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  • 1.
    Dessirier, Benoît
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    A new scripting library for modeling flow and transport in fractured rock with channel networks2018In: Computers & Geosciences, ISSN 0098-3004, E-ISSN 1873-7803, Vol. 111, p. 181-189Article in journal (Refereed)
    Abstract [en]

    Deep crystalline bedrock formations are targeted to host spent nuclear fuel owing to their overall low permeability. They are however highly heterogeneous and only a few preferential paths pertaining to a small set of dominant rock fractures usually carry most of the flow or mass fluxes, a behavior known as channeling that needs to be accounted for in the performance assessment of repositories. Channel network models have been developed and used to investigate the effect of channeling. They are usually simpler than discrete fracture networks based on rock fracture mappings and rely on idealized full or sparsely populated lattices of channels. This study reexamines the minimal requirements to describe a channel network in terms of groundwater flow and solute transport, leading to an extended description suitable for unstructured arbitrary networks of channels. An implementation of this formalism in a Python scripting library is presented and released along with this article. A new algebraic multigrid preconditioner delivers a significant speedup in the flow solution step compared to previous channel network codes. 3D visualization is readily available for verification and interpretation of the results by exporting the results to an open and free dedicated software. The new code is applied to three example cases to verify its results on full uncorrelated lattices of channels, sparsely populated percolation lattices and to exemplify the use of unstructured networks to accommodate knowledge on local rock fractures.

  • 2.
    Doughty, Christine
    et al.
    Lawrence Berkeley Natl Lab, Berkeley, CA 94720 USA..
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Lawrence Berkeley Natl Lab, Berkeley, CA 94720 USA..
    Rosberg, Jan-Erik
    Lund Univ, Lund, Sweden..
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Dobson, Patrick F.
    Lawrence Berkeley Natl Lab, Berkeley, CA 94720 USA..
    Birkholzer, Jens T.
    Lawrence Berkeley Natl Lab, Berkeley, CA 94720 USA..
    Flowing fluid electrical conductivity logging of a deep borehole during and following drilling: estimation of transmissivity, water salinity and hydraulic head of conductive zones2017In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 25, no 2, p. 501-517Article in journal (Refereed)
    Abstract [en]

    Flowing fluid electrical conductivity (FFEC) logging is a hydrogeologic testing method that is usually conducted in an existing borehole. However, for the 2,500-m deep COSC-1 borehole, drilled at re, central Sweden, it was done within the drilling period during a scheduled 1-day break, thus having a negligible impact on the drilling schedule, yet providing important information on depths of hydraulically conductive zones and their transmissivities and salinities. This paper presents a reanalysis of this set of data together with a new FFEC logging data set obtained soon after drilling was completed, also over a period of 1 day, but with a different pumping rate and water-level drawdown. Their joint analysis not only results in better estimates of transmissivity and salinity in the conducting fractures intercepted by the borehole, but also yields the hydraulic head values of these fractures, an important piece of information for the understanding of hydraulic structure of the subsurface. Two additional FFEC logging tests were done about 1 year later, and are used to confirm and refine this analysis. Results show that from 250 to 2,000 m depths, there are seven distinct hydraulically conductive zones with different hydraulic heads and low transmissivity values. For the final test, conducted with a much smaller water-level drawdown, inflow ceased from some of the conductive zones, confirming that their hydraulic heads are below the hydraulic head measured in the wellbore under non-pumped conditions. The challenges accompanying 1-day FFEC logging are summarized, along with lessons learned in addressing them.

  • 3. Doughty, Christine
    et al.
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Yabuuchi, Satoshi
    Kunimaru, Takanori
    Flowing fluid electric conductivity logging for a deep artesian well in fractured rock with regional flow2013In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 482, p. 1-13Article in journal (Refereed)
    Abstract [en]

    The flowing fluid electric conductivity (FFEC) logging method is a well-logging technique that may be used to estimate flow rate, salinity, transmissivity, and hydraulic head of individual fractures or high-permeability zones intersected by a wellbore. Wellbore fluid is first replaced with fluid of a contrasting electric conductivity, then repeated FEC logging is done while the well is pumped. Zones where fluid flows into the wellbore show peaks in the FEC logs, which may be analyzed to infer inflow rate and salinity of the individual fractures. Conducting the procedure with two or more pumping rates (multi-rate FFEC logging) enables individual fracture transmissivity and hydraulic head to be determined. Here we describe the first application of the multi-rate FFEC logging method to an artesian well, using a 500-m well in fractured rock at Horonobe, Japan. An additional new factor at the site is the presence of regional groundwater flow, which heretofore has only been studied with synthetic data. FFEC logging was conducted for two different pumping rates. Several analysis techniques had to be adapted to account for the artesian nature of the well. The results were subsequently compared with independent salinity measurements and transmissivity and hydraulic head values obtained from packer tests in the same well. Despite non-ideal operating conditions, multi-rate FFEC logging successfully determined flow rate, salinity, and transmissivity of 17 conducting fractures intercepted by the logged section of the borehole, including two fractures with regional groundwater flow. Predictions of hydraulic head were less accurate, a not unexpected result in light of operational problems and the form of the equation for hydraulic head, which involves the difference between two uncertain quantities. This study illustrates the strengths and weaknesses of the multi-rate FFEC logging method applied to artesian wells. In conjunction with previous studies, it demonstrates the usefulness of the method for a broad range of conditions encountered in subsurface fractured rock.

  • 4.
    Figueiredo, B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Study of the Potential Fault Reactivation Induced by CO2 Injection in a Three-Layer Storage Formation.2015Conference paper (Other academic)
    Abstract
  • 5.
    Figueiredo, B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Rutqvist, Jonny
    Bensabat, Jac
    Niemi, A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Parameter sensitivity analysis on potential fault reactivation induced by CO2 injection in a multi-layer storage formation.2015Conference paper (Other academic)
    Abstract
  • 6.
    Figueiredo, B.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Rutqvist, Jonny
    Niemi, A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Study of the influenceof geological features and key parameters on coupled hydro-mechanical processesin hydraulic fracturing of shale-gas reservoirs.2017Conference paper (Other academic)
    Abstract
  • 7.
    Figueiredo, Bruno
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Lawrence Berkeley National Laboratory, Berkeley USA.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Georg, Lindgren
    Swedish Radiation Safety Authority, Stockholm, Sweden.
    Review: The state-of-art of sparse channel models and their applicability to performance assessment of radioactive waste repositories in fractured crystalline formations2016In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 24, no 7, p. 1607-1622Article in journal (Other academic)
    Abstract [en]

