Reconnaissance and Follow-Up Resistivity Surveying of New Zealand Geothermal Fields

Abstract

Geophysics Division's reconnaissance resistivity mapping programme which began in 1963 is planned to map all of the Central Volcanic Region (CVR) of New Zealand with fixed-spacing (M/2 = 500 m or 1000 m) Schlumberger electrode arrays. With about half the CVR already covered, many geothermal fields have been identified, including some with only minor surface thermal manifestations. Since the planned areal coverage is only about one field station per square kilometre and, in some places, problems have been experienced because of either questionable data or data gaps over inaccessible regions, the reconnaissance maps indicate only the approximate outlines of the geothermal fields. More detailed resistivity measurements have been done over many of the New Zealand fields being appraised for development to delineate the geothermal reservoirs more precisely. Several resistivity measuring techniques have been applied, with the multiple-source bipole-dipole method being most commonly used. For each field, a simplified interpretation of the resistivity data is given in the form of a lateral resistivity boundary zone which is inferred to represent the edge of the hot water reservoir.