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Created: Thu, 02 Apr 2009, 22:22:44 EST by Miss Bronwyn Muller on behalf of Library - Information Access Service