Seismic Velocity Uncertainties and their Effect on Geothermal Predictions: A Case Study

Rabbel, Wolfgang; Jusri, Tomi; Köhn, D.; Motra, Hem Bahadur; Niederau, Jan; Schreiter, L.; Thorwart, Martin; Wuttke, Frank

doi:10.1016/j.egypro.2017.08.178

Cited by 10 publications

(12 citation statements)

References 6 publications

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“…A starting 1‐D

P

wave velocity model was built considering velocity models obtained in different studies and with different methods (De Matteis et al, ; Rabbel et al, ; Saccorotti et al, ). The first location of each event was calculated using HYPOCENTER, an algorithm based on the Geiger's method (Lienert, ).…”

Section: Methodsmentioning

confidence: 99%

“…Initial and final 1‐D

P

wave velocity models used to locate and relocate the recorded seismic events. The starting velocity model obtained from the literature (Saccorotti et al, ; De Matteis et al, ; Rabbel et al, ) is shown in gray, and the velocity model for the Lago area obtained by simultaneously inverting for hypocenters and velocity model is shown in black.…”

Section: Methodsmentioning

confidence: 99%

“…The model refines the initial velocity model by introducing (or removing) layers and recalibrating the velocity of the existing ones. The inversion process added four new layers (0.5, 1.5, 2.0, and 4.0 km depth) and removed the 3.7 km depth layer from the original model derived from De Matteis et al (2008),Saccorotti et al (2014), andRabbel et al (2017). Velocities were reduced until 1.5 km depth and increased until 4.5 km depth.…”

mentioning

confidence: 99%

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Tectonic and Anthropogenic Microseismic Activity While Drilling Toward Supercritical Conditions in the Larderello‐Travale Geothermal Field, Italy

et al. 2020

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This study investigates the seismic activity occurring at the Larderello‐Travale geothermal field, central Italy, from June 2017 to January 2018. We deployed a network composed of nine broadband stations around the Venelle 2 well drilling for supercritical fluids. During the experiment, we recognize two types of seismic events (type 1 and type 2). Type‐1 events have clear P and S wave arrivals and occur in clusters both above and below the K‐horizon, which is a seismic reflector marking a debated transition zone at depth. The distribution and evolution of the seismic sequences suggest that the K‐horizon could be interpreted as a fluid‐rich region at near‐lithostatic pressures. Type‐2 events usually occur in swarms and show a periodic pattern, a narrow frequency band, and almost identical waveforms. Their source is estimated to be located near the well, and their occurrence ceases after about 3 weeks from the conclusion of the drilling. We propose a causal link with the drilling operations where pressure fronts inside the well may promote phase changes and fluid flow across the drilled formations. Our study sheds light on the fluid‐driven tectonic and anthropogenic seismic activity at the Larderello‐Travale geothermal field. More generally, we show that microseismic activity occurring during drilling in high‐pressure and high‐temperature conditions can remain at low magnitudes and that geothermal wells targeting geothermal fluids in such systems may be handled safely despite the critical conditions encountered at depth. The drilling of the Venelle 2 well is an encouraging example for the development of geothermal energy in critical conditions.

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“…A starting 1‐D

P

Section: Methodsmentioning

confidence: 99%

“…Initial and final 1‐D

P

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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Tectonic and Anthropogenic Microseismic Activity While Drilling Toward Supercritical Conditions in the Larderello‐Travale Geothermal Field, Italy

et al. 2020

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“…For the Metamorphic Unit, we adopted a velocity value of 5150 m/s, which is within the velocity range (i.e., 4400-5500 m/s) suggested by several authors (e.g., [6,9,13,18,76]). This velocity value was defined after analyzing the data observed in the Vp logs and in laboratory measurements of unfractured rocks from the Mica-schist complex and Gneiss complex in the depth range 1000-3500 m, as reported in the literature and summarized as follows [6,[71][72][73][74][75].…”

Section: Velocity Modelmentioning

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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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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Improvement of seismic velocity model by selective removal of irrelevant velocity variations

2021

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Seismic Velocity Uncertainties and their Effect on Geothermal Predictions: A Case Study

Cited by 10 publications

References 6 publications

Tectonic and Anthropogenic Microseismic Activity While Drilling Toward Supercritical Conditions in the Larderello‐Travale Geothermal Field, Italy

Tectonic and Anthropogenic Microseismic Activity While Drilling Toward Supercritical Conditions in the Larderello‐Travale Geothermal Field, Italy

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

Improvement of seismic velocity model by selective removal of irrelevant velocity variations

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