Comparing permeability of fault zones of geothermal and non-geothermal regions, compiled in a global fault zone permeability database.

English Abstract:

Fault zones are important fluid conduits in geothermal reservoirs, and the permeability of fault zones is also an important parameter in models assessing deep groundwater flow in sedimentary basins. In this study we conducted a review and compilation of existing fault zone hydrogeological data in various regions of the world, including many faulted sedimentary basins. The database focusses on fault zone permeability and conceptual permeability models published in multidisciplinary literature (structural- and hydro-geology, engineering geology, and geothermal projects among others). In regions with the largest data clusters, the occurrence of different dominant hydrogeologic effects of fault zones (barrier / conduit), and the locally estimated permeability magnitudes, were tabulated and compared for different geologic regions, lithologies, depths. Various data biases, as related to tests of fault zones, are also explored and compared.

The data from developed geothermal projects are compared to other fault permeability estimates at thermal springs (analytical and numerical solution of Darcy flux driven by convective heat flow). Starting with the methodology applied in Japan by Hanano and Kajiwara (1999) and regional mapping by Muraoka et al. (2006), a similar methodology is applied to other regions where hot thermal springs occur. 2D numerical flow models of heat+water flow are used to explore the assumptions and parameter sensitivities of these methods. Fault permeability data from sedimentary basins are compared globally with geothermal heat flux, depth, reservoir size and scale of measurement, number of wells drilled, and other parameters. These results are also compared to non-geothermal hydrogeological data of fault zone permeability in these regions.

The research result lead to a key question - are fault permeability data from developed geothermal fields transferable and/or scalable, or useful in any way, to exploration in geothermally undeveloped sedimentary basins?