    Laboratory and field experiments done on fractured rock show that flow and solute transport often occur along flow channels. ‘Sparse channels’ refers to the case where these channels are characterised by flow in long flow paths separated from each other by large spacings relative to the size of flow domain. A literature study is presented that brings together information useful to assess whether a sparse-channel network concept is an appropriate representation of the flow system in tight fractured rock of low transmissivity, such as that around a nuclear waste repository in deep crystalline rocks. A number of observations are made in this review. First, conventional fracture network models may lead to inaccurate results for flow and solute transport in tight fractured rocks. Secondly, a flow dimension of 1, as determined by the analysis of pressure data in well testing, may be indicative of channelised flow, but such interpretation is not unique or definitive. Thirdly, in sparse channels, the percolation may be more influenced by the fracture shape than the fracture size and orientation but further studies are needed. Fourthly, the migration of radionuclides from a waste canister in a repository to the biosphere may be strongly influenced by the type of model used (e.g. discrete fracture network, channel model). Fifthly, the determination of appropriateness of representing an in situ flow system by a sparse-channel network model needs parameters usually neglected in site characterisation, such as the density of channels or fracture intersections.

  • 8.
    Figueiredo, Bruno
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Rutqvist, Jonny
    Bensabat, Jac
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Coupled hydro-mechanical processes and fault reactivation induced by Co-2 Injection in a three-layer storage formation2015In: International Journal of Greenhouse Gas Control, ISSN 1750-5836, E-ISSN 1878-0148, Vol. 39, p. 432-448Article in journal (Refereed)
    Abstract [en]

    The interaction between mechanical deformation and fluid flow in fault zones gives rise to a host of coupled hydro-mechanical processes fundamental to fault instability, induced seismicity, and associated fluid migration. Fault stability is studied in the context of the Heletz site which was chosen as a test site for CO2 injection experiment in the framework of the EU-MUSTANG project. The potential reservoir for CO2 storage at the Heletz site consists of three sandstone layers that are approximately one, two and nine meters in thickness, separated by impermeable shale layers of various thicknesses, and overlaid by a five-meter limestone and a thick impermeable shale, which serves as caprock. The storage formation is intersected by two pre-existing sub-vertical normal faults (F1 and F2) on two opposite sides of the injection point. A hydro-mechanical model was developed to study the interaction between mechanical deformation and fluid flow in the two faults during CO2 injection and storage. We evaluate the consequences caused by potential fault reactivation, namely, the fault slip and the CO2 leakage through the caprock. The difference in the results obtained by considering the three-layer storage formation as an equivalent single-layer storage formation is analysed. It was found that for the two cases the pore pressure evolution is similar, but the differences in the evolution of CO2 saturation are significant, which is attributed to the differences in CO2 spread in a single and three-layer storage. No fault reactivation was observed in either case. A sensitivity analysis was made to study the influence of the fault dip angle, the ratio between the horizontal and vertical stresses, the offset of the layers across fault F2, the initial permeability of the fault and the permeability of the confinement formations. Results show that reactivation of faults Fl and F2 is most sensitive to the stress ratio, the initial permeability of the faults and the permeability of the confinement formations. The offset of the layers across the fault F2 was also found to be an important parameter, mainly because an offset leads to an increase in CO2 leakage. Changes in permeability were found to be small because plastic shear strains induced by the reactivation of the faults and associated increase in volumetric strains and permeability, occur mainly in a fault section of only 10 m length, which is the approximate total thickness of the storage layers.

  • 9.
    Figueiredo, Bruno
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Univ Calif Berkeley, Lawrence Berkeley Natl Lab, Berkeley, CA 94720 USA..
    Rutqvist, Jonny
    Univ Calif Berkeley, Lawrence Berkeley Natl Lab, Berkeley, CA 94720 USA..
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    A study of changes in deep fractured rock permeability due to coupled hydro-mechanical effects2015In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 79, p. 70-85Article in journal (Refereed)
    Abstract [en]

    This paper presents a numerical study of the hydro-mechanical behaviour of a fractured rock domain at 1000 m depth below the land surface as a function of different levels of fluid pore pressure. A 2D fractured rock domain is adopted based on data obtained from outcrop mapping, displaying multiple fracture sets, fracture intersections, dead-end and curved fractures. A continuum based numerical model is used to evaluate the effects of compressive boundary stresses, cracking by tension failure in the intact rock and fractures and shear displacement along fractures on its equivalent permeability. Two in situ stress boundary conditions are considered: an isotropic case SR1 with the two horizontal boundary compressive stresses having the same magnitude, and an anisotropic case SR2 with the ratio between these compressive stress components set to be 2. In the SR2 case, changes in the local stress and stress ratio distributions due to different fluid pore pressure levels are anisotropic and more significant than in the SR1 case, because of tension failures in the intact rock forming bridges between fractures. These failure regions opened new flow connections between fractures and thereby caused important anisotropic changes in the flow paths, and significant decrease in local gradients of fluid pore pressure. The equivalent permeability increases sharply when the fluid pore pressure is approximately 90% of the magnitude of the minimum stress at the boundaries of the fractured rock domain. Results show that the equivalent permeability of the fractured rock domain is most sensitive to the fractures normal stiffness, the permeability of the tension failure regions and the power-law exponent for permeability change.

  • 10.
    Figueiredo, Bruno
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Lawrence Berkeley National Laboratory, Berkeley, California.
    Rutqvist, Jonny
    Lawrence Berkeley National Laboratory.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Study of hydraulic fracturing processes in shale formations with complex geological settings2017In: Journal of Petroleum Science and Engineering, ISSN 0920-4105, E-ISSN 1873-4715, Vol. 152, p. 361-374Article in journal (Refereed)
    Abstract [en]

