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Drilling cost effectiveness and feasibility of high-temperature drilling - Reykjavik, Iceland, Workshop4
Drilling cost effectiveness and feasibility of high-temperature drilling - Reykjavik, Iceland, Workshop4
1-5 July 2007 ISOR
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Challenges faced in drilling high-temperature geothermal wells in Iceland
Now, in the year 2007, ten high-temperature 
geothermal areas in Iceland have been explored by 
deep drilling and the generation is 420 MWe and 450 
MWt are at six sites. The drilling effort has accelerated 
in the last few years as the geothermal industry has 
found a new market in selling electricity to large 
aluminium smelters. Previously the local market for 
district heating, electricity and steam to industry was 
the driving force.
Drilling into high-temperature geothermal reservoirs in 
Iceland started in 1940. Some 200 HT wells have been 
drilled which fit the definition of exceeding 200°C at 
1000 m depth. Intensive drilling started half a century 
ago and now four drilling rigs are active drilling such 
wells to depths of 2000-3000 m, half of them 
directional. These wells are of two basic designs, either 
having 9-5/8“ or 13-3/8“ production casing. There are a 
total of four overlapping casing strings, each one 
cemented in place, and the open hole either has a 
slotted liner or is „barefoot“. The depth of each casing 
string overlaps roughly about 1/3 of the intended depth 
for the interval being drilled for safety. Most wells are 
very productive, capable of yielding 5-15 MWe of 
electricity, but the best ones 20 MWe. The latest power 
plants, at Hellisheiði 90 MWe and at Reykjanes 100 
MWe, require only 6 and 10 production wells 
respectively. All or part of the wastewater is reinjected 
into wells at all sites, each one capable of accepting up 
to 250 l/s.
Initially, there was not much knowledge available on HT 
drilling initially, but over the years the technology has 
improved and lessons have been learned. The 
presentation will focus on the successes as well as the 
most serious difficulties that relate specifically to the 
geothermal environment such as: blow-outs inside the 
well or outside, casing damages, wellhead failures, 
cementing, material selection, coring. Case histories are 
presented. The successes in geothermal drilling have to 
do with much faster drilling and good well outputs. The 
time to drill a well has been reduced by the use of 
modern drilling rigs and equipment, mud motors and 
aerated drilling fluids and less time is spent on 
cementing loss zones. The structure of the drilling 
contracts, standardization of well design and 
professionalism of the drilling crews are important 
factors in reducing the time to drill a well. A drilling 
contract was awarded with 50 wells, based on 
international tendering. Geothermal utilization in 
Iceland has thus become an industry where 
reproducabel results are obtained and risks have been 
reduced. It now takes some 35 days to drill down to 
2500 m, including the time for rig transport.
The HT wells typically encounter temperatures well 
above 300°C without drilling problems, even with mud 
motors and MWD equipment, as the well temperature 
stays below 100°C due to mud/water circulation. There 
is rapid heating-up once he circulation stops but there 
is usually a time-window within which logging tools can 
be run. As the rigs are reaching ever greater depths 
the temperature can be expected to increase and now 
the Iceland Deep Drilling Project (IDDP) will target 
zones where supercritical temperatures are to be 
expected (>374°C for fresh water, higher for saline). 
Drilling in temperatures of 400-500°C poses a new 
Id: 32
Place: ISOR
Grensasvegur 9
Room: Vidgelmir
Starting date:
03-Jul-2007   09:00
Duration: 20'
Primary Authors: Mr. THORHALLSSON, Sverrir
Presenters: Mr. THORHALLSSON, Sverrir
Material: slides Slides

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