Proposed Methodology for Assessment and Ranking of Geothermal Systems

Abstract

Geothermal resources most suited for large-scale electricity generation are those with high temperature (commonly >250°C) reservoirs, yet small power and direct use schemes may be possible using low-moderate temperature (<150-220°C) resources. The nature of thermal springs in Thailand, India, Malaysia, Vietnam or elsewhere in Asia differ to active geothermal systems elsewhere, and any methodology for their assessment must be robust and consistently applied. We employ a two-stage approach that sets a minimum temperature to identify areas with potential, followed by a second-stage assessment (based on a numerical scoring) to evaluate a range of resource characteristics, that help identify and prioritise areas with potential for utilisation. Our Stage One Assessment identifies sites that discharge water (or steam) of 60oC. By setting a minimum discharge (surface) temperature, we endeavor no area with potential for power generation is overlooked. Sites that meet the Stage One Assessment Criteria are then evaluated using a Stage Two Assessment, incorporating indicators of resource temperature, permeability, fluid flow, geological structure, heat source, reservoir characteristics, extent and type of surface thermal activity, proximity to other thermal areas, insight from previous geoscientific surveys and the history of drilling in the area. Arbitrary ‘high’, ‘intermediate’ and ‘low’ scores are attributed to each Stage Two Criteria. No area is excessively “penalised” if it scores lowly in regard to one parameter, but displays other positive attributes. By utilising a scoring system, thermal areas that meet the Stage One Criteria can be ranked for development or prioritisation for detailed (potentially expensive) exploration (i.e., geophysical surveys, exploration drilling etc.), at reduced financial risk.