The IDDP Success Story - Highlights
G.O. FRIÐLEIFSSON, B. PÁLSSON, B. STEFÁNSSON, A. ALBERTSSON, Þ. GÍSLASON, E. GUNNLAUGSSON, H.H. THORSTEINSSON, J. KETILSSON, S. SAETHER. C. SÖRLIE, W.A. ELDERS, R.A. ZIERENBERG
This paper highlights the main achievements attained by the Iceland Deep Drilling Project (IDDP), which is aimed at investigating the supercritical geothermal resources in Iceland. In 2008-2009 the well IDDP-1 in the Krafla geothermal field in NE Iceland, was planned to be drilled as a production well from the surface down to about 4.5 km depth. After severe drilling difficulties and getting stuck twice, which required side tracking, drilling had to be terminated at only 2,104 m depth, when it became clear that we had drilled into ~900°C molten rhyolite (magma). Despite this unexpected situation the IDDP consortium decided to attempt to flow test the well. A sacrificial casing was inserted and cemented towards the bottom of the well and a perforated liner ~100 m long closest to the magma. A successful flow test was then conducted until 2012 during which the hostile fluid chemistry was successfully dealt with. The world’s first Magma-EGS system had been created. During the flow test the IDDP-1 was the world’s hottest production well producing 452°C superheated steam at 142 bars. Its power production potential for electrical generation reached up to 36 MWe for untreated steam. However, to enable its utilization chemical cleaning of the steam was necessary and would have resulted in lower power output. The successful mitigation method used involved a simple wet scrubbing of the steam, cleaning out all silica, chlorine and sulfur. The operator at Krafla was just about to scale up the pilot test to use the steam for the installed steam turbines when failure of several surface valves called for rapid cooling of the well resulting in severe casing failures. After close inspection attempts to repaired it had to be abandoned and the well had to be plugged up by cement. Nevertheless – the successful experiment had opened a window for enhanced power production at Krafla by creating a Magma Enhanced Geothermal System (MEGS). When considering the size of the huge magma chamber situated at shallow depth in Krafla power production could probably be multiplied by an order of magnitude from the currently installed capacity of 60 MWe. Before that happens, however, several engineering challenges need to be dealt with related to casing integrity, cementing issues and the quality of surface valves and other surface installations. The second IDDP well, IDDP-2 was drilled in 2016-2017 into the Reykjanes saline geothermal system in SW Iceland. An existing 2.5 km deep production well, RN-15, was deepened and cased to almost 3 km depth, and then drilled to 4,650 m slant depth, corresponding to about 4.5 km vertical depth from surface. Supercritical conditions (426°C at 340 bars) were measured during drilling at ~4,550 m depth. The well was deepened by additional 100 m, a liner inserted, and a 6” pilot hole and 3 successive drill cores retrieved from the very bottom of the well. Coring was attempted 13 times below 3 km depth, altogether returning some 27 m of drill cores. As the well was drilled with total circulation losses most of the time these core samples comprise almost the only rock samples from the well below 2.5 km depth. Petrological studies, on mineral assemblages, chemistry and fluid inclusions from the drill cores, show absolutely a unique data set from a sheeted dike complex currently at temperatures up to 600°C near the bottom of the well. The active geological settings at Reykjanes is an analogue of the root zones of the world’s oceanic black smokers and drilling into such rocks at such extreme temperatures is unprecedented. A major achievement of the IDDP-2 well was to demonstrate that it is possible to drill into a supercritical geothermal reservoir, while there are shallower feed points that produce subcritical fluids. Whether the mixture of the saline fluid from different depths will be capable of generating electric power remains to be seen. Nevertheless, the major success of the IDDP-2 well is the finding of primary and/or enhanced deep permeability in very hot rocks. The implication of this finding needs to be evaluated in the wider context of worldwide supercritical geothermal systems. Firstly, it appears that the exploitable volume of the geothermal reservoir needs to be expanded about 1 km downwards, from about 3 km towards ~4 km depth. Current reservoir models have fixed the bottom at about 3 km depth, which need to be modified. Secondly, multiple feed zones were detected during the entire drilling to the bottom of the well. Part of the circulation losses may relate to induced fracturing by thermal and/or hydraulic cracking from the several km long cold-water column during drilling. Nevertheless, it is clear from the drill core samples that open fractures, partly mineralized, also exist at great depths and apparently contain chemically hostile brine fluid, based on fluid inclusion data. It is quite clear also that huge volumes of water can be injected into the very hot rocks immediately beneath the conventional geothermal reservoir. Therefore, a deep superhot EGS system can be created. This would both enhance and extend the lifetime of the harvestable geothermal system and to demonstrate this will surely be a part of the IDDP success story. The data already gathered from the DEEPEGS Demonstration Well – IDDP-2 - is of paramount importance for future economics of high temperature geothermal systems comparable to Reykjanes. The IDDP-2 well has been heating up since September 2018 after almost 1.5 years of continuous cold-water injection, including the lost fluid circulation during drilling. This fluid loss amounts up to 1.5-2.0 million tons of fresh water. A flow test is expected to begin in September 2019 and data from the flow test should be available to report at the WGC-2020. The fluids produced will be both contaminated by fresh water at the beginning, and a mixture from several feed zones from different depths with increasing temperatures towards the bottom. Well IDDP-3 is planned to be drilled to 4-5 km depth at Hellisheidi within the Hengill volcano sometime after 2020.
|        Topic: Advanced Technology (Magma, Geopressure, etc.)||Paper Number: 37000|