Prame Chopra | The Australian National University (original) (raw)

Papers by Prame Chopra

Methods in Experimental Physics, 1986

Research over the last 10 years has indicated that Australia has a significant geothermal energy ... more Research over the last 10 years has indicated that Australia has a significant geothermal energy resource. Regions of high crustal temperature at depths ≤5km may be economic targets for hot dry rock technology. A new database of temperature measurements made in 5722 wells across Australia has been used to construct improved maps of the spatial distribution of temperature in the Australian crust. The new database, Austherm04, builds upon the earlier work of Somerville et al. (1994) by greatly improving data quality control and by including temperature data from a further 1430 wells. Whilst there has been some enhancement of the overall spatial coverage when compared with the earlier work, the bulk of the new data are still largely clustered within the same provinces that dominate the Somerville et. al. dataset. As a result, data distribution across the continent still tends to be rather patchy and irregular with some regions well represented and others not.

Australia continues to make modest use of its geothermal energy resources. The only electric powe... more Australia continues to make modest use of its geothermal energy resources. The only electric power generation from geothermal energy currently in operation in Australia is the 150 kW binary cycle plant at Birdsville in SW Queensland. This plant uses 98°C artesian water from the Great Artesian Basin to generate much of the town's annual power requirements. Direct use of geothermal waters continues to be an important source of energy in the city of Portland in western Victoria. Water pumped from a 1400 metre deep bore at a temperature of 58°C is used to heat many of the municipal buildings and public facilities. Geothermal waters are also used for spas at Moree, near Barradine and at Lightning Ridge in New South Wales and at two developments in Victoria on the Mornington Peninsula, south of Melbourne. Ground source heat pumps are also finding increased use in Australia in both commercial and residential applications. Significant research and development of Hot Dry Rock (HDR) energy is underway and a number of companies have been formed to explore for and develop this form of geothermal energy. Most advanced is an HDR project in the Cooper Basin region of north east South Australia. Here a 4.4 km deep borehole has been drilled as part of an extensive commercial project. An extensive underground heat exchanger has been created in granite at this depth with in-situ temperatures >250°C. The drilling of a second deep borehole in 2004 is to be followed by a planned circulation test in early 2005. The known scale of this resource is so large that it could meet all of Australia's electricity generation requirements for centuries. The main purpose of the current work is to evaluate the likely economics of such a development. Other HDR projects, including one in the Hunter Valley of New South Wales, have also been active in the period 2000-2005.

American Geophysical Union eBooks, 1986

The Australian journal of emergency management, 1998

ACT is a consortium of organisations interested in Internet delivery of digital spatial data and ... more ACT is a consortium of organisations interested in Internet delivery of digital spatial data and dealing with ongoing problems faced due to which widespread use of image data in emergency response work is prevented. The Australian Earth Data On-line (AEDOL) has developed a working prototype system, which show-cases many of the key components of a comprehensive Internet delivery system and by using the ER-MAPPER package, AEDOL can merge geographic data and satellite data.

INTRODUCTION The small town of Birdsville (13953’E 2521’S) is situated in arid south west Queensl... more INTRODUCTION The small town of Birdsville (13953’E 2521’S) is situated in arid south west Queensland approximately 1000 miles northwest of the state capital Brisbane (Figure 1) and on the edge of the Simpson Desert. Because of its remote location, the town is not connected to the Australian national power grid and requires its own power generation facilities. Established in the 1870s, Birdsville takes its name from the prolific bird life that soon arrives when the nearby Diamantina River intermittently fills with water. The town currently has a population of around 100 people and is sustained economically mainly by adventure tourism.

Tectonophysics, Sep 1, 1997

The transient creep behaviour of two natural dunites has been investigated at temperatures betwee... more The transient creep behaviour of two natural dunites has been investigated at temperatures between 1373 and 1573 K and a confining pressure of 300 MPa in a high-resolution gas-medium deformation apparatus. The specimens were deformed in constant stress experiments in the presence of an aqueous phase and were oriented perpendicular to foliation. The results confirm the finding of earlier workers that the high-temperature transient flow properties of olivine rocks can be effectively modelled in terms of a Burgers' body rheology. Observations of time-dependent strain recovery after unloading further support this model. The viscosity in the transient regime (η1) is found to have the same sensitivity to temperature and stress (within the errors of each estimate) as has been found previously for steady-state creep viscosity (η2). Thus the ratio η2η1 is found to be relatively insensitive to temperature and stress with values between 0.17 and 0.67. These values are higher than the η2η1 = 0.1 that has generally been assumed in geophysical modelling of upper mantle transient deformation but are similar to the results of previous experiments with olivine single crystals. The ratio of the shear moduli in the transient and steady-state regimes (μ2μ1) is found to be weakly sensitive to temperature at 250 MPa stress and 300 MPa confining pressure. The value of μ2μ1 decreases slowly as temperature increases. For the present experiments 0.05 < μ2μ1 < 0.36 which is comparable to the range of values reported in previous studies.

