Deep Slimhole Drilling for Geothermal Exploration

Abstract

In many high temperature geothermal fields, exploration proceeds directly from surface methods (geology, chemistry and geophysics) to standard diameter geothermal wells. This is particularly the case where well targets are readily and confidently defined. However, as exploration moves from the easily developed fields toward those that are more challenging, the uncertainties in siting initial wells become greater while at the same time drilling costs have risen. Over the past 15 years, technological advances and cost advantages have seen deep slimhole drilling become increasingly utilized for geothermal resource exploration and delineation. While shallow slimholes have been widely used for temperature gradient mapping to delineate deeper resources, this can produce misleading results if the wells do not penetrate into the permeable reservoir. It is now possible to drill inclined wells deeper, with smaller drilling equipment, and with improved well control to actually test the reservoir of many types of geothermal resource.