Passive monitoring and 3D imaging of the bedrock response to the 2018 Espoo/Helsinki geothermal stimulation

2020 ◽  
Author(s):  
George Taylor ◽  
Gregor Hillers
Keyword(s):  
Seismic Velocity ◽  
Imaging Techniques ◽  
Body Wave ◽  
Coda Wave ◽  
Geothermal System ◽  
Enhanced Geothermal Systems ◽  
Induced Earthquakes ◽  
Borehole Data ◽  
Passive Monitoring ◽  
Short Period

<p>In recent years several deep geothermal energy projects have been forced to close following the occurrence of large seismic events associated with the stimulation of the surrounding bedrock. In 2018, an enhanced geothermal system (EGS) experiment performed in Helsinki, Finland concluded with no seismicity exceeding the threshold magnitude and thus provides an intriguing showcase for future stimulation experiments in similar environments. During the 49 days of the experiment, the five-stage injection of ~18,000 cubic meters water stimulated many thousands of earthquakes. Like in all previous stimulation cases the earthquake data constitute the primary source for the assessment of the scientific and operational aspects of the reservoir response. Here we apply ambient noise based monitoring and imaging techniques to data collected by 100 short period three-component stations that were organized in three large arrays consisting of nominally 25 stations, in addition to three small four-station arrays, and 10 single stations, during a 100 day period. We compute daily nine-component noise correlations between all stations pairs except for the intra-array pairs in a frequency range between 0.5 and 10 Hz. We measure waveform delays within our correlation functions as a function of frequency and lag time using the Continuous Wavelet Transform. We then invert these observations using a Markov chain Monte Carlo method to obtain the temporal variation in seismic velocity dv/v during the injection. By exploiting the variable spatial sensitivities of the surface- and body-wave components at different coda-wave lapse times and frequencies, we are able to image the medium response to the stimulation in both time and space. We compare the estimated seismic velocity variations to other observations such as H<sup>2</sup>/V<sup>2</sup>, as well as dv/v observations obtained from collocated borehole data. Importantly, we also compare the observed medium response to seismicity and pumping parameters. Our results suggest that we are able to resolve medium changes that are not solely associated with the induced earthquakes, but also potential signatures of fluid content or pressure changes in the bedrock. The combined observations of seismicity, pumping parameters and dv/v changes collected in this experiment can further advance passive monitoring techniques in the context of enhanced geothermal systems, and facilitate a more comprehensive analysis of fluid-rock interactions that may occur aseismically.</p>

A Seismic Network to Monitor the 2020 EGS Stimulation in the Espoo/Helsinki Area, Southern Finland

2021 ◽  
Author(s):  
Annukka E. Rintamäki ◽  
Gregor Hillers ◽  
Tommi A. T. Vuorinen ◽  
Tuija Luhta ◽  
Jonathan M. Pownall ◽  
...  
Keyword(s):  
Seismic Analysis ◽  
Signal To Noise Ratio ◽  
Public Awareness ◽  
Seismic Network ◽  
Geothermal System ◽  
Induced Earthquakes ◽  
Data Set ◽  
Short Period ◽  
Wide Range ◽  
Good Signal

Abstract We present the deployment of a seismic network in the Helsinki capital area of Finland that was installed to monitor the response to the second stimulation phase of an ∼6-kilometer-deep enhanced geothermal system in 2020. The network consists of a dozen permanent broadband stations and more than 100, predominantly short-period, temporary stations. This 2020 deployment is characterized by a mix of single stations and arrays with diverse configurations. It covers a larger area and exhibits a smaller azimuthal gap compared with the network that monitored the first stimulation in 2018. We surveyed the outcropping rocks at one of the large array sites to study surface expressions of shear or weakness zones that are possibly connected to the stimulated volume at depth. We link the relatively large number of macroseismic reports received during the stimulation to an increased public awareness of the project together with an increased sensitivity because the second stimulation occurred during the local COVID-19 mobility restrictions. The spatial distribution of the reports seems to be controlled by the radiation pattern of the induced earthquakes and hence by the stress state in the reservoir. The continuous records contain strong energy at high frequencies above 50 Hz that is attributed to anthropogenic processes in the densely populated urban area. However, the exceptionally low attenuation of the bedrock yields good signal-to-noise ratio seismograms of the induced small events, the largest of which was magnitude ML 1.2. The signal quality of the obtained noise correlation functions is similarly very good. The data set has been collected to underpin a wide range of seismic analysis techniques for complementary scientific studies of the evolving reservoir processes and the induced event properties. These scientific studies should inform the legislation and educate the public for transparent decision making around geothermal power generation.

