Geothermal Energy Exploration Research Articles

3D induced-polarization data inversion for complex resistivity

The conductive and capacitive material properties of the subsurface can be quantified through the frequency-dependent complex resistivity. However, the routine three-dimensional (3D) interpretation of voluminous induced polarization (IP) data sets still poses a challenge due to large computational demands and solution nonuniqueness. We have developed a flexible methodology for 3D (spectral) IP data inversion. Our inversion algorithm is adapted from a frequency-domain electromagnetic (EM) inversion method primarily developed for large-scale hydrocarbon and geothermal energy exploration purposes. The method has proven to be efficient by implementing the nonlinear conjugate gradient method with hierarchical parallelism and by using an optimal finite-difference forward modeling mesh design scheme. The method allows for a large range of survey scales, providing a tool for both exploration and environmental applications. We experimented with an image focusing technique to improve the poor depth resolution of surface data sets with small survey spreads. The algorithm’s underlying forward modeling operator properly accounts for EM coupling effects; thus, traditionally used EM coupling correction procedures are not needed. The methodology was applied to both synthetic and field data. We tested the benefit of directly inverting EM coupling contaminated data using a synthetic large-scale exploration data set. Afterward, we further tested the monitoring capability of our method by inverting time-lapse data from an environmental remediation experiment near Rifle, Colorado. Similar trends observed in both our solution and another 2D inversion were in accordance with previous findings about the IP effects due to subsurface microbial activity.

Characterising uncertainty when solving for 3D temperature: New tools for the Australian geothermal energy exploration sector

An extension of previously developed methods to calculate in-situ 3D temperature directly from 3D geology models in 3D GeoModeller software now allows for quantification of the uncertainty associated with those calculations. This work is being collaboratively undertaken by Intrepid Geophysics and Geoscience Australia, and will offer Australia?s geothermal industry both: i) a new predictive tool helping to reduce the risk of Enhanced Geothermal System (EGS) exploration and heat resource estimation, and ii) stochastic temperature and heat flow maps of Australia.

Mass transfer and porosity evolution during low temperature water–rock interaction in gneisses of the simano nappe: Arvigo, Val Calanca, Swiss Alps

Late Alpine fissures and fractures in amphibolite-facies basement gneisses at Arvigo (Val Calanca, Swiss Alps) show distinct cm-sized reaction selvages parallel to the fracture walls that composed of subgreenschist facies assemblages produced by the interaction of water present in the fracture porosity with the old high-grade gneiss assemblages. The process of selvage or reaction-vein formation occurred in the brittle deformation regime and at temperatures characteristic of, first the prehnite-pumpellyite facies and then later of the zeolite facies. The vein formation occurred during uplift and cooling at very late stages of the Alpine orogeny. The reaction veins are composed of a selvage of altered gneiss on both sides of the central fracture and a central zone with fissure minerals that have been growing in the open fracture pore space. The central zone of the Arvigo veins contains an early assemblage with epidote, prehnite and chlorite and a late succession sequence of various species of zeolite. The veins of the Arvigo quarry are convincing evidence that fracture fluids in gneiss and granite have the potential to precipitate Ca–zeolite. This is an important find because many fluids recovered from deep continental drill holes and from geothermal energy exploration are found to be oversaturated in respect to a number of Ca–zeolite species. Vein formation during late uplift and cooling of the Alps occurred at continuously decreasing T and at hydrostatic pressure: (1) coexisting prehnite/epidote records temperatures of 330–380°C, (2) chlorite formation at temperature of 333 ± 32°C and (3) formation of zeolites <250°C. In the selvages the prime reaction is the replacement of plagioclase by albite along a sharp reaction front that separates the selvage from unaltered gneiss. In addition to albitisation, chloritisation of biotite is the second important reaction in the alteration process. The reactions release components for the formation of Ca–Al silicates. The water–rock interaction is associated with a depletion of Al, Si, Ca, Fe and K in the altered wall rock. The overall reaction is associated with an increase in porosity of up to 14.2 ± 2.2% in the selvage zone (altered wall rock), caused by the volume decrease during albitisation and the removal of biotite. The propagation of the sharp reaction front through the gneiss matrix occurred via a dissolution-reprecipitation mechanism. Zeolite formation is tied to the plagioclase alteration reaction in the rock matrix, which releases components for zeolite formation to a CO2-poor aqueous liquid.

