Exploitation Strategies to Minimize Decline Rate at Lumut Balai Area, PT. Pertamina Geothermal Energy, Indonesia

Abstract

Lumut Balai is one of the prospective geothermal fields in Sumatra which is located in South Sumatra Province, Indonesia. It has been operated 1 unit of geothermal power plant with installed capacity 55 MWe in 2020, will be following to another 55 MWe in 2023. Based on the reservoir characterization, Lumut Balai is classified as a medium to high enthalpy reservoir, with wellhead flowing pressure around 6-9 barg, with pressure line 4-5 barg. There are 3 well pads as the production wells such as Cluster 1, 6, and 9. Due to anticipate Transient Pressure Effect of reservoir exploitation and the small difference between WHP operation, Pipeline, Separator and Turbine Inet pressure about 2-3 barg, it needs production management and strategies to minimize the significance of the decline rate. There are several strategies to manage the exploitation of Lumut Balai reservoir, the first strategy is to operate the throttle valve into the optimum open valve around 40 to 50% with WHP 6-7 barg and operate the production rate of each well without disturbing the stability of steam supply at 2400 ton/hr to the plant through changing the valve open and exercise the valve, secondly reducing the effect of reservoir cooling due to injection through reinjection well which is located far from production area, thirdly monitoring scale development in well and surface facilities regularly, finally maintenance reliability of existing turbine power plant with SSC 6.8 t/hr/MW, Inlet pressure 4.3 barg and monitoring steam quality frequently. Eventually, Lumut Balai geothermal field has no significance production decline with rating percentage less than 1% for TPE period in 9 months.