Tectonophysics, Mar 1, 1999

The development of crystallographic preferred orientations (CPO) and grain misorientation distrib... more The development of crystallographic preferred orientations (CPO) and grain misorientation distributions (MOD) in fine-grained (0.5-30 µm) olivine rocks, experimentally deformed by diffusion creep and dislocation creep has been investigated. The use of electron back-scattered diffraction (EBSD), in a scanning electron microscope (SEM), has enabled the measurement of CPO in rocks which are too fine-grained to be measured by conventional U-stage methods. Our objective is to study the influence of deformation and recrystallisation mechanisms on the CPO and MOD. The olivine rocks studied were deformed in uni-axial compression, in a gas-medium apparatus, to 17-24% strain at temperatures of 1200-1300ºC and 300 MPa confining pressures. The samples show a trend of weaker CPO with lower flow stress which may be related to an increasing component of grain boundary sliding and diffusion creep. In the diffusion creep regime the CPO and MOD are weak to random, whereas in the dislocation creep regime the CPO and MOD are non-random but the MOD is principally controlled by the CPO. These results confirm the idea, based on studies from metals, that the CPO and MOD in olivine are characteristic of the deformation mechanism. Dynamic recrystallisation during dislocation creep results in the occurrence of more intermediate-angle (10-40º) grain boundaries than expected from the CPO. In local areas of complete recrystallisation the MOD is controlled by the CPO which implies that the statistical MOD retains no signature of the initial recrystallisation process. In the dislocation creep regime small grains have a weaker CPO compared to large grains. This result is consistent with predictions from deformation mechanism maps which indicate that the fine recrystallised grains deform by a combination of dislocation creep and grain boundary sliding. The grain boundaries found in the deformed olivine polycrystals are predominately high-angle boundaries with misorientations between 60 and 117º. No obvious evidence has been found for the occurrence of preferred misorientation, or special, grain boundaries.

ASEG extended abstracts, Dec 1, 2004

A set of temperature data from 61 deep petroleum wells drilled in the Cooper Basin of South Austr... more A set of temperature data from 61 deep petroleum wells drilled in the Cooper Basin of South Australia has been used to test the accuracy of four commonly used models of borehole thermal reequilibration. Models tested include the Horner plot as derived from Bullard (1947), the theoretical dual-media zero circulation cylindrical model of Cooper and Jones (1959), the empirical semi-log plot of Pitt (1986) and the exponential model of Nakaya (1953). The selected models have been fitted to bottom-of-hole temperature data recorded during the recovery period of each well, and are used to predict a value for True Formation Temperature (TFT). These values are then compared with actual temperature measurements derived from Cement Bond Logs (CBL). Recorded on average 482 days after the end of drilling, these temperature measurements are likely to represent TFT. Analysis of the accuracy of model prediction relative to CBL temperature suggests that on average most models tend to underestimate TFT to some degree. The magnitude of this bias is found to be dependent upon assumptions implicit in each model. In most cases, model prediction is improved where at least one perturbed bottom hole temperature (BHT) has been recorded ≥ 20 hours after the end of drilling. To date the best results are derived from the semi-log plot extrapolated to 50 hours.

