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The classic Ghyben-Herzberg estimate of the depth of the freshwater-saltwater interface together with the Dupuit approximation is a useful tool for developing analytical solutions to many seawater intrusion problems. On the basis of these assumptions, Strack (1976) developed a single-potential theory to calculate critical pumping rates in a coastal pumping scenario. The sharp interface assumption and, in particular, this analytical solution are widely used to study seawater intrusion and the sustainable management of groundwater resources in coastal aquifers. The sharp interface assumption neglects mixing and implicitly assumes that salt water remains static. Consequently, this approximation overestimates the penetration of the saltwater front and underestimates the critical pumping rates that ensure a freshwater supply. We investigate the error introduced by adopting the sharp interface approximation, and we include the effects of dispersion on the formulation of Strack (1976). To this end, we perform numerical three-dimensional variable density flow simulations. We find that Strack's equations can be extended to the case of mixing zone if the density factor is multiplied by an empirically derived dispersion factor [1 - (α T/ b′) 1/6], where α T is transverse dispersivity and b' is aquifer thickness. We find that this factor can be used not only to estimate the critical pumping rate but also to correct the Ghyben-Herzberg estimate of the interface depth. Its simplicity facilitates the generalization of sharp interface analytical solutions and good predictions of seawater penetration for a broad range of conditions. Copyright 2011 by the American Geophysical Union. ; The first author gratefully acknowledges the receipt of an FI award from the autonomous government of Catalonia for the period during which this work was carried out. We would also like to thank the associate editor and the reviewers for their constructive comments, which significantly improved the manuscript quality. ; Peer Reviewed

Dissolution of carbon dioxide (CO2) injected into saline aquifers causes an unstable high-density diffusive front. Understanding how instability fingers develop has received much attention because they accelerate dissolution trapping, which favours long-term sequestration. The time for the onset of convection as the dominant transport mechanism has been traditionally studied by neglecting dispersion and treating the CO2brine interface as a prescribed concentration boundary by analogy to a thermal convection problem. This work explores the effect of these simplifications. Results show that accounting for the CO2 mass flux across the prescribed concentration boundary has little effect on the onset of convection. However, accounting for dispersion causes a reduction of up to two orders of magnitude on the onset time. This implies that CO2 dissolution can be accelerated by activating dispersion as a transport mechanism, which can be achieved adopting a fluctuating injection regime. © 2009 Cambridge University Press. ; Financial support of the Spanish Ministry of Science and Innovation (MICINN) through the PSE-CO2 project (PSE-120000-2007- 6), of the Spanish Government through the Fundacio´ n Ciudad de la Energ´ıa-CIUDEN and the European Union through project MUSTANG (FP7-ENERGY-2008-1, project number 227286). ; Peer Reviewed

3rd Workshop of CODE-BRIGHT Users. 2011, Barcelona. ; Anthropogenic CO2 emissions are expected to continue to increase worldwide in the next decades. This could dramatically increase CO2 concentrations in the atmosphere. One potential mitigation action is CO2 permanent storage in deep saline aquifers. CO2 is injected as a supercritical fluid (temperature and pressure higher than 31.1 ºC and 7.38 MPa, respectively) so as to obtain a relatively high density that minimizes the volume occupied by this greenhouse gas. CO2 density is highly dependent on temperature and pressure because of its high compressibility (Vilarrasa et al., 2010a), adopting a wide range of values (450-800 kg/m3). Since CO2 is lighter than brine, flow is affected by buoyancy. Buoyancy produces an upslope migration of the CO2 bubble in sloping aquifers. The post-injection fate of CO2 in sloping aquifers has been investigated (e.g. Hesse et al., 2008; Elenius et al., 2010) but without considering the actual shape of the CO2 bubble at the end of injection. However, the shape of the CO2 bubble at the end of injection affects its posterior evolution (McMinn & Juanes, 2009). Gasda et al. (2008) studied the effect of a slope up to 1º during the injection period using a 2D model, which represents injection through a horizontal well. However, CO2 injection through a vertical well, which implies a 3D geometry, has not yet been investigated.CO2 will be injected in the Hontomín CO2 pilot storage site, Burgos (Spain). Hontomín is the site for the CO2 storage Technology Demonstration Plant (TDP) of the Compostilla OXYCFB300 project, operated by Energy City Foundation (CIUDEN). CO2 will be injected through a vertical well in a flank of a dome-like structure with a slope close to 20º at a depth around 1450 m. CO2 injection tests are aimed to gain knowledge on trapping mechanisms and CO2 bubble and pressure evolution. Pressure evolution is important for assessing the caprock integrity and to avoid the open up of preferential paths for CO2 leakage (Vilarrasa et al., 2010b, 2011). These processes are relatively well known in horizontal aquifers, but a high uncertainty still exists in sloping aquifers. ; V.V. wishes to acknowledge the Spanish Ministry of Science and Innovation (MCI), through the "Formación de Profesorado Universitario", and the "Colegio de Ingenieros de Caminos, Canales y Puertos – Catalunya" for their financial support. Additionally, we would like to acknowledge the Spanish Government (Ministry of Industry, Tourism and Trade) through the CUIDEN foundation (project ALM/09/18; www.ciuden.es) and the 'MUSTANG' project (from the European Community's Seventh Framework Programme FP7/2007-2013 under grant agreement nº227286 ; www.co2mustang.eu) for their financial support. ; Peer reviewed

