scholarly journals The response of a fractured crystalline reservoir to natural pressure buildup: Experiment results from the Bedretto Lab

2021 ◽  
Author(s):  
Alexis Shakas ◽  
Nima Gholizadeh ◽  
Marian Hertrich ◽  
Quinn Wenning ◽  
Hansruedi Maurer ◽  
...  
Keyword(s):  
Fractured Rock ◽  
Ambient Pressure ◽  
Time Lapse ◽  
Swiss Alps ◽  
Pressure Buildup ◽  
Stress Changes ◽  
Natural Pressure ◽  
As Stress ◽  
Ground Penetrating ◽  
Pressure Changes

<p>The Bedretto Underground Laboratory for Geosciences and GeoEnergies, located in the Swiss Alps and situated under more than 1 km of granitic overburden, offers a unique field site to study processes in fractured rock. Currently, a total of six boreholes are available, four of them being permanently instrumented with monitoring equipment, and two dedicated as stimulation boreholes. One of the monitoring boreholes contains permanent packed-off intervals which record pressure changes and flow rate. The remaining three are instrumented with a variety of sensors, including fiber-optic micro-strain sensors, temperature monitoring, permanent geophones and accelerometers. All monitoring boreholes are either sealed with packers or cemented, and only the stimulation boreholes allow for outflow. During a period of several weeks, we were able to seal the two stimulation boreholes and allow the reservoir to approach ambient pressure conditions (more than 3 MPa at the wellhead) while we monitored the response of the reservoir. The pressure buildup shows not only in the pressure data, but also as stress changes in the reservoir. During a depressurization phase, we quickly opened one borehole and subsequently performed time-lapse single-hole Ground Penetrating Radar (GPR) measurements. At a second depressurization phase, we continued the GPR measurements while opening the second borehole in a controlled manner. The changes in strain, pressure and GPR reflectivity illuminate the response of the reservoir when moving from ambient to atmospheric pressure at the wellhead, and reveal processes such as wellbore storage, pore-pressure variations and ultimately permeability changes in the reservoir.</p>

Time-lapse ground penetrating radar difference reflection imaging of saline tracer flow in fractured rock

Geophysics ◽  
2020 ◽  
Vol 85 (3) ◽  
pp. H25-H37 ◽  
Author(s):  
Peter-Lasse Giertzuch ◽  
Joseph Doetsch ◽  
Mohammadreza Jalali ◽  
Alexis Shakas ◽  
Cédric Schmelzbach ◽  
...  
Keyword(s):  
Ground Penetrating Radar ◽  
Fractured Rock ◽  
Sampling Rate ◽  
Time Lapse ◽  
Transport Processes ◽  
Local Data ◽  
Tracer Injection ◽  
Flow Through ◽  
Reflection Imaging ◽  
Ground Penetrating

The characterization of flow and transport processes in fractured rock is challenging because they cannot be observed directly and hydrologic tests can only provide sparse and local data. Time-lapse ground penetrating radar (GPR) can be a valuable tool to monitor such processes in the subsurface, but it requires highly reproducible data. As part of a tracer injection experiment at the Grimsel Test Site (GTS) in Switzerland, borehole reflection GPR data were acquired in a time-lapse survey to monitor saline tracer flow through a fracture network in crystalline rock. Because the reflections from the tracer in the sub-mm fractures appear extremely weak, a differencing approach has been necessary to identify the tracer signal. Furthermore, several processing steps and corrections had to be applied to meet the reproducibility requirements. These steps include (1) single-trace preprocessing, (2) temporal trace alignment, (3) correction of sampling rate fluctuations, (4) spatial trace alignment, (5) spike removal, and (6) postprocessing procedures applied to the difference images. This allowed successful tracer propagation monitoring with a clear signal that revealed two separate tracer flow paths. The GPR results are confirmed by conductivity meters that were placed in boreholes in the GTS. If sufficient data processing is applied, GPR is shown to be capable of resolving tracer flow through sub-mm aperture fractures by difference reflection imaging even in challenging surroundings where many reflectors are present.

scholarly journals Ground-penetrating-radar response to fracture-fluid salinity: Why lower frequencies are favorable for resolving salinity changes

