Advanced seismic processing/imaging techniques and their potential for geothermal exploration

Schmelzbach, Cédric; Greenhalgh, Stewart; Reiser, Fabienne; Girard, Jean-François; Bretaudeau, François; Capar, Laure; Bitri, Adnand

doi:10.1190/int-2016-0017.1

Cited by 30 publications

(16 citation statements)

References 132 publications

(147 reference statements)

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“…The K-horizon upper boundary is shown in black. 5 Geofluids A digital elevation model (DEM) with a resolution of 20 m (http://www.sinanet.isprambiente.it/it/sia-ispra/ download-mais/dem20/view) and a geological map (i.e., http://www502.regione.toscana.it/geoscopio/geologia.html) were used to better constrain the geological surfaces at a shallow level.…”

Section: Methodsmentioning

confidence: 99%

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Synthetic Seismic Reflection Modelling in a Supercritical Geothermal System: An Image of the K-Horizon in the Larderello Field (Italy)

et al. 2019

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We tested synthetic seismic reflection modelling along a seismic line (CROP-18A) in the geothermal field at Larderello (Italy). This seismic line is characterized by a discontinuous but locally very bright seismic marker, named K-horizon, which has been associated with various geological processes, including the presence of fluids at supercritical conditions. Geological and geophysical data were integrated in order to develop a 3D subsurface model of a portion of the Larderello field, where extremely high heat flow values have been recorded. In the study area, the K-horizon is particularly shallow and supercritical deep conditions were accessed at depth. The 2D model of the main geological units up to the K-horizon was extracted from the 3D model along the CROP-18A and used to generate the synthetic TWT stacked seismic sections which were then compared with the observed stacked CROP-18A seismic section. To build the synthetic sections, generated through the exploding reflector approach, a 2D velocity model was created assigning to each pixel of the model a constant P-wave velocity corresponding to the related geological unit. The geophysical parameters and the geological model reconstructions used in the modelling process derive from a multidisciplinary integration process including geological outcrop analogues, core samples, and geophysical and laboratory information. Two geophysical models were used to test the seismic response of the K-horizon, which is associated with (1) a lithological discontinuity or (2) a physically perturbed layer, represented by a randomized velocity distribution in a thin layer. For the latter geophysical model (i.e., the physically perturbed layer), we have tested three different scenarios changing the shape and the thickness of the modelled layer. Despite the reliable calibration implied by the use of homogeneous units, the seismic modelling clearly shows that the physically perturbed layer provides a better explanation of the reflectivity features associated with the K-horizon.

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Section: Methodsmentioning

confidence: 99%

“…Exploration strategies of geothermal reservoirs may significantly benefit from synthetic seismic reflection profiles that enable prospective features on acquired seismic reflection data to be detected and the geological-geophysical interpretation and model reconstructions to be calibrated ( [4][5][6] and references therein).…”

Section: Introductionmentioning

confidence: 99%

Synthetic Seismic Reflection Modelling in a Supercritical Geothermal System: An Image of the K-Horizon in the Larderello Field (Italy)

et al. 2019

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“…The methodology is based on the latest petroleum techniques which have progressed significantly since 2010 [3]. Detailed seismic-reflection images of reservoirs are an essential pre-requisite to assess the feasibility of geothermal projects and to reduce the risk associated with expensive drilling programs [4].…”

Section: D Seismic To Design a Geothermal Doublet (Or Triplet) Of Bomentioning

confidence: 99%

3D seismic for design and derisking of dual geothermal boreholes in sedimentary sequences and new prospects in the Paris Basin (Adapted methodology using petroleum industry techniques)