Australian States and Northern Territory acreage update at APPEA 2010

Peter Green is the Geoscience Manager: Energy Geoscience in the Geological Survey Queensland and has extensive experience in basin studies, geoscience and the development of petroleum regulation in Queensland. This paper provides a summary of the land releases for petroleum exploration for onshore areas and coastal waters of Australia for 2010. The summaries include upstream petroleum acreage opportunities for the states and the Northern Territory, and geothermal energy exploration opportunities. The rise in interest in export liquefied natural gas projects has ensured petroleum exploration and production has remained strong. Interest in acquiring petroleum acreage to explore for both conventional and non-conventional plays remains high. Australian state and the Northern Territory governments continue to provide access to land and promotional opportunities for companies to undertake exploration and development of our petroleum resources. Acreage on offer provides a mix of exploration opportunities from conventional oil and gas through to the unconventional plays such as shale gas and tight gas. This change in acreage on offer reflects the changing nature of the onshore petroleum industry in Australia.

Australian States and Northern Territory acreage update at APPEA 2009

Richard Sellers is the executive director of minerals and energy in the Northern Territory and has extensive experience with the management of natural resources and working specifically with business, regional and Indigenous groups on development programs. He has previously held roles as Executive Director—Fisheries and Director—Legal and Policy in the former Northern Territory Department of Primary Industry and Fisheries. This paper covers the annual presentation of exploration activity in onshore and coastal waters in Australia’s states and the Northern Territory. Included is a summary of upstream petroleum acreage opportunities for 2009 in the states and Northern Territory as well as geothermal energy exploration opportunities. While there have been increasing levels of exploration in recent years, there are large areas that remain under explored and the opportunity for future discoveries remains. State and the Northern Territory Governments have continued to undertake initiatives to attract and facilitate accelerated exploration and promote nationally and internationally these opportunities in frontier and production areas.

Forward prediction of spatial temperature variation from 3D geology models

Collaborative work is under way to develop an accessible method for rapid calculation of the spatial variation of temperature directly from a 3D geology model. The need for a tool of this nature stems from Australia?s emerging geothermal energy exploration and production industry. The prohibitive cost and huge task involved in acquiring comprehensive sets of heat flow data, means that the ability to accurately model heat flow at surface, and/or predict 3D temperature distribution for a modelled part of the crust will be key to supporting this industry and possibly others. Here we explain the approach we have taken. The Mount Painter region in South Australia is used as a case study to showcase the developments.

Australian states and Northern Territory acreage update at APPEA 2008

This is the annual presentation of what’s happening in onshore and coastal waters exploration in Australia’s states and the Northern Territory. The main focus of these jurisdictions’ annual report at the APPEA conference is upstream petroleum acreage opportunities. Exploration for geothermal energy resources will also be covered. There are many and diverse exploration opportunities in onshore frontier and producing Australian basins available for explorers in 2008, including geothermal energy exploration opportunities. The number of onshore Australian acreage applications has been steadily increasing in recent years and this has resulted in higher levels of drilling and seismic acquisition, but large areas remain untouched by modern exploration. Australian state governments continue initiatives to encourage exploration to realise their natural resource endowments including: pre-competitive basin studies; speedy and cost-effective provision of digital exploration data; provision of effective land access regimes; transparent regulatory regimes; internationally competitive royalty regimes; and, promotion of acreage releases nationally and internationally.

An integrated geophysical study of the northern Kenya rift

The Kenyan part of the East African rift is among the most studied rift zones in the world. It is characterized by: (1) a classic rift valley, (2) sheer escarpments along the faulted borders of the rift valley, (3) voluminous volcanics that flowed from faults and fissures along the rift, and (4) axial and flank volcanoes where magma flow was most intense. In northern Kenya, the rift faults formed in an area where the lithosphere was weakened and stretched by Cretaceous-Paleogene extension, and in central and southern Kenya, it formed along old zones of weakness at the contact between the Archean Tanzania craton and the Proterozoic Mozambique orogenic belt. Recent geophysical investigations focused on the tectonic evolution of the East African rift and on exploration for geothermal energy in the southern portion of the Kenyan rift provide considerable information and insight on the structure and evolution of the lithosphere. In the north, a variety of other data exist. However, the lack of an integrated regional analysis of these data was the motivation for this study. Our study began with the collection and compilation of gravity data, and then we used the seismic refraction results from the Kenya Rift International Seismic Project (KRISP), published seismic reflection data, aeromagnetic data, and geologic and drilling data as constraints in the construction of integrated gravity models. These models and gravity anomaly maps provide insight on spatial variations in crustal thickness and upper mantle structure. In addition, they show the distribution of basins and help characterize the distribution of magmatism along the axis of the northern sector of the rift. Our main observations are the following: (1) the region of thinning and anomalous mantle widens northward in agreement with previous studies showing that the crust thins from about 35 km in the south to 20 km in the north; (2) as observed in the south, gravity highs observed along the axis are due to mafic bodies associated with the main volcanic centers, densification of the upper crust due to diking, and horst blocks where Precambrian basement has been brought to or near the surface; (3) the axis of the rift is marked by a series of high amplitude magnetic anomalies whose wavelengths are less than 2.5 km, the positive anomalies coinciding closely with known Quaternary volcanoes.

