Sumit Mukhopadhyay | Lawrence Berkeley National Laboratory (original) (raw)
Papers by Sumit Mukhopadhyay
Journal of Statistical Physics, 1994
We use the finite-size scaling method to estimate the critical exponent λ that characterizes the ... more We use the finite-size scaling method to estimate the critical exponent λ that characterizes the scaling behavior of conductivity and permeability anisotropy near the percolation thresholdp c . Here λ is defined by the scaling lawk l /k t −1∼(p−p c )λ, wherek t andk t are the conductivity or permeability of the system in the direction of the macroscopic potential gradient and perpendicular to this direction, respectively. The results are λ(d=2)≃0.819±0.011 and λ(d=3)≃0.518±0.001. We interpret these results in terms of the structure of percolation clusters and their chemical distance. We also compare our results with the predictions of a scaling theory for λ due to Straley, and propose that λ(d=2)=t-βB , wheret is the critical exponent of the conductivity or permeability of the system, and βB is the critical exponent of the backbone of percolation clusters.
Physical Review E, 1996
... Muhammad Sahimi1,2 and Sumit Mukhopadhyay1,* 1Department of Chemical Engineering, University ... more ... Muhammad Sahimi1,2 and Sumit Mukhopadhyay1,* 1Department of Chemical Engineering, University of Southern California, Los Angeles, California 90089-1211 2Hochstleistungsrech enzentrum, Kernforschungsanlage Jülich, D-52425 Jülich 1, Germany Received 27 March ...
Chemical Engineering Science, 2000
The problem of estimating the e!ective grid block permeabilities of a "eld-scale porous medium wi... more The problem of estimating the e!ective grid block permeabilities of a "eld-scale porous medium with long-range correlations is studied. Both isotropic and anisotropic porous media are considered. The grid blocks are represented by networks of bonds the permeabilities of which are distributed according to three di!erent stochastic functions that generate long-range correlations, two of which are fractal distribution. A new perturbation expansion for estimating the e!ective permeabilities of the system is presented which, at the lowest order, yields an anisotropic e!ective-medium approximation (AEMA). The e!ective permeabilities are also estimated by a renormalization group (RG) method, as well as computer simulations. The RG method and AEMA both provide reasonable estimates of the e!ective permeabilities. However, if the porous medium contains zones of very low permeabilities, then the predictions of the two methods are not very accurate. Two methods are suggested to increase the accuracy of the predictions. We also show that as the volume fraction p of the low-permeability zones of the porous medium increases, the anisotropy of the medium decreases. : S 0 0 0 9 -2 5 0 9 ( 0 0 ) 0 0 0 9 8 -1
Journal of Contaminant Hydrology, 2006
We describe the use of a flow-focusing microfluidic reactor to measure the kinetics of the CdSe-t... more We describe the use of a flow-focusing microfluidic reactor to measure the kinetics of the CdSe-to-Ag 2 Se nanocrystal cation exchange reaction using micro-X-ray absorption spectroscopy (µXAS). The small microreactor dimensions facilitate the millisecond mixing of CdSe nanocrystals and Ag + reactant solutions, and the transposition of the reaction time onto spatial coordinates enables the in situ observation of the millisecond reaction using µXAS. Selenium K-edge absorption spectra show the progression of CdSe nanocrystals to Ag 2 Se over the course of 100 ms without the presence of long-lived intermediates. These results, along with supporting stopped-flow absorption experiments, suggest that this nanocrystal cation exchange reaction is highly efficient and provide insight into how the reaction progresses in individual particles. This experiment illustrates the value and potential of in situ microfluidic X-ray synchrotron techniques for detailed studies of the millisecond structural transformations of nanoparticles and other solution-phase reactions in which diffusive mixing initiates changes in local bond structures or oxidation states. † Part of the "Giacinto Scoles Festschrift".
