Revised hydrogeological model of the hydrothermal system Waiwera (New Zealand)

<p>The geothermal hot water reservoir underlying the coastal township of Waiwera, northern Auckland Region, New Zealand, has been commercially utilized since 1863. The reservoir is complex in nature, as it is controlled by several coupled processes, namely flow, heat transfer and species transport. At the base of the aquifer, geothermal water of around 50°C enters. Meanwhile, freshwater percolates from the west and saltwater penetrates from the sea in the east. Understanding of the system’s dynamics is vital, as decades of unregulated, excessive abstraction resulted in the loss of previously artesian conditions. To protect the reservoir and secure the livelihoods of businesses, a Water Management Plan by The Auckland Regional Council was declared in the 1980s [1]. In attempts to describe the complex dynamics of the reservoir system with the goal of supplementing sustainable decision-making, studies in the past decades have brought forth several predictive models [2]. These models ranged from being purely data driven statistical [3] to fully coupled process simulations [1].<br><br>Our objective was to improve upon previous numerical models by introducing an updated geological model, in which the findings of a recently undertaken field campaign were integrated [4]. A static 2D Model was firstly reconstructed and verified to earlier multivariate regression model results. Furthermore, the model was expanded spatially into the third dimension. In difference to previous models, the influence of basic geologic structures and the sea water level onto the geothermal system are accounted for. Notably, the orientation of dipped horizontal layers as well as major regional faults are implemented from updated field data [4]. Additionally, the model now includes the regional topography extracted from a digital elevation model and further combined with the coastal bathymetry. Parameters relating to the hydrogeological properties of the strata along with the thermophysical properties of water with respect to depth were applied. Lastly, the catchment area and water balance of the study region are considered.<br><br>The simulation results provide new insights on the geothermal reservoir’s natural state. Numerical simulations considering coupled fluid flow as well as heat and species transport have been carried out using the in-house TRANSport Simulation Environment [5], which has been previously verified against different density-driven flow benchmarks [1]. The revised geological model improves the agreement between observations and simulations in view of the timely and spatial development of water level, temperature and species concentrations, and thus enables more reliable predictions required for water management planning.<br><br>[1] Kühn M., Stöfen H. (2005):<br>      Hydrogeology Journal, 13, 606–626,<br>      https://doi.org/10.1007/s10040-004-0377-6<br><br>[2] Kühn M., Altmannsberger C. (2016):<br>      Energy Procedia, 97, 403-410,<br>      https://doi.org/10.1016/j.egypro.2016.10.034<br><br>[3] Kühn M., Schöne T. (2017):<br>      Energy Procedia, 125, 571-579,<br>      https://doi.org/10.1016/j.egypro.2017.08.196<br><br>[4] Präg M., Becker I., Hilgers C., Walter T.R., Kühn M. (2020):<br>      Advances in Geosciences, 54, 165-171,<br>      https://doi.org/10.5194/adgeo-54-165-2020<br><br>[5] Kempka T. (2020):<br>      Adv. Geosci., 54, 67–77,<br>      https://doi.org/10.5194/adgeo-54-67-2020</p>

Multi-level approach analysis of liquefaction susceptibility: an application to three municipalities of Ischia Island

