Long-Term Dipole-Dipole Resistivity Monitoring at the Cerro Prieto Geothermal Field

Abstract

Dipole-dipole resistivity measurements for the combined purposed of reservoir delineation and reservoir monitoring were first made at Cerro Prieto in 1978 and have continued on approximately an annual basis since then. Two 20 km long dipole-dipole lines with permanently emplaced electrodes at 1 km spacings were established over the field area. Resistivity remeasurements have been made on one lien at 6 to 18 month intervals using a 25 KW generator capable of up to 80A output and a microprocessor controlled signal averaging receiver. This high power low noise system provided highly accurate measurements even at large transmitter receiver separations. Standard error calculations for collected data indicate errors less than 5% for all points.