| Abstract |
The exploration and development of low-enthalpy geothermal resources is now actively pursued in the Western Canada Sedimentary Basin, with at least five small commercial projects underway. Despite strong interest in development of these resources, none of the projects is close to commercial power production, and large-scale commercial investment has not yet materialized. In this paper, we identify critical problems that presently restrain development and identify research strategies for addressing those issues. Foremost among these problems are the lack of rigorous approaches to assessing risk and commercial value and the lack of risk mitigation strategies. Rigorous consideration of value in basin-hosted geothermal resources is underpinned by geoscience and engineering. Commercial value is related to temperature and volume of hot water (or rock), flow rates, and concentrations of dissolved minerals, all which have been shown to vary spatially within basin-hosted geothermal fields. Spatial variability in these properties can be predicted through geophysical, petrophysical and geochemical models and characterized through geostatistical approaches. Dynamic models grounded in hydrologic and geochemical principles show that temporal variation can also be significant. Risk associated with predictions of resource size is related to sparse subsurface datasets and can be assessed and characterized with geoscience principles. Risk also results from feedback between production and reservoir systems and can include modifications to the reservoir or production system during production. For example, in carbonate-hosted geothermal fields, injection of cool spent water can dissolve reservoir rock, with possible consequences of early cold plume breakthrough from injection to production wells. Damage to reservoir rock can occur during injection operations and damage to production systems can occur through scaling. An additional class of risk is associated with real or perceived damage to the ground surface or stakeholder populations. Risk mitigation primarily involves two types of assessment. First, it requires consideration of sources of uncertainty in valuation of the resource and identification of dataset that would reduce that uncertainty. For example, if there are gaps in the characterization of subsurface temperatures or flow rates, wells can be drilled to collect that data. Second, surveillance tools can provide real-time monitoring of reservoir behavior to identify developing problems and modify production systems before the problems impact resource values. The oil and gas industry has for at least 30 years addressed problems in valuation of resources and assessment of risk through petroleum system analysis, developing approaches that are fundamentally grounded in geoscience. While a petroleum systems analysis may not directly translate to basin-hosted geothermal resources, many aspects of the basic framework can apply. The Tu Deh-Kah geothermal resource in northeastern British Columbia is hosted in Devonian Slave Point carbonates in a now depleted gas field and is currently being developed by the Fort Nelson First Nation (FNFN). Research groups at the University of Alberta and the University of British Columbia are now collaborating with the FNFN in studies to develop a “geothermal systems†approach for valuation and risk analysis. Results to date highlight several issues related to valuation and risk: (1) variability in water temperature at a field scale; (2) uncertainty in the extent, location and orientation of fracture systems that could affect water flow during production; (3) the presence of residual gas that may affect water flow in the reservoir and production systems; (4) the viability of repurposing existing oil and gas infrastructure for geothermal production. |