Source: Water Resources Research
Geothermal energy abounds in Iceland, the North Atlantic island nation with regular, high-profile volcanic eruptions. The island’s active magmatism and volcanism support six geothermal plants, which account for more than 25% of the country’s overall electricity needs. Geothermal energy heats nearly 85% of the homes on the island.
Krafla, in the northern part of the island, is one of Iceland’s active geothermal-producing regions. Krafla’s high-temperature geothermal system sits in a volcanic caldera and has produced energy for more than 40 years. However, despite this intensive energy production, a reservoir model of the Krafla geothermal system has not been published in peer-reviewed literature since the 1980s, leaving a data void and potentially untapped resources.
In a new study, Scott et al. present a new 3D natural state model of the Krafla geothermal system. To develop the model, the authors inserted data from the extensively drilled geothermal field into a Bayesian framework. Bayesian models digest uncertainty from the input parameters, quantify uncertainty in the results, and use Markov chain Monte Carlo sampling methods to generate statistics.
This model is one of the first to extend to the deep, supercritical roots near the heat source of an exploited geothermal system. The results revealed unexpected contrasts across the drilled area. In the western part of the production field, wells indicate a 0.5- to 1-kilometer-thick liquid reservoir with temperatures that hover around 210°C (410°F). The liquid reservoir sits atop a deeper, even hotter, boiling reservoir. Meanwhile, in the eastern part of the field, boiling conditions extend from the surface to the maximum depth of the wells, approximately 2 kilometers below the surface.
The model explains temperature differences across the field in terms of the variable permeability of the region’s volcanic rocks and input of heat from the deep magmatic heat source. The model suggests that the extent of the supercritical fluid zone overlying Krafla’s magmatic heat source has been underestimated. Therefore, it also indicates the presence of a significant untapped resource in the geothermal field.
The study showcases how advanced statistical modeling and modern data collection can illuminate difficult-to-access energy resources. In addition, the model is a dynamic entity that will only improve as more data become available. (Water Resources Research, https://doi.org/10.1029/2021WR031254, 2022)
—Aaron Sidder, Science Writer