Geothermal drilling techniques

Abstract

This report is a general description of three geothermal drilling methods which were selected by the author for consideration during the training programme. They are important for their potential applications in geothermal drilling in El Salvador. First, the directional drilling method is described including a study of all the implied characteristics and special equipment required. In addition, the question of where to drill a geothermal well using either a neglected well platform or an unused platform needs to be considered. Directional drilling means increased drilling costs but these costs can be offset by lowering the cost of platform preparation and time. This method also allows drilling in inaccessible mountainous areas where geothermal reservoirs are frequently found. Air drilling with its use of a percussive and rotative tool is the second method described in this report. This results in a high rate of penetration and consequently substantial savings in drilling operations. Cable tool drilling is the third and last method described in this report. Although it is an outdated method, the author considered its use important for efficient use of time during initial penetration of geothermal wells. In El Salvador, all drilling stages are made with big rigs, but it is possible to drill the first hole with a cable tool rig used for fresh water wells.