Geophysics ◽  
2008 ◽  
Vol 73 (5) ◽  
pp. J25-J30 ◽  
Author(s):  
Georgios P. Tsoflias ◽  
Matthew W. Becker
Keyword(s):  
Electrical Conductivity ◽  
Ground Penetrating Radar ◽  
Field Experiments ◽  
Fractured Rock ◽  
Low Frequency ◽  
Signal Amplitude ◽  
Time Lapse ◽  
Fracture Aperture ◽  
Fracture Fluid ◽  
Ground Penetrating

Time-lapse ground-penetrating-radar (GPR) surveys exploit signal-amplitude changes to monitor saline tracers in fractures and to identify groundwater flow paths. However, the relationships between GPR signal amplitude, phase, and frequency with fracture aperture and fluid electrical conductivity are not well understood. We used analytical modeling, numerical simulations, and field experiments of multifrequency GPR to investigate these relationships for a millimeter-scale-aperture fracture saturated with water of varying salinity. We found that the response of lower-frequency radar signals detects changes in fluid salinity better than the response of higher-frequency signals. Increasing fluid electrical conductivity decreases low-frequency GPR signal wavelength, which improves its thin-layer resolution capability. We concluded that lower signal frequencies, such as [Formula: see text], and saline tracers of up to [Formula: see text] conductivity are preferable when using GPR to monitor flow in fractured rock. Furthermore, we found that GPR amplitude and phase responses are detectable in the field and predictable by EM theory and modeling; therefore, they can be related to fracture aperture and fluid salinity for hydrologic investigations of fractured-rock flow and transport properties.

scholarly journals 4D Tracer Flow Reconstruction in Fractured Rock through Borehole GPR Monitoring

2021 ◽  
Author(s):  
Peter-Lasse Giertzuch ◽  
Joseph Doetsch ◽  
Alexis Shakas ◽  
Mohammadreza Jalali ◽  
Bernard Brixel ◽  
...  
Keyword(s):  
Fractured Rock ◽  
Time Lapse ◽  
Test Site ◽  
Crystalline Rock ◽  
Flow Paths ◽  
Tracer Injection ◽  
Flow Reconstruction ◽  
Fracture Apertures ◽  
Ground Penetrating ◽  
Engineering Projects

Abstract. Two borehole ground penetrating radar (GPR) surveys were conducted during saline tracer injection experiments in fully-saturated crystalline rock at the Grimsel Test Site in Switzerland. The saline tracer is characterized by an increased electrical conductivity in comparison to formation water. It was injected under steady state flow conditions into the rock mass that features sub-mm fracture apertures. The GPR surveys were designed as time-lapse reflection GPR from separate boreholes and a time-lapse transmission survey between the two boreholes. The local increase in conductivity, introduced by the injected tracer, was captured by GPR in terms of reflectivity increase for the reflection surveys, and attenuation increase for the transmission survey. Data processing and difference imaging was used to extract the tracer signal in the reflection surveys, despite the presence of multiple static reflectors that could shadow the tracer reflection. The transmission survey was analyzed by a difference attenuation inversion scheme, targeting conductivity changes in the tomography plane. By combining the time-lapse difference reflection images, it was possible to reconstruct and visualize the tracer propagation in 3D. This was achieved by calculating the potential radially-symmetric tracer reflection locations in each survey and determining their intersections, to delineate the possible tracer locations. Localization ambiguity imposed by the lack of a third borehole for a full triangulation was reduced by including the attenuation tomography results into the analysis. The resulting tracer flow reconstruction was found to be in good agreement with data from conductivity sensors in multiple observation locations in the experiment volume and gave a realistic visualization of the hydrological processes during the tracer experiments. Our methodology proved to be successful for characterizing flow paths related with geothermal reservoirs in crystalline rocks, but it can be transferred in a straightforward manner to other applications, such as radioactive repository monitoring or civil engineering projects.

scholarly journals Imaging of phase changes and fluid movement in and between reservoirs at Teal South

2015 ◽  
Vol 3 (2) ◽  
pp. SP53-SP65 ◽  
Author(s):  
Nayyer Islam ◽  
Mohamed A. Ezawi ◽  
Wayne D. Pennington
Keyword(s):  
Oil And Gas ◽  
Time Lapse ◽  
Phase Changes ◽  
Data Sets ◽  
Fluid Movement ◽  
Gas Leakage ◽  
Highly Sensitive ◽  
Stress Changes ◽  
The One ◽  
Pressure Changes

