PRACTICAL DESIGN OF A HIGH-VOLTAGE PULSED POWER SUPPLY FOR DOWNHOLE PLASMA ENHANCED GEOTHERMAL DRILLING

Energy demand worldwide has grown by 14% over the last decade driven by increasing industrialization and stronger heating and cooling needs in some regions. At a time when society is becoming increasingly aware of the declining reserves of fossil fuels along with environmental issues such as fossil-fuel-sourced greenhouse gas (GHG) emissions, use of renewable and sustainable energy sources is the appropriate and applicable choice. Geothermal energy is one form of a sustainable source, which has certain advantages that make it a viable solution for helping meet the world’s energy needs. Geothermal drilling is done most often through hard rocks rather than through the softer, sedimentary rocks of petroleum-bearing formations. The harder rock lithology decreases the rate at which drilling occurs and increases the wear and tear on drilling tools. These factors add up to significant time and money expenditure. In order to make geothermal drilling more efficient and cost-effective, new technologies need to be developed. We focus on a novel geothermal drilling technology where we weaken the rock formation before the drill bit makes contact with it by locally directing high energy shockwaves at the rock formation using electrically induced microsecond plasma discharges in liquids. The shockwave results in microscale fractures in the rock formation, and the resulting lower compressive strength lithology is easier to drill. To generate the microsecond high energy pulsed plasma discharge, our concept uses existing components of a drilling bottom hole assembly (BHA) such as the mud motor and alternator to generate power in situ. This thesis focuses on the design, assembly and characterization of the major electrical circuit required to generate the electrically induced microsecond high energy plasma discharge. Finally we designed a bottom hole assembly where the proposed plasma enhanced rock reduction may be used and we characterized the performance of an 80 J per pulse rectification Cockcroft Walton generator (CWG) circuit at atmospheric pressure and room temperature (at different input ac power frequencies)