48 páginas, 8 figuras. ; The correct characterization of the effective reactive transport dynamics is an important issue for modeling reactive transport on the Darcy scale, specifically in situations in which reactions are localized, that is when different reactions occur in different portions of the porous medium. Under such conditions the conventional approach of homogenizing only the porous medium chemistry is not appropriate. We consider here reactive transport in a porous medium that is characterized by mass transfer between a mobile and a distribution of immobile regions. Chemical and physical heterogeneity are reflected by distributions of kinetic reaction rate constants and residence times in the immobile zones. We derive an effective reactive transport equation for the mobile solute that is characterized by non-local physical mass transfer and reaction terms. Specifically, chemical heterogeneity is upscaled in terms of a reactive memory function that integrates both chemical and physical heterogeneity. Mass transfer limitations due to physical heterogeneity yield effective kinetic rate coefficients that can be much smaller than the volumetric average of the local scale coefficients. These results help to explain and quantify the often reported discrepancy between observed field reaction rate constants and the ones obtained under well mixed laboratory conditions. Furthermore, these results indicate that transport under physical and chemical heterogeneity cannot be upscaled separately. ; The authors thank the editor Al Valocchi and Insa Neuweiler and an anonymous reviewer for their insightful comments and suggestions. The authors acknowledge the support of CIUDEN, the ANR project COLINER and the European Union project MUSTANG and CIUDEN. ; Peer reviewed

The injection of supercritical carbon dioxide (CO2) in deep saline aquifers leads to the formation of a CO2 rich phase plume that tends to float over the resident brine. As pressure builds up, CO2 density will increase because of its high compressibility. Current analytical solutions do not account for CO2 compressibility and consider a volumetric injection rate that is uniformly distributed along the whole thickness of the aquifer, which is unrealistic. Furthermore, the slope of the CO2 pressure with respect to the logarithm of distance obtained from these solutions differs from that of numerical solutions. We develop a semianalytical solution for the CO2 plume geometry and fluid pressure evolution, accounting for CO2 compressibility and buoyancy effects in the injection well, so CO2 is not uniformly injected along the aquifer thickness. We formulate the problem in terms of a CO2 potential that facilitates solution in horizontal layers, with which we discretize the aquifer. Capillary pressure is considered at the interface between the CO2 rich phase and the aqueous phase. When a prescribed CO2 mass flow rate is injected, CO2 advances initially through the top portion of the aquifer. As CO2 is being injected, the CO2 plume advances not only laterally, but also vertically downwards. However, the CO2 plume does not necessarily occupy the whole thickness of the aquifer. We found that even in the cases in which the CO2 plume reaches the bottom of the aquifer, most of the injected CO2 enters the aquifer through the layers at the top. Both CO2 plume position and fluid pressure compare well with numerical simulations. This solution permits quick evaluations of the CO2 plume position and fluid pressure distribution when injecting supercritical CO2 in a deep saline aquifer. © 2013 Springer Science+Business Media Dordrecht. ; This work has been funded by Fundación Ciudad de la Energía (Spanish Government) (www.ciuden.es) and 35 by the European Union through the "European Energy Programme for Recovery" and the Compostilla OXYCFB300 project. We also want to acknowledge the financial support received from the 'MUSTANG' (www.co2mustang.eu) and 'PANACEA' (www.panacea-co2.org) projects (from the European Community's Seventh Framework Programme FP7/2007-2013 under grant agreements nº 227286 and nº 282900, respectively). ; Peer Reviewed

