| Title | Conceptual modelling of the Krafla geothermal area, NE-Iceland and lessons on constructing a workflow |
|---|---|
| Authors | Þorsteinsdóttir, U; Helgadóttir, H M; Hersir, G P; Einarsson, G E |
| Year | 2016 |
| Conference | European Geothermal Congress |
| Keywords | IMAGE, Workflow, Krafla, geothermal, conceptual model, Iceland, Pico Alto |
| Abstract | The Krafla high temperature geothermal area is located within the Krafla caldera in the Neovolcanic zone in NE-Iceland. The caldera was formed around 100.000 years ago. An extensive activity in the area has since filled it with volcanic material. Geothermal exploration in Krafla was initiated in 1969 and the first wells were drilled in 1974. The power plant was commissioned in 1978, currently producing 60 MWe. Conceptual modelling of the Krafla brownfield has gone through a few phases since geothermal research began (a brownfield is a geothermal field that has been subject to extensive exploration and drilling). The first model was presented in 1977, another two models were published in the eighties. These models are still valid today in many respects. The most recent revision of the conceptual model is from 2015. This extensive experience provides the basis within the IMAGE project (Integrated Methods for Advanced Geothermal Exploration) for a workflow of a 3D model representation and visualization which will be applied to the Pico Alto geothermal greenfield in Terceira island in the Azores (a greenfield is a geothermal field that has not been subject to extensive exploration and drilling). ISOR applies the Petrel 3D software platform to incorporate into the Krafla conceptual model data from both the exploration phase and from the development/production phase. This has resulted in various 3D models; a geological facies model, a temperature model based on well data, an alteration model and a resistivity model. The 3D petrophysical model will e.g. be updated with recent seismic velocity models which are partly based on IMAGE’s Vertical Seismic Profile experiment (VSP) done in mid-2014 to test if zones of magma, supercritical fluid, superheated steam and high permeability can be revealed. The first step of geothermal conceptual modelling is to incorporate data from the exploration phase. These data include surface data such as geological mapping (surface geology, faults and fractures, geothermal surface manifestations), aerial images and topography and geophysical data such as resistivity, results based on magnetic and gravity studies and location of micro-earthquakes. Data from the development phase such as well paths and eventually data from boreholes (cutting analysis, lithological logs, and pressure and temperature logs) are incorporated as well. These data include lithology (stratigraphy) from each well resulting in a geological facies model; alteration (alteration zones, appearance of temperature dependent alteration minerals) leading to an alteration model; aquifers in relation to the structural mapping, intrusions and lithological contacts; temperature logs which with time result in a formation temperature model and geophysical logs such as resistivity, neutron-neutron, gamma and sonic log, as well as televiewer data. A well-organized workflow leading to a conceptual model is based on the alternative models resulting from all the different geothermal disciplines. Its purpose is a better understanding of the properties and processes taking place in the reservoir with the aim of finding high temperature and high permeability for successful well siting. A conceptual model is subject to constant recalibration and to be updated as new and additional knowledge is acquired – there is no such thing as a final conceptual model. |