496 research outputs found
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Imaging of a fluid injection process using geophysical data - A didactic example
In many subsurface industrial applications, fluids are injected into or withdrawn from a geologic formation. It is of practical interest to quantify precisely where, when, and by how much the injected fluid alters the state of the subsurface. Routine geophysical monitoring of such processes attempts to image the way that geophysical properties, such as seismic velocities or electrical conductivity, change through time and space and to then make qualitative inferences as to where the injected fluid has migrated. The more rigorous formulation of the time-lapse geophysical inverse problem forecasts how the subsurface evolves during the course of a fluid-injection application. Using time-lapse geophysical signals as the data to be matched, the model unknowns to be estimated are the multiphysics forward-modeling parameters controlling the fluid-injection process. Properly reproducing the geophysical signature of the flow process, subsequent simulations can predict the fluid migration and alteration in the subsurface. The dynamic nature of fluid-injection processes renders imaging problems more complex than conventional geophysical imaging for static targets. This work intents to clarify the related hydrogeophysical parameter estimation concepts
Advanced Vadose Zone Simulations Using TOUGH
The vadose zone can be characterized as a complex subsurface system in which intricate physical and biogeochemical processes occur in response to a variety of natural forcings and human activities. This makes it difficult to describe, understand, and predict the behavior of this specific subsurface system. The TOUGH nonisothermal multiphase flow simulators are well-suited to perform advanced vadose zone studies. The conceptual models underlying the TOUGH simulators are capable of representing features specific to the vadose zone, and of addressing a variety of coupled phenomena. Moreover, the simulators are integrated into software tools that enable advanced data analysis, optimization, and system-level modeling. We discuss fundamental and computational challenges in simulating vadose zone processes, review recent advances in modeling such systems, and demonstrate some capabilities of the TOUGH suite of codes using illustrative examples
Acoustic power absorption and enhancement generated by slow and fast MHD waves
We used long duration, high quality, unresolved (Sun-as-a star) observations
collected by the ground based network BiSON and by the instruments GOLF and
VIRGO on board the ESA/NASA SOHO satellite to search for solar-cycle-related
changes in mode characteristics in velocity and continuum intensity for the
frequency range between 2.5mHz < nu < 6.8mHz. Over the ascending phase of solar
cycle 23 we found a suppression in the p-mode amplitudes both in the velocity
and intensity data between 2.5mHz <nu< 4.5mHz with a maximum suppression for
frequencies in the range between 2.5mHz <nu< 3.5mHz. The size of the amplitude
suppression is 13+-2 per cent for the velocity and 9+-2 per cent for the
intensity observations. Over the range 4.5mHz <nu< 5.5mHz the findings hint
within the errors to a null change both in the velocity and intensity
amplitudes. At still higher frequencies, in the so called High-frequency
Interference Peaks (HIPs) between 5.8mHz <nu < 6.8mHz, we found an enhancement
in the velocity amplitudes with the maximum 36+-7 per cent occurring for 6.3mHz
<nu< 6.8mHz. However, in intensity observations we found a rather smaller
enhancement of about 5+-2 per cent in the same interval. There is evidence that
the frequency dependence of solar-cycle velocity amplitude changes is
consistent with the theory behind the mode conversion of acoustic waves in a
non-vertical magnetic field, but there are some problems with the intensity
data, which may be due to the height in the solar atmosphere at which the VIRGO
data are taken.Comment: Accepted for publication in A&A. 10 pages, 9 figures
Evidence of increasing acoustic emissivity at high frequency with solar cycle 23 in Sun-as-a-star observations
We used long high-quality unresolved (Sun-as-a-star observations) data
collected by GOLF and VIRGO instruments on board the ESA/NASA SOHO satellite to
investigate the amplitude variation with solar cycle 23 in the high-frequency
band (5.7 < nu< 6.3 mHz). We found an enhancement of acoustic emissivity over
the ascending phase of about 18+-3 in velocity observations and a slight
enhancement of 3+-2 in intensity. Mode conversion from fast acoustic to fast
magneto-acoustic waves could explain the enhancement in velocity observations.
These findings open up the possibility to apply the same technique to stellar
intensity data, in order to investigate stellar-magnetic activity.Comment: Proceedings of the Stellar Pulsation. Santa Fe, USA. 3 pages, 5
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Seepage Calibration Model and Seepage Testing Data
The purpose of this Model Report is to document the Seepage Calibration Model (SCM). The SCM was developed (1) to establish the conceptual basis for the Seepage Model for Performance Assessment (SMPA), and (2) to derive seepage-relevant, model-related parameters and their distributions for use in the SMPA and seepage abstraction in support of the Total System Performance Assessment for License Application (TSPA-LA). This Model Report has been revised in response to a comprehensive, regulatory-focused evaluation performed by the Regulatory Integration Team [''Technical Work Plan for: Regulatory Integration Evaluation of Analysis and Model Reports Supporting the TSPA-LA'' (BSC 2004 [DIRS 169653])]. The SCM is intended to be used only within this Model Report for the estimation of seepage-relevant parameters through calibration of the model against seepage-rate data from liquid-release tests performed in several niches along the Exploratory Studies Facility (ESF) Main Drift and in the Cross-Drift. The SCM does not predict seepage into waste emplacement drifts under thermal or ambient conditions. Seepage predictions for waste emplacement drifts under ambient conditions will be performed with the SMPA [''Seepage Model for PA Including Drift Collapse'' (BSC 2004 [DIRS 167652])], which inherits the conceptual basis and model-related parameters from the SCM. Seepage during the thermal period is examined separately in the Thermal Hydrologic (TH) Seepage Model [see ''Drift-Scale Coupled Processes (DST and TH Seepage) Models'' (BSC 2004 [DIRS 170338])]. The scope of this work is (1) to evaluate seepage rates measured during liquid-release experiments performed in several niches in the Exploratory Studies Facility (ESF) and in the Cross-Drift, which was excavated for enhanced characterization of the repository block (ECRB); (2) to evaluate air-permeability data measured in boreholes above the niches and the Cross-Drift to obtain the permeability structure for the seepage model; (3) to use inverse modeling to calibrate the SCM and to estimate seepage-relevant, model-related parameters on the drift scale; (4) to estimate the epistemic uncertainty of the derived parameters, based on the goodness-of-fit to the observed data and the sensitivity of calculated seepage with respect to the parameters of interest; (5) to characterize the aleatory uncertainty of the parameters as a result of spatial variability; (6) to evaluate prediction uncertainty based on linear uncertainty-propagation analyses and Monte Carlo simulations; (7) to validate the SCM during model development, and validate the SCM using the post-development activities outlined in the Technical Work Plan (TWP); (8) to provide the technical basis for the resolution of unconfirmed issues previously labeled ''to be verified'' (TBV); and (9) to provide the technical basis for screening of certain seepage-related features, events, and processes (FEPs)
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