In the expanding geothermal sector, the push to drill deeper and reach hotter formations is leading to increased basement drilling, which presents different challenges than those posed by sedimentary basins. This study evaluates the feasibility of drilling an advanced geothermal system (AGS), a closed-loop, unconventional geothermal system, in the Pannonian Basin basement of Romania. Key drilling objectives included achieving high instantaneous rate of penetration (ROP) and extended bit life in anticipated hard rock while also identifying and addressing operational limitations through optimized bottomhole assembly (BHA) and drillstring design.
Introduction
The Pannonian Basin, extending 50–100 km into Romania along the Hungarian border, is a well-documented geothermal anomaly with heat-flow densities ranging from 50 to 130 mW/m². Its abundant geothermal resources have historically been tapped for heating, primarily in greenhouses using classical thermal water production.
To reduce reliance on natural reservoirs, two innovative reservoir-independent approaches have emerged: enhanced geothermal systems (EGS) using hydraulic fracturing and closed-loop systems [also referred to AGS]. EGS adapts oil and gas fracturing techniques to create pathways in impermeable rock, circulating water to extract heat. Though effective in areas lacking aquifers, EGS faces challenges from induced seismicity and high costs.
