Steam Production from the Expanded Two-Phase Region in the Southern Negros Geothermal Production Field, Philippines

Abstract

The Southern Negros Geothermal Production Field (SNGPF) in Central Philippines, has been supplying steam to the 112.5MW (3x37.5) power plant in Palinpinon 1 and the 80MW (4x20) modular plants in Palinpinon 2 in the last 27 and 17 years, respectively. Field exploitation has induced field wide reservoir changes that constantly affected the capability to sustain steam supply to the power plants. Pressure drawdown and injection returns were the two major processes that controlled prevailing reservoir conditions at any time during the production period, together with mineral deposition and cool acidic fluid inflow albeit at lesser extent.
Extensive monitoring of the physical and chemical changes in reservoir fluid properties facilitated the careful understanding of reservoir response to exploitation. This also led to the timely formulation and implementation of reservoir management strategies and well interventions that effectively addressed the various problems affecting steam supply. Most important of these strategies were the transfer of the bulk of injection load away from the Puhagan area towards Ticala and Malaunay sectors in Palinpinon 1, and the controlled brine injection into specific injection wells known to have strong communication with the production sector. The full load operation of Palinpinon 1 plant and the commissioning of the modular plants in Palinpinon 2 also considerably promoted the expansion of the existing shallow two phase zone that became the potential source of additional steam to the Palinpinon geothermal power plants.
Steam production from this highly two-phase region has been proven viable initially in 2004 with the commercial re-utilization of the once-acidic well NJ6D and the recovery in 2006 of the commercial outputs of pre-maturely decommissioned wells, PN21D and PN17D affected by injection returns early in the production stage. This was followed by the successful conversion of in-field injection wells, PN6RD and PN9RD into producers in 2008. To date, a total of 63 kg/sec of additional steam equivalent to 25.0MW is realized from the contribution of the two phase region. In addition, future make-up wells are now also being considered to be drilled in the area.