<p>The Emilia-Romagna seismic sequence in 2012 has increased the interest among Italian researchers in predicting liquefaction under seismic shaking, and in the evaluation of damage induced to structures. A number of studies were carried out during the last decade to evaluate the liquefaction susceptibility of different areas of the Italian Peninsula. Some of these studies have been focused on the territorial analysis of Naples (Evangelista & Santucci de Magistris, 2011; Silvestri & d’Onofrio, 2014), which highlighted how saturated pyroclastic soils present along the coastal areas may be interested by liquefaction phenomenon. On such a basis, the present study aims at evaluating the liquefaction susceptibility throughout the area of three municipalities (Casamicciola, Lacco Ameno and Forio) of Ischia Island in the gulf of Naples (Italy), recently hit by a Ml 4 earthquake.  The coastal zones of these municipalities are characterised by the predominance of saturated pyroclastic granular deposits. The assessment was performed through a multi-level approach, i.e. by increasing level of complexity. First, the potentially liquefiable areas were delimited by combining in a Geographic Information System (GIS) data on the average seasonal depth of the water table (Piscopo et al. 2019) and on the lithological classification of the surface deposits (Seismic Microzonation, 2017). At some representative sites in these potentially liquefiable areas, simplified analyses were carried out using SPT-based semi-empirical methods (Idriss & Boulanger, 2014). The results of such analyses led to choose a specific site on which to perform non-linear ‘coupled’ dynamic analyses in time domain with the SCOSSA code (Tropeano et al. 2019). The results of the coupled analyses in terms of excess pore water pressure ratio (r<sub>u</sub>) then allowed the evaluation of the ‘Induced Damage Parameter’ (Chiaradonna et al. 2020), related to the free-field post-seismic volumetric consolidation settlement, which was classified as ‘moderate’ in this case. The procedure adopted may be a valid proposal for prompt evaluations of the liquefaction susceptibility, which allows to pass from a semi-qualitative assessment at a territorial scale to a quantitative assessment at the scale of a specific site.</p><p>References:</p><p>Boulanger R.W.,Idriss I.M. (2014). <em>CPT and SPT based liquefaction triggering procedures</em>. Report No. UCD/CGM-14/01, Center for Geotechnical Modeling, University of California, Davis.</p><p>Chiaradonna A.,Lirer S.,Flora A., 2020. <em>A liquefaction potential integral index based on pore pressure build-up</em>. Engineering Geology, 272, 1-13.</p><p>Evangelista L.,Santucci de Magistris F. (2011). <em>Upgrading the simplified assessment of the liquefaction susceptivity for the city of Naples, Italy</em>. Proc of the V International Conference on Earthquake Geotechnical Engineering, Santiago, 10–13 January 2011, Paper n. 8.10.</p><p>Piscopo V.,Lotti V.,Formica F.,Lana F.,Pianese L., 2019. <em>Groundwater flow in the Ischia volcanic island (Italy) and its implications for thermal water abstraction</em>. Hydrogeology Journal, 28, 1-23</p><p>Silvestri F.,d’Onofrio A. (2014). <em>Risposta sismica e stabilità dei centri abitati e infrastrutture</em>. Relazione generale I Sessione “Analisi e gestione del rischio sismico”. Atti del XXV Convegno Nazionale AGI: La Geotecnica nella difesa del territorio e delle infrastrutture dalle calamità naturali.</p><p>Tropeano G.,Chiaradonna A.,d’Onofrio A.,Silvestri F. (2019). <em>A numerical model for non-linear coupled analysis of the seismic response of liquefiable soils</em>. Computers and Geotechnics, 105(2019):211–227, doi.org/10.1016/j.compgeo.2018.09.008</p><p> </p><p> </p>

Reviewing our options: How can we address climate change impacts in hydrogeological studies?

<p>Arguably, the groundwater community has responded more slowly to the challenges posed by climate change than other fields of (hydrological) science. However, in recent years a strong increase in studies addressing climate change impacts on groundwater is observed, and recommendations on the methodology of such studies have been developed and discussed (e.g. Holman et al., Hydrogeology Journal, 2012). Following the common practice in other fields of climate change research, it was suggested that assessments of climate change impacts on groundwater should be based on multiple emission scenarios and a range of global and regional climate models. This scenario-based, top-down approach involves the propagation of multi-model ensembles through a model chain starting from emission scenarios to global and regional climate models to impact models such as hydrological and groundwater models. However, as the uncertainty increases at each step of the model chain, the uncertainty in the assessment of local climate change impacts and the resulting recommendations for adaptation options likely are very high and thus of little use in practice. A vulnerability-based, bottom-up approach starting from the identification and analysis of the factors that are relevant for coping with climate change in a given system, therefore, was proposed as a complementary approach (e.g. Wilby and Dessai, Weather, 2010). “Storylines” (Shephard et al., Climatic Change, 2018) that aim at representing uncertainty in physical aspects of climate change in an event-based rather than probabilistic way appear to be consistent with the latter concept. In this poster we relate these concepts of climate change research to methodological frameworks established in hydrogeological research (e.g. multi-model approaches). We present an overview of potential tools, such as trading-space-for-time, historical data analysis, sensitivity analysis, climate projections and controlled experiments, that can be used to study climate change impacts, and we discuss their role and applicability within more general methodological frameworks.</p>

Coupled Hydro-Mechanical Modeling of Fracture Normal Displacement and Fluid Pressures during a SIMFIP (step-rate injection method for fracture in-situ properties) Test

