The Iceland Deep Drilling Project (IDDP) is a program of geothermal exploration and technology development that aims to produce fluids for electric power generation from deep wells which tap reservoirs at supercritical conditions. This will require drilling to a depth of about 5 km in order to reach hydrothermal fluids at temperatures ranging from 450°C to ~600°C and at pressure of 23-26 MPa. This quest poses new challenges for drilling technology, well test equipment, and fluid production facilities, while at the same time offering the possibility of exploring the deeper parts of active geothermal systems.
Iceland GeoSurvey (ÍSOR) has been one of the main consultants from the beginning of the project to this day.
A geothermal production well, RN-17, was deepened to 3.1 km in the year 2005. The rocks penetrated consisted of tholeiites, hyaloclastites, marine sediments, pillow basalts, and relatively coarse-grained diabase dikes. The well became blocked during a flow test. Attempts to recondition the well failed and the well had to be abandoned.
Krafla - IDDP-1
The first project well, IDDP-1, was drilled into the Krafla Central Volcano, Northeast Iceland. This well is located between Leirhnjúkur and the Víti crater in the central part of the active geothermal area,. The objective was to drill a well that would be 8½” in diameter in the production section down to a depth of as much as 4,500 m. Drilling commenced in June of 2008 and was continued at intervals until the well was completed in the beginning of July 2009.
Three drill rigs were employed for the task at different times, depending on availability and suitability.
The drilling of IDDP-1 proved to be a trying task. The target depth of 4,500 m was never reached, since magma was encountered at approximately 2,100 m, precluding further progress. A magma pocket was breached a number of times and on each occasion magma flowed into the well and exerted a lift on the drill string. The presence of the magma was confirmed when fragments of freshly quenched glass were brought to the surface by the circulation fluid.
Analyses of the quenched glass revealed that it was rhyolitic in composition. The evolved composition of the magma was somewhat intriguing, since the most recent eruption in Krafla extruded basaltic magma exclusively. Outcrops of rhyolitic rocks are found in Krafla. More importantly, intrusives of similar composition are found at various depths in the Krafla well field, reflecting the presence of shallow intrusions of such magma in this area. Research is under way to define the size and age of the present intrusion, in order to place it in the context of recent volcanic activity in Krafla, such as the Krafla Fires of 1975-84.
At this stage further progress was deemed impossible, so drilling was abandoned and the well completed. Feed zones were located close to the intrusion, so a 9 5/8” production casing was installed from the top of the well and almost down to the bottom. The casing was perforated between 1958 and 2080 m depth to permit future testing of the permeable zones in the deepest part of the well. The well was initially kept cold by injection of water, but on August 11, 2009 the recovery process commenced. During the fall and winter the recovery was monitored by regular temperature and pressure logs. It is evident that the well is too shallow to produce the targeted supercritical fluids, since this would require temperatures above 374°C and pressures in excess of 221 bar. Temperature and pressure logs so far have indicated that the reservoir fluid may be superheated in the immediate vicinity of the magma, and fluid temperatures are expected eventually to exceed 350°C at 150 bar. Flow tests will be carried out in 2010 to determine the yield of the feed zones and the composition of the fluids. Wells previously drilled to similar depths in the vicinity of IDDP-1 have proven powerful, but only for a short period of time.
During 2011-2015 the Reykjavik Energy (OR) and HS Orka hf (HS) intend to drill wells IDDP-2 at Hengill, and IDDP-3 at Reykjanes, at their own cost, down to approximately 4 km depth and cement in the production casings. Already, OR has purchased all the casings to production depths and a 2500 class master valve. Both wells will be made available for deepening into the supercritical zone by the IDDP, with possible participation by the scientific community.