CO2 will remain in supercritical (SC) state (i.e. p>7.382MPa and T>31.04°C) under the pressure (p) and temperature (T) conditions appropriate for geological storage. Thus, it is usually assumed that CO2 will reach the aquifer in SC conditions. However, inflowing CO2 does not need to be in thermal equilibrium with the aquifer. In fact, surface operations are simpler for liquid than for SC CO2, because CO2 is transported in liquid state. Yet, problems might arise because of thermal stresses induced by cold CO2 injection and because of phase changes in the injection tubing or in the formation. Here, we propose liquid CO2 injection and analyze its evolution and the thermo-hydro-mechanical response of the formation and the caprock. We find that injecting CO2 in liquid state is energetically more efficient than in SC state because liquid CO2 is denser than SC CO2, leading to a lower overpressure not only at the wellhead, but also in the reservoir because a smaller fluid volume is displaced. Cold CO2 injection cools down the formation around the injection well. Further away, CO2 equilibrates thermally with the medium in an abrupt front. The liquid CO2 region close to the injection well advances far behind the SC CO2 interface. While the SC CO2 region is dominated by gravity override, the liquid CO2 region displays a steeper front because viscous forces dominate (liquid CO2 is not only denser, but also more viscous than SC CO2). The temperature decrease close to the injection well induces a stress reduction due to thermal contraction of the media. This can lead to shear slip of pre-existing fractures in the aquifer for large temperature contrasts in stiff rocks, which could enhance injectivity. In contrast, the mechanical stability of the caprock is improved in stress regimes where the maximum principal stress is the vertical. © 2013 Elsevier Ltd. ; V.V. wishes to acknowledge the Spanish Ministry of Science and Innovation (MCI), through the "Formación de Profesorado Universitario" Program, and the "Colegio de Ingenieros de Caminos, Canales y Puertos – Catalunya" for their financial support. This work has been funded by Fundación Ciudad de la Energía (Spanish Government) (www.ciuden.es) through the project ALM/09/018 and by the European Union through the "European Energy Programme for Recovery" and the Compostilla OXYCFB300 project. We also want to acknowledge the financial support received from the 'MUSTANG' (www.co2mustang.eu) and 'PANACEA' (www.panacea-co2.org) projects (from the European Community's Seventh Framework Programme FP7/2007–2013 under grant agreements nos. 227286 and 282900, respectively). ; Peer Reviewed

The presence of low permeability regions within porous media impacts solute transport and the distribution of species concentrations. Therefore, (bio)chemical reactions are equally affected. Multirate Mass Transfer (MRMT) models can be used to represent this anomalous transport process. MRMT conceptualizes the medium as a set of multiple continua: one mobile zone and multiple immobile zones. It simulates species transport in mobile and immobile zones simultaneously, which are related by first-order mass exchange. Numerical modeling of reactive transport in this kind of multicontinua media is complex and demanding because of the high dimensionality of the problem. In this paper, we establish the governing equations of reactive transport in multicontinuum media incorporating chemical kinetics into the governing equations. We propose a general numerical solution of reactive transport with MRMT by applying direct substitution approach (DSA) based on Newton-Raphson method. The efficiency of the proposed algorithm benefits of the block structure of the system, which allows us to eliminate immobile zones equations and leads to significant savings in CPU time. We test the validity of the developed solution by comparison with other numerical and analytical solutions. ; The authors acknowledge the support of project NITREM initiated and funded by EIT (European Institute of Innovation and Technology), and the Water-JPI European Union project MARadentro, project number PCI2019-103425-WW2017. ; Peer reviewed

Finding a numerical method to model solute transport in porous media with high heterogeneity is crucial, especially when chemical reactions are involved. The phase space formulation termed the multi-advective water mixing approach (MAWMA) was proposed to address this issue. The water parcel method (WP) may be obtained by discretizing MAWMA in space, time, and velocity. WP needs two transition matrices of velocity to reproduce advection (Markovian in space) and mixing (Markovian in time), separately. The matrices express the transition probability of water instead of individual solute concentration. This entails a change in concept, since the entire transport phenomenon is defined by the water phase. Concentration is reduced to a chemical attribute. The water transition matrix is obtained and is demonstrated to be constant in time. Moreover, the WP method is compared with the classic random walk method (RW) in a high heterogeneous domain. Results show that the WP adequately reproduces advection and dispersion, but overestimates mixing because mixing is a sub-velocity phase process. The WP method must, therefore, be extended to take into account incomplete mixing within velocity classes. ; This research was funded by MICINN (Spanish government) through MEDISTRAES project II and III (grant numbers CGL2013-48869-C2-2-R and PID2019-110212RB-C22). J.S.-S. wishes to acknowledge the financial support from the AGAUR (Generalitat de Catalunya, Spain) through the "Grant for universities and research centers for the recruitment of new research personnel (FI-DGR 2013)". IDAEA-CSIC is a Centre of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Project CEX2018-000794-S). ; Peer reviewed