Journal of Contaminant Hydrology, 2005
We describe the use of a flow-focusing microfluidic reactor to measure the kinetics of the CdSe-t... more We describe the use of a flow-focusing microfluidic reactor to measure the kinetics of the CdSe-to-Ag 2 Se nanocrystal cation exchange reaction using micro-X-ray absorption spectroscopy (µXAS). The small microreactor dimensions facilitate the millisecond mixing of CdSe nanocrystals and Ag + reactant solutions, and the transposition of the reaction time onto spatial coordinates enables the in situ observation of the millisecond reaction using µXAS. Selenium K-edge absorption spectra show the progression of CdSe nanocrystals to Ag 2 Se over the course of 100 ms without the presence of long-lived intermediates. These results, along with supporting stopped-flow absorption experiments, suggest that this nanocrystal cation exchange reaction is highly efficient and provide insight into how the reaction progresses in individual particles. This experiment illustrates the value and potential of in situ microfluidic X-ray synchrotron techniques for detailed studies of the millisecond structural transformations of nanoparticles and other solution-phase reactions in which diffusive mixing initiates changes in local bond structures or oxidation states. † Part of the "Giacinto Scoles Festschrift".
Water Resources Research, 2008
1] Flowing fluid temperature logging (FFTL) has recently been proposed as a method to locate flow... more 1] Flowing fluid temperature logging (FFTL) has recently been proposed as a method to locate flowing fractures. We argue that FFTL, backed up by data from high-precision distributed temperature sensors, can be a useful tool in locating flowing fractures and in estimating the transport properties of unsaturated fractured rocks. We have developed the theoretical background needed to analyze data from FFTL. In this article, we present a simplified conceptualization of FFTL in unsaturated fractured rock and develop a semi-analytical solution for spatial and temporal variations of pressure and temperature inside a borehole in response to an applied perturbation (pumping of air from the borehole). We compare the semi-analytical solution with predictions from the TOUGH2 numerical simulator. On the basis of the semi-analytical solution, we propose a method to estimate the permeability of the fracture continuum surrounding the borehole. Using this proposed method, we estimated the effective fracture continuum permeability of the unsaturated rock hosting the Drift Scale Test (DST) at Yucca Mountain, Nevada. Our estimate compares well with previous independent estimates for fracture permeability of the DST host rock. The conceptual model of FFTL presented in this article is based on the assumptions of single-phase flow, convection-only heat transfer, and negligible change in system state of the rock formation. In a sequel article, we extend the conceptual model to evaluate some of these assumptions. In that paper, we also perform inverse modeling of FFTL data to estimate, in addition to permeability, other transport parameters (such as porosity and thermal conductivity) of unsaturated fractured rocks.
Water Resources Research, 2007
Nuclear Technology, 2004
... Résumé / Abstract. Predicting the amount of water that may seep into waste emplacement drifts... more ... Résumé / Abstract. Predicting the amount of water that may seep into waste emplacement drifts is important for assessing the performance of the proposed geologic repository for spent nuclearfuel and high-level radioactive waste at Yucca Mountain, Nevada. ...
Reviews of Geophysics, 2009
This paper is a review of the research that led to an in-depth understanding of flow and transpor... more This paper is a review of the research that led to an in-depth understanding of flow and transport processes under strong heat stimulation in fractured, porous rock. It first describes the anticipated multiple processes that come into play in a partially saturated, fractured porous volcanic tuff geological formation when it is subject to a heat source such as that originating from the decay of radionuclides. The rationale is then given for numerical modeling being a key element in the study of multiple processes that are coupled. The paper outlines how the conceptualization and the numerical modeling of the problem evolved, progressing from the simplified to the more realistic. Examples of numerical models are presented so as to illustrate the advancement and maturation of the research over the last 2 decades. The most recent model applied to in situ field thermal tests is characterized by (1) incorporation of a full set of thermal-hydrological processes into a numerical simulator, (2) realistic representation of the field test geometry in three dimensions, and (3) use of site-specific characterization data for model inputs. Model predictions were carried out prior to initiation of data collection, and the model results were compared to diverse sets of measurements. The approach of close integration between modeling and field measurements has yielded a better understanding of how coupled thermal hydrological processes produce redistribution of moisture within the rock, which affects local permeability values and subsequently the flow of liquid and gases. The fluid flow, in turn, will change the temperature field. We end with a note on future research opportunities, specifically those incorporating chemical, mechanical, and microbiological factors into the study of thermal and hydrological processes.