    Hydraulic fracturing has been applied to extract gas from shale-gas reservoirs. Complicated geological settings,such as spatial variability of the rock mass properties, local heterogeneities, complex in situ stress field, and preexistingbedding planes and faults, could make hydraulic fracturing a challenging task. In order to effectivelyand economically recover gas from such reservoirs, it is crucial to explore how hydraulic fracturing performs insuch complex geological settings. For this purpose, numerical modelling plays an important role because suchconditions cannot be reproduced by laboratory experiments. This paper focuses on the analysis of the influenceof confining formations and pre-existing bedding planes and faults on the hydraulically-induced propagation ofa vertical fracture, which will be called injection fracture, in a shale-gas reservoir. An elastic-brittle model basedon material property degradation was implemented in a 2D finite-difference scheme and used for rock elementssubjected to tension and shear failure. A base case is considered, in which the ratio SR between the magnitudesof the horizontal and vertical stresses, the permeability kc of the confining formations, the elastic modulus Epand initial permeability kp of the bedding plane and the initial fault permeability kF are fixed at reasonablevalues. In addition, the influence of multiple bedding planes, is investigated. Changes in pore pressure andpermeability due to high pressure injection lasting 2 h were analysed. Results show that in our case during theinjection period the fracture reaches the confining formations and if the permeability of those layers issignificantly larger than that of the shale, the pore pressure at the extended fracture tip decreases and fracturepropagation becomes slower. After shut-in, the pore pressure decreases more and the fracture does notpropagate any more. For bedding planes oriented perpendicular to the maximum principal stress direction andwith the same elastic properties as the shale formation, results were found not to be influenced by theirpresence. In such a scenario, the impact of multiple bedding planes on fracture propagation is negligible. On theother hand, a bedding plane softer than the surrounding shale formation leads to a fracture propagationasymmetrical vertically with respect to the centre of the injection fracture with a more limited upward fracturepropagation. A pre-existing fault leads to a decrease in fracture propagation because of fault reactivation withshear failure. This results in a smaller increase in injection fracture permeability and a slight higher injectionpressure than that observed without the fault. Overall, results of a sensitivity analysis show that fracturepropagation is influenced by the stress ratio SR, the permeability kc of the confining formations and the initialpermeability kp of the bedding plane more than the other major parameters.

    The full text will be freely available from 2019-03-07 08:00
  • 11.
    Figueiredo, Bruno
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Lawrence Berkeley Natl Lab, Berkeley, CA USA..
    Rutqvist, Jonny
    Lawrence Berkeley Natl Lab, Berkeley, CA USA..
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    The effects of nearby fractures on hydraulically induced fracture propagation and permeability changes2017In: Engineering Geology, ISSN 0013-7952, E-ISSN 1872-6917, Vol. 228, p. 197-213Article in journal (Refereed)
    Abstract [en]

    Fracture propagation caused by hydraulic fracturing operations can be significantly influenced by adjacent fractures. This paper presents a detailed coupled hydro-mechanical analysis to study the effects of nearby natural fractures on hydraulically induced fracture propagation and changes in fracture permeability. Two rock domains were considered in comparison: FD1, with one fracture, and FD2, with two adjacent parallel or non-parallel fractures. It was assumed that water injection occurred in a borehole that intersected the single fracture in FD1 and one of the two fractures in FD2. Simulations were made for a time period of 3 h with an injection period of 2 h followed by 1 h of shut-in. An elastic-brittle model based on the degradation of material properties was implemented in a 2D finite-difference scheme and used for elements of the intact rock subjected to tension and shear failure. The intact rock was considered to have a low but non-negligible permeability. A verification study against analytical solutions showed that the fracture propagation and stress concentrations due to differential boundary stresses could be accurately represented by our model. Next, a base case was considered, in which the stress ratio (SR) between the magnitudes of the maximum and minimum boundary stresses, the permeability k(R) of the intact rock and the initial permeability k(TF) of the tension failure regions were fixed. In FD2, the distance d(F) between the two natural fractures defined by the closest distance was also fixed. The results showed that in both rock domains, the fracture started to propagate when the pore pressure was approximately 85% of the magnitude of the minimum boundary stress. The propagation of a single fracture was significantly greater than the propagation of a double fracture system because, in the latter case, the pore pressure decreased when the two fractures connected. As a result, changes in permeability in FD2 were smaller than in FD1. At the end of injection, the maximum ratios between the final and initial permeability of the natural fractures were found to be approximately 3 and 2 for rock domains FD1 and FD2, respectively. For non-parallel fractures, the controlling factor for fracture propagation was the separation between the tips of the pressurised fracture and the neighbouring non-pressurised fracture. A sensitivity study was conducted to study the influence of the key parameters d(F), SR, k(R) and k(TF) on the simulation results. Fracture propagation showed more sensitivity to d(F) and SR than to the other parameters.

  • 12. Guglielmi, Yves
    et al.
    Cappa, Frederic
    Lancon, Herve
    Janowczyk, Jean Bernard
    Rutqvist, Jonny
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Wang, J. S. Y.
    ISRM Suggested Method for Step-Rate Injection Method for Fracture In-Situ Properties (SIMFIP): Using a 3-Components Borehole Deformation Sensor2014In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 47, no 1, p. 303-311Article in journal (Refereed)
  • 13.
    Larsson, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Doughty, Christine
    Lawrence Berkeley National Laboratory, CA, USA.
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Understanding the effect of single fracture heterogeneity from single well injection withdrawal (SWIW) tests2013In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 21, no 8, p. 1691-1700Article in journal (Refereed)
    Abstract [en]

    The single well injection withdrawal (SWIW) tracer test on a fracture or fracture zone is a method used to estimate its tracer retardation properties.  In this study, the effects of single fracture aperture heterogeneity on SWIW test tracer breakthrough curves are examined by numerical modelling. The effects of the matrix diffusion and sorption is accounted for by using a particle tracking method through the addition of a time delay added to the advective transport time. For a given diffusion and sorption property value (Pm) and for a heterogeneous fracture, the peak concentration is larger compared to a homogeneous fracture. The cumulative breakthrough curve for a heterogeneous fracture is similar to that for a homogeneous fracture and a less sorptive/diffusive tracer. It is demonstrated that the fracture area that meets the flowing water, the so-called specific flow-wetted surface (sFWS) of the fracture, can be determined by comparing the observed breakthrough curve for a heterogeneous fracture with that for a homogeneous fracture. SWIW tests are also simulated with a regional pressure gradient present. The results point to the possibility of distinguishing the effect of the regional pressure gradient from that of diffusion through the use of multiple tracers with different Pm-values. 

  • 14.
    Larsson, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    A study of flow-wetted surface area in a single fracture as a function of its hydraulic conductivity distribution2012In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 48, p. W01508-Article in journal (Refereed)
    Abstract [en]

    The contact area between flowing water and rock-the flow-wetted surface (FWS)-is a main factor controlling the rock-matrix diffusion and sorption of flowing solute in a rock fracture. Flow channeling, therefore, has a strong effect on the retardation of mass transport due to the resulting lower contact area. This work presents a systematic study of the dependency between fracture aperture statistics and FWS in strongly heterogeneous fractures. Particle tracking is used to determine the transversal width of the particle flow lines, FWS, and beta factor, where beta is a variable that has been proposed as controlling tracer retention. The conductivity distribution over the fracture is assumed to be lognormal with standard deviation (sigma(ln) (K)) ranging from 0.23 to 4.61, with correlation lengths from 2% to 18% of the width of the flow domain. Results show a clear dependency between the specific flow-wetted surface (sFWS), defined as FWS divided by the total fracture area, and the standard deviation of the logarithm of fracture conductivity. The behavior is independent of the correlation length for the range of correlation lengths tested. The results are presented in the form of type curves and an empirical equation that provide a simple way to determine the sFWS as a function of sigma(ln) (K). This information can then be used to adjust the results of large-scale fracture network simulations by taking into account the effect of single fracture heterogeneity, an effect that is in practice infeasible to directly take into account in large-scale fracture network simulations.