Exploration Geophysics, Jun 1, 1989

Springer eBooks, 1984

In our ongoing research on the thermal conductivity of rocks, we noticed that the effect of grain... more In our ongoing research on the thermal conductivity of rocks, we noticed that the effect of grain boundaries commonly appeared to be insignificant relative to that of lamellar structures, such as twin planes, exsolution lamellae, and inclusions, within the grains. It has been found that these lamellae scatter phonons with a wavelength-independent rate [1]. In marble (recrystallized calcite), these scatterers appeared to be twin planes, since the twin spacing was approximately equal to the average phonon mean free path. To confirm this, we have measured the thermal conductivity of natural and plastically deformed single-crystal calcite (CaCO3) and marble. Calcite samples with their long direction parallel to the [001] direction were cut from a large single crystal. These samples were deformed by applying a differential stress along this direction in a gas medium deformation apparatus operating at a confining pressure of 300 MPs at room temperature. This deformation geometry results in pronounced twinning [2]; and very little or no intracrystalline slip. The spacing of the twin planes in each specimen was determined from thin sections using an optical microscope. The Carrara marble specimens were deformed in a gas-medium deformation apparatus at 300 MPa confining pressure and temperatures of 500° C (heavily twinned) and 700° C (moderately twinned) in a similar manner to that described in [3]. As can be seen in Fig. 1, the low-temperature conductivity, A, of the twinned calcite is very much smaller than that of the undeformed material. A similar effect is observed in the twinned marbles, although to a lesser extent.

Methods in Experimental Physics, 1987

ABSTRACT

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1987

Geothermal energy manifests itself in spectacular fashion in many places on the Earth’s surface. ... more Geothermal energy manifests itself in spectacular fashion in many places on the Earth’s surface. Volcanoes sporadically emit very large quantities of heat, but the extent of this heat is dwarfed by the cumulative magnitude of the heat that is liberated through the earth’s surface by thermal conduction (Morgan, 1984). Heat flow through the surface of the continental crust results from both the conduction of heat from the upper mantle and from radiogenic heat produced within it, principally from the decay of isotopes of the elements potassium, thorium and uranium. In most continental regions, it is the radiogenic heat from within the crust that provides the major contribution to heat flow. However this heat flow only translates into high near-surface temperatures if the heat-producing region is overlain by rocks with low thermal conductivities. When this fortuitous combination occurs in the upper crust, rock temperatures may be high enough to constitute an exploitable energy resource using hot rock geothermal energy (HRGE) technologies. Australia is well endowed with such conditions.

Springer eBooks, 1984

Ion-etching of fiducial markers has allowed, for the first time, direct observation and measureme... more Ion-etching of fiducial markers has allowed, for the first time, direct observation and measurement of strain distribution in some materials of geological interest deformed in compression at high temperatures (above 700°C). Deformation of two polycrystalline materials, one olivine rich, the other consisting of calcite, has been briefly investigated on the basis of this new practical method.

Methods in Experimental Physics, 1986

Research over the last 10 years has indicated that Australia has a significant geothermal energy ... more Research over the last 10 years has indicated that Australia has a significant geothermal energy resource. Regions of high crustal temperature at depths ≤5km may be economic targets for hot dry rock technology. A new database of temperature measurements made in 5722 wells across Australia has been used to construct improved maps of the spatial distribution of temperature in the Australian crust. The new database, Austherm04, builds upon the earlier work of Somerville et al. (1994) by greatly improving data quality control and by including temperature data from a further 1430 wells. Whilst there has been some enhancement of the overall spatial coverage when compared with the earlier work, the bulk of the new data are still largely clustered within the same provinces that dominate the Somerville et. al. dataset. As a result, data distribution across the continent still tends to be rather patchy and irregular with some regions well represented and others not.

Australia continues to make modest use of its geothermal energy resources. The only electric powe... more Australia continues to make modest use of its geothermal energy resources. The only electric power generation from geothermal energy currently in operation in Australia is the 150 kW binary cycle plant at Birdsville in SW Queensland. This plant uses 98°C artesian water from the Great Artesian Basin to generate much of the town's annual power requirements. Direct use of geothermal waters continues to be an important source of energy in the city of Portland in western Victoria. Water pumped from a 1400 metre deep bore at a temperature of 58°C is used to heat many of the municipal buildings and public facilities. Geothermal waters are also used for spas at Moree, near Barradine and at Lightning Ridge in New South Wales and at two developments in Victoria on the Mornington Peninsula, south of Melbourne. Ground source heat pumps are also finding increased use in Australia in both commercial and residential applications. Significant research and development of Hot Dry Rock (HDR) energy is underway and a number of companies have been formed to explore for and develop this form of geothermal energy. Most advanced is an HDR project in the Cooper Basin region of north east South Australia. Here a 4.4 km deep borehole has been drilled as part of an extensive commercial project. An extensive underground heat exchanger has been created in granite at this depth with in-situ temperatures >250°C. The drilling of a second deep borehole in 2004 is to be followed by a planned circulation test in early 2005. The known scale of this resource is so large that it could meet all of Australia's electricity generation requirements for centuries. The main purpose of the current work is to evaluate the likely economics of such a development. Other HDR projects, including one in the Hunter Valley of New South Wales, have also been active in the period 2000-2005.

