Mahanagdong Reservoir Response to the Termination of Infield Cold Reinjection

Abstract

The Mahanagdong geothermal resource has been continuously extracted to provide steam supply to the power plants since their commissioning in 1997. The resource experienced natural decline attributed to pressure drawdown, cooling and wellbore scaling for its 26 years of utilization. One of the main drivers of the Mahanagdong steam production decline was the reservoir cooling caused by the infield cold reinjection due to the limitation of both hot and cold brine/condensate conveyance to the distant reinjection pad. The condensate lines were upgraded as well as the maximization of the hot brine reinjection main line thereby reducing the dumped brine and transferring the cold reinjection outfield. Thermal recovery was observed after the termination of infield cold reinjection but led to an aggressive wellbore scaling as an outcome. The mixing of reservoir fluid with metal-ion and HCO3- rich peripheral water that encroached the production sector promoted the wellbore scale formation upon boiling. Treatment program using polymeric scale inhibitor is applied to address the wellbore scaling and the use of metal ion dispersant will also be tested in the field to inhibit the metal-bearing mineral scale formation.