A Procedure for the Extraction of Multiple Body Wave Traveltimes From Seismological Waveform Data

1991 ◽  
Vol 02 (01) ◽  
pp. 276-283 ◽  
Author(s):  
GÖTZ H.R. BOKELMANN ◽  
PAUL G. SILVER
Keyword(s):  
Travel Time ◽  
Seismic Velocity ◽  
Body Wave ◽  
Path Model ◽  
Nonlinear Dependence ◽  
Model Parameters ◽  
Time Inversion ◽  
Waveform Data ◽  
Short Period ◽  
Period Data

A scheme for extracting multiple phase body wave traveltimes is presented which is most applicable to teleseismic broadband and short period data from permanent and portable instruments. The method specifically allows for the nonlinear dependence of waveforms on travel time by performing a nonlinear search over a reduced set of “projected model parameters”. This reduced set is found by splitting the method into two parts, the nonlinear dependence of waveforms on traveltime perturbations (particularly strong for broadband and short period data) and the linearizable dependence of travel time perturbations on variations in seismic velocity. By use of generalized inverse, the traveltime perturbations can be adequately characterized by a reduced number of linear combinations of model parameters. Consequently, the nonlinear search is performed over an optimally compact model space. The technique can consider simultaneously a large number of body wave phases creating a systematic methodology for extracting large numbers of traveltimes from single source-receiver pairs. The resulting path model may or may not be of physical significance; the primary goal is the extraction of travel times that may be subsequently used for a more comprehensive travel time inversion.

Monitoring deep fractured reservoirs with ambient noise correlation: importance of acousto-elastic effects

2020 ◽  
Author(s):  
Jérôme Azzola ◽  
Jean Schmittbuhl ◽  
Dimitri Zigone ◽  
Olivier Lengliné ◽  
Frédéric Masson
Keyword(s):  
Numerical Model ◽  
Ambient Noise ◽  
Seismic Velocity ◽  
Low Cost ◽  
Fractured Reservoirs ◽  
Coda Wave ◽  
Hydraulic Pressure ◽  
Noise Correlation ◽  
Enhanced Geothermal Systems ◽  
Geothermal Systems

<p>An emerging technique for a continuous and low cost geophysical monitoring of deep reservoirs like Enhanced Geothermal Systems (EGS) is based on ambient seismic noise correlation and in particular Coda Wave Interferometry (CWI) from temporal stacks of ambient noise cross-correlation functions (or ANCCFs). We present here a forward numerical model simulating the propagation of scattered waves through a reservoir during its deformation, including non-linear acousto-elastic effects. Our approach is based on the case study of the Rittershoffen geothermal reservoir (France). We validate the numerical model by reproducing seasonal variations of the relative changes in seismic velocity observed from ANCCFs and provide a physical interpretation of this seismic signal. We extend our modelling to the in-situ deformation of the reservoir by considering either a hydraulic pressure increase or an aseismic shear of an embedded fault. The sensitivity of the scattered waves to small strain perturbations enables to detect small travel time changes as dt/t ~ 10<sup>-5</sup>, which opens perspectives for the application of ambient noise based techniques to the continuous monitoring of local mechanisms in deep geothermal reservoirs.</p>

Channel waves in cross‐borehole data

Geophysics ◽  
1992 ◽  
Vol 57 (2) ◽  
pp. 334-342 ◽  
Author(s):  
Larry R. Lines ◽  
Kenneth R. Kelly ◽  
John Queen
Keyword(s):  
Seismic Velocity ◽  
Test Facility ◽  
Equation Modeling ◽  
Borehole Data ◽  
Geological Information ◽  
Channel Wave ◽  
First Arrival ◽  
Borehole Seismic ◽  
Seismic Velocity Contrasts ◽  
Ray Bending

Layered geological formations with large seismic velocity contrasts can effectively create channel waves in cross‐borehole seismic data. The existence of channel waves for such waveguides can be confirmed by ray tracing, wave equation modeling, and modal analysis. Channel wave arrivals are identified in cross‐borehole data recorded at Conoco’s Newkirk test facility. For these data, where velocity contrasts are about 2 to 1, tomography based on first arrival traveltimes, is limited due to problems with extreme ray bending and seismic shadow zones. However, it may be possible to extract geological information using channel wave information. The seismometer differencing method appears to be a promising approach for detecting waveguide boundaries by use of cross‐borehole data.

