This themed issue of Geomechanics for Energy and the Environment ‘SEG-2015-Part II’, presents papers selected from extended abstracts submitted to the Symposium on Energy Geotechnics (SEG-2015) held in the Civil Engineering School of the Universitat Politècnica de Catalunya in Barcelona, Spain, between June 2nd and 4th, 2015. This symposium SEG-2015 was the first event organized by the Technical Committee TC308 of the International Society for Soil Mechanics and Geotechnical Engineering, which will have continuity in the next symposium SEG-2018 to be held in the École Polytechnique Fédérale de Lausanne (Lausanne, Switzerland). The first issue ‘SEG-2015-Part I’ appeared just before the 1st International Conference on Energy Geotechnics (ICEG-2016), which was held in Kiel (Germany) at the end of August 2016. The second volume ‘SEG-2015-Part II’ on December 2016 will thus close a first cycle of successful conferences and publications along this
initial stage of TC308.Peer ReviewedPostprint (author's final draft

Romero Morales, Enrique Edgar

Sánchez, Marcelo

Geomechanics for Energy and the Environment

English

UPCommons. Portal del coneixement obert de la UPC

JOURNAL: Geomechanics for Energy and the Environment DATE:  December 2016 TITLE:  Themed Issue on Selected Papers SEG2015 – Part II  GUEST EDITORS:   Enrique Romero1    Marcelo Sanchez2       Author 1 Enrique Romero Director of Research  Division of Geotechnical Engineering and Geosciences Department of Civil and Environmental Engineering. Universitat Politècnica de Catalunya c/ Jordi Girona, 1-3 Campus Nord UPC, Edificio D-2  08034 Barcelona, Spain  Tel:  (+34) 934016888  Fax: (+34) 934017251 Corresponding author: E-mail: Enrique.romero-morales@upc.edu   Author 2 Marcelo Sanchez Associate Professor Zachry Department of Civil Engineering. Texas A&M University College Station Texas 77843-3136, USA Telephone: (+1) 979 862 6604 Fax:  (+1) 979 862 7696       Introduction This themed issue of Geomechanics for Energy and the Environment ‘SEG-2015-Part II’, presents papers selected from extended abstracts submitted to the Symposium on Energy Geotechnics (SEG-2015) held in the Civil Engineering School of the Universitat Politècnica de Catalunya in Barcelona, Spain, between June 2nd and 4th, 2015. This symposium SEG-2015 was the first event organized by the Technical Committee TC308 of the International Society for Soil Mechanics and Geotechnical Engineering, which will have continuity in the next symposium SEG-2018 to be held in the École Polytechnique Fédérale de Lausanne (Lausanne, Switzerland). The first issue ‘SEG-2015-Part I’ appeared just before the 1st International Conference on Energy Geotechnics (ICEG-2016), which was held in Kiel (Germany) at the end of August 2016. The second volume ‘SEG-2015-Part II’ on December 2016 will thus close a first cycle of successful conferences and publications along this initial stage of TC308.  Contributions to this SEG-2015 issue This special issue consists of seven papers selected from the invited and technical presentations of SEG-2015 after a peer-review process. As with the first issue, the idea was to bring together a series of papers covering different topics and applications within the various ‘Task Force’ areas, in which sessions of SEG-2015 were organised and TC308 has channelled its activities. This way, the papers selected address the following topics: energy geo-storage and geo-structures (three papers); high-level radioactive waste disposal (three papers); and unconventional hydrocarbon (one paper).  The selected papers also cover a wide scope of multi-scale processes, ranging from large-scale reservoir geomechanics, tunnel geothermal plants and geothermal energy piles to lower scale phenomena dealing with thermal conductivity in sedimentary deep host argillaceous rocks, and clay-water interactions in clay-based engineered barriers during hydration. Different coupled phenomena are addressed in the papers, which highlight the need for a sound understanding of the multi-physics process involved and a coupled consideration of the thermo-hydro-mechanical behaviour of soils and rocks, not only from modelling point of view but also from experimental standpoint. Thermo-mechanical aspects are discussed during the hydration of clay-based engineered barriers, heating of deep argillaceous formations, and axial thermal strains and stresses on piles subjected to heating and cooling operations. Coupled thermo-hydraulic phenomena are used to explain pore water pressure increase and loss of shaft friction of geothermal piles placed in low-permeability clays, as well as on the effects of the hydrogeological conditions on the operation of tunnel geothermal plants. Finally, hydro-mechanical issues arise when describing fracture propagation during injection and on reservoir subsidence. Underground structures (tunnels) with a large surface in contact with the ground provide an excellent opportunity to integrate geothermal plants for renewable energy source. The German experience in two tunnel geothermal plants (Stuttgart Fasanenhof tunnel and Jenbach tunnel in the Tyrol) over several years of operation is presented in the paper by Buhmann et al.[1]. The authors describe the geothermal activation of the tunnel to geothermally exploit the lining through an absorber pipework system, in which the tunnel air temperature is a key factor for the heat flux from the tunnel. The authors focus on the energy extraction capacity and the effects that the geothermal activation has on the subsurface temperature. Shallow geothermal energy piles for heating and cooling of buildings are also an important topic in this issue, in which two contributions are included. The paper by Faizal et al. [2] deals with a full-scale experimental investigation to study the influence of different types of operations (intermittent and continuous for 24 hours) on energy extracted, on ground and pile temperatures, as well as on the effects of the thermal loads on the piles (axial thermal strains and stresses). The authors observed that the energy extracted from the ground was higher under lower operating hours. The thermal impact on the piles also induced lower average thermal stresses when using the intermittent operation. The paper by Fuentes et al. [3] studies the effects of non-isothermal conditions on low-permeability and saturated clays adjacent to geothermal piles. Numerical simulations, in which soil permeability and compressibility are key parameters, allow estimating the pore pressure increase in these soils during heating that reduces the shaft resistance of the piles. These effects are particularly important in soils that are used as heat sink during sustained periods. The numerical solution is applied to a real case that allows explaining the loss of shaft friction of a heated pile. Three papers in this volume address particular issues of deep geological disposal for the isolation of high-level radioactive waste. Not only the engineered barriers (made up of compacted swelling clays), but also the host argillaceous rock are subjected to coupled thermal, hydraulic and mechanical phenomena induced by the heat-emitting nature of the nuclear waste and the properties of the multi-barrier isolation system. In this particular context, the paper by Villar et al. [4] explores the hydration process of engineered barriers under high temperature field based on laboratory work using highly instrumented cylindrical cells. The aim of the tests is to mimic in the laboratory the conditions of different barrier materials used in a large-scale in situ test (HE-E performed at the Mont Terri Underground Laboratory, Switzerland). The authors use new types of sealing materials, namely high-density bentonite pellets and a binary mixture made up of silica sand and bentonite powder (65/35). The reported results are useful for the validation of thermo-hydro-mechanical models and as benchmark exercise. On the other hand, the paper by Jacinto et al. [5] deals with a much lower scale of the behaviour of engineered barriers focusing on clay-water interaction during hydration process of compacted bentonite to define water density variations inside small pores. Different laws for the water density are considered to describe the water retention properties. These laws, which depend on the hydration state of the expansive clay, take into account the amount of water in the interlayer space and the adsorbed one on the external surface of clay particles. Model predictions during hydration taking into account the variation of water density compared to simulations at constant water density show that major differences occur at long-term conditions (time for saturation increases substantially with variable water density). The contribution of Romero et al. [6] studies another important component of the multi-barrier concept for long-term isolation of high-level radioactive waste: the geological barrier. Particularly it focuses on determining the thermal conductivity of deep sedimentary clay formations using two different laboratory setups (direct thermal conductivity setup and cell for heating pulse tests). Careful sample pre-conditioning protocols to restore rock in situ conditions are followed before the heating tests. Heating pulse tests are interpreted with coupled numerical models, which are also used to back-analyse thermal parameters that are consistent with direct measurements. The article discusses the importance of the pre-conditioning protocols to restore sample saturation, particularly on retrieval of deep sedimentary clays that may undergo opening of fissures along bedding planes.  Oil and gas reservoir problems are also another challenge of energy geomechanics. Because of the large scale involved, the information about rock properties is generally very limited. In addition, the geomechanical properties are affected by the highly heterogeneous character of the formations. The paper by Pereira et al. [7] deals with the quantification of uncertainties in reservoir geomechanical problems, particularly with the use of non-probabilistic methods. Two application problems (estimation of the fracture pressure and subsidence) are selected to compare the results obtained by a deterministic study, a probabilistic analysis and a non-probabilistic study based on evidence theory. The authors conclude that the evidence theory is very convenient because the decision making process becomes easier in this case. Furthermore, the evidence theory provides more complete information than the probabilistic method and is very well suited for incorporating additional (new) evidences as they become available, reducing consequently the uncertainty of the results.   Acknowledgments We are indebted to the Civil Engineering School of the Universitat Politècnica de Catalunya for their support to organize the SEG-2015. Special thanks in this respect go to Prof. Sebastià Olivella, Dean of the School at the time, and to the Cátedra Universitat Politècnica de Catalunya - Endesa Red ‘Victoriano Muñoz Oms’.   References [1] Buhmann P, Moormann C, Westrich B, Pralle N, Friedemann W. Tunnel geothermics a German experience with renewable energy concepts in tunnel projects. Geomechanics for Energy and the Environment (2016), http://dx.doi.org/10.1016/j.gete.2016.10.006 [2] Faizal M, Bouazza A, Singh RM. An experimental investigation of the influence of intermittent and continuous operating modes on the thermal behaviour of a full scale geothermal energy pile. Geomechanics for Energy and the Environment (2016), http://dx.doi.org/10.1016/j.gete.2016.08.001 [3] Fuentes R, Pinyol N, Alonso EE. Effect of temperature induced excess porewater pressures on the shaft bearing capacity of geothermal piles. Geomechanics for Energy and the Environment (2016), http://dx.doi.org/10.1016/j.gete.2016.10.003 [4] Villar MV, Martín PL, Romero FJ, Iglesias RJ, Gutiérrez-Rodrigo V. Saturation of barrier materials under thermal gradient. Geomechanics for Energy and the Environment (2016), http://dx.doi.org/10.1016/j.gete.2016.05.004. [5] Jacinto AC, Ledesma A, Demagistri A. Effect of the clay–waterinteraction in the hydration of compacted bentonite used in engineered barriers. Geomechanics for Energy and the Environment (2016), http://dx.doi.org/10.1016/j.gete.2016.10.002 [6] Romero E, Sau N, Lima A, Van Baelen H, Sillen X, Li X. Studying the thermal conductivity of a deep Eocene clay formation: Direct measurements vs back-analysis results. Geomechanics for Energy and the Environment (2016), http://dx.doi.org/10.1016/j.gete.2016.10.005 [7] Pereira LC, Sánchez M, Guimarães LdN. Uncertainty quantification for reservoir geomechanics. Geomechanics for Energy and the Environment (2016), http://dx.doi.org/10.1016/j.gete.2016.11.001   

Themed issue on selected papers SEG2015: part II

Enrique Romero

Marcelo Sánchez

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Themed Issue on Selected Papers SEG2015 — Part II

This themed issue of Geomechanics for Energy and the Environment ‘SEG-2015-Part II’, presents papers selected from extended abstracts submitted to the Symposium on Energy Geotechnics (SEG-2015) held in the Civil Engineering School of the Universitat Politècnica de Catalunya in Barcelona, Spain, between June 2nd and 4th, 2015. This symposium SEG-2015 was the first event organized by the Technical Committee TC308 of the International Society for Soil Mechanics and Geotechnical Engineering, which will have continuity in the next symposium SEG-2018 to be held in the École Polytechnique Fédérale de Lausanne (Lausanne, Switzerland). The first issue ‘SEG-2015-Part I’ appeared just before the 1st International Conference on Energy Geotechnics (ICEG-2016), which was held in Kiel (Germany) at the end of August 2016. The second volume ‘SEG-2015-Part II’ on December 2016 will thus close a first cycle of successful conferences and publications along this

initial stage of TC308.Peer Reviewe

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UPCommons (Universitat Politècnica de Catalunya)

https://upcommons.upc.edu/bitstream/2117/102756/7/Introduction%20GETE%20Special%20Issue%20II%20Romero%20Sanchez.pdf

Themed issue on selected papers SEG2015: part II

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