Reservoir Management During 15 Years of Exploitation: Southern Negros Geothermal Production Field

Abstract

The Southern Negros Geothermal Production Field in the Philippines has been exploited for electrical energy production since 1983. Steam production has been affected by the problems encountered in the production and reinjection wells, namely, mineral deposition in the wellbore and in the formation, reinjection fluid returns, acidic fluid intrusions, and pressure drawdown. PNOC-EDC, through intensive monitoring and thorough understanding of the field's behavior under exploitation, was able to formulate immediate and long-term reservoir management strategies for the sustainability of the resource. Foremost was the shifting of the bulk of injection away from the production area in 1989 to address the problem on reinjection fluid returns.

PNOC-EDC proceeded to totally eliminate infield injection and permit the expansion of the shallow two-phase zone. Together with the strategy of prioritizing the utilization of high enthalpy wells, the reinjection load was reduced. Later on, the promotion of 'deep injection' was adopted which minimized drawdown rate by providing pressure support and reheated recharge to the production sector. In addition to work-overs and drilling of make-up and replacement wells, the steam productivity of the field for the last 15 years was also maintained through newer technologies such as acid stimulation.