EXPLORATION HIGHLIGHTS FOR 2006

Key business indicators show an upward trend in exploration activity in Australia during 2006. The year was marked by fluctuating high oil prices, a strong uptake of acreage in most basins, and increased levels of drilling activity and seismic acquisition. Market demand for product, production infrastructure and the fruition of several development projects have pushed the level of exploration activity in both offshore and onshore basins. Despite this trend and the spread of tenements, almost all petroleum discoveries made during 2006 were located within 15 km of existing (but often undeveloped) fields.The Carnarvon Basin continued to be the focus of most offshore exploration activity during 2006, with the highest levels of 3D seismic acquisition and exploration/appraisal/development drilling in the country. Discoveries in the Carnarvon Basin also covered the broadest range of water depths—extending from the oil and gas discoveries made by Apache on the inboard margin of the Barrow Subbasin, to the deepwater gas discoveries at Clio–1 and Chandon–1 by Chevron. Several large gas discoveries were made in the Carnarvon and Bonaparte basins and provide significant tie-back opportunities to existing and planned infrastructure. The Bonaparte Basin also saw significantly increased levels of 2D and 3D seismic acquisition during 2006. Onshore, the Cooper/Eromanga basins continued to experience the highest level of drilling activity and seismic acquisition, while maintaining an overall high drilling success rate. For the first time in many years, data acquisition also occurred in frontier basins like the Daly (Northern Territory), Darling (New South Wales), Tasmanian (Tasmania) and Faust/Capel basins (Lord Howe Rise region).Coal seam methane (CSM) exploration maintained a strong performance in 2006, particularly in Queensland, while South Australia, Queensland and Victoria continue to lead the way with large tracts of acreage gazetted for geothermal energy exploration.

Evaluation of The Existing State of Geothermal Exploration and Development in Nigeria

Relatively little expenditure for hydroelectricity and fossil fuels have had a restraining influence on levels of exploration and development for geothermal energy resources in Nigeria for the past several years. The focus of development has been in the areas of low temperature geothermal energy involving the exploration and assessment of hot spring resources primarily for recreational applications – although possibly for other direct uses depending on local infrastructure and access to appropriate energy markets. The geological structure of Nigeria influences geothermal exploration extent within each geological province. Sedimentary basins in Nigeria have been explored for hydrocarbons for several decades, thus the oil companies collected large subsurface temperature data basis. But not much is known about geothermal conditions within Nigerian Precambrian crystalline province. On the basis of BHT data from oil wells it has been found that geothermal gradient in Niger Delta ranges from 1.5 to 4.9°C/100m and in Anambra Basin (directly to the north) it can reach 5.7°C/100m. Exploration for geothermal energy in northern Nigeria based on shallow water wells (down to 600 m deep) was carried out over 20 years ago. The other aspect of geothermal exploration in Nigeria is investigating of the thermal springs and seepages, which occur mainly within sediments of the Middle and Upper Benue Trough. The water of the warmest springs in that area: Akiri and Ruwan Zafi have the temperature about 56°C and it suggests the occurrence of some geothermal anomalies. So far, there are probably only three (direct) geothermal energy utilisation sites in Nigeria. The Ikogosi warm spring (37°C) located in south-western part of the country, in Ekiti state, the Wikki warm spring (39°C) located in Bauchi (North-eastern) part of Nigeria and the Rafin Rewa spring (42°C) located in Plateau (North-central) state of Nigeria. Hence this paper reviews the current status of the geothermal industry (both high and low temperature) in Nigeria.