  • 15.
    Larsson, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    An observed error in PMPATH particle tracking algorithm for MODFLOW in case of varying porosity and a proposed correction2012In: Computers & Geosciences, ISSN 0098-3004, E-ISSN 1873-7803, Vol. 45, p. 1-3Article in journal (Refereed)
    Abstract [en]

    MODFLOW (Harbaugh and McDonald, 1996) is a code widely used for groundwater modeling. It has been used for numerous projects and thousands of articles have been published with results of MODFLOW, since the code was first released in 1983. Numerous codes have been developed around MODFLOW, the pre- and post processing code Processing MODFLOW (Chiang, 2005) being one example. This code includes the advective particle tracking code PMPATH (Chiang, 2005), especially convenient and commonly used for stochastic groundwater modeling analyses as it includes an easy-to-use random field generator. The particle tracking code has been regularly used to simulate the advective transport of contaminants and tracers (e.g. Stauffer, 2005; Hefting et al., 2006; Dhiman and Keshari, 2006).

    A suspected error in the PMPATH code was found by us, when studying flow and particle transport in a strongly heterogeneous hydraulic conductivity fields with co-varying porosity. It emerged in the form of calculated particle flow paths converging into narrower and narrower channels. After many attempts to understand the results turned out to be unsuccessful, we decided to check into details of the code and discovered a significant but non-obvious error. This error is discussed in this paper and a procedure to obtain the correct flow paths and travel times is proposed. 

  • 16.
    Larsson, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Comparison of transport persistence and dispersion length for strongly heterogeneous conductivity fields2008Conference paper (Other academic)
    Abstract [en]

    When modelling transport in fractured and other strongly heterogeneous media, the classical ADE-approach with a continuum dispersion coefficient is usually not applicable. This has led to the development of alternative approaches, often based on particle tracking. When upscaling travel time information by means of particle travel time distributions, it is, however, not obvious how the distributions of travel times among neighbouring elements should be spatially correlated. In our earlier works (Öhman et al, WRR 2005, WO3016, Oden at al. WRR 2008, WO2421) we have introduced the concept of transport persistence to account for this 'memory' of travel times. Transport persistence is a distance that, for example, a fast particle remains fast. The present study investigates the nature of transport persistence for different characteristics of the underlying hydraulic conductivity field – defined through the standard deviation and correlation length of K – and compares it to the classical dispersion length that can also be determined based on the statistical characteristics of the conductivity field. Flow and particle tracking simulations are carried out for heterogeneous conductivity fields for ten different combinations of standard deviation and correlation length values. Sixty realizations are considered for each combination, and for each realization a large number particles are released. The relationship between the transport persistence distance and the dispersion length is examined. Preliminary results indicate that the correlation between the two concepts depends on the values of the standard deviations of hydraulic conductivity, i.e., the degree of heterogeneity and transport channelling. Implications of these results will be discussed.

  • 17.
    Larsson, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Odén, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Neretnieks, Ivars
    School of Chemical Science and Engineering, KTH, Stockholm.
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    A new approach to account for fracture aperture variability when modeling solute transport in fracture networks2013In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 49, no 4, p. 2241-2252Article in journal (Refereed)
    Abstract [en]

    A simple yet effective method is presented to include the effects of fracture aperture variability into the modeling of solute transport in fracture networks with matrix diffusion and linear sorption. Variable apertures cause different degrees of flow channeling, which in turn influence the contact area available for these retarding processes. Our approach is based on the concept of specific flow-wetted surface (sFWS), which is the fraction of the contact area over the total fracture surface area. Larsson et al. [2012] studied the relationship between sFWS and the standard deviation σln K  of the conductivity distribution over the fracture plane. Here an approach is presented to incorporate this into a fracture network model. With this model, solute transport through fracture networks is then analyzed. The cases of sFWS=0 and sFWS=1 correspond to those of no matrix diffusion and full matrix diffusion respectively. In between, a sFWS break point value can be defined, above which the median solute arrival time is proportional to the square of sFWS. For values below the critical sFWS (more channeled cases), the change is much slower, converging to that of no matrix diffusion. Results also indicate that details of assigning sFWS values for individual fractures in a network are not crucial; results of tracer transport are essentially identical to a case where all fractures have the mean σln K (or corresponding mean sFWS) value. This is obviously due to the averaging effect of the network.

  • 18.
    Latham, John-Paul
    et al.
    Department of Earth Science and Engineering, Imperial College, London, UK.
    Xiang, Jiansheng
    Belayneh, Mandefro
    Nick, Hamidreza M
    Tsang, Chin-Fu
    Department of Earth Science and Engineering, Imperial College, London, UK.
    Blunt, Martin J
    Modelling stress-dependent permeability in fractured rock including effects of propagating and bending fractures2013In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 57, p. 100-112Article in journal (Refereed)
    Abstract [en]

    The influence of in-situ stresses on flow processes in fractured rock is investigated using a novelmodelling approach. The combined finite-discrete element method (FEMDEM) is used to model thedeformation of a fractured rock mass. The fracture wall displacements and aperture changes aremodelled in response to uniaxial and biaxial stress states. The resultant changes in flow properties ofthe rock mass are investigated using the Complex Systems Modelling Platform (CSMPþþ). CSMPþþisused to model single-phase flow through fractures with variable aperture and a permeable rock matrix.The study is based on a geological outcrop mapping of a low density fracture pattern that includes therealism of intersections, bends and segmented features. By applying far-field (boundary) stresses to asquare region, geologically important phenomena are modelled including fracture-dependent stressheterogeneity, the re-activation of pre-existing fractures (i.e. opening, closing and shearing), thepropagation of new fractures and the development of fault zones. Flow anisotropy is investigated undervarious applied stresses and matrix permeabilities. In-situ stress conditions that encourage a closing offractures together with a more pervasive matrix-dominated flow are identified. These are comparedwith conditions supporting more localised flow where fractures are prone to dilatational shearing andcan be more easily exploited by fluids. The natural fracture geometries modelled in this work are notperfectly straight, promoting fracture segments that dilate as they shear. We have demonstrated theintroduction of several realistic processes that have an influence on natural systems: fractures canpropagate with wing cracks; there is the potential for new fractures to connect with existing fractures,thus increasing the connectivity and flow; blocks can rotate when bounded by fractures, bent fractureslead to locally different aperture development; highly heterogeneous stress distributions emergenaturally. Results presented in this work provide a mechanically rigorous demonstration that a changein the stress state can cause reactivation of pre-existing fractures and channelling of flow in criticallystressed fractures.