Drouiller

Hanot²,

Gillot

et al. 2019

Oil Gas Sci. Technol. – Rev. IFP Energies nouvelles

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The use of existing geological and structural maps, previous 2D seismic profiles, boreholes and correlation models between these data is sufficient to understand basin structure and thermal systems on a regional scale. However, this is not sufficient on a scale of a geothermal site to be sure of the hydraulic connectivity (or of the presence of a permeability barrier) between two boreholes 1.5 or 2 km apart. To ensure that there is enough hydraulic connectivity, it i s necessary to understand the controls on the network of fractures which affects the aquifer (fracture permeability) and the physical properties of the rock, namely the porosity and clay content in order to obtain a matrix permeability. The latest generation of broadband (six octaves) 3D seismic reflection will provide the following information: the similarity attribute will give an accurate structural map of the fault network at the seismic resolution and, in many cases, at a higher resolution than seismic; seismic velocity anisotropy analysis techniques will make it possible to visualize a 3D volume of information on the fracture network [Michel et al. (2013) Application of Azimuthal Seismic Inversion for Shale Gas Reservoir – Proceedings of the 11th SEGJ International Symposium, Yokohama]; acoustic impedance inversion or petrophysical inversion techniques will predict the porosity throughout the whole volume of the aquifer from a porosity log recorded in a pilot-hole. It allows a real 3D mapping of predicted porosity inside the aquifer much more reliably than from modelling alone. These seismic techniques were initially developed for petroleum exploration and development. They have rapidly progressed throughout the last decade, both in acquisition, processing and interpretation with new methodologies and high-performance softwares. They are efficient for modelling reservoirs to be produced. And, consequently, they can be used for geothermal applications as data to design dual deviated drillings with horizontal drains in carbonate and clastic reservoirs – not only for new projects, but also to revisit old ones to improve their performance or develop another reservoir. Broadband 3D seismic will secure the exploration of Triassic sandstones which stay an interesting prospect for deep geothermal projects. New prospects are proposed in the Paris Basin: Regional faults overlap the substratum. Inside faulted zones, hydrothermal circulations arriving by convection at the top of granitic basement could be geothermal objectives, as in the Alsace Upper Rhine Graben. A production pilot site is suggested to test superimposed aquifers and a regional fault and, at the same time, two different architectures of boreholes doublets: horizontal drains for aquifers and deviated wells for crossing a regional fault. The first site that will use this approach could be instrumented and used as an experiment with a small addition of measurements and sensors, thus becoming a showcase for geothermal energy in France. The objective of this experiment would be to determine the transit time, the heating time of the re-injected water and the circulation speed to define the optimal direction, spacing and length of drains, and also, to realize the thermal modelling of the site for different options.

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“…Crystalline rock has been identified as the key host rock for geothermal energy exploitations (Brown et al, 2012) . The detailed geophysical and geological characterization of crystalline rock volumes are important steps in planning and managing geothermal reservoirs (e.g., Schmelzbach et al, 2016) . Before exploiting geothermal energy, the hydraulic transmissivity within the reservoir needs to be enhanced to allow for sufficient fluid flow at depths where temperatures are adequately high.…”

Section: Introductionmentioning

confidence: 99%

Characterizing a decametre-scale granitic reservoir using GPR and seismic methods – A case study for preparing hydraulic stimulations

Doetsch

Krietsch

Schmelzbach

et al. 2020

Preprint

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Abstract. Ground-penetrating radar (GPR) and seismic imaging have proven to be important tools for the characterization of rock volumes. Both methods provide information about the physical rock mass properties and geology structures away from boreholes or tunnel walls. Here, we present the results from a geophysical characterization campaign that was conducted in preparation for a decametre-scale hydraulic stimulation experiment in the crystalline rock volume at the Grimsel Test Site (Central Switzerland). For this characterization experiment, we used tunnel based GPR reflection imaging as well as seismic traveltime tomography to investigate the volumes between several tunnels and boreholes. The interpretation of the GPR data with respect to geological structures is based on the unmigrated and migrated images. For the tomographic analysis of the seismic first-arrival traveltime data, we inverted for an anisotropic velocity model described by the Thomsen parameters v0, ϵ and δ to account for the rock mass foliation. Subsequently, the GPR and seismic images were interpreted in combination with the geological model of the test volume and the known in-situ stress states. We found that the ductile shear zones are clearly imaged by GPR and show an increase in seismic anisotropy due to a stronger foliation, while they are not visible in the P-wave (v0) velocity model. Regions of decreased seismic p-wave velocity, however, correlate with regions of high fracture density. For geophysical characterization of potential deep geothermal reservoirs, our results imply that wireline compatible borehole GPR should be considered for shear zone characterization, and that seismic anisotropy and velocity information are desirable to acquire in order to gain information about ductile shear zones and fracture density, respectively.

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Advanced seismic processing/imaging techniques and their potential for geothermal exploration

Cited by 30 publications

References 132 publications

Synthetic Seismic Reflection Modelling in a Supercritical Geothermal System: An Image of the K-Horizon in the Larderello Field (Italy)

Synthetic Seismic Reflection Modelling in a Supercritical Geothermal System: An Image of the K-Horizon in the Larderello Field (Italy)

3D seismic for design and derisking of dual geothermal boreholes in sedimentary sequences and new prospects in the Paris Basin (Adapted methodology using petroleum industry techniques)

Characterizing a decametre-scale granitic reservoir using GPR and seismic methods – A case study for preparing hydraulic stimulations

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