Geothermal Potential in Queensland

Hot rocks occur at depth over significant areas of Queensland offering a number of targets for geothermal energy extraction. On the published maps showing temperatures at 5 kilometre depths, the area beneath the Cooper and Eromanga Basins in southwest Queensland shows as the largest area of hot rocks. Much of this area is underlain by low grade meta-sedimentary rocks. The meta-sedimentary rocks are intruded by granites of different ages. In the central Eromanga Basin, the granites are of Middle Ordovician age. They are s-type granites and are not high heat producing. In the southwest, the granites are of mid Silurian age. They are also s-types and not high heat producing. None the less, they have high residual heat. The Late Carboniferous, high heat producing granite at Habernero in South Australia does cross the border into Queensland, but has no known equivalents in Queensland. High heat producing granites are common in the Mount Isa area and extend under the Eromanga Basin. High heat producing granites are present beneath the Carpentaria Basin. Several heat anomalies of unknown cause occur in western central Queensland. There are limited heat flow measurements in north Queensland. Although there are many high heat producing granites, there are no apparent insulating blanket rocks. The youngest basalt flows in north Queensland are 10,000 years old and new flows could yet occur-there may be heat associated with magma chambers. There are hot springs and warm springs in the area, but they are poorly understood. Exploration for geothermal energy will begin in Queensland in 2006 with the grant of exploration permits.

A preliminary regional geothermal assessment of Victoria, Australia

In 2005, the State of Victoria passed the Geothermal Energy Resources Act, which provides a new framework for the large-scale commercial exploration and extraction of geothermal energy in the State at depths greater than 1 000 m and at temperatures greater than 70 °C. Small-scale projects, such as balneology, ground heat pumps and aquaculture, are excluded, and these will continue to be regulated by existing planning, environmental and water legislation. The first stage of a regional geothermal assessment is the collection and integration of all relevant geological, geophysical and geochemical data from previous studies on the water, minerals and petroleum resources in the study area. Previous studies have attempted to map the geothermal prospectivity in Victoria, though the reliability of the data collected, and the sources of the data used in these studies, have often been questionable. Consequently, GeoScience Victoria has attempted to identify and collate all open-file geothermal data collected to date in Victoria. In addition, where possible, all of the published data have been traced to their original sources and quality-assessed. The resulting temperature database is considered robust and has been used to construct a preliminary `depth to 150°C' map for the Gippsland and Otway basins.

The application of the high-frequency electromagnetic sounding method in the exploration of underground thermal water

High-frequency electromagnetic sounding is an electromagnetic exploration method using the natural high-frequency electromagnetic field as a field source. It has higher resolution and greater depth penetration than the direct current method and is especially fit for geothermal energy exploration and low-and mid-level groundwater detection. We introduce a successful application of high-frequency electromagnetic sounding for evaluating geothermal water resources. The high frequency electromagnetic system (MT-U5A with a frequency range from 10 KHz to 1 Hz) is first applied to sample field data from China. A remote reference station is used to assure sampled data quality. We then perform 2D inversion image processing with the electrical method data. The results basically indicate the spatial distribution of underground geothermal water and provide favorable clues to finding the sources of the subsurface geothermal water in this area.

Thermodynamic Analysis of an Absorption/Compression Refrigeration System Using Geothermal Energy

This article presents the potential use and exploration of geothermal energy for cooling applications using a combined absorption/compression system. The considered system uses R134a for the compression part and the cool water-ammonia for the absorption part of the installation. The geothermal temperature source is in the range 343-349K, the condensation temperature is 308 K, and in order to produce ice, the R134a evaporation temperature is 263 K. The COP is about 5.4. Therefore, based on the typical geothermal energy sources in Tunisia which present a refrigeration potential power of 9.1 MW, the quantity of ice that could be produced is about 82 tons per hour. The greenhouse gas emissions should thus be reduced by about 5884 tons of CO2 per year, which represents (59%).

