Geochemical Reconnaissance of Fluids from the Krafla and Nesjavellir Thermal Areas, Iceland: Baseline Studies in Support of the IDDP

Abstract

Reconnaissance studies of the fluid chemistries of the Krafla and Nesjavellir systems have been undertaken to provide some insights into the nature of fluid components in these systems, and the reservoir processes that may be affecting them. The preliminary work reported here is being used to steer a more extensive project incorporating IDDP well discharges. With this, we aim to build an interpretive framework for understanding the role of supercritical (IDDP) fluid contributions in the evolution of the fluid chemistries in these (and similar) systems.

High temperatures and production enthalpies characterise the deeper reservoir environments in both systems. Three end-member compositional components have been identified in both systems, including meteoric, geothermal, and mantle (i.e., magmatic fluid) components.

At Nesjavellir, the well discharges from NG-5 and NG-10 show the largest magmatic fraction whereas those from NJ-11 show the largest geothermal component fraction. At Krafla, the fluid evolution is somewhat more complex, with discharges from KJ-34 and KJ-19 showing the largest magmatic component. Both systems show evidence of extensive vapour loss which has depleted the fluids of its geothermal and meteoric signatures.