Drilling Techniques for Deep Wellbores

Abstract

Drilling costs stand for about 70 % of the total costs of a deep geothermal project. The drilling technique used in deep geothermal projects has been adopted for the most part from the oil and gas industry. The drilling technique used in geothermal projects, however, must satisfy higher requirements because of the combination of high temperatures, high volume fluxes and typically high concentrations of aggressive and corrosive solutes in the produced fluid. Borehole diameters are larger because of the high volume fluxes. In contrast to oil and gas wells, wellbores in the geothermal industry must provide evidence for an operation life of 30 years. Geothermal wells pump hot salty fluids directly along the casing to the surface. In contrast, oil wells produce hydrocarbons along a liner protecting the casing. The costs for a deep drillhole in the geothermal industry is higher by a factor of 2–5 compared to boreholes in the oil and gas industry