We have reexamined the poststack seismic legacy and time-lapse data sets from the Teal South field in the Gulf of Mexico for insight into regional pressure changes from production at one reservoir and its effects on neighboring unproduced reservoirs. We support previous predictions of oil and gas leakage from neighboring reservoirs by providing direct evidence for leakage through 3D mapping of the hydrocarbons themselves. The use of the squared instantaneous amplitude as an attribute allowed visualization of the large amplitude changes while minimizing the appearance of noise. The use of translucency in the 3D time-lapse difference volumes assisted in identifying features of interest that had been unrecognized in earlier studies. For example, this investigation found that hydrocarbons appeared to have escaped from one small (unproduced) reservoir through its spill point, only to be trapped in a nearby structure, from which it ultimately escaped through that trap’s spill point. Such fluid migration can occur in a period of a few years due to production, not geologic time. Time-lapse studies such as the one presented here can be very helpful in identifying such fluid movement, particularly in highly porous and unconsolidated reservoirs that are highly sensitive to pore-fluid type and stress changes.

scholarly journals Computing Localized Breakthrough Curves and Velocities of Saline Tracer from Ground Penetrating Radar Monitoring Experiments in Fractured Rock

Energies ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2949
Author(s):  
Peter-Lasse Giertzuch ◽  
Alexis Shakas ◽  
Joseph Doetsch ◽  
Bernard Brixel ◽  
Mohammadreza Jalali ◽  
...  
Keyword(s):  
Electrical Conductivity ◽  
Ground Penetrating Radar ◽  
Fractured Rock ◽  
Time Lapse ◽  
Test Site ◽  
Breakthrough Curves ◽  
Flow Path ◽  
Transport Processes ◽  
Grimsel Test Site ◽  
Ground Penetrating

Solute tracer tests are an established method for the characterization of flow and transport processes in fractured rock. Such tests are often monitored with borehole sensors which offer high temporal sampling and signal to noise ratio, but only limited spatial deployment possibilities. Ground penetrating radar (GPR) is sensitive to electromagnetic properties, and can thus be used to monitor the transport behavior of electrically conductive tracers. Since GPR waves can sample large volumes that are practically inaccessible by traditional borehole sensors, they are expected to increase the spatial resolution of tracer experiments. In this manuscript, we describe two approaches to infer quantitative hydrological data from time-lapse borehole reflection GPR experiments with saline tracers in fractured rock. An important prerequisite of our method includes the generation of GPR data difference images. We show how the calculation of difference radar breakthrough curves (DRBTC) allows to retrieve relative electrical conductivity breakthrough curves for theoretically arbitrary locations in the subsurface. For sufficiently small fracture apertures we found the relation between the DRBTC values and the electrical conductivity in the fracture to be quasi-linear. Additionally, we describe a flow path reconstruction procedure that allows computing approximate flow path distances using reflection GPR data from at least two boreholes. From the temporal information during the time-lapse GPR surveys, we are finally able to calculate flow-path averaged tracer velocities. Our new methods were applied to a field data set that was acquired at the Grimsel Test Site in Switzerland. DRBTCs were successfully calculated for previously inaccessible locations in the experimental rock volume and the flow path averaged velocity field was found to be in good accordance with previous studies at the Grimsel Test Site.

scholarly journals Four-dimensional tracer flow reconstruction in fractured rock through borehole ground-penetrating radar (GPR) monitoring

Solid Earth ◽  
2021 ◽  
Vol 12 (7) ◽  
pp. 1497-1513
Author(s):  
Peter-Lasse Giertzuch ◽  
Joseph Doetsch ◽  
Alexis Shakas ◽  
Mohammadreza Jalali ◽  
Bernard Brixel ◽  
...  
Keyword(s):  
Ground Penetrating Radar ◽  
Fractured Rock ◽  
Time Lapse ◽  
Test Site ◽  
Crystalline Rock ◽  
Flow Paths ◽  
Tracer Injection ◽  
Flow Reconstruction ◽  
Fracture Apertures ◽  
Ground Penetrating