Water Resources Research, 2009
1] A simple conceptual model has been recently developed for analyzing pressure and temperature d... more 1] A simple conceptual model has been recently developed for analyzing pressure and temperature data from flowing fluid temperature logging (FFTL) in unsaturated fractured rock. Using this conceptual model, we developed an analytical solution for FFTL pressure response, and a semianalytical solution for FFTL temperature response. We also proposed a method for estimating fracture permeability from FFTL temperature data. The conceptual model was based on some simplifying assumptions, particularly that a single-phase airflow model was used. In this paper, we develop a more comprehensive numerical model of multiphase flow and heat transfer associated with FFTL. Using this numerical model, we perform a number of forward simulations to determine the parameters that have the strongest influence on the pressure and temperature response from FFTL. We then use the iTOUGH2 optimization code to estimate these most sensitive parameters through inverse modeling and to quantify the uncertainties associated with these estimated parameters. We conclude that FFTL can be utilized to determine permeability, porosity, and thermal conductivity of the fracture rock. Two other parameters, which are not properties of the fractured rock, have strong influence on FFTL response. These are pressure and temperature in the borehole that were at equilibrium with the fractured rock formation at the beginning of FFTL. We illustrate how these parameters can also be estimated from FFTL data. from flowing fluid temperature logging data in unsaturated fractured rock using multiphase inverse modeling, Water Resour. Res., 45, W04414,
Reviews of Geophysics, 2009
... Modeling that is not the subject of this review paper—incorporating coupled chemical [Xu et a... more ... Modeling that is not the subject of this review paper—incorporating coupled chemical [Xu et al., 2001; Spycher et al., 2003; Sonnenthal et al., 2005; Mukhopadhyay et al., 2006] and mechanical [Rutqvist et al., 2004; 2005] processes—was initiated in the late 1990, and ...
Water Resources Research, 2006
Water Resources Research, 2009
1] A simple conceptual model has been recently developed for analyzing pressure and temperature d... more 1] A simple conceptual model has been recently developed for analyzing pressure and temperature data from flowing fluid temperature logging (FFTL) in unsaturated fractured rock. Using this conceptual model, we developed an analytical solution for FFTL pressure response, and a semianalytical solution for FFTL temperature response. We also proposed a method for estimating fracture permeability from FFTL temperature data. The conceptual model was based on some simplifying assumptions, particularly that a single-phase airflow model was used. In this paper, we develop a more comprehensive numerical model of multiphase flow and heat transfer associated with FFTL. Using this numerical model, we perform a number of forward simulations to determine the parameters that have the strongest influence on the pressure and temperature response from FFTL. We then use the iTOUGH2 optimization code to estimate these most sensitive parameters through inverse modeling and to quantify the uncertainties associated with these estimated parameters. We conclude that FFTL can be utilized to determine permeability, porosity, and thermal conductivity of the fracture rock. Two other parameters, which are not properties of the fractured rock, have strong influence on FFTL response. These are pressure and temperature in the borehole that were at equilibrium with the fractured rock formation at the beginning of FFTL. We illustrate how these parameters can also be estimated from FFTL data. from flowing fluid temperature logging data in unsaturated fractured rock using multiphase inverse modeling, Water Resour. Res., 45, W04414,
Vadose Zone Journal, 2004
Predicting the amount of water that may seep into waste emplacement tunnels (drifts) is important... more Predicting the amount of water that may seep into waste emplacement tunnels (drifts) is important for assessing the performance of the proposed geologic repository for high-level radioactive waste at Yucca Mountain, Nevada. The repository will be located in thick, partially saturated fractured tuff that-for the first several hundred years after emplacement-will be heated to above-boiling temperatures as a result of heat generation from the decay of radioactive waste. Heating of rock water to above-boiling conditions induces water saturation changes and perturbs water fluxes that affect the potential for water seepage into drifts. In this paper, we describe numerical analyses of the coupled thermal-hydrological (TH) processes in the vicinity of waste emplacement drifts, evaluate the potential of seepage during the heating phase of the repository, and discuss the implications for the performance of the site. In addition to the capillary barrier at the rock-drift interface-independent of the thermal conditions-a second barrier exists to downward percolation at above-boiling conditions. This barrier is caused by vaporization of water in the fractured rock overlying the repository. A TOUGH2 dual-permeability simulation model was developed to analyze the combined effect of these two barriers; it accounts for all relevant TH processes in response to heating, while incorporating the capillary barrier condition at the drift wall. Model results are presented for a variety of simulation cases that cover the expected variability and uncertainty of relevant rock properties and boundary conditions.
