1. Keilir Institute of Technology Kruszewski
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Figure 1.1 Measured temperatures (left) and pressures (right) with saturation conditions in Icelandic high-temperature
well (data provided by Sverrir Thorhallsson)
SLIMHOLE WELL DESIGN FOR GEOTHERMAL EXPLORATION
AND RESERVOIR ASSESSMENT
Michał Kruszewski
Keilir Institute of Technology, Reykjanesbær, Iceland and Faculty of Drilling, Oil and Gas at AGH
University of Science and Technology, Cracow, Poland
mehowkruszewski@gmail.com
ABSTRACT
Following paper describes slimhole casing programs for geothermal exploration with application of
a new Code of Practice from New Zealand (2015). The “worst possible case” was considered as the
basis of design for drilling in a high-temperature geothermal area, i.e. when temperature and pressure
follows the boiling point depth curve (BPD). The paper includes casing design for a 2000 m deep
vertical well with water level at 200 m as an example. Different methods of determining the minimum
casing setting depths are presented. The well design involves establishing loading criteria that the
casing has to withstand i.e.: burst, collapse and tension/compression. The wellhead
pressure/temperature was established by calculating an isenthalpic steam column up the well, using
X-steam, an Excel add-in. Based on the calculation of stresses and the casing material properties at
elevated temperatures the steel grade, casing diameter, weight (thickness) and casing connections are
selected. Two casing programs were considered of slightly different diameters, drilled by
conventional rotary drilling and wireline coring.
1. Introduction
Cost of drilling associated with geothermal exploration is affecting industry growth and development.
To meet growing requirements for inexpensive and environmentally-friendly ways of reservoir
assessment of new geothermal areas, slimhole drilling technology can be applied. Drilling for wells
with diameter less than 6 inches is set as the criteria for slimholes. They are less costly than normal
production-size holes, as the crew, rigs, cementing, drilling fluids, casing, tubing and locations are
smaller. This technology can be also applied in remote areas, where helicopter-portable rigs can be