An Approach to Geothermal Development

Abstract

After about twenty years of geothermal energy development in New Zealand, progress is still hampered by incomplete knowledge. In sane cases, this has led to unnecessary capital expenditure. Lack of accessibility of the medium and its complexity are major obstacles to achieving a better understanding, and the interpretation of field geophysical surveys is often tedious and may be open to ambiguity. There is no substitute for a properly logged drill-hole, with backup studies on the geology and geochemistry encountered, but exploratory drilling is expensive and often difficult to justify to an industry geared to "production psychology."

Most of the advances made in New Zealand have been achieved by compromise. Boreholes intended for production have been used as research holes during the drilling phase. Since production holes may be sited in quite dense clusters, a very detailed picture can be established within a geothermal field. Of course, the drawback to this approach is that few, if any, holes are available for study outside the field. This is an important gap in the geothermal information at the present time; it does not seem possible to determine precisely the volume of hot-water resource available without knowing the vertical temperature gradients at depth between the obviously active geothermal fields.