Reservoir Changes as Manifested in the Geochemical Signature of Production Fluids: Maibarara Geothermal Field, Philippines

Abstract

The 32 MW Maibarara Geothermal Power Facility (MGPF) is located on the northwest flank of the inactive stratovolcano, Mt. Makiling, about 70km south of Manila, Philippines. The facility consists of 1x20 MW and 1x12 MW geothermal steam turbines. The 20MW Maibarara-1 Geothermal Power Plant (M1GPP) has been in operation since February 2014 while the 12 MW Maibarara-2 Geothermal Power Plant (M2GPP) was commissioned in April 2018. The production wells, power facility and reinjection wells are located in a compact area of around 7.5 hectares. Three wells provide steam to the two power plants while the effluents are injected back into the reservoir via two (2) reinjection wells. Production and reinjection in Maibarara is concentrated in a 2.5 km2 resource area and with continuous mass extraction, changes occur in the reservoir. These changes are directly manifested in the chemistry of the production wells and in turn provide an insight on how to manage the reservoir. This paper discusses the field’s geochemical response to production since its first commercial operation in 2014 and the subsequent capacity expansion in 2018.