Water Resources Research, 2007
Water Resources Research, 2007
1] A general approach is presented here that allows estimation of field-scale thermal properties ... more 1] A general approach is presented here that allows estimation of field-scale thermal properties of unsaturated rock using temperature data collected from in situ heater tests. The approach is used to determine the thermal conductivities of the host rock of the Drift Scale Test (DST) at Yucca Mountain, Nevada. The DST was designed to obtain thermal, hydrological, mechanical, and chemical (THMC) data at Yucca Mountain. Sophisticated numerical models have been developed to analyze these THMC data. However, though the objective of those models was to analyze ''field-scale'' (of the order of tens of meters) THMC data, thermal conductivities measured from ''laboratory-scale'' core samples have been used as input parameters. While using laboratory-scale thermal conductivity values in field-scale models can be justified, such applications introduce uncertainties in model predictions. Temperature data from the DST provide an opportunity to resolve some of these uncertainties. These temperature data can be used to estimate the thermal conductivity of the DST rock, and given the large volume of rock affected by heating at the DST, such an estimate will be a reliable thermal conductivity value for field-scale application. An analytical solution is developed for the temperature rise in the DST rock; and using a nonlinear fitting routine, a best fit estimate of field-scale thermal conductivity is obtained. Temperature data from the DST show evidence of a below-boiling zone (wet) and an above-boiling zone (dry). Estimates of thermal conductivity for both these zones are obtained in this paper. Sensitivity of these estimates to the input heating power is also investigated. The estimated thermal conductivity values are compared with core measurements and those estimated from geostatistical simulations.
Journal of Contaminant Hydrology, 2003
Understanding thermally driven coupled hydrological, mechanical, and chemical processes in unsatu... more Understanding thermally driven coupled hydrological, mechanical, and chemical processes in unsaturated fractured tuff is essential for evaluating the performance of the potential radioactive waste repository at Yucca Mountain, Nevada. The Drift Scale Test (DST), intended for acquiring such an understanding of these processes, has generated a huge volume of temperature and moisture redistribution data. Sophisticated thermal-hydrological (TH) conceptual models have yielded a good fit between simulation results and those measured data. However, some uncertainties in understanding the TH processes associated with the DST still exist. This paper evaluates these uncertainties and provides quantitative estimates of the range of these uncertainties. Of particular interest for the DST are the uncertainties resulting from the unmonitored loss of vapor through an open bulkhead of the test. There was concern that the outcome from the test might have been significantly altered by these losses. Using alternative conceptual models, we illustrate that predicted mean temperatures from the DST are within 1 degrees C of the measured mean temperatures through the first 2 years of heating. The simulated spatial and temporal evolution of drying and condensation fronts is found to be qualitatively consistent with measured saturation data. Energy and mass balance computation shows that no more than 13% of the input energy is lost because of vapor leaving the test domain through the bulkhead. The change in average saturation in fractures is also relatively small. For a hypothetical situation in which no vapor is allowed to exit through the bulkhead, the simulated average fracture saturation is not qualitatively different enough to be discerned by measured moisture redistribution data. This leads us to conclude that the DST, despite the uncertainties associated with open field testing, has provided an excellent understanding of the TH processes.
Water Resources Research, 2002
The Large Block Test (LBT) at Yucca Mountain, Nevada, is unique because of its size, which is lar... more The Large Block Test (LBT) at Yucca Mountain, Nevada, is unique because of its size, which is large enough to include a number of large fractures, while still small enough so that boundary conditions and heterogeneities can be adequately controlled or characterized. Extensive mapping of the test block has established the presence of many small and large fractures. Preheat air
Water Resources Research, 2002
1] The Large Block Test (LBT) at Yucca Mountain, Nevada, is unique because of its size, which is ... more 1] The Large Block Test (LBT) at Yucca Mountain, Nevada, is unique because of its size, which is large enough to include a number of large fractures, while still small enough so that boundary conditions and heterogeneities can be adequately controlled or characterized. Extensive mapping of the test block has established the presence of many small and large fractures. Preheat air injection testing has also revealed that the block is highly heterogeneous, with fracture permeability varying more than four orders of magnitude. We hypothesize that these large fractures and the resulting heterogeneity play a significant role in the development of coupled thermal-hydrological (TH) processes in the LBT. A large volume of TH data, including temperature and saturation measurements, has been collected from the LBT. Some of these temperature data from the LBT, particularly those recorded by sensors TT1-14 and TT2-14, appear anomalous. We show that these anomalous temperature data can be understood only if heterogeneity is invoked.
