Target verified during directional drilling program in geothermal system with emphasis on the Krafla high temperature area

Research at the Krafla geothermal area in NE Iceland began in 1969 and is still ongoing. Geologists, geochemists, geophysicists and engineers have been a main part of the geothermal research programs. Surface exploration survey and mapping started early in the 1970’s, in accordance with a newly established exploration program for high temperature areas in Iceland. It continued with exploration drilling in 1974 followed by production drilling.
Geothermal drilling in high temperature areas in Iceland has a long history, performed by domestic expertise, labor and drilling companies. The last decade directional drilling has been adopted in four of every five wells drilled in high temperature drilling projects in Iceland. Generally exploration drilling starts with vertical wells to investigate the main physical parameters, like temperature, pressure, permeability and quality of the geothermal fluid. The next step is localizing permeable zones for future steam production by utilizing directional drilling. Fracture and dike complexes are common targets inside the measured resistivity anomaly that commonly outlines the extent of geothermal system. The wells are measured with a north-seeking gyroscopic logging tool on a regular basis during drilling in order to monitor the development of inclination and direction, azimuth. Thereby it is known where the drill-bit is almost all time with good certainty. Circulation losses and pressure drops are specific evidence of increasing permeability particularly if it coincides with changes in the strata. At that time that circulation losses or pressure drops occur, it often becomes the moment to reevaluate the premises of the drilling target. In addition temperature logs during drilling establish valuable information like localizing exactly feed or high permeability zones. Therefore it is recommended to run a temperature log if it is necessary to stop drilling, i.e. change the bit or change the BHA.