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Technology Explained
Potter Drilling’s technology drills boreholes using a process called spallation. The process starts by applying a high-intensity fluid stream to a rock surface to expand the crystalline grains within the rock. When the grains expand, micro-fractures occur in the rock and small particles called spalls are ejected. The process is accelerated by several factors including inherent stress in the rock formation.
An animation of how hydrothermal spallation works.
Potter Drilling is not the first company to develop spallation drilling technology. Air spallation drilling was used commercially from 1947 through 1961 for ore mining and was adapted to geothermal drilling by the Department of Energy in the 1970s. Air spallation demonstrated impressive drilling performance, producing 8 inch to 12 inch boreholes to depths of 1,100 feet at rates faster than 50 feet per hour in solid granite.
Potter Drilling’s technology differs from prior air based techniques in that it uses hot fluid rather than air to spall rock. Because spallation occurs in a water filled borehole, Potter Drilling’s technology can be used to drill to depths required for universal EGS (12,000 to 30,000 feet).
Fluid-based hydrothermal spallation has the following advantages:
Greater wellbore stability: Fluid-filled boreholes are more stable and require fewer casing intervals.
Increased buoyancy for spalls: Fluid can be used to carry spalls to the surface from extreme depths.
More heat flux and faster rates of penetration: Fluid heat transfer surpasses the impressive performance demonstrated in air-based spallation technologies.
Hydrothermal spallation was invented and patented by cofounder Bob Potter and Jefferson Tester of MIT. The patent is owned by MIT and licensed exclusively to Potter Drilling.
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