Journal of Statistical Physics, 1994
We use the finite-size scaling method to estimate the critical exponent λ that characterizes the ... more We use the finite-size scaling method to estimate the critical exponent λ that characterizes the scaling behavior of conductivity and permeability anisotropy near the percolation thresholdp c . Here λ is defined by the scaling lawk l /k t −1∼(p−p c )λ, wherek t andk t are the conductivity or permeability of the system in the direction of the macroscopic potential gradient and perpendicular to this direction, respectively. The results are λ(d=2)≃0.819±0.011 and λ(d=3)≃0.518±0.001. We interpret these results in terms of the structure of percolation clusters and their chemical distance. We also compare our results with the predictions of a scaling theory for λ due to Straley, and propose that λ(d=2)=t-βB , wheret is the critical exponent of the conductivity or permeability of the system, and βB is the critical exponent of the backbone of percolation clusters.
Physical Review E, 1996
... Muhammad Sahimi1,2 and Sumit Mukhopadhyay1,* 1Department of Chemical Engineering, University ... more ... Muhammad Sahimi1,2 and Sumit Mukhopadhyay1,* 1Department of Chemical Engineering, University of Southern California, Los Angeles, California 90089-1211 2Hochstleistungsrech enzentrum, Kernforschungsanlage Jülich, D-52425 Jülich 1, Germany Received 27 March ...
Chemical Engineering Science, 2000
The problem of estimating the e!ective grid block permeabilities of a "eld-scale porous medium wi... more The problem of estimating the e!ective grid block permeabilities of a "eld-scale porous medium with long-range correlations is studied. Both isotropic and anisotropic porous media are considered. The grid blocks are represented by networks of bonds the permeabilities of which are distributed according to three di!erent stochastic functions that generate long-range correlations, two of which are fractal distribution. A new perturbation expansion for estimating the e!ective permeabilities of the system is presented which, at the lowest order, yields an anisotropic e!ective-medium approximation (AEMA). The e!ective permeabilities are also estimated by a renormalization group (RG) method, as well as computer simulations. The RG method and AEMA both provide reasonable estimates of the e!ective permeabilities. However, if the porous medium contains zones of very low permeabilities, then the predictions of the two methods are not very accurate. Two methods are suggested to increase the accuracy of the predictions. We also show that as the volume fraction p of the low-permeability zones of the porous medium increases, the anisotropy of the medium decreases. : S 0 0 0 9 -2 5 0 9 ( 0 0 ) 0 0 0 9 8 -1
Journal of Contaminant Hydrology, 2006
We describe the use of a flow-focusing microfluidic reactor to measure the kinetics of the CdSe-t... more We describe the use of a flow-focusing microfluidic reactor to measure the kinetics of the CdSe-to-Ag 2 Se nanocrystal cation exchange reaction using micro-X-ray absorption spectroscopy (µXAS). The small microreactor dimensions facilitate the millisecond mixing of CdSe nanocrystals and Ag + reactant solutions, and the transposition of the reaction time onto spatial coordinates enables the in situ observation of the millisecond reaction using µXAS. Selenium K-edge absorption spectra show the progression of CdSe nanocrystals to Ag 2 Se over the course of 100 ms without the presence of long-lived intermediates. These results, along with supporting stopped-flow absorption experiments, suggest that this nanocrystal cation exchange reaction is highly efficient and provide insight into how the reaction progresses in individual particles. This experiment illustrates the value and potential of in situ microfluidic X-ray synchrotron techniques for detailed studies of the millisecond structural transformations of nanoparticles and other solution-phase reactions in which diffusive mixing initiates changes in local bond structures or oxidation states. † Part of the "Giacinto Scoles Festschrift".