  • 19. Lei, Q
    et al.
    Latham, J-P
    Xiang, J
    Tsang, C-F
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Polyaxial stress-induced variable aperture model for persistent 3D fracture networks.2015In: Geomechanics for Energy and the Environment, ISSN 0315-0941, E-ISSN 2049-6060, Vol. 1, p. 34-47Article in journal (Refereed)
  • 20. Lei, Q
    et al.
    Latham, J-P
    Xiang, J
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Role of natural fractures in damage evolution around tunnel excavation in fractured rocks2017In: Engineering Geology, ISSN 0013-7952, E-ISSN 1872-6917, Vol. 231, p. 100-113Article in journal (Refereed)
    Abstract [en]

    This paper studies the role of pre-existing fractures in the damage evolution around tunnel excavation in fractured rocks. The length distribution of natural fractures can be described by a power law model, whose exponent a defines the relative proportion of large and small fractures in the system. The larger a is, the higher proportion of small fractures is. A series of two-dimensional discrete fracture networks (DENs) associated with different length exponent a and fracture intensity P-21 is generated to represent various scenarios of distributed preexisting fractures in the rock. The geomechanical behaviour of the fractured rock embedded with DFN geometry in response to isotropic/anisotropic in-situ stress conditions and excavation-induced perturbations is simulated using the hybrid finite-discrete element method (FEMDEM), which can capture the deformation of intact rocks, the interaction of matrix blocks, the displacement of natural fractures, and the propagation of new cracks. An excavation damaged zone (EDZ) develops around the man-made opening as a result of reactivation of preexisting fractures and propagation of wing cracks. The simulation results show that when a is small, the system which is dominated by large fractures can remain stable after excavation given that P-21 is not very high; however, intensive structurally-governed kinematic instability can occur if P-21 is sufficiently high and the fracture spacing is much smaller than the tunnel size. With the increase of a, the system becomes more dominated by small fractures, and the EDZ is mainly created by the coalescence of small fractures near the tunnel boundary. The results of this study have important implications for designing stable underground openings for radioactive waste repositories as well as other engineering facilities that are intended to generate minimal damage in the host rock mass.

  • 21.
    Lei, Qinghua
    et al.
    Imperial Coll London, Dept Earth Sci & Engn, London, England..
    Latham, John-Paul
    Imperial Coll London, Dept Earth Sci & Engn, London, England..
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Lawrence Berkeley Natl Lab, USA..
    The use of discrete fracture networks for modelling coupled geomechanical and hydrological behaviour of fractured rocks2017In: Computers and geotechnics, ISSN 0266-352X, E-ISSN 1873-7633, Vol. 85, p. 151-176Article, review/survey (Refereed)
    Abstract [en]

    We present a discussion of the state-of-the-art on the use of discrete fracture networks (DFNs) for modelling geometrical characteristics, geomechanical evolution and hydromechanical (HM) behaviour of natural fracture networks in rock. The DFN models considered include those based on geological mapping, stochastic generation and geomechanical simulation. Different types of continuum, discontinuum and hybrid geomechanical models that integrate DFN information are summarised. Numerical studies aiming at investigating geomechanical effects on fluid flow in DFNs are reviewed. The paper finally provides recommendations for advancing the modelling of coupled HM processes in fractured rocks through more physically-based DFN generation and geomechanical simulation.

  • 22.
    Lei, Qinghua
    et al.
    Department of Earth Science and Engineering, Imperial College London, London, UK,.
    Latham, John-Paul
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Xiang, Jiansheng
    Lang, Philipp
    A new approach to upscaling fracture network models while preserving geostatistical and geomechanical characteristics2015In: Journal of Geophysical Research: Solid Earth, ISSN 0148-0227, Vol. 120, no 7, p. 4784-4807Article in journal (Refereed)
    Abstract [en]

    A new approach to upscaling two-dimensional fracture network models is proposed for preserving geostatistical and geomechanical characteristics of a smaller-scale “source” fracture pattern. First, the scaling properties of an outcrop system are examined in terms of spatial organization, lengths, connectivity, and normal/shear displacements using fractal geometry and power law relations. The fracture pattern is observed to be nonfractal with the fractal dimension D≈ 2, while its length distribution tends to follow a power law with the exponent 2<a<3. To introduce a realistic distribution of fracture aperture and shear displacement, a geomechanical model using the combined finite-discrete element method captures the response of a fractured rock sample with a domain size L = 2munder in situ stresses. Next, a novel scheme accommodating discrete-time random walks in recursive self-referencing lattices is developed to nucleate and propagate fractures together with their stress- and scale-dependent attributes into larger domains of up to 54m× 54 m. The advantages of this approach include preserving the nonplanarity of natural cracks, capturing the existence of long fractures, retaining the realism of variable apertures, and respecting the stress dependency of displacement-length correlations. Hydraulic behavior of multiscale growth realizations is modeled by single-phase flow simulation, where distinct permeability scaling trends are observed for different geomechanical scenarios. A transition zone is identified where flow structure shifts from extremely channeled to distributed as the network scale increases. The results of this paper have implications for upscaling network characteristics for reservoir simulation.

  • 23. Lei, Qinghua
    et al.
    Latham, John-Paul
    Xiang, Jiansheng
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Lang, Philipp
    Guo, Liwei
    Effects of geomechanical changes on the validity of a discrete fracture network representation of a realistic two-dimensional fractured rock2014In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 70, p. 507-523Article in journal (Refereed)
    Abstract [en]

    This paper aims to examine the validity of the discrete fracture network (DFN) method in representing a realistic two-dimensional fractured rock in terms of their geomechanical response to in situ stresses and hydraulic behaviour in a steady state fluid held. First, a real fracture network is extracted from the geological map of an actual rock outcrop, which is termed the analogue fracture network (AFN). Multiple DFN realisations are created using the statistics oldie analogue pattern. A conductivity parameter that was found to have a linear relationship with the conductivity of 2D fracture networks is included to further enhance network similarity. A series of numerical experiments are designed with far-field stresses applied at a range of angles to the rock domains and their geomechanical response is modelled using the combined finite discrete element method (FEMDEM). A geomechanical comparison between the AFN and as DFN equivalents is made based on phenomena such as heterogeneity of fracture-dependent stress contours, sliding between pre-existing fracture walls, coalescence of propagating fractures and variability of aperture distribution. Furthermore, an indirect hydro-mechanical (HM) coupling is applied and the hydraulic behaviour of the porous rock models is investigated using the hybrid finite element-finite volume method (FEFVM). A further comparison is conducted focusing on the hydraulic behaviour of the AFN and DFNs under the effects of geomechanical changes. The results show that although DFNs may represent an AFN quite well for fixed mechanical conditions, such a representation may not be dependable if mechanical changes occur. 

