High Pressure Water Jet Drilling in Hot Dry Rocks

Abstract

The development of geothermal energy stored in magma or hot dry rocks lacking a hot water circulation system is being considered as one of the new means of supplying energy. To extract heat from such heat source, an artificial circulation system must be devised (Refs. 1 &2). Thus, it is necessary to develop methods for drilling, slotting and/or cutting these high temperature rocks in order to provide paths of water. High speed ~ater jet drilling and cutting have been thought to be favorable methods for such purpose, because unsteady internal tensile thermal stresses are induced near the rock surface by high cooling power of these impinging jets (Refs. 3 & 4) in addition to the enormous hydraulic erosive power. Some first step experimental studies were previously performed using hot imitation rocks and relatively low speed water jets by the authors (refs. 5 to 9). For the some data of the them a correlation equation was derived from the dimensional and multivariate analyses (Ref. 10).