Exploration and Delineation Drilling in a High-Temperature Geothermal Reservoir: Northern Negros Geothermal Field, Central Philippines

Abstract

The Northern Negros geothermal field is located in Negros island, Central Philippines, and lies on the northwestern flank of Mt. Canlaon. It is underlain by two stratigraphic units - Pleistocene-Recent Canlaon Volcanics and Late Miocene-Pliocene Talave Formation.
Results of exploration and delineation drilling show that the center of the geothermal system lies in Pataan sector where hot neutral brine is presently upflowing along permeable faults. Mineralogic data and borehole surveys indicate that hot fluids with temperature of ~280-290?C are flowing at -1500 m MSL beneath wells PT-5D, PT-7D and possibly, PT-8D. The hot