Development of exploration methods for reservoir characterization in conduction dominated geothermal play types

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Geothermal reservoirs are a green energy resource commonly utilized in high-heat flow areas with recent volcanic or tectonic activity. Enhanced or Engineered Geothermal Systems (EGS) technology allows heat extraction from reservoirs of average to low heat flow and has significantly increased not only the world-wide but also Canada’s geothermal potential. While EGS for basement rock utilization, known as hot-dry rock, has been studied since several years, the use of hydrothermal resources in hot sedimentary aquifers is in its early stages. Alberta hosts geothermal play types that are dominated by conductive heat transport. This proposal is the start of applied geothermal research in Alberta to evaluate conduction dominated geothermal play types; the geologic controls therein on fluid flow, permeability and porosity; and the processes and methods to determine favorable drill sites and pay zones for geothermal use. According to the new geothermal play type catalog of Moeck (submitted), there are three conduction dominated geothermal play types: (I) hot sedimentary aquifers in intracratonic basins that are lithofacies controlled, (II) hot sedimentary aquifers in orogenic belts and foreland basins that are predominantely fault controlled, and (III) crystalline basement rock with no significant formation fluids. These three play types shall be studied in this proposal; however, the focus on research shall be on the second type (orogenic belts and foreland basis). In Project 1, outcrop analogues in the Rocky Mountain Front ranges shall be studied for fault zone dimensions and fault throw related permeability distribution. The dimensions of fault zonation shall be determined, along with their relation to fault kinematics, permeability and porosity in each zone. This will assist structural interpretation of reflection seismic data, where only the fault throw is identifiable. Methods employed will include detailed structural geological mapping of fault zones with emphasis on fracture networks and rock sampling for measuring petrophysical parameters. Petrographic thin section analysis aims to determine micro-scale processes that influence porosity and permeability. Data from these two aspects of the study will be integrated into 3D geological maps. In Project 2, lithofacies controls on permeability distribution shall be identified by well logs employing the Thomas-Stieber method, that allows the identification of clean sand layers in heterogeneous sandstones. Clean sandstones represent generally high-porosity sections and, thus, the location of pay zones. The quantification of pay zones may help to delineate high productivity and injectivity zones in laminated sandstone. Thin sections will be petrographically analysed to determine if the porosity is controlled by shale particles (i.e. primary porosity) or dissolution-recrystallization seams (i.e. secondary porosity). Shale types will be also identified by spectral gamma logs and integrated with petrographic results to improve the Thomas-Stieber method for geothermal reservoir evaluation. The Project 3 deals with a new concept that uses supercritical CO2 as efficient thermal fluid for utilizing low heat flow basement rock for geothermal applications. Albertan basement rocks shall be characterized on porosity, permeability, bulk modulus, thermal conductivity and heat capacity as a function of temperature, pressure and lithology. Additionally, the density, viscosity, thermal conductivity and heat capacity of supercritical CO2 will be determined at temperatures and pressures relevant for potential efficient use from crystalline basement rock. The results from this proposal will be relevant for utilization concepts in the wide range of conduction dominated geothermal play types worldwide.