<p>Characterization of coupled hydro-mechanical (HM) processes in rock fractures is important for several key geosciences applications, such as rock slope stability, enhanced geothermal systems, and hydraulic fracturing. In-situ experimentation of these processes is challenging, and presently very few techniques exist for quantifying the parameters needed to calibrate hydromechanical models for fractured rocks at field scales. One recent field technology is the step-rate injection method for fracture in-situ properties (SIMFIP) developed by Guglielmi et al. (2014). The method measures simultaneously the time evolution of flow rate, pressure and three-dimensional deformation of the test interval at high resolution.</p><p>In June 2019 a set of SIMFIP experiments was carried out in Åre, Sweden, in the COSC-1 borehole. This is a 2.5 km deep borehole aimed primarily for scientific investigations and the fractures and intact rock sections in the borehole are well characterized. Based on the earlier characterization work, three sections were selected for SIMFIP testing: one intact rock section, one section containing a conductive fracture and one section containing a non-conductive fracture (Niemi et al., in prep.).</p><p>In this study, a coupled HM model is developed to represent the key coupled processes occurring during these SIMFIP tests. A fully-coupled vertex-centered finite volume scheme and a decoupled finite element model are implemented independently to simulate the elastic deformations and changes in pressure induced by the step-rate injection or flow back of given water volumes. Specifically, the two models are implemented in the commercial simulator COMSOL Multiphysics (sequentially coupled FEM), and the free-open source academic code DuMu<sup>X</sup> based on the models of Beck (2019). The models are used to match the pressure recorded by the high precision sensors in the test interval. A parametric study is carried out to mimic the fracture extension and step-down stages of the experiments and to investigate the influence of the key hydromechanical parameters (hydraulic aperture, permeability, storativity, and elastic moduli) on the observed data. The resulting coupled hydromechanical model will be further developed to study the three-dimensional deformation of the borehole section under the SIMFIP test.</p><p> </p><p>Beck M (2019) Conceptual approaches for the analysis of coupled hydraulic and geomechanical processes. Ph.D. Thesis, Stuttgart University</p><p>Guglielmi Y, Cappa F, Lançon H, Janowczyk JB, Rutqvist J, Tsang CF, and Wang JSY. (2014) ISRM Suggested Method for Step-Rate Injection Method for Fracture In-Situ Properties (SIMFIP): Using a 3-Components Borehole Deformation Sensor. Rock Mech Rock Eng 47:303–311. https://doi.org/10.1007/s00603-013-0517-1</p><p>Niemi, Auli, Yves Guglielmi, Patrick Dobson, Paul Cook, Chris Juhlin, Chin-Fu Tsang, Benoit Dessirier, Alexandru Tatomir, Henning Lorenz, Farzad Basirat, Bjarne Almqvist, Emil Lundberg and Jan-Erik Rosberg 'Coupled hydro-mechanical experiments on fractures in deep crystalline rock at COSC-1 – Field test procedures and first results’. Manuscript under preparation, to be submitted to Hydrogeology Journal.</p>

Unmanned arial system imaging and refined geologic modelling of the Waiwera geothermal Reservoir