The offshore Castor Underground Gas Storage (UGS) project had to be halted after gas injection triggered three M4 earthquakes, each larger than any ever induced by UGS. The mechanisms that induced seismicity in the crystalline basement at 5–10 km depth after gas injection at 1.7 km depth remain unknown. Here, we propose a combination of mechanisms to explain the observed seismicity. First, the critically stressed Amposta fault, bounding the storage formation, crept by the superposition of well‐known overpressure effects and buoyancy of the relatively light injected gas. This aseismic slip brought an unmapped critically stressed fault in the hydraulically disconnected crystalline basement to failure. We attribute the delay between induced earthquakes to the pressure drop associated to expansion of areas where earthquakes slips cause further instabilities. Earthquakes occur only after these pressure drops have dissipated. Understanding triggering mechanisms is key to forecast induced seismicity and successfully design deep underground operations. ; The authors would like to acknowledge Álvaro González for sharing the catalogs that were used in Cesca et al. (2014). Funding: Víctor Vilarrasa acknowledges funding from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Program through the Starting Grant GEoREST (www.georest.eu) (grant agreement No. 801809). Antonio Villaseñor acknowledges funding from Spanish Ministry of Science and Innovation grant CGL2017‐88864‐R. IDAEA‐CSIC is a Center of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Project CEX2018‐000794‐S). ICM‐CSIC is a Center of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Project CEX2019‐000928‐S). ; Peer reviewed

Geologic carbon storage, as well as other geoenergy applications, such as geothermal energy, seasonal natural gas storage and subsurface energy storage imply fluid injection and/or extraction that causes changes in rock stress field and may induce (micro)seismicity. If felt, seismicity has a negative effect on public perception and may jeopardize wellbore stability and damage infrastructure. Thus, induced earthquakes should be minimized to successfully deploy geo-energies. However, numerous processes may trigger induced seismicity, which contribute to making it complex and translates into a limited forecast ability of current predictive models.We review the triggering mechanisms of induced seismicity. Specifically, we analyze (1) the impact of pore pressure evolution and the effect that properties of the injected fluid have on fracture and/or fault stability; (2) non-isothermal effects caused by the fact that the injected fluid usually reaches the injection formation at a lower temperature than that of the rock, inducing rock contraction, thermal stress reduction and stress redistribution around the cooled region; (3) local stress changes induced when lowpermeability faults cross the injection formation, which may reduce their stability and eventually cause fault reactivation; (4) stress transfer caused by seismic or aseismic slip; and (5) geochemical effects, which may be especially relevant in carbonate-containing formations. We also review characterization techniques developed by the authors to reduce the uncertainty in rock properties and subsurface heterogeneity both for the screening of injection sites and for the operation of projects. Based on the review, we propose a methodology based on proper site characterization, monitoring and pressure management to minimize induced seismicity. ; Víctor Vilarrasa acknowledges funding from the European Research Council (ERC) under the European Union's Horizon 2020 Research and Innovation Programme (grant agreement no. 801809). Jonny Rutqvist acknowledges funding by the Assistant Secretary for Fossil Energy, National Energy Technology Laboratory, National Risk Assessment Partnership of the U.S. Department of Energy to the Lawrence Berkeley National Laboratory under contract no. DEAC02-05CH11231. ; Peer reviewed

