Underbalanced geothermal well workover combining traditional oil & gas with innovative cuttings removal technologies to develop sustainable energy resources

Our responsibility to tackle climate change and commitment to transition towards sustainable energy resources is demanding unprecedented focus, equally from countries and organizations. Traditional oil and gas technologies have a place in also exploring sustainable energy resources and thus help reduce carbon footprint. One such technology is Underbalance Drilling (UBD) which has been widely used in oil and gas drilling operations to mitigate drilling problems and enhance reservoir productivity and characterization. The technology had limited use in geothermal drilling applications and is rarely implemented during workover operations.
The UBD workover system based on straight air and produced water was modeled together with Fraunhofer IEG to accurate ECD requirements. Numerous challenges were resolved during the planning stage, including limited space at the rig site, limited workover rig capabilities, production handling at the surface, hole cleaning and most crucially managing hot formation water with temperatures reaching as high as 100-110 °C on the surface. A nimble UBD system was designed using a multiphase simulator to ensure a minimum underbalanced equipment footprint at the rig site. A strategy was also developed to ensure the surface temperature was kept within the surface equipment operating temperature range whereas the produced water was reinjected into a neighboring well for adequate fluid management at the surface.
The paper will further discuss the implementation of good hole-cleaning practices and strategies implemented to manage an efficient and constant flow regime from the well. Overall, the concept of a UBD multiphase workover was proven successful in geothermal wells and important lessons learned during operations could be implemented in improving operational efficiency in subsequent wells.