American Geophysical Union eBooks, 1986

The Australian journal of emergency management, 1998

ACT is a consortium of organisations interested in Internet delivery of digital spatial data and ... more ACT is a consortium of organisations interested in Internet delivery of digital spatial data and dealing with ongoing problems faced due to which widespread use of image data in emergency response work is prevented. The Australian Earth Data On-line (AEDOL) has developed a working prototype system, which show-cases many of the key components of a comprehensive Internet delivery system and by using the ER-MAPPER package, AEDOL can merge geographic data and satellite data.

INTRODUCTION The small town of Birdsville (13953’E 2521’S) is situated in arid south west Queensl... more INTRODUCTION The small town of Birdsville (13953’E 2521’S) is situated in arid south west Queensland approximately 1000 miles northwest of the state capital Brisbane (Figure 1) and on the edge of the Simpson Desert. Because of its remote location, the town is not connected to the Australian national power grid and requires its own power generation facilities. Established in the 1870s, Birdsville takes its name from the prolific bird life that soon arrives when the nearby Diamantina River intermittently fills with water. The town currently has a population of around 100 people and is sustained economically mainly by adventure tourism.

Tectonophysics, Sep 1, 1997

The transient creep behaviour of two natural dunites has been investigated at temperatures betwee... more The transient creep behaviour of two natural dunites has been investigated at temperatures between 1373 and 1573 K and a confining pressure of 300 MPa in a high-resolution gas-medium deformation apparatus. The specimens were deformed in constant stress experiments in the presence of an aqueous phase and were oriented perpendicular to foliation. The results confirm the finding of earlier workers that the high-temperature transient flow properties of olivine rocks can be effectively modelled in terms of a Burgers' body rheology. Observations of time-dependent strain recovery after unloading further support this model. The viscosity in the transient regime (η1) is found to have the same sensitivity to temperature and stress (within the errors of each estimate) as has been found previously for steady-state creep viscosity (η2). Thus the ratio η2η1 is found to be relatively insensitive to temperature and stress with values between 0.17 and 0.67. These values are higher than the η2η1 = 0.1 that has generally been assumed in geophysical modelling of upper mantle transient deformation but are similar to the results of previous experiments with olivine single crystals. The ratio of the shear moduli in the transient and steady-state regimes (μ2μ1) is found to be weakly sensitive to temperature at 250 MPa stress and 300 MPa confining pressure. The value of μ2μ1 decreases slowly as temperature increases. For the present experiments 0.05 < μ2μ1 < 0.36 which is comparable to the range of values reported in previous studies.

Tectonophysics, Mar 1, 1999

The development of crystallographic preferred orientations (CPO) and grain misorientation distrib... more The development of crystallographic preferred orientations (CPO) and grain misorientation distributions (MOD) in fine-grained (0.5-30 µm) olivine rocks, experimentally deformed by diffusion creep and dislocation creep has been investigated. The use of electron back-scattered diffraction (EBSD), in a scanning electron microscope (SEM), has enabled the measurement of CPO in rocks which are too fine-grained to be measured by conventional U-stage methods. Our objective is to study the influence of deformation and recrystallisation mechanisms on the CPO and MOD. The olivine rocks studied were deformed in uni-axial compression, in a gas-medium apparatus, to 17-24% strain at temperatures of 1200-1300ºC and 300 MPa confining pressures. The samples show a trend of weaker CPO with lower flow stress which may be related to an increasing component of grain boundary sliding and diffusion creep. In the diffusion creep regime the CPO and MOD are weak to random, whereas in the dislocation creep regime the CPO and MOD are non-random but the MOD is principally controlled by the CPO. These results confirm the idea, based on studies from metals, that the CPO and MOD in olivine are characteristic of the deformation mechanism. Dynamic recrystallisation during dislocation creep results in the occurrence of more intermediate-angle (10-40º) grain boundaries than expected from the CPO. In local areas of complete recrystallisation the MOD is controlled by the CPO which implies that the statistical MOD retains no signature of the initial recrystallisation process. In the dislocation creep regime small grains have a weaker CPO compared to large grains. This result is consistent with predictions from deformation mechanism maps which indicate that the fine recrystallised grains deform by a combination of dislocation creep and grain boundary sliding. The grain boundaries found in the deformed olivine polycrystals are predominately high-angle boundaries with misorientations between 60 and 117º. No obvious evidence has been found for the occurrence of preferred misorientation, or special, grain boundaries.