The earthquake of September 19, 2017 in Mexico caused catastrophic damage in the state of Morelos to more than 23 thousand structures in almost all municipalities. After an earthquake, emergency actions in the area are of great importance to support society, rescue trapped people as well as to assess the structural condition of the structures, and in this way, mitigate the negative effects. Unfortunately, society is not prepared to contain major disasters, and it can be very difficult to face a major emergency without the right conditions. The earthquake of September 19, with magnitude 7.1 and epicenter less than 75 km away, caused an emergency never expected in the state of Morelos, because of the damage it produced, which put Morelos' emergency system to the test. In particular, researchers from the National Institute of Electricity and Clean Energies (INEEL) initiated inspection actions in the buildings of their own institute, and subsequently placed themselves under the orders of the Civil Protection office of the State of Morelos to carry out post-seismic inspections of government buildings, schools and, in general, the homes of Morelos. The main task was to decide if the buildings were able to be inhabited again, if they should be evicted for a detailed review or if they should be demolished due to their high risk of collapse. The support was not only oriented to the post-seismic evaluation of the buildings, but was the beginning of working days with the State authorities, which will result in the improvement of the emergency plans and, above all, in the update of the design standards. ; El sismo del 19 de septiembre de 2017 en México causó daños catastróficos en el estado de Morelos que afectaron a más de 23 000 inmuebles en prácticamente todos losmunicipios del estado. Después de un sismo, resultan de gran importancia las acciones de emergencia existentes en la región para dar apoyo a la sociedad, tanto en el rescate de personas atrapadas como en la evaluación de la ondición estructural que presentan los ...

Evaluating the proportion in which waters from different origins are mixed in a given water sample is relevant for many hydrogeological problems, such as quantifying total recharge, assessing groundwater pollution risks, or managing water resources. Our work is motivated by urban hydrogeology, where waters with different chemical signature can be identified (losses from water supply and sewage networks, infiltration from surface runoff and other water bodies, lateral aquifers inflows, ⋯). The relative contribution of different sources to total recharge can be quantified by means of solute mass balances, but application is hindered by the large number of potential origins. Hence, the need to incorporate data from a large number of conservative species, the uncertainty in sources concentrations and measurement errors. We present a methodology to compute mixing ratios and end-members composition, which consists of (i) Identification of potential recharge sources, (ii) Selection of tracers, (iii) Characterization of the hydrochemical composition of potential recharge sources and mixed water samples, and (iv) Computation of mixing ratios and reevaluation of end-members. The analysis performed in a data set from samples of the Barcelona city aquifers suggests that the main contributors to total recharge are the water supply network losses (22%), the sewage network losses (30%), rainfall, concentrated in the non-urbanized areas (17%), from runoff infiltration (20%), and the Besòs River (11%). Regarding species, halogens (chloride, fluoride and bromide), sulfate, total nitrogen, and stable isotopes (18O, 2H, and 34S) behaved quite conservatively. Boron, residual alkalinity, EDTA and Zn did not. Yet, including these species in the computations did not affect significantly the proportion estimations. ; This work has been done in the framework of a project supported by Ajuntament de Barcelona (Barcelona City Council) and Clavegueram de Barcelona (CLABSA). Also, has been partially financed by the projects 2009 SGR 103 and 2009 SGR 1057 from the Catalan Government. ; Peer Reviewed

We measure groundwater flux and thermal parameters around a borehole performing a heat dissipation test by heating the armor of a single fiber-optic cable and interpreting the resulting heating curves with a new analytical method. The procedure is similar to thermal response tests, but benefitting from the high spatial and temporal resolution of distributed temperature sensing and lasting longer, so as to measure advective dissipation. Field installation relies on an innovative method in hydrogeology, which is based on the installation of the FO cable in the annular space of the well, close to the aquifer matrix. The proposed new analytical method, expands the traditional Moving Infinitesimal Line Source Model to account for the effects of the field set up and cable materials. In fact, we show that the resulting temperature build-up goes through four periods easy to identify using the log derivative of temperature (dT/d (ln(t))): Initial response, skin (cable insulation), conduction dominated and advection dominated. We test the proposed method in an unconsolidated shallow aquifer with controlled pumping. Results are of the same order of magnitude of independent estimates of groundwater velocity. ; This work was funded by the projects CGL2016-77122-C2−1−R / 2-R and PID2019-110212RB-C22 / C21 of the Spanish Government. We would like to thank SIMMAR (Serveis Integrals de Manteniment del Maresme) and the Consell Comarcal del Maresme in the construction of the research site. We would like to acknowledge Sensornet (UK) for their support and collaboration. We would also like to thank Dr. Javier Benitez Buelga for his collaboration in designing and setting up the fiber-optic field installation. The author Albert Folch is a Serra Húnter Fellow. ; Peer reviewed