A numerical study of the mechanism of injection-induced and triggered seismicity at the Pohang Enhanced Geothermal Systems project, South Korea

2021 ◽  
Author(s):  
Kwang-Il Kim ◽  
Hwajung Yoo ◽  
Seheok Park ◽  
Juhyi Yim ◽  
Linmao Xie ◽  
...  
Keyword(s):  
South Korea ◽  
Numerical Study ◽  
Geothermal System ◽  
Enhanced Geothermal Systems ◽  
Hydraulic Stimulation ◽  
Triggered Seismicity ◽  
Induced Stress ◽  
Shear Slip ◽  
Stress Dependent ◽  
The Impact

<p>Hydraulic stimulation for the creation of an Enhanced Geothermal System (EGS) reservoir could potentially reactivate a nearby fault and result in man-made earthquakes. In November 15, 2017, an M<sub>w</sub> 5.5 earthquake, the second largest after the initiation of the South Korean national instrumental monitoring system, occurred near an EGS project in Pohang, South Korea. The earthquake occurred on a previously unmapped fault, that is here denoted the M<sub>w</sub> 5.5 Fault. A number of previous studies to model the hydraulic stimulation in the Pohang EGS project have been carried out to identify the mechanism of seismic events. Those previous studies focused on coupled hydro-mechanical processes without the consideration of pre-existing fractures and thermal effects. This study presents an investigation of the mechanisms of induced and triggered seismicity in the Pohang EGS project through three-dimensional coupled thermo-hydro-mechanical numerical simulations. Fractures intersecting the open-hole sections of two deep boreholes, PX-1 and PX-2, clearly indicated by field observations are modeled along with the M<sub>w</sub> 5.5 Fault. Models of stress-dependent permeability models are calibrated based on the numerical reproduction of the pressure-time evolution during the field hydraulic stimulations. The Coulomb failure stress change at the M<sub>w</sub> 5.5 Fault is calculated to quantify the impact of five hydraulic stimulations. In the case of PX-2 stimulations, the pore pressure buildup results in a volumetric expansion of the reservoir and thereby the perturbation of stresses is transferred to the M<sub>w</sub> 5.5 Fault. The volumetric contraction of the reservoir by the temperature reduction could slightly perturb the stress distribution at the M<sub>w</sub> 5.5 Fault. In the case of PX-1 stimulations, shear slip of the PX-1 fracture is explicitly modeled. The modeling shows that transfer of the shear stress drop by the shear slip stabilizes the M<sub>w</sub> 5.5 Fault, which is consistent with the field observation that the seismicity was not induced at the M<sub>w</sub> 5.5 Fault by the PX-1 stimulations. The cooling-induced thermal stress additionally reduces the effective normal stress of PX-1 fracture. Thus, some additional shear slip of the PX-1 fracture is induced by the thermal effect. However, the modeling shows that for both PX-1 and PX-2 stimulations, thermally-induced stress perturbations are very small compared to pressure-induced stress perturbations.</p>

scholarly journals Analysis of Enhanced Geothermal System Development Scenarios for District Heating and Cooling of the Göttingen University Campus

Geosciences ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 349
Author(s):  
Dmitry Romanov ◽  
Bernd Leiss
Keyword(s):  
Net Present Value ◽  
District Heating ◽  
Reservoir Modeling ◽  
Geothermal System ◽  
Heat Output ◽  
Enhanced Geothermal Systems ◽  
University Campus ◽  
Energy Potential ◽  
Reference Case ◽  
Heating And Cooling

The huge energy potential of Enhanced Geothermal Systems (EGS) makes them perspective sources of non-intermittent renewable energy for the future. This paper focuses on potential scenarios of EGS development in a locally and in regard to geothermal exploration, poorly known geological setting—the Variscan fold-and-thrust belt —for district heating and cooling of the Göttingen University campus. On average, the considered single EGS doublet might cover about 20% of the heat demand and 6% of the cooling demand of the campus. The levelized cost of heat (LCOH), net present value (NPV) and CO2 abatement cost were evaluated with the help of a spreadsheet-based model. As a result, the majority of scenarios of the reference case are currently not profitable. Based on the analysis, EGS heat output should be at least 11 MWth (with the brine flow rate being 40 l/s and wellhead temperature being 140 °C) for a potentially profitable project. These parameters can be a target for subsurface investigation, reservoir modeling and hydraulic stimulation at a later stage. However, sensitivity analysis presented some conditions that yield better results. Among the most influential parameters on the outcome are subsidies for research wells, proximity to the campus, temperature drawdown and drilling costs. If realized, the EGS project in Göttingen might save up to 18,100 t CO2 (34%) annually.

