Sketch-based modelling and flow diagnostics for geothermal exploration

Sketch-based geological modelling with flow diagnostics provides an interactive and intuitive prototyping approach to quickly build geomodels and generate quantitative results to evaluate volumetrics and flow behaviour. This approach allows users to rapidly test the sensitivity of model outputs to different geological concepts and uncertain parameters, and informs selection of geological concepts, scales and resolutions to be investigated in more detailed models. Existing applications focussed on production, connectivity and storage of fluids and ignored or oversimplified thermal aspects. Furthermore, geothermal exploration relies on different types of constraining data. As part of the FindHeat project (findheat.eu), we investigate how the sketching and prototyping approaches can be applied to geothermal exploration and integrated with other tools.

Rapid Reservoir Modelling (RRM) is a free open-source sketch-based geological modelling tool with an intuitive interface that allows users to rapidly sketch geological models in 3D (bitbucket.org/rapidreservoirmodelling/rrm). Geological models that capture the essence of the geothermal target and related uncertainty can be created within minutes. Geological operators ensure correct truncation relationships between 3D surfaces by the modelling engine. Flow diagnostics then computes key indicators of predicted flow and storage behaviour within seconds.

Two aspects of sketch-based modelling with flow diagnostics can be adapted for use in geothermal exploration:  
(1) Scenario screening to capture uncertainty in geological concepts cannot be achieved by changing a numerical variable but can be varied easily by sketching the different concepts, such as lateral connectivity, continuity and geometry of geological heterogeneities that act as flow barriers and pathways. Capturing multiple different concepts is time-consuming in conventional modelling approaches, and in practice is rarely carried out in geothermal projects.
(2) Mini-models and hierarchical models can be used to derive effective properties and thereby capture the effects of multiscale geological heterogeneity. This approach has been successfully applied to date to upscale single-phase permeability, relative permeability curves and capillary pressure curves, but can similarly be applied to upscale thermal conductivity and heat capacity. Models with varying complexity of heterogeneity are sketched at the smallest relevant scale, and effective properties are calculated. Calculated effective properties can then be used to populate models sketched at larger scale. Similarly electrical resistivity and seismic velocity can be upscaled to support inversion of seismic and magnetotelluric surveys.