Journal of Contaminant Hydrology, 2005
We describe the use of a flow-focusing microfluidic reactor to measure the kinetics of the CdSe-t... more We describe the use of a flow-focusing microfluidic reactor to measure the kinetics of the CdSe-to-Ag 2 Se nanocrystal cation exchange reaction using micro-X-ray absorption spectroscopy (µXAS). The small microreactor dimensions facilitate the millisecond mixing of CdSe nanocrystals and Ag + reactant solutions, and the transposition of the reaction time onto spatial coordinates enables the in situ observation of the millisecond reaction using µXAS. Selenium K-edge absorption spectra show the progression of CdSe nanocrystals to Ag 2 Se over the course of 100 ms without the presence of long-lived intermediates. These results, along with supporting stopped-flow absorption experiments, suggest that this nanocrystal cation exchange reaction is highly efficient and provide insight into how the reaction progresses in individual particles. This experiment illustrates the value and potential of in situ microfluidic X-ray synchrotron techniques for detailed studies of the millisecond structural transformations of nanoparticles and other solution-phase reactions in which diffusive mixing initiates changes in local bond structures or oxidation states. † Part of the "Giacinto Scoles Festschrift".
Water Resources Research, 2008
1] Flowing fluid temperature logging (FFTL) has recently been proposed as a method to locate flow... more 1] Flowing fluid temperature logging (FFTL) has recently been proposed as a method to locate flowing fractures. We argue that FFTL, backed up by data from high-precision distributed temperature sensors, can be a useful tool in locating flowing fractures and in estimating the transport properties of unsaturated fractured rocks. We have developed the theoretical background needed to analyze data from FFTL. In this article, we present a simplified conceptualization of FFTL in unsaturated fractured rock and develop a semi-analytical solution for spatial and temporal variations of pressure and temperature inside a borehole in response to an applied perturbation (pumping of air from the borehole). We compare the semi-analytical solution with predictions from the TOUGH2 numerical simulator. On the basis of the semi-analytical solution, we propose a method to estimate the permeability of the fracture continuum surrounding the borehole. Using this proposed method, we estimated the effective fracture continuum permeability of the unsaturated rock hosting the Drift Scale Test (DST) at Yucca Mountain, Nevada. Our estimate compares well with previous independent estimates for fracture permeability of the DST host rock. The conceptual model of FFTL presented in this article is based on the assumptions of single-phase flow, convection-only heat transfer, and negligible change in system state of the rock formation. In a sequel article, we extend the conceptual model to evaluate some of these assumptions. In that paper, we also perform inverse modeling of FFTL data to estimate, in addition to permeability, other transport parameters (such as porosity and thermal conductivity) of unsaturated fractured rocks.
Water Resources Research, 2007
Nuclear Technology, 2004
... Résumé / Abstract. Predicting the amount of water that may seep into waste emplacement drifts... more ... Résumé / Abstract. Predicting the amount of water that may seep into waste emplacement drifts is important for assessing the performance of the proposed geologic repository for spent nuclearfuel and high-level radioactive waste at Yucca Mountain, Nevada. ...
Reviews of Geophysics, 2009
This paper is a review of the research that led to an in-depth understanding of flow and transpor... more This paper is a review of the research that led to an in-depth understanding of flow and transport processes under strong heat stimulation in fractured, porous rock. It first describes the anticipated multiple processes that come into play in a partially saturated, fractured porous volcanic tuff geological formation when it is subject to a heat source such as that originating from the decay of radionuclides. The rationale is then given for numerical modeling being a key element in the study of multiple processes that are coupled. The paper outlines how the conceptualization and the numerical modeling of the problem evolved, progressing from the simplified to the more realistic. Examples of numerical models are presented so as to illustrate the advancement and maturation of the research over the last 2 decades. The most recent model applied to in situ field thermal tests is characterized by (1) incorporation of a full set of thermal-hydrological processes into a numerical simulator, (2) realistic representation of the field test geometry in three dimensions, and (3) use of site-specific characterization data for model inputs. Model predictions were carried out prior to initiation of data collection, and the model results were compared to diverse sets of measurements. The approach of close integration between modeling and field measurements has yielded a better understanding of how coupled thermal hydrological processes produce redistribution of moisture within the rock, which affects local permeability values and subsequently the flow of liquid and gases. The fluid flow, in turn, will change the temperature field. We end with a note on future research opportunities, specifically those incorporating chemical, mechanical, and microbiological factors into the study of thermal and hydrological processes.
