Novel concepts to construct cost effective geothermal wells with Electro Pulse Power Technology – DEEPLIGHT. Description of the calibrated EPP hydraulic model. D4.1

The DEEPLIGHT project is developing Electro Pulse Power (EPP) drilling technology. EPP is a novel non-mechanical rock-breaking method that unlike conventional rotary drilling, uses ultra-short high-voltage electric discharges between electrodes to fragment rock. The EPP rock breaking mechanism results in rock fragments with a wider spread in size and shape compared to conventional drilled cuttings. To assess the viability of EPP drilling in geothermal wells, it is paramount to investigate the requirements to remove cuttings from the well and optimize fluid conditions during drilling. A semi-empirical physics-based model was built applying the typical hole cleaning formulas used in conventional drilling. The model was adapted to the EPP cuttings characteristics and drilling fluids. A test set-up, so-called “cuttings flow loop” at TNO’s Rijswijk Centre for Sustainable Geo-energy, was used to perform a series of test. A dedicated test matrix was designed to investigate the impact of various operational parameters on hole cleaning. For example, both water and a viscous fluid were used to simulate drilling mud of different rheologies, while sand cuttings of varying sizes and concentrations were injected to investigate their behaviour under different flow regimes, inclinations and pipe rotations. The flow loop’s transparent outer pipe made it possible to visually understand what leads to the formation of the cutting beds and how the various cutting transportation regimes could be linked to the measured pressure drop over the pipe. The tests ,their results and implication for mud selection are described in Deeplight deliverable D4.2 “Flow test results and design/operational considerations for mud selection in EPP drilling” The calibrated model can predict hole-cleaning quality based on minimal measurements, i.e. pressure. Furthermore, the model can be used to lower the power requirements for hole cleaning. The findings will be used as design input for further tool development and broader implementation of EPP technology in geothermal energy projects. This will facilitate faster, more energy-efficient, and lower risk well construction in hard-rock environments.