Controlled Pressure Drilling Applications for Enhanced Geothermal Systems

The adoption of new technologies, like controlled pressure drilling (CPD), has been identified as a way of reducing well costs associated with deep enhanced geothermal systems (EGS). CPD methods, particularly air drilling (AD), managed pressure drilling (MPD) and underbalanced drilling (UBD), are an aggregation of techniques that utilize a closed and pressurized wellbore by utilizing a rotating control device (RCD) instead of the conventional practice of drilling with the hole open to the atmosphere. The utilization of these methods usually translates to more effective and efficient drilling operations. Though these methods, especially air drilling, have commonly been used to drill conventional geothermal wells, they have not yet been largely utilized in improving the drilling operations of EGS systems. In EGS drilling, MPD and UBD methods have been tried, but AD, which has the greatest potential among the three to increase the drilling rate in hard rocks, has hardly been involved. This paper focuses on the potential of CPD methods, whether individually or in combination, for improving the economics of drilling EGS systems, in light of recent advances in CPD technology.