Water Resources Research, 2009
1] A simple conceptual model has been recently developed for analyzing pressure and temperature d... more 1] A simple conceptual model has been recently developed for analyzing pressure and temperature data from flowing fluid temperature logging (FFTL) in unsaturated fractured rock. Using this conceptual model, we developed an analytical solution for FFTL pressure response, and a semianalytical solution for FFTL temperature response. We also proposed a method for estimating fracture permeability from FFTL temperature data. The conceptual model was based on some simplifying assumptions, particularly that a single-phase airflow model was used. In this paper, we develop a more comprehensive numerical model of multiphase flow and heat transfer associated with FFTL. Using this numerical model, we perform a number of forward simulations to determine the parameters that have the strongest influence on the pressure and temperature response from FFTL. We then use the iTOUGH2 optimization code to estimate these most sensitive parameters through inverse modeling and to quantify the uncertainties associated with these estimated parameters. We conclude that FFTL can be utilized to determine permeability, porosity, and thermal conductivity of the fracture rock. Two other parameters, which are not properties of the fractured rock, have strong influence on FFTL response. These are pressure and temperature in the borehole that were at equilibrium with the fractured rock formation at the beginning of FFTL. We illustrate how these parameters can also be estimated from FFTL data. from flowing fluid temperature logging data in unsaturated fractured rock using multiphase inverse modeling, Water Resour. Res., 45, W04414,
Reviews of Geophysics, 2009
... Modeling that is not the subject of this review paper—incorporating coupled chemical [Xu et a... more ... Modeling that is not the subject of this review paper—incorporating coupled chemical [Xu et al., 2001; Spycher et al., 2003; Sonnenthal et al., 2005; Mukhopadhyay et al., 2006] and mechanical [Rutqvist et al., 2004; 2005] processes—was initiated in the late 1990, and ...
Water Resources Research, 2006
Water Resources Research, 2009
1] A simple conceptual model has been recently developed for analyzing pressure and temperature d... more 1] A simple conceptual model has been recently developed for analyzing pressure and temperature data from flowing fluid temperature logging (FFTL) in unsaturated fractured rock. Using this conceptual model, we developed an analytical solution for FFTL pressure response, and a semianalytical solution for FFTL temperature response. We also proposed a method for estimating fracture permeability from FFTL temperature data. The conceptual model was based on some simplifying assumptions, particularly that a single-phase airflow model was used. In this paper, we develop a more comprehensive numerical model of multiphase flow and heat transfer associated with FFTL. Using this numerical model, we perform a number of forward simulations to determine the parameters that have the strongest influence on the pressure and temperature response from FFTL. We then use the iTOUGH2 optimization code to estimate these most sensitive parameters through inverse modeling and to quantify the uncertainties associated with these estimated parameters. We conclude that FFTL can be utilized to determine permeability, porosity, and thermal conductivity of the fracture rock. Two other parameters, which are not properties of the fractured rock, have strong influence on FFTL response. These are pressure and temperature in the borehole that were at equilibrium with the fractured rock formation at the beginning of FFTL. We illustrate how these parameters can also be estimated from FFTL data. from flowing fluid temperature logging data in unsaturated fractured rock using multiphase inverse modeling, Water Resour. Res., 45, W04414,
Vadose Zone Journal, 2004
Predicting the amount of water that may seep into waste emplacement tunnels (drifts) is important... more Predicting the amount of water that may seep into waste emplacement tunnels (drifts) is important for assessing the performance of the proposed geologic repository for high-level radioactive waste at Yucca Mountain, Nevada. The repository will be located in thick, partially saturated fractured tuff that-for the first several hundred years after emplacement-will be heated to above-boiling temperatures as a result of heat generation from the decay of radioactive waste. Heating of rock water to above-boiling conditions induces water saturation changes and perturbs water fluxes that affect the potential for water seepage into drifts. In this paper, we describe numerical analyses of the coupled thermal-hydrological (TH) processes in the vicinity of waste emplacement drifts, evaluate the potential of seepage during the heating phase of the repository, and discuss the implications for the performance of the site. In addition to the capillary barrier at the rock-drift interface-independent of the thermal conditions-a second barrier exists to downward percolation at above-boiling conditions. This barrier is caused by vaporization of water in the fractured rock overlying the repository. A TOUGH2 dual-permeability simulation model was developed to analyze the combined effect of these two barriers; it accounts for all relevant TH processes in response to heating, while incorporating the capillary barrier condition at the drift wall. Model results are presented for a variety of simulation cases that cover the expected variability and uncertainty of relevant rock properties and boundary conditions.