Abstract. Two borehole ground-penetrating radar (GPR) surveys were conducted during saline tracer injection experiments in fully saturated crystalline rock at the Grimsel Test Site in Switzerland. The saline tracer is characterized by an increased electrical conductivity in comparison to formation water. It was injected under steady-state flow conditions into the rock mass that features sub-millimeter fracture apertures. The GPR surveys were designed as time-lapse reflection GPR from separate boreholes and a time-lapse transmission survey between the two boreholes. The local increase in conductivity, introduced by the injected tracer, was captured by GPR in terms of reflectivity increase for the reflection surveys, and attenuation increase for the transmission survey. Data processing and difference imaging was used to extract the tracer signal in the reflection surveys, despite the presence of multiple static reflectors that could shadow the tracer reflection. The transmission survey was analyzed by a difference attenuation inversion scheme, targeting conductivity changes in the tomography plane. By combining the time-lapse difference reflection images, it was possible to reconstruct and visualize the tracer propagation in 3D. This was achieved by calculating the potential radially symmetric tracer reflection locations in each survey and determining their intersections, to delineate the possible tracer locations. Localization ambiguity imposed by the lack of a third borehole for a full triangulation was reduced by including the attenuation tomography results in the analysis. The resulting tracer flow reconstruction was found to be in good agreement with data from conductivity sensors in multiple observation locations in the experiment volume and gave a realistic visualization of the hydrological processes during the tracer experiments. Our methodology was demonstrated to be applicable for monitoring tracer flow and transport and characterizing flow paths related to geothermal reservoirs in crystalline rocks, but it can be transferred in a straightforward manner to other applications, such as radioactive repository monitoring or civil engineering projects.

Pressure Gradients Affecting the Labyrinth during Hypobaric Pressure

1997 ◽  
Vol 106 (6) ◽  
pp. 495-502 ◽  
Author(s):  
Konrád S. Konrádsson ◽  
Björn I. R. Carlborg ◽  
Joseph C. Farmer
Keyword(s):  
Cerebrospinal Fluid ◽  
Eustachian Tube ◽  
Ambient Pressure ◽  
Pressure Gradients ◽  
Cochlear Aqueduct ◽  
Fluid Compartment ◽  
Large Pressure ◽  
Fluid Compartments ◽  
Pressure Changes ◽  
Considerable Pressure

Hypobaric effects on the perilymph pressure were investigated in 18 cats. The perilymph, tympanic cavity, cerebrospinal fluid, and systemic and ambient pressure changes were continuously recorded relative to the atmospheric pressure. The pressure equilibration of the eustachian tube and the cochlear aqueduct was studied, as well as the effects of blocking these channels. During ascent, the physiologic opening of the eustachian tube reduced the pressure gradients across the tympanic membrane. The patent cochlear aqueduct equilibrated perilymph pressure to cerebrospinal fluid compartment levels with a considerable pressure gradient across the oval and round windows. With the aqueduct blocked, the pressure decrease within the labyrinth and tympanic cavities was limited, resulting in large pressure gradients toward the chamber and the cerebrospinal fluid compartments, respectively. We conclude that closed cavities with limited pressure release capacities are the cause of the pressure gradients. The strain exerted by these pressure gradients is potentially harmful to the ear.

scholarly journals Ice thickness distribution of all Swiss glaciers based on extended ground-penetrating radar data and glaciological modeling

2021 ◽  
pp. 1-19
Author(s):  
Melchior Grab ◽  
Enrico Mattea ◽  
Andreas Bauder ◽  
Matthias Huss ◽  
Lasse Rabenstein ◽  
...  
Keyword(s):  
Ground Penetrating Radar ◽  
Thickness Distribution ◽  
Radar Data ◽  
Tourism Industry ◽  
Swiss Alps ◽  
Ice Thickness ◽  
Hazard Management ◽  
Bed Topography ◽  
Ice Volume ◽  
Ground Penetrating

Abstract Accurate knowledge of the ice thickness distribution and glacier bed topography is essential for predicting dynamic glacier changes and the future developments of downstream hydrology, which are impacting the energy sector, tourism industry and natural hazard management. Using AIR-ETH, a new helicopter-borne ground-penetrating radar (GPR) platform, we measured the ice thickness of all large and most medium-sized glaciers in the Swiss Alps during the years 2016–20. Most of these had either never or only partially been surveyed before. With this new dataset, 251 glaciers – making up 81% of the glacierized area – are now covered by GPR surveys. For obtaining a comprehensive estimate of the overall glacier ice volume, ice thickness distribution and glacier bed topography, we combined this large amount of data with two independent modeling algorithms. This resulted in new maps of the glacier bed topography with unprecedented accuracy. The total glacier volume in the Swiss Alps was determined to be 58.7 ± 2.5 km3 in the year 2016. By projecting these results based on mass-balance data, we estimated a total ice volume of 52.9 ± 2.7 km3 for the year 2020. Data and modeling results are accessible in the form of the SwissGlacierThickness-R2020 data package.

