Resource Conceptual Models of Volcano-Hosted Geothermal Reservoirs for Exploration Well Targeting and Resource Capacity Assessment: Construction, Pitfalls and Challenges

摘要

Building geothermal resource conceptual models to support assessments of well targets and resource capacity is a widely recommended geothermal industry best practice, with potentially serious pitfalls if important data is collected without adequate consideration of its conceptual context and uncertainty. The process is illustrated by a detailed step-by-step example of the construction of an exploration conceptual model for a synthetic volcano-hosted geothermal reservoir using a representative data set including the geochemistry of hot springs and fumaroles, maps of surface geology and structure, and images of the low resistivity clay cap using magnetotelluric (MT) surveys. A range of conceptual models representative of both data and conceptual uncertainty supports well targeting and resource capacity risk assessments. Well targeting failures in recent geothermal exploration and development projects have highlighted pitfalls in the conceptual model approach and also its resilience in identifying remedies and focusing attention on unresolved challenges. For example, MT surveys typically avoid incised drainages and so may fail to detect extensive outcrop of propylitic alteration that implies a higher probability of encountering relict alteration that is relatively cool and low in permeability. As prospects that fit the exploration assessment methods outlined in this paper are drilled, the remaining prospects are a poorer fit to the paradigm. Whatever alternative data sets are gathered to reduce risk in the remaining prospects, it is likely that they will more effectively address well targeting and resource capacity risk using a conceptual model approach.