Alternative Boundary Concepts for Geothermal Fields

Abstract

The basic tool used to outline the subsurface extent of liquid dominated geothermal fields in the Volcanic Zone has been various forms of resistivity mapping. Boundary zones derived using this method have been shown to consistently outline the areas of hot geothermal resource down to the depths so far explored and these geophysical boundaries have become the commonly accepted "field boundaries". As a geothermal exploration programme proceeds, a better understanding of the sub-surface conditions unfolds, and boundaries derived using other scientific disciplines can be defined. Today, any geothermal development is likely to require reinjection of separated water and condensate. In order to properly assess the potential effects of a field development on the environment - subsurface and surface - alternative types of boundary need to be recognised. This paper compares some different boundary types, using resistivity, geology, geochemistry, permeability and temperature characteristics.