  • 24.
    Lorenz, Henning
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Rosberg, Jan-Erik
    Lund University, Engineering Geology.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Bjelm, Leif
    Lund University, Engineering Geology.
    Almqvist, Bjarne Sven Gustav
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Berthet, Théo
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Conze, Ronald
    GFZ Potsdam, Scientific Drilling.
    Gee, David Godfrey
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Klonowska, Iwona
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.
    Pascal, Christophe
    Ruhr University Bochum, Germany.
    Pedersen, Karsten
    Chalmers University of Technology.
    Roberts, Nick M. W.
    British Geological Survey.
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Lawrence Berkeley Laboratory, USA.
    COSC-1 -€“ drilling of a subduction-related allochthon in the Palaeozoic Caledonide orogen of Scandinavia2015In: Scientific Drilling, ISSN 1816-8957, E-ISSN 1816-3459, Vol. 19, p. 1-11Article in journal (Refereed)
  • 25.
    Niemi, Auli
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Bensabat, Jacob
    Bear, Jacob
    Carrera, Jesus
    Gouze, Philippe
    Hazeldine, Stuart
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Sauter, Martin
    Tsang, Chin-Fu
    A Multiple Space and Time Scale Approach for the Characterization and Modeling of Deep Saline Formations for CO2 storage.2009In: Proceedings of 8th Annual Conference on Carbon Capture & Sequestration May 4th - 7th, 2009 Pittsburgh, Pennsylvania., 2009Conference paper (Refereed)
    Abstract
  • 26. Odén, Magnus
    et al.
    Niemi, A.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Regional channelized transport in fractured media with matrix diffusion and linear sorption2008In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 44, article id W02421Article in journal (Refereed)
  • 27.
    Rasmusson, Kristina
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Yvonne
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Rasmusson, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Pan, Lehua
    Univ Calif Berkeley, USA.
    Fagerlund, Fritjof
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Bensabat, Jacob
    EWRE, Environm & Water Resources Engn Ltd, Haifa, Israel.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Distribution of injected CO2 in a stratified saline reservoir accounting for coupled wellbore-reservoir flow2015In: Greenhouse Gases: Science and Technology, E-ISSN 2152-3878, Vol. 5, no 4, p. 419-436Article in journal (Refereed)
    Abstract [en]

    Geological storage in sedimentary basins is considered a viable technology in mitigating atmospheric CO2 emissions. Alternating high and low permeability strata are common in these basins. The distribution of injected CO2 among such layers affects e.g. CO2 storage efficiency, capacity and plume footprint. A numerical study on the distribution of injected CO2 into a multi-layered reservoir, accounting for coupled wellbore-reservoir flow, was carried out using the T2Well/ECO2N code. A site-specific case as well as a more general case were considered. Properties and processes governing the distribution of sequestrated CO2 were identified and the potential to operationally modify the distribution was investigated. The distribution of CO2 was seen to differ from that of injected water, i.e. it was not proportional to the transmissivity of the layers. The results indicate that caution should be taken when performing numerical simulations of CO2 injection into layered formations. Ignoring coupled wellbore-reservoir flow and instead adopting a simple boundary condition at the injection well, such as an inflow rate proportional to the transmissivity of each layer, may result in significant underestimation of the proportion of CO2 ending up in the shallower layers, as not all relevant processes are accounted for. This discrepancy has been thoroughly investigated and quantified for several CO2 sequestration scenarios.

  • 28. Rutqvist, Jonny
    et al.
    Figueiredo, Bruno
    Hu, Mengsu
    Tsang, C-F
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Chapter 7: Continuum Modeling of Hydraulic Fracturing in Complex Fractured Rock Masses.2018In: Hydraulic Fracture Modeling / [ed] Yu-Shu Wu, Cambridge, Massachusetts: Gulf Professional Publishing, 2018, p. 195-217Chapter in book (Refereed)
  • 29.
    Sharma, Prabhakar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Fagerlund, Fritjof
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Bensabat, Jacob
    EWRE Ltd, Israel.
    Pezard, Philippe
    Geosciences Montpellier, CNRS, Universite Montpellier, Montpellier, France.
    Flowing Fluid Electric Conductivity logging method as a tool to characterize the hydraulic conducitivity strucure of a target layer for CO2 injection2011Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    Understanding of the detailed permeability structure and internal heterogeneity of the target layers of CO2injection is important for any successful injection project. Yet, determining this structure by traditional hydraulictesting may be prohibitively cumbersome and expensive, while information obtained from core logs may not givea full picture of the connected permeability.Flowing FEC (Fluid electric conductivity) method provides a quick way of determining the hydraulic conductivitystructure of a reservoir layer. In combination with traditional pumping tests that can provide overallinterval transmissivities, the method can be used for obtaining a more detailed picture of the distribution of thetransmissivities, information that is crucial for CO2 injection experiments where the internal heterogeneity of thetarget layer may greatly influence the distribution of CO2. The method has been previously been successfullyapplied to several applications, ranging from granitic rock to mudstone formations (Doughty et al., 2008; Tsangand Doughty, 2003) and is here being used for preliminary hydraulic characterization of the target CO2 injectionlayer of the Heletz, Israel, the main injection site of the MUSTANG project.In this approach the wellbore water is first replaced by water of a constant salinity distinctly different fromthat of formation water. Next, the well is shut in and an electric conductivity probe is used to scan the FEC ofborehole fluid as a function of depth. After this, the well is pumped at constant rate, during which a series FEClogs at successive times are obtained. At depth locations where water enters the borehole, the logs display peaks.Analysis of the time evolution and skewness of these peaks allows estimation of the flow rate qi and salinity C,and further, if two or more logs are taken at different well flow rates, the initial ambient pressure heads hi of eachindividual inflow/feed point I can also be estimated. The depth resolution of the inflow locations is typically 10cm.These data can used to define the detailed transmissivity/permeability structure of the reservoir layer.The present presentation discusses the application of the method for characterizing the target layer of the Heletzinjection experiment, in terms of the data, model analysis and comparison of the results to those from core samples.

