Methods of Early Geothermal Energy Resource Assessment - A Modern Conceptual and Mathematical Model

Abstract

Early in a geothermal field development the owners and financiers want to know a number of MWe capacity of the plant that can be sustained by the field although very limited information about the field has been gathered. In the past 50 years 3 methods of early assessment have been developed, each based on different concepts, mathematics, and statistics. The “Volumetric method” was implemented more than 40 years ago, when no history or data from many fields and boreholes were available. It is basically a static energy calculation and it can provide an early estimate of MWe capacity, normally greater than the real one. The ”Monte Carlo” Simulation based method produces a wide range of possible solutions, and then a statistical probabilistic value can determine the final geothermal field estimate of MWe. The application to real cases (e.g. Iceland) proved that the resulting estimates are still above the true value, possibly because it is based on the same linear static formula of the volumetric method. We propose a novel method of early capacity estimate based on a more realistic exponential decay formulation, adjusted using the true statistical dynamic sampling from different real fields developed during the last 50 years, and statistical decay data from over 5,000 wells drilled. The first tests on real cases provide more realistic estimates of the MWe capacity compared to the traditional ones.