Water Resources Research, 2007
Water Resources Research, 2007
1] A general approach is presented here that allows estimation of field-scale thermal properties ... more 1] A general approach is presented here that allows estimation of field-scale thermal properties of unsaturated rock using temperature data collected from in situ heater tests. The approach is used to determine the thermal conductivities of the host rock of the Drift Scale Test (DST) at Yucca Mountain, Nevada. The DST was designed to obtain thermal, hydrological, mechanical, and chemical (THMC) data at Yucca Mountain. Sophisticated numerical models have been developed to analyze these THMC data. However, though the objective of those models was to analyze ''field-scale'' (of the order of tens of meters) THMC data, thermal conductivities measured from ''laboratory-scale'' core samples have been used as input parameters. While using laboratory-scale thermal conductivity values in field-scale models can be justified, such applications introduce uncertainties in model predictions. Temperature data from the DST provide an opportunity to resolve some of these uncertainties. These temperature data can be used to estimate the thermal conductivity of the DST rock, and given the large volume of rock affected by heating at the DST, such an estimate will be a reliable thermal conductivity value for field-scale application. An analytical solution is developed for the temperature rise in the DST rock; and using a nonlinear fitting routine, a best fit estimate of field-scale thermal conductivity is obtained. Temperature data from the DST show evidence of a below-boiling zone (wet) and an above-boiling zone (dry). Estimates of thermal conductivity for both these zones are obtained in this paper. Sensitivity of these estimates to the input heating power is also investigated. The estimated thermal conductivity values are compared with core measurements and those estimated from geostatistical simulations.
Journal of Contaminant Hydrology, 2003
Understanding thermally driven coupled hydrological, mechanical, and chemical processes in unsatu... more Understanding thermally driven coupled hydrological, mechanical, and chemical processes in unsaturated fractured tuff is essential for evaluating the performance of the potential radioactive waste repository at Yucca Mountain, Nevada. The Drift Scale Test (DST), intended for acquiring such an understanding of these processes, has generated a huge volume of temperature and moisture redistribution data. Sophisticated thermal-hydrological (TH) conceptual models have yielded a good fit between simulation results and those measured data. However, some uncertainties in understanding the TH processes associated with the DST still exist. This paper evaluates these uncertainties and provides quantitative estimates of the range of these uncertainties. Of particular interest for the DST are the uncertainties resulting from the unmonitored loss of vapor through an open bulkhead of the test. There was concern that the outcome from the test might have been significantly altered by these losses. Using alternative conceptual models, we illustrate that predicted mean temperatures from the DST are within 1 degrees C of the measured mean temperatures through the first 2 years of heating. The simulated spatial and temporal evolution of drying and condensation fronts is found to be qualitatively consistent with measured saturation data. Energy and mass balance computation shows that no more than 13% of the input energy is lost because of vapor leaving the test domain through the bulkhead. The change in average saturation in fractures is also relatively small. For a hypothetical situation in which no vapor is allowed to exit through the bulkhead, the simulated average fracture saturation is not qualitatively different enough to be discerned by measured moisture redistribution data. This leads us to conclude that the DST, despite the uncertainties associated with open field testing, has provided an excellent understanding of the TH processes.
Water Resources Research, 2002
The Large Block Test (LBT) at Yucca Mountain, Nevada, is unique because of its size, which is lar... more The Large Block Test (LBT) at Yucca Mountain, Nevada, is unique because of its size, which is large enough to include a number of large fractures, while still small enough so that boundary conditions and heterogeneities can be adequately controlled or characterized. Extensive mapping of the test block has established the presence of many small and large fractures. Preheat air
Water Resources Research, 2002
1] The Large Block Test (LBT) at Yucca Mountain, Nevada, is unique because of its size, which is ... more 1] The Large Block Test (LBT) at Yucca Mountain, Nevada, is unique because of its size, which is large enough to include a number of large fractures, while still small enough so that boundary conditions and heterogeneities can be adequately controlled or characterized. Extensive mapping of the test block has established the presence of many small and large fractures. Preheat air injection testing has also revealed that the block is highly heterogeneous, with fracture permeability varying more than four orders of magnitude. We hypothesize that these large fractures and the resulting heterogeneity play a significant role in the development of coupled thermal-hydrological (TH) processes in the LBT. A large volume of TH data, including temperature and saturation measurements, has been collected from the LBT. Some of these temperature data from the LBT, particularly those recorded by sensors TT1-14 and TT2-14, appear anomalous. We show that these anomalous temperature data can be understood only if heterogeneity is invoked.