    Tsang, C. F. and C. Doughty, Multirate flowing fluid electric conductivity logging method, Water ResourcesResearch, 39, 12, 1354-1362 (10.1029/2003WR002308), 2003.

    Doughty, C., C.-F. Tsang, K. Hatanaka, S. Yabuuchi, and H. Kurikami. Application of direct-fitting, massintegral, and multirate methods to analysis of flowing fluid electric conductivity logs from Horonobe, Japan,WaterResour. Res., Vol. 44, doi:10.1029/2007WR006441, 2008.

  • 30.
    Sharma, Prabhakar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Chin-Fu
    Lawrence Berkeley National Laboratory.
    Doughty, Christine
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Bensabat, Jacob
    EWRE ltd, Haifa, Israel.
    Feasibility of Long-term Monitoring of Deep Hydrogeology with Flowing Fluid Electric Conductivity Logging Method2015In: Dynamics of Fluids and Transport in Fractured-Porous Media / [ed] Faybishenko, B., Gale, J. and Benson, S., American Geophysical Union , 2015Chapter in book (Refereed)
    Abstract [en]

    The flowing fluid electrical conductivity (FFEC) logging method has been used in deep boreholes to obtain estimates for the transmissivity, salinity of formation water, hydraulic head, and formation water flow rate of hydraulically conducting layers. In this paper, we proposed a modified FFEC logging procedure, involving a setup of a string of EC/T probes in the borehole, to passively monitor long-term temporal changes in local flow rates in a brine formation composed of multiple layers with different transmissivities over a period of months or years. The local flows in the layers can vary over time, for instance, as a result of seasonal or climatic changes. In the case of supercritical CO2 storage in the deep subsurface, the local flow pattern of the storage formation will be disturbed and furthermore it may change with time as the low density and low viscosity CO2 enters more and more into the transmissive layers and interacts with in situ water and rock. The present paper explores the possibility of using the FFEC method for such long-term monitoring in an observation well. The feasibility is demonstrated with field data from the Outokumpu test site in Finland.

  • 31.
    Sharma, Prabhakar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Chin-Fu
    Lawrence Berkeley National Laboratory.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Use of FFEC logging for long-term monitoring of regional flow in multi-layer aquifer system2013Conference paper (Refereed)
    Abstract [en]

    The flowing fluid electrical conductivity (FFEC) logging method has been successfully used in deep boreholes to estimate the transmissivity, salinity of formation water, hydraulic head, and regional flow rate of hydraulically conducting layers as a function of depth, and to do so in much less time than conventional well logging methods. In this method, the wellbore fluid electrical conductivity (FEC) is measured over depth for a series of time periods under pumping condition, after replacement of wellbore water with deionized water or water of salinity distinctly different from that of the formation. These FEC profiles are analyzed by fitting to an one-dimensional advection-dispersion equation. In this presentation, we modified the FFEC procedure to monitor the temporal changes in regional flows in a deep formation with multiple conductive layers for periods of months and years. Regional flows in the layers can vary, for instance, due to changes in subsurface flow recharge or discharge rates. In the event of CO2 injection in the deep subsurface for geological storage of supercritical CO2, the regional flow pattern of the storage formation will be disturbed and may change with time as the low density and low viscosity CO2 enters more and more into the conductive layers. The present study explores the possibility of using the FFEC method for such a  long-term monitoring of the flow velocity of formation water in an observation well. We assume the conductive layers in the storage formation to have different values of transmissivity. Results indicate that potential long-term temporal changes in regional flow in the layers can be estimated at a monitoring well by the FFEC method. Conditions for the applicability of this method are discussed.

  • 32.
    Sharma, Prabhakar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Chin-Fu
    Lawrence Berkeley National Laboratory.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Bensabat, Jacob
    EWRE ltd, Haifa, Israel.
    Flowing Fluid Electrical Conductivity Logging at the Heletz Site for Detailed Hydraulic Information for CO2 injection2012Conference paper (Refereed)
    Abstract
  • 33.
    Sharma, Prabhakar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Nalanda Univ, Sch Ecol & Environm Studies, Nalanda 803116, Bihar, India.
    Tsang, Chin-Fu
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    T. Kukkonen, Ilmo
    Univ Helsinki, Dept Phys, Helsinki, Finland.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Analysis of 6‑year fluid electric conductivity logs to evaluate the hydraulic structure of the deep drill hole at Outokumpu, Finland2016In: International journal of earth sciences, ISSN 1437-3254, E-ISSN 1437-3262, Vol. 105, no 5, p. 1549-1562Article in journal (Refereed)
    Abstract [en]

    Over the last two decades, the flowing fluid electric conductivity (FFEC) logging method has been applied in boreholes in the well-testing mode to evaluate the transmissivity, hydraulic head, and formation water electrical conductivity as a function of depth with a resolution of about 10–20 cm. FFEC profiles along the borehole are obtained under both shut-in and pumping conditions in a logging procedure that lasts only 3 or 4 days. A method for analyzing these FFEC logs has been developed and successfully employed to obtain formation parameters in a number of field studies. The present paper concerns the analysis of a unique set of FFEC logs that were taken from a deep borehole reaching down to 2.5 km at Outokumpu, Finland, over a 6-year time period. The borehole intersects paleoproterozoic metasedimentary, granitoid, and ophiolite- derived rocks. After the well was drilled, completed, and cleaned up, FFEC logs were obtained after 7, 433, 597, 948, and 2036 days. In analyzing these five profiles, we discovered the need to account for salinity diffusion from water in the formation to the borehole. Analysis results include the identification of 15 hydraulically conducting zones along the borehole, the calculation of flow rates associated with these 15 zones, as well as the estimation of the variation of formation water electrical conductivity as a function of depth. The calculated flow rates were used to obtain the tentative hydraulic conductivity values at these 15 depth levels.