ASEG extended abstracts, Dec 1, 2004

A set of temperature data from 61 deep petroleum wells drilled in the Cooper Basin of South Austr... more A set of temperature data from 61 deep petroleum wells drilled in the Cooper Basin of South Australia has been used to test the accuracy of four commonly used models of borehole thermal reequilibration. Models tested include the Horner plot as derived from Bullard (1947), the theoretical dual-media zero circulation cylindrical model of Cooper and Jones (1959), the empirical semi-log plot of Pitt (1986) and the exponential model of Nakaya (1953). The selected models have been fitted to bottom-of-hole temperature data recorded during the recovery period of each well, and are used to predict a value for True Formation Temperature (TFT). These values are then compared with actual temperature measurements derived from Cement Bond Logs (CBL). Recorded on average 482 days after the end of drilling, these temperature measurements are likely to represent TFT. Analysis of the accuracy of model prediction relative to CBL temperature suggests that on average most models tend to underestimate TFT to some degree. The magnitude of this bias is found to be dependent upon assumptions implicit in each model. In most cases, model prediction is improved where at least one perturbed bottom hole temperature (BHT) has been recorded ≥ 20 hours after the end of drilling. To date the best results are derived from the semi-log plot extrapolated to 50 hours.

Exploration Geophysics, Jun 1, 1989

Springer eBooks, 1984

In our ongoing research on the thermal conductivity of rocks, we noticed that the effect of grain... more In our ongoing research on the thermal conductivity of rocks, we noticed that the effect of grain boundaries commonly appeared to be insignificant relative to that of lamellar structures, such as twin planes, exsolution lamellae, and inclusions, within the grains. It has been found that these lamellae scatter phonons with a wavelength-independent rate [1]. In marble (recrystallized calcite), these scatterers appeared to be twin planes, since the twin spacing was approximately equal to the average phonon mean free path. To confirm this, we have measured the thermal conductivity of natural and plastically deformed single-crystal calcite (CaCO3) and marble. Calcite samples with their long direction parallel to the [001] direction were cut from a large single crystal. These samples were deformed by applying a differential stress along this direction in a gas medium deformation apparatus operating at a confining pressure of 300 MPs at room temperature. This deformation geometry results in pronounced twinning [2]; and very little or no intracrystalline slip. The spacing of the twin planes in each specimen was determined from thin sections using an optical microscope. The Carrara marble specimens were deformed in a gas-medium deformation apparatus at 300 MPa confining pressure and temperatures of 500° C (heavily twinned) and 700° C (moderately twinned) in a similar manner to that described in [3]. As can be seen in Fig. 1, the low-temperature conductivity, A, of the twinned calcite is very much smaller than that of the undeformed material. A similar effect is observed in the twinned marbles, although to a lesser extent.

Methods in Experimental Physics, 1987

ABSTRACT

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1987

Geothermal energy manifests itself in spectacular fashion in many places on the Earth’s surface. ... more Geothermal energy manifests itself in spectacular fashion in many places on the Earth’s surface. Volcanoes sporadically emit very large quantities of heat, but the extent of this heat is dwarfed by the cumulative magnitude of the heat that is liberated through the earth’s surface by thermal conduction (Morgan, 1984). Heat flow through the surface of the continental crust results from both the conduction of heat from the upper mantle and from radiogenic heat produced within it, principally from the decay of isotopes of the elements potassium, thorium and uranium. In most continental regions, it is the radiogenic heat from within the crust that provides the major contribution to heat flow. However this heat flow only translates into high near-surface temperatures if the heat-producing region is overlain by rocks with low thermal conductivities. When this fortuitous combination occurs in the upper crust, rock temperatures may be high enough to constitute an exploitable energy resource using hot rock geothermal energy (HRGE) technologies. Australia is well endowed with such conditions.

Springer eBooks, 1984

Ion-etching of fiducial markers has allowed, for the first time, direct observation and measureme... more Ion-etching of fiducial markers has allowed, for the first time, direct observation and measurement of strain distribution in some materials of geological interest deformed in compression at high temperatures (above 700°C). Deformation of two polycrystalline materials, one olivine rich, the other consisting of calcite, has been briefly investigated on the basis of this new practical method.