Ice or rock matrix? Improved quantitative imaging of Alpine permafrost evolution through time-lapse petrophysical joint inversion

2021 ◽  
Author(s):  
Johanna Klahold ◽  
Christian Hauck ◽  
Florian Wagner
Keyword(s):  
Liquid Water ◽  
Joint Inversion ◽  
Time Lapse ◽  
Swiss Alps ◽  
Permafrost Degradation ◽  
Rock Matrix ◽  
Validation Data ◽  
Water Ice ◽  
Borehole Temperature ◽  
Ice Content

<p>Quantitative estimation of pore fractions filled with liquid water, ice and air is one of the prerequisites in many permafrost studies and forms the basis for a process-based understanding of permafrost and the hazard potential of its degradation in the context of global warming. The volumetric ice content is however difficult to retrieve, since standard borehole temperature monitoring is unable to provide any ice content estimation. Geophysical methods offer opportunities to image distributions of permafrost constituents in a non-invasive manner. A petrophysical joint inversion was recently developed to determine volumetric water, ice, air and rock contents from seismic refraction and electrical resistivity data. This approach benefits from the complementary sensitivities of seismic and electrical data to the phase change between ice and liquid water. A remaining weak point was the unresolved petrophysical ambiguity between ice and rock matrix. Within this study, the petrophysical joint inversion approach is extended along the time axis and respective temporal constraints are introduced. If the porosity (and other time-invariant properties like pore water resistivity or Archie exponents) can be assumed invariant over the considered time period, water, ice and air contents can be estimated together with a temporally constant (but spatially variable) porosity distribution. It is hypothesized that including multiple time steps in the inverse problem increases the ratio of data and parameters and leads to a more accurate distinction between ice and rock content. Based on a synthetic example and a field data set from an Alpine permafrost site (Schilthorn, Swiss Alps) it is demonstrated that the developed time-lapse petrophysical joint inversion provides physically plausible solutions, in particular improved estimates for the volumetric fractions of ice and rock. The field application is evaluated with independent validation data including thaw depths derived from borehole temperature measurements and shows generally good agreement. As opposed to the conventional petrophysical joint inversion, its time-lapse extension succeeds in providing reasonable estimates of permafrost degradation at the Schilthorn monitoring site without <em>a priori </em>constraints on the porosity model.</p>

scholarly journals Reflection tomography of time-lapse GPR data for studying dynamic unsaturated flow phenomena

2020 ◽  
Vol 24 (1) ◽  
pp. 159-167 ◽  
Author(s):  
Adam R. Mangel ◽  
Stephen M. J. Moysey ◽  
John Bradford
Keyword(s):  
Data Collection ◽  
Water Content ◽  
Unsaturated Flow ◽  
Time Lapse ◽  
New Method ◽  
Wetting Front ◽  
Empirical Estimates ◽  
Flow Phenomena ◽  
Ground Penetrating ◽  
Reflection Tomography

Abstract. Ground-penetrating radar (GPR) reflection tomography algorithms allow non-invasive monitoring of water content changes resulting from flow in the vadose zone. The approach requires multi-offset GPR data that are traditionally slow to collect. We automate GPR data collection to reduce the survey time significantly, thereby making this approach to hydrologic monitoring feasible. The method was evaluated using numerical simulations and laboratory experiments that suggest reflection tomography can provide water content estimates to within 5 % vol vol−1–10 % vol vol−1 for the synthetic studies, whereas the empirical estimates were typically within 5 %–15 % of measurements from in situ probes. Both studies show larger observed errors in water content near the periphery of the wetting front, beyond which additional reflectors were not present to provide data coverage. Overall, coupling automated GPR data collection with reflection tomography provides a new method for informing models of subsurface hydrologic processes and a new method for determining transient 2-D soil moisture distributions.

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