| Abstract |
The Iceland Deep Drilling Project (IDDP) is exploring the technical and economic feasibility of producing supercritical geothermal resources. In 2016 the IDDP-2 well was drilled in the Reykjanes saline geothermal system in southwestern Iceland, on the landward extension of the Mid -Atlantic ridge, where we can study an analogue of the root zone of a black smoker. In 2009, Phase 1 of the IDDP was unsuccessful in reaching supercritical conditions in the Krafla volcanic caldera in northeastern Iceland when the IDDP-1 well unexpectedly encountered a rhyolitic magma of 900°C at a depth of only 2.1 km. The wellhead temperature was 453°C with sufficient enthalpy and flow to generate ~35 MWe. In August 2016, Phase 2 of the IDDP-2 began by deepening an existing production well of 2.5 km depth to a total depth of 4659m. Below 3.3 km depth total losses of circulation occurred that could not be cured by lost circulation materials of by multiple attempts at cementing. Consequently, the drilling continued 'blind' to full depth, with no return of drill cuttings. We made 13 attempts to take drill cores below 3 km deep, half of which recovered some cores. These cores are basalts and dolerites with alteration that ranges from green-schist facies to hornblende hornfels (lower amphibolite) facies, which suggests temperatures of metamorphism >450°C. Following an initial report on IDDP-2 drilling, scheduled for mid-2017, IDDP's scientific team and collaborators will conduct detailed petrological, petrophysical and geochemical analyzes of cores and results will be reported in a special issue of a major scientific journal. When drilling was completed, early in January 2017, we measured temperature, pressure and injectivity after only 6 days of heating. Supercritical conditions were measured at the bottom of the well of 427°C at 340 bar pressure. These logs showed the main permeable zones at depths of 3360m, 4200m, 4370m and 4550m. Estimates suggest that ~30% of 40 l/s injected into the well entered the three deeper feed zones. We will try to improve this permeability by continuing massive stimulation by injecting cold water with the objective of demonstrating the feasibility of enhanced geothermal systems (EGS) at high temperatures. While it is too early to speculate on the energy potential of this well and its economics, the ID DP-2 is a milestone in the development of geothermal resources and the study of hydrothermal systems. It seems to be the first well that successfully penetrated supercritical conditions, with potentially very high power output, and in which the contact metamorphism in the action of lower amphibolite facies can be observed. The drilling of the IDDP-2 was funded by the field operator HS Orka, by the industrial consortium of IDDP, and by the oil company Statoil. The International Continental Drilling Program and the IDDP scientific program funded the core drilling. |