Wairakei Geothermal Field Boundary: Insights from Recent Geophysics and Reservoir Information

Abstract

Resistivity from conventional DC surveys has been historically regarded a useful indicator of the Wairakei field boundary. It is also accepted that the penetration of DC resistivity methods is limited to shallow ( less than 500 m) depths. In order to address limitations in the depth of penetration, we present an up-to-date review of geoscientific and reservoir data with emphasis on the delineation of the field boundary at depths greater than 500 m. Based on interpretation of well pressures (P) and temperatures (T), we classified selected wells into infield, peripheral and outfield. Field wide extrapolation of the PT boundaries is carried out with the aid of recently (post-2009) acquired geophysics, namely magnetotellurics and microseismicity. At depths greater than 3 km, the modern field boundary is mainly constrained by microseismicity. Three-dimensional complexities of the field boundaries are evidenced through our analysis.