Flow test results and design/operational considerations for mud selection in EPP drilling. D4.2

The DEEPLIGHT project aims to develop the Electro Pulse Power (EPP) drilling technology for cost-effective geothermal wells. The novel rock breaking mechanism requires modelling and experimental validation to optimize hole cleaning during EPP drilling operations which was covered by Work Package 4. The research focuses on understanding the impact of flow rate, pipe rotation, cutting concentration, and rheology on hole cleaning while considering the EPP specific particle size distribution as created by the EPP rock breaking mechanism. Experiments are conducted at the Rijswijk Centre for Sustainable Geo-Energy to validate and calibrate a physics-based semi empirical model. The study aims to identify the minimum threshold combination of these factors to initiate effective hole cleaning across different inclinations. Key findings indicate that pipe rotation significantly enhances cuttings transport, especially for coarser particles. Inclination effects are size-dependent, with finer solids showing better performance under inclined conditions. Higher-viscosity drilling fluids generally improve hole cleaning efficiency, particularly for larger cuttings. The study also highlights the importance of controlled drilling rates to maintain stable transport and minimize the hydraulics power required to clean the hole. Additionally, a Computational Fluid Dynamics (CFD) study was conducted to improve the hydraulic design of the EPP electrode. The study revealed that adding viscosity to the drilling fluid and using rotation significantly enhance hole cleaning around the electrodes. The findings suggest that future work should focus on optimizing electrode configurations. Overall, WP4 of the DEEPLIGHT project demonstrates that the integrated approach combining experimental data, modelling, and CFD analysis provides a robust framework for optimizing drilling operations and enhancing hole cleaning performance. To conclude, viscous drilling fluids and rotation are essential elements in the EPP tool design and operational planning.