  • 34.
    Tsang, Chin-Fu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Barnichon, J. D.
    Birkholzer, J.
    Li, X. L.
    Liu, H. H.
    Sillen, X.
    Coupled thermo-hydro-mechanical processes in the near field of a high-level radioactive waste repository in clay formations2012In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 49, p. 31-44Article in journal (Refereed)
    Abstract [en]

    The present paper provides an overview of key coupled thermo-hydro-mechanical (THM) processes in clay formations that would result from the development of a high-level radioactive waste repository. Here, in this paper, clay formations include plastic clay such as the Boom Clay of Belgium, as well as more indurated clay such as the Callovo-Oxfordian and Upper Toarcian of France and Opalinus Clay of Switzerland. First, we briefly introduce and describe four major Underground Research Laboratories (URLs) that have been devoted to clay repository research over the last few decades. Much of the research results in this area have been gained through investigations in these URLs and their supporting laboratory and modeling research activities. Then, the basic elements in the development of a waste repository in clays are presented in terms of four distinct stages in repository development. For each of these four stages, key processes and outstanding issues are discussed. A summary of the important areas of research needs and some general remarks then conclude this paper.

  • 35.
    Tsang, Chin-Fu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Lawrence Berkeley Natl Lab, Berkeley, CA USA.
    Figueiredo, Bruno
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Importance of stress effects on inputs to fracture network models used for subsurface flow and transport studies2018In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 101, p. 13-17Article in journal (Refereed)
  • 36.
    Tsang, Chin-Fu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Neretnieks, Ivars
    Tsang, Yvonne
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Hydrologic issues associated with nuclear waste repositories2015In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 51, no 9, p. 6923-6972Article, review/survey (Refereed)
    Abstract [en]

    Significant progress in hydrology, especially in subsurface flow and solute transport, has been made over the last 35 years because of sustained interest in underground nuclear waste repositories. The present paper provides an overview of the key hydrologic issues involved, and to highlight advances in their understanding and treatment because of these efforts. The focus is not on the development of radioactive waste repositories and their safety assessment, but instead on the advances in hydrologic science that have emerged from such studies. Work and results associated with three rock types which are being considered to host the repositories, are reviewed, with a different emphasis for each rock type. The first rock type is fractured crystalline rock, for which the discussion will be mainly on flow and transport in saturated fractured rock. The second rock type is unsaturated tuff, for which the emphasis will be on flow from the shallow subsurface through the unsaturated zone to the repository. The third rock type is clay-rich formations, whose permeability is very low in an undisturbed state. In this case, the emphasis will be on hydrologic issues that arise from mechanical and thermal disturbances; i.e., on the relevant coupled thermo-hydro-mechanical processes. The extensive research results, especially those from multi-year large-scale underground research laboratory investigations, represent a rich body of information and data that can form the basis for further development in the related areas of hydrologic research.

  • 37.
    Tsang, Chin-Fu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Deep hydrogeology: a discussion of issues and research needs2013In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 21, no 8, p. 1687-1690Article in journal (Other academic)
  • 38.
    Tsang, Chin-Fu
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Lawrence Berkeley Natl Lab, Berkeley, CA 94720 USA.
    Rosberg, Jan-Erik
    Lund Univ, Lund, Sweden.
    Sharma, Prabhakar
    Nalanda University, Nalanda, Bihar, India.
    Berthet, Theo
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Juhlin, Christopher
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Hydrologic testing during drilling: application of the flowing fluid electrical conductivity (FFEC) logging method to drilling of a deep borehole2016In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 24, no 6, p. 1333-1341Article in journal (Refereed)
    Abstract [en]

    Drilling of a deep borehole does not normally allow for hydrologic testing during the drilling period. It is only done when drilling experiences a large loss (or high return) of drilling fluid due to penetration of a large-transmissivity zone. The paper proposes the possibility of conducting flowing fluid electrical conductivity (FFEC) logging during the drilling period, with negligible impact on the drilling schedule, yet providing important information on depth locations of both high- and low-transmissivity zones and their hydraulic properties. The information can be used to guide downhole fluid sampling and post-drilling detailed testing of the borehole. The method has been applied to the drilling of a 2,500-m borehole at Åre, central Sweden, firstly when the drilling reached 1,600 m, and then when the drilling reached the target depth of 2,500 m. Results unveil eight hydraulically active zones from 300 m down to borehole bottom, with depths determined to within the order of a meter. Further, the first set of data allows the estimation of hydraulic transmissivity values of the six hydraulically conductive zones found from 300 to 1,600 m, which are very low and range over one order of magnitude.

  • 39.
    Öhman, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Niemi, Auli
    Tsang, Chin-Fu
    A Regional-Scale Particle-Tracking Method for Nonstationary Fractured Media2005In: Water Resources Research, ISSN 0043-1397, Vol. 41, no W0316, p. 1-16Article in journal (Refereed)
    Abstract
  • 40.
    Öhman, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Air and Water Science.
    Tsang, Chin-Fu
    Probabilistic Estimation of Fracture Transmissivity from Wellbore Hydraulic Data Accounting for Depth-Dependent Anisotropic Rock Stress2005In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 42, no 5-6, p. 793-804Article in journal (Refereed)
    Abstract [en]

    A new method is introduced that incorporates the use of hydrological and rock mechanical data in assigning transmissivities for fracture-network models. The hydrological data comes from fixed-interval packer tests carried out in a borehole and the rock-mechanical data are the prevailing in situ depth-dependent stress-field and the stress-closure relationship of fractures.

    In the model, the fracture transmissivity distribution is considered to be constituted of two components, one deterministic stress-induced component and the other a stochastic component that describes the intrinsic variability of fractures in a network. The outcome is a tensorial description of fracture transmissivities in an anisotropic stress-regime, where the transmissivity for an arbitrarily oriented fracture in the network is determined by its orientation in relation to the ambient stress-field. These transmissivities are conditioned such that the overall results satisfy the hydraulic packer test data. The suggested procedure is applied to an example data set from a site at Sellafield, England.

    The results show that the probabilistic approach, relying on hydraulic data alone, may underestimate the true variability in fracture transmissivities, since the typically vertical boreholes entail a sampling bias towards horizontal fractures that are predominantly subject to vertical stress. The suggested method helps to account for the true underlying three-dimensional variability that is incompletely resolved by using the hydraulic borehole data alone. This method is likely to have the largest impact at low stress-levels, in strongly anisotropic stress-fields, for borehole directions parallel to one principal stress, and for fracture network geometries characterized by sets orthogonal to the three principal stresses.

  • 41.
    Öhman, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Niemi, Auli
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Tsang, Chin-Fu
    Öhman, J., A. Niemi, and C.-F. Tsang (2005), Probabilistic Estimation of Fracture Transmissivity from Wellbore Hydraulic Data Accounting for Depth-Dependent Anisotropic Rock Stress. Int. Journal of Rock Mechanics and Min. Sciences. 42(5-6): 793-804.2005In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 42, no 5-6, p. 793-804Article in journal (Refereed)
    Abstract
1 - 41 of 41
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