scholarly journals Antarctic Upper Mantle Rheology

2021 ◽  
pp. M56-2020-19
Author(s):  
E. R. Ivins ◽  
W. van der Wal ◽  
D. A. Wiens ◽  
A. J. Lloyd ◽  
L. Caron
Keyword(s):  
Wave Velocity ◽  
Upper Mantle ◽  
Effective Viscosity ◽  
Seismic Velocity ◽  
Imaging Techniques ◽  
Three Dimensional ◽  
Velocity Model ◽  
Mantle Flow ◽  
S Wave ◽  
Velocity Changes

AbstractThe Antarctic mantle and lithosphere are known to have large lateral contrasts in seismic velocity and tectonic history. These contrasts suggest differences in the response time scale of mantle flow across the continent, similar to those documented between the northeastern and southwestern upper mantle of North America. Glacial isostatic adjustment and geodynamical modeling rely on independent estimates of lateral variability in effective viscosity. Recent improvements in imaging techniques and the distribution of seismic stations now allow resolution of both lateral and vertical variability of seismic velocity, making detailed inferences about lateral viscosity variations possible. Geodetic and paleo sea-level investigations of Antarctica provide quantitative ways of independently assessing the three-dimensional mantle viscosity structure. While observational and causal connections between inferred lateral viscosity variability and seismic velocity changes are qualitatively reconciled, significant improvements in the quantitative relations between effective viscosity anomalies and those imaged by P- and S-wave tomography have remained elusive. Here we describe several methods for estimating effective viscosity from S-wave velocity. We then present and compare maps of the viscosity variability beneath Antarctica based on the recent S-wave velocity model ANT-20 using three different approaches.

Integrated and frequency-band magnitude, two alternative measures of the size of an earthquake

1970 ◽  
Vol 60 (3) ◽  
pp. 917-937 ◽  
Author(s):  
B. F. Howell ◽  
G. M. Lundquist ◽  
S. K. Yiu
Keyword(s):  
Transfer Function ◽  
Frequency Domain ◽  
Frequency Band ◽  
Transfer Functions ◽  
Body Wave ◽  
Average Amplitude ◽  
Equivalent Quantity ◽  
Short Period ◽  
Alternative Measures ◽  
Body Wave Magnitude

Abstract Integrated magnitude substitutes the r.m.s. average amplitude over a pre-selected interval for the peak amplitude in the conventional body-wave magnitude formula. Frequency-band magnitude uses an equivalent quantity in the frequency domain. Integrated magnitude exhibits less scatter than conventional body-wave magnitude for short-period seismograms. Frequency-band magnitude exhibits less scatter than body-wave magnitude or integrated magnitude for both long- and short-period seismograms. The scatter of frequency-band magnitude is probably due to real azimuthal effects, crustal-transfer-function variations, errors in compensation for seismograph response, microseismic moise and uncertainties in the compensation for attenuation with distance. To observe azimuthal variations clearly, the crustal-transfer functions and seismograph response need to be known more precisely than was the case in this experiment, because these two sources of scatter can be large enough to explain all of the observed variations.

Investigation of ambient noise seismological methods on a bridge model

2021 ◽  
Author(s):  
Chun-Man Liao ◽  
Franziska Mehrkens ◽  
Celine Hadziioannou ◽  
Ernst Niederleithinger
Keyword(s):  
Wave Propagation ◽  
Large Scale ◽  
Seismic Velocity ◽  
Measurement Data ◽  
Correlation Coefficients ◽  
Coda Wave ◽  
Velocity Change ◽  
Promising Tool ◽  
Bridge Model ◽  
Noise Measurements

<p>The aim of this work is to investigate the application of seismological noise-based monitoring for bridge structures. A large-scale two-span concrete bridge model with a build-in post-tensioning system, which is exposed to environmental conditions, is chosen as our experimental test structure. Ambient seismic noise measurements were carried out under different pre-stressed conditions. Using the seismic interferometry technique, which is applied to the measurement data in the frequency domain, we reconstruct waveforms that relate to wave propagation in the structure. The coda wave interferometry technique is then implemented by comparing two waveforms recorded in two pre-stress states. Any relative seismic velocity changes are identified by determining the correlation coefficients and reveal the influence of the pre-stressing force. The decrease of the wave propagation velocity indicates the loss of the pre-stress and weakening stiffness due to opening or event extension of cracks. We conclude that the seismological methods used to estimate velocity change can be a promising tool for structural health monitoring of civil structures.</p>

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