Modeling Thermally Induced Failure of Brittle Geomaterials

Abstract

Geothermal power promises clean, renewable, reliable and potentially widely-available energy, but is limited by high initial capital costs. Widespread adoption of geothermal energy will require access to deeply buried geothermal sources in granitic basement rocks at high temperatures and pressures. Exploiting these resources necessitates novel methods for drilling, stimulation, and maintenance, under operating conditions that are difficult or impossible to test in laboratory settings. In such environments, physically rigorous numerical modeling tools are vital to highlight potential risks, guide process optimization and reduce the uncertainties involved in these developing technologies.A drilling technology with the potential to reduced the costs associated with geothermal power is Thermal Spallation Drilling (TSD) -a novel drilling technique in which small particles (spalls) are released from the rock surface by rapid heating. While TSD has the potential to improve drilling rates of brittle granitic rocks that are typical for geothermal wells, the coupled thermomechanical processes involved in TSD are poorly described, making system control and optimization difficult for this drilling technology.The project examined the factors influencing thermal spallation of hard basement rocks. Under the project, high-resolution simulations employing Lawrence Livermore's GEODYN code were used to model spallability of different rock types as a function of grain size distribution and depth, at conditions appropriate for geothermal wells. Data collected from these simulations was used to provide qualitative information on the rocks and conditions best suited to Thermal Spallation Drilling and related rock reduction technologies. The results of the simulations were analyzed to extract parameters for future validation of empirical models describing thermal spallation at the borehole scale.

Simulating electropulse fracture of granitic rock

“…A Voronoi tesselation is used to generate the rock microstructure, with the Voronoi cells representing individual mineral grains (Figure 3). To obtain the desired volumetric percentage and grain size of each of the mineral types, initially randomly distributed cell volumes were iteratively relaxed until the desired material composition was achieved [59,60,61]. The rock composition properties are shown in Table 3, and the generated material microstructure is shown in Figure 3.…”

Micromechanical modeling of thermal spallation in granitic rock

“…The rock microstructures employed in the simulations are created by fitting the cells in a Voronoi tessellation to a target grain-size distributions [29]. Voronoi cells are generated from a set of random points, and each cell is assigned a target volume.…”

Equivalent Circuit Models: An Effective Tool to Simulate Electric/Dielectric Properties of Ores—An Example Using Granite

“…Walsh and his groups conducted some simulation works related to the HV pulse liberation of ores [11,12], using Voronoi tessellation in order to simulate the mineral distribution in the granite rocks. Their works considered the minerals of granite to understand their behaviors under HV electric applications.…”