Hazardous waste storage, disposal, remediation, and closure

Hazardous waste storage, disposal, remediation, and closure

Geology of kilauea volcano

This paper summarizes studies of the structure, stratigraphy, petrology, drill holes, eruption frequency, and volcanic and seismic hazards of Kilauea volcano. All the volcano is discussed, but the focus is on its lower cast rift zone (LERZ) because active exploration for geothermal energy is concentrated in that area. Kilauea probably has several separate hydrothermal-convection systems that develop in response to the dynamic behavior of the volcano and the influx of abundant meteoric water. Important features of some of these hydrothermal-convection systems are known through studies of surface geology and drill holes. Observations of eruptions during the past two centuries, detailed geologic mapping, radiocarbon dating, and paleomagnetic secular-variation studies indicate that Kilauea has erupted frequently from its summit and two radial rift zones during Quaternary time. Petrologic studies have established that Kilauea erupts only tholeiitic basalt. Extensive ash deposits at Kilauea's summit and on its LERZ record locally violent, but temporary, disruptions of local hydrothermal-convection systems during the interaction of water or steam with magma. Recent drill holes on the LERZ provide data on the temperatures of the hydrothermal-convection systems, intensity of dike intrusion, porosity and permeability, and an increasing amount of hydrothermal alteration with depth. The prehistoric and historic record of volcanic and seismic activity indicates that magma will continue to be supplied to deep and shallow reservoirs beneath Kilauea's summit and rift zones and that the volcano will be affected by eruptions and earthquakes for many thousands of years.

Iterated function systems for geothermal energy exploration

A simple method for enhancing geothermal resource exploration is proposed. This utilizes iterated function systems (IFS). Both the hardware and software packages are readily available.

Deep wells in Denmark 1935-1990. Lithostratigraphic subdivision

The lithostratigraphic data presented here represent the mid-1991 status of the lithostratigraphic database at the Geological Survey of Denmark. The database comprises basic well information such as well location, company, completion date, depths and seismic two-way travel times to top and base of lithostratigraphic units recognized in the wells. Well location maps, a stratigraphic scheme and a list of selected references are included in the present publication. The aim of the presentation is to make these abundant data available to those working with subsurface geology in Denmark and adjacent areas. The key information are depths and seismic two-way travel times to top and base of lithostratigraphic units. The units are primarily recognized by means of petrophysical wireline logs measured in the wells. The boundaries of the units are indicated by significant changes in log pattern and readings as defined in the relevant publications (see reference list). The stratigraphic subdivision of the individual wells has been undertaken over the years by various geologists at the Survey and the level of subdivision thus depends on the data and time available when the subdivision was made. The database is, however, continuously revised as new wells or further work increase our knowledge of the subsurface. The database contains all exploration and appraisal wells drilled on Danish territory. The wells are included irrespective of whether the purpose was exploration for hydrocarbons, geothermal energy, or investigation of possible sites of waste-deposits or gas-storage. However, the wells drilled on the Tostrup salt structure are not included nor are production, observation and injection wells from oil or gas fields since the additional stratigraphic information provided by such wells is generally limited. Wells related to exploration and production of rock salt are not included in the database; most of these were drilled before 1953 and are dealt with in Sorgenfrei &amp; Buch (1964, Table 1, p. 14-17). Further information concerning available logs, reports, and geological samples obtained from the wells, together with information on casings, bit sizes, and test intervals can be found in the Well Data Summary Sheets, vol. 1-16. These can be ordered from the Geological Survey of Denmark. Exploration data in Denmark are in most cases, subject to a 5-year confidentiality period. Therefore, the tables of wells drilled after mid-1986 only show data released by the Danish Energy Agency, such as location, total depth and lithostratigraphic unit at total depth. A few new wells have been released, however, due to relinquished concessions. These wells (Borg-1, Felicia-I, lbenholt-1, Mejrup-1) are presented with full data sets. Furthermore, DONG has permitted release of data from the Stenlille-2, -3, -4, -5, and -6 wells. The authors acknowledge the work of their colleagues who contributed to the database, especially Ole Vejbæk and Jens Jørgen Møller who initiated the data base together with Jens Christian Olsen. Heinke Andersen, Bent Katz, and Uli Heyden are thanked for technical assistance. Jon Ineson (Geological Survey of Denmark) and Olaf Michelsen (University of Arhus) made valuable comments on the manuscript.

Lidar search for atmospheric atomic mercury in Icelandic geothermal fields

A search for atmospheric atomic mercury as a possible tracer gas for geothermal energy exploration was performed in three Icelandic geothermal fields using the differential absorption lidar technique. Contrary to expectations, concentrations basically only at the Atlantic background value of about 2 ng/m3 were found in Iceland.

Geothermal energy potential and utilization in Turkey

The regional distribution of the geothermal energy potential in Turkey, recent surveys, and utilization areas are described. The present and future roles of geothermal energy and their economic aspects are discussed. The implications of geothermal energy exploration and utilization are noted. Recommendations are made to expand geothermal-energy development.