<p>The utilization of geothermal reservoirs as alternative energy source is becoming increasingly important worldwide. Details of rock properties, structures, heat transfer and resulting interactions are the basis for the implementation of a sustainable reservoir management, but are often not well enough understood. The investigated warm water reservoir in Waiwera, New Zealand, has been known for many centuries. Triggered by overproduction in the third quarter of the 20th century, the reservoir pressure dropped significantly and in the 1970s the natural seeps on the beach dried up [1]. However, the shutdown of the main user's pumps (Waiwera Thermal Pools) in 2018 led to renewed temporary and location-specific artesian activity. The question now is whether the seeps on the beach will also reappear?</p><p>Hydrogeological models are the basis for a sustainable management of groundwater resources. The key point for the Waiwera reservoir is the amount of geothermal water which is permanently available. However, models are also used to describe the current hydraulic and thermal situation of the study area [2].</p><p>An expedition was carried out in 2019 to investigate the artesian activity of the reservoir, which has been observed again since 2018, and to build a new geological model. For the first time, thermal cameras carried by unmanned aerial systems (UAS) show the emergence of warm water at the beach and photogrammetric analyses carried out allow structural and lithological mapping on exposed cliffs where localized thermal anomalies were identified for the first time. The Waitemata formation found there is considered as analogue of the reservoir rock and thus serves for an improved understanding of the subsurface reservoir properties. The analyses show individual water and heat conducting lithologies and thus provide details about geological units that also constitute the geothermal reservoir at depth.</p><p>Based on the field exploration and the associated structural interpretations, a geological and thermal 3D model is now available for the first time, which will be employed to improve calibration of the hydraulic conditions of the warm water reservoir. Further, the model will be applied in the context of a sustainable reservoir management to clarify the question about the natural seeps on the beach. The reappearance of artesian activity in the Waiwera area due to significant adaptation of production rates is unique but the improved understanding of the interaction between rock properties, existing structures and heat transfer will also enable other reservoirs to be better understood.</p><p>[1] Kühn M., Stöfen H. (2005) A reactive flow model of the geothermal reservoir Waiwera, New Zealand. Hydrogeology Journal 13, 606-626</p><p>[2] Kühn M., Altmannsberger C., Hens C. (2016) Waiwera’s warm water reservoir – What is the significance of models? Grundwasser 21, 107-117</p>

Analysis of flow and pressure data for the estimation of fracture generation and propagation – first model results from coupled hydromechanical experiments in COSC-1 borehole in deep crystalline rock, Åre, Sweden

<p>Characterization of the coupled hydro-mechanical properties of rock fractures has become an increasingly important field of geosciences research, relevant for a number of key applications. Examples include analysis of enhanced geothermal systems, hydraulic fracturing operations, CO<sub>2</sub> geological storage, nuclear waste disposal and mining operations. A newly developed technology that allows conducting advanced experimentation of the coupled HM processes in the field is the step-rate injection method for fracture in-situ properties (SIMFIP) by Guglielmi et al. (2014). The SIMFIP method is unique in that it measures simultaneously the time evolution of flow rate, pressure and 3D deformation of a packed off borehole interval.  </p><p>During June 2019 a field campaign was carried out in Åre, Sweden, where the SIMFIP was applied in the COSC-1 scientific borehole to estimate the fracturing and fracture propagation behavior during hydraulic stimulation in some previously well-characterized rock sections. Three intervals were investigated: an unfractured section (intact rock) at 485.2 m depth, a non-conductive steeply dipping fracture at 515.1 m depth, and a section with a gently dipping hydraulically conductive fracture at 504.5 m depth (Niemi et al., in prep.). </p><p>As a first step for analyzing the results, this work aims to develop a simple hydrologic model for the interpretation of the collected pressure and flow data during different stages of the experiments. Modeling has been used to estimate the key parameters of the induced and propagated fractures such as the length, aperture and geometry, based on the pressure response during the water injection and abstraction steps. A numerical model based on COMSOL Multiphysics combining the fluid flow within the fracture and rock domains was developed and the permeability of fractures was defined by the well-known cubic law function of the local fracture aperture. The initial low injection-pressure data for the test interval without any fracture were used to find the parameters of the packed off borehole interval. Consequently, these parameters were used in the analysis of the case with a conducting fracture, as well as the case with a non-conducting fracture. Models in agreement with the observed pressures and injection flow rates could be defined for all the three cases, allowing parameters to be estimated for the length and aperture of the induced fractures in each case.</p><p> </p><p>Guglielmi Y, Cappa F, Lançon H, Janowczyk JB, Rutqvist J, Tsang CF and Wang JSY. (2014) ISRM Suggested Method for Step-Rate Injection Method for Fracture In-Situ Properties (SIMFIP): Using a 3-Components Borehole Deformation Sensor. Rock Mech Rock Eng 47:303–311. https://doi.org/10.1007/s00603-013-0517-1</p><p>Niemi, Auli, Yves Guglielmi, Patrick Dobson, Paul Cook, Chris Juhlin, Chin-Fu Tsang, Benoit Dessirier, Alexandru Tatomir, Henning Lorenz, Farzad Basirat, Bjarne Almqvist, Emil Lundberg and Jan-Erik Rosberg 'Coupled hydro-mechanical experiments on fractures in deep crystalline rock at COSC-1 – Field test procedures and first results’. Manuscript under preparation, to be submitted to Hydrogeology Journal.</p><p> </p><p> </p>