Electromagnetic methods for exploration and monitoring of enhanced geothermal systems – A virtual experiment

Börner, Jana H.; Bär, Matthias; Spitzer, Klaus

doi:10.1016/j.geothermics.2015.01.011

Cited by 20 publications

(11 citation statements)

References 27 publications

(26 reference statements)

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“…The time-lapse continuous monitoring MT study at Habanero highlights the need for favourable geological settings to achieve significant change in resistivity in EGS reservoirs. Despite these limitations, the MT method shows potential as a complementary method to micro-seismic in fluid monitoring for unconventional resource exploration because of its sensitivity to conductivity contrasts caused by fluids (Baria, et al 2004, Börner, et al 2015, Cladouhos, et al 2013, Cuenot, et al 2008, Peacock, et al 2013, Peacock, et al 2012, Wohlenberg and Keppler 1987.…”

Section: Discussionmentioning

confidence: 99%

Magnetotelluric monitoring of hydraulic fracture stimulation at the Habanero Enhanced Geothermal System, Cooper Basin, South Australia

Didana

Thiel²,

Heinson

et al. 2016

ASEG Extended Abstracts

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SUMMARYMagnetotelluric (MT) data were collected across the Habanero Enhanced Geothermal System project in the Cooper Basin, South Australia. A baseline regional MT survey consisting of two profiles was collected to delineate the pre-injection resistivity structure. Two dimensional inversions of the MT data reveal three main resistivity structures to a depth of 5 km. The low resistivity surface layer (about 1.5 km thick) is interpreted as poorly consolidated sediments of Lake Eyre and Eromanga Basins. Below the conductive layer, a zone with relatively high resistivity with thickness of 2 km can be correlated to consolidated Cooper Basin sediments. A high resistivity zone below depths of 3.5 km is interpreted as the hot intrusive granodiorite (granite) of the Big Lake Suite with low porosity and permeability. This deep structure is also related to the Habanero EGS reservoir. The second MT survey was conducted during stimulation of Habanero-4 well by Geodynamics Ltd, where 36.5 ML of water with a resistivity of 13 Ωm (at 25°C) was injected at a relatively continuous rate of between 27-53 L/s over 14 days at a depth of almost 4 km. Analysis of pre-and post-injection residual phase tensors for periods greater than 10 s indicate conductive fractures oriented in a N/NNE direction. Apparent resistivity maps also revealed that injected fluids possibly propagated towards N/NNE direction. This result is in agreement with the micro-seismic events with an area of 4 km 2 observed during fluid injection, as well as orientation of pre-existing N-S striking sub-horizontal fractures susceptible to slip due to stimulation. The MT responses close to injection show on average 5% decrease in apparent resistivity at periods greater than 10 s. The main reasons for observing subtle changes in resistivity at Habanero EGS is the screening effect of the conductive thick sedimentary cover (about 3.6 km thick) and the presence of preexisting saline fluids with resistivity of 0.1 Ωm (equivalent to salinity of 16.1 g/L at 240°C) in the natural fractures. Overall, the MT monitoring at Habanero EGS highlights the need for favourable geological settings to measure significant changes in resistivity in EGS reservoirs.

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Section: Discussionmentioning

confidence: 99%

Magnetotelluric monitoring of hydraulic fracture stimulation at the Habanero Enhanced Geothermal System, Cooper Basin, South Australia

Didana

Thiel²,

Heinson

et al. 2016

ASEG Extended Abstracts

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“…A comprehensive review of CSEM methods for exploration and monitoring of hydrocarbon reservoirs is provided by Streich (2016). But targets under investigation also include CO 2 storage applications (Streich et al 2010;Vilamajó et al 2013;Zhdanov et al 2013;Börner et al 2015b) or geothermal reservoirs (Börner et al 2015a). Nearly all of the published work concludes that monitoring of the investigated subsurface process is feasible with CSEM techniques, though a few authors point out that the expected time-lapse responses are probably close to the detectability threshold (Tietze et al 2015; see also Streich 2016).…”

Section: Controlled-source Electromagnetic Monitoringmentioning

confidence: 99%

Repeatability of land-based controlled-source electromagnetic measurements in industrialized areas and including vertical electric fields

Tietze

Ritter²,

Patzer³

et al. 2019

Geophysical Journal International

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Over the last decade, an increasing number of numerical studies have proposed controlledsource electromagnetic (CSEM) techniques for monitoring of fluid flow in reservoirs, for example, in the framework of hydrocarbon production or CO 2 storage scenarios. A fundamental prerequisite for any monitoring application in practice is repeatability of the measurements, particularly in areas with high noise levels.Here, we report on CSEM data acquired across a producing oil field on land in three consecutive surveys between 2014 and 2016. As major conductivity changes in the reservoir structure are not expected for this time frame, the data sets provide an excellent basis to study accuracy and repeatability of such measurements over a time span of 2.5 yr.Our results show that uncertainties of single CSEM measurements lie between 0.1 and 10 per cent with a focus around 1 per cent in all surveys. For source-receiver offsets <2 km uncertainties are in the range of ∼0.1-0.3 per cent, proportional to the transfer function amplitudes, and are dominated by intrinsic noise of the measuring system. At source-receiver distances >4 km external noise resulting from natural electromagnetic field variations and powered installations dominates uncertainties that assume minimum absolute values of 10 −9 -10 −10 V A −1 m −1 with lowest values at frequencies between 0.1 and 10 Hz.Overall, repeatability of CSEM measurements depends on a range of factors, including source-receiver distances, component of the transfer function, source-polarization and relocation errors, in particular at sites close to the source, where the geometry and characteristics of the source fields vary rapidly in space. Best repeatability was observed for receiver stations at 2-4 km distance from the source and frequencies <20 Hz. At these stations, phases and amplitudes of transfer functions usually agreed within ±1 • and ±5 per cent between measurements. Such values are in a range as expected from time-lapse signals due to resistivity changes in target (reservoir) formations. Hence, precise surveying procedures are essential.We also measured the vertical electric field (E z ) with a newly developed receiver chain in a 200 m deep observation borehole. The vertical electric field component shows generally higher sensitivity to resistivity changes in reservoir structures than the horizontal electric fields measured at surface. Although amplitudes of E z are about one to two orders of magnitude smaller than amplitudes of horizontal electric fields, recordings of E z are stable. More importantly, E z transfer functions of three measurements between 2015 and 2016 show excellent quality and repeatability within <±2 • and <±5 per cent, similar as horizontal electric fields indicating that noise conditions at depth improve when compared with sensors at surface.

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“…Electromagnetic methods have been extensively used in the exploration of geothermal systems ( [1,[43][44][45] among others). Low resistivity anomalies associated with ascending hydrothermal brines can easily be detected with these methods, and a clear relationship between low resistivity anomalies and high temperature zones can be established ( [44], and references herein) which is the case for different hydrothermal areas that have been extensively studied, such as Iceland [43,46], New Zealand [47][48][49], Guadeloupe Island [50], and Italy [51].…”

Section: Relation Between Resistivity Anomalies and Ground Temperaturementioning

confidence: 99%

Imaging Thermal Anomalies in Hot Dry Rock Geothermal Systems from Near-Surface Geophysical Modelling

et al. 2019

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Convective hydrothermal systems have been extensively studied using electrical and electromagnetic methods given the strong correlation between low conductivity anomalies associated with hydrothermal brines and high temperature areas. However, studies addressing the application of similar geophysical methods to hot dry rock geothermal systems are very limited in the literature. The Timanfaya volcanic area, located on Lanzarote Island (Canary Islands), comprises one of these hot dry rock systems, where ground temperatures ranging from 250 to 605 °C have been recorded in pyroclastic deposits at shallow (<70 m) depths. With the aim of characterizing the geophysical signature of the high ground temperature areas, three different geophysical techniques (ground penetrating radar, electromagnetic induction and magnetic prospecting) were applied in a well-known geothermal area located inside Timanfaya National Park. The area with the highest ground temperatures was correlated with the location that exhibited strong ground penetrating radar reflections, high resistivity values and low magnetic anomalies. Moreover, the high ground temperature imaging results depicted a shallow, bowl-shaped body that narrowed and deepened vertically to a depth greater than 45 m. The ground penetrating radar survey was repeated three years later and exhibited subtle variations of the signal reflection patterns, or signatures, suggesting a certain temporal variation of the ground temperature. By identifying similar areas with the same geophysical signature, up to four additional geothermal areas were revealed. We conclude that the combined use of ground penetrating radar, electromagnetic induction and magnetic methods constitutes a valuable tool to locate and study both the geometry at depth and seasonal variability of geothermal areas associated with hot dry rock systems.

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Electromagnetic methods for exploration and monitoring of enhanced geothermal systems – A virtual experiment

Cited by 20 publications

References 27 publications

Magnetotelluric monitoring of hydraulic fracture stimulation at the Habanero Enhanced Geothermal System, Cooper Basin, South Australia

Magnetotelluric monitoring of hydraulic fracture stimulation at the Habanero Enhanced Geothermal System, Cooper Basin, South Australia

Repeatability of land-based controlled-source electromagnetic measurements in industrialized areas and including vertical electric fields

Imaging Thermal Anomalies in Hot Dry Rock Geothermal Systems from Near-Surface Geophysical Modelling

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