| Title | 3D Conceptual Model and Numerical Model HvÃthólar Sub-area at Krafla Geothermal Field, Iceland |
|---|---|
| Authors | Nataly CASTILLO RUIZ, Juliet Ann NEWSON, Egill JÚLÃUSSON, Anette Kærgaard MORTENSEN |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | Krafla, HvÃthólar, 3D conceptual model, Reservoir |
| Abstract | This paper reviews the 3D conceptual model for the HvÃthólar sub-area in the southern zone of the Krafla geothermal field. HvÃthólar is one of 6 sub-areas in south Krafla, located at the intersection of the boundary of Krafla caldera and the NNE-SSW striking fissure swarms of the North Volcanic Zone. HvÃthólar is the only southern sub-area connected to the Krafla power station and has exhibited a considerable production decline throughout 1990–2013. According to a lumped simulation, HvÃtholar reservoir follows a two-tank open system with a volume of 6.00004 km3. The enthalpy of HvÃthólar wells is approximately 1200 kJ/kg; chemically it presents a low concentration of Cl- and high CO2. To date, most studies support the hypothesis that HvÃthólar characteristics and behaviour are due to the lack of a heat recharge (cooling intrusion) and that the sub-area is in a phase of waning. An improved understanding of heat source location and permeability variations will provide the basis of future utilisation decisions. This study presents two alternative conceptual models for HvÃthólar to determine the extent of utilisation of the asset. The model developed in this study extends along Vestursvæði, HvÃthólar, and Sandabotnaskarð sub-areas with a combined area of 30km2. An update of the geological model was carried out based on data from shallow and deep wells along the southern part of Krafla geothermal field. Data from geothermal surface exploration was integrated with the geological data in Leapfrog Geothermal software to facilitate visualisation as well as a more realistic representation of the geological model in the TOUGH2 permeability structure grid. The two discussed conceptual models locate HvÃthólar sub-are inside (M1) and outside (M2) the Krafla caldera. The study focusses on the location of heat source for this sub-area, and the permeability structure at the south intersection of the caldera boundary and fissure swarm. Each of the conceptual models was validated with TOUGH2 simulations under the premise that a better natural state match will be obtained with the most reasonable permeability structure. |