MODELLING OF CONDITIONS CLOSE TO GEOTHERMAL HEAT SOURCES Sæunn Halldórsdóttir (ÍSOR), Inga Berre (UiB), Eirik Keilegavlen (UiB) and Guðni Axelsson (ÍSOR) Photo: Auður Agla, ÍSOR
Heat transfer in geothermal systems Intimate contact between circulating fluids and hot boundary rock of the magma is maintained over the lifetime of the activity (Björnsson, S. and Stefánsson, 1987) Bjornsson S., Stefansson V. (1987) Heat and Mass Transport in Geothermal Reservoirs. In: Bear J., Corapcioglu M.Y. (eds) Advances in Transport Phenomena in Porous Media. NATO ASI Series (Series E: Applied Sciences), vol 128. Springer, Dordrecht
Convective downward migration (CDM) volcanic geothermal systems upflow heating zone Reservoir, T0 Cracked zone Björnsson (2005), modified from Bodvarsson (1983) Heat source Lister (1974) Lister, CRB(1974). On the penetration of water into hot rock.geophysical Journal International,39.3: 465-509.6 Bodvarsson, G(1983). Terrestrial energy currents and transfer in Iceland.Continental and Oceanic Rifts,8, 271-282 Björnsson, A: Development of thought on the nature of geothermal fields in Iceland from medieval times to the present. Proceedings World Geothermal Congress, 2005, Antalya Turkey, 24-29. apríl. Pp. 11.
Motivation: Drilling into supercritical conditions
Modelling migration of fractures into hot-rock Mathematical problem, previous mathematical and analytical modelling work Lister (1974, 1982) Axelsson (1985) Bodvarsson (1983) Lister, CRB (1974). On the penetration of water into hot rock. Geophysical Journal International,39.3: 465-509.6 Bodvarsson, G (1983). Terrestrial energy currents and transfer in Iceland. Continental and Oceanic Rifts,8, 271-282 Axelsson, G.: Hydrology and thermomechanics of liquid-dominated hydrothermal systems in Iceland. PhD- Thesis. Oregon State University, USA, (1985).
State of the Art Modelling of supercritical temperature and pressure conditions in geothermal systems Two possible areas of focus: Injection of supercritical fluids to mimic conditions measured in wells. Traditional production modelling approach Model the roots of geothermal systems, i.e. conditions close to geothermal heat sources. Natural state modelling approach, knowledge of geological setting is important Scott et al. (2016) observed that host rock permeability and composition, intrusion depth, intrusion geometry, and strain rate play important roles Scott, S., Driesner, T., and Weis, P.: The thermal structure and temporal evolution of high-enthalpy geothermal systems, Geothermics, 62, (2016), 33-47.
Insight from field cases: Krafla, NE-Iceland Axelsson et al. (2014) Axelsson, G,Egilson, T&Gylfadóttir, S(2014). Modelling of temperature conditions near the bottom of well IDDP-1 in Krafla, Northeast Iceland. Geothermics, 49, 49 57 Thorgilsson, G, Axelsson, G, Berthet, JC, Magnúsdóttir, L, Árnason, K, Gunnarsson, G&Júlíusson, E: Modelling the Deep Roots of Volcanic Geothermal Systems. Proceedings of the Fourty-Second Workshop on Geothermal Reservoir Engineering, Stanford University, California (2018). Scott, S., Driesner, T., and Weis, P.: Hydrology of a supercritical flow zone near a magmatic intrusion in the IDDP-1 well Insights from numerical modeling, Proceedings,World Geothermal Congress 2015, Melbourne, Australia, (2015b), 5 p. Thorgilsson et al. (2018)
Insight from field cases: Taupo Volcanic Zone, New Zealand The spatial distribution of the geothermal fields in the Taupo Volcanic Zone, New Zealand (Kissling & Weir, 2005) Main purpose, simulate correct heat flow per surface area and location of heat plumes (up-flows) This also means, simulate correct heat transfer from the geothermal heat sources Kissling, W. M.and Weir, G. J. (2005). The spatial distribution of the geothermal fields in the Taupo Volcanic Zone, New Zealand. Journal of Volcanology and Geothermal Research, 145(1-2), 136-150.
Phase change is important Rate of heat transfer in geothermal system is affected by CDM process (direct contact with hot-rock) Two-phase convection is important heat transfer mechanism in geothermal systems and phase change can enhance convection In Scott et al. (2017) models for saline hydrothermal systems: heat transfer is maximized by phase separation occurring via condensation for deep (> 4 km) systems whereas less efficient heat transfer occurs via boiling in shallower (< 2.5 km) systems Heat source? Scott, S., Driesner, T., and Weis, P.: Boiling and condensation of saline geothermal fluids above magmatic intrusions, Geophysical Research Letters, 44, (2017), doi:10.1002/2016gl071891
Modelling of flow in fractures and opening of fractures Berre et al. (2018) Is CDM a governing process for heat transfer in the deep roots of geothermal system? Mathematical modelling based on a discrete fracture-matrix conceptual model of the domain Present work assumes a functional relationship between permeability & temperature We will dig into this by modelling the processes that lead to the alterations of permeability Berre, I, Doster, F & Keilegavlen, E (2018). Flow in fractured porous media: A review of conceptual models and discretization approaches, Transport in Porous Media. https://doi.org/10.1007/s11242-018-1171-6
Thermo-mechanical modelling in PorePy Keilegavlen et al. (2017) PorePy is an open-source software framework, aimed at simulation of flow and transport in three-dimensional fractured reservoirs The software provides models for rock mechanics, poroelasticity and coupling with fracture deformation models Finite-volume discretization (FV) DFM Keilegavlen, E, Fumagalli, A, Berge,R,Stefansson, I & Berre, I (2017). An Open-Source Simulation Tool for Flow and Transport in Deformable Fractured RocksarXiv:1712.00460 Stefansson, I., Berre, I. & Keilegavlen, E. (2018): Finite-Volume Discretisations for Flow in Fractured Porous Media. Trans Porous Med 124: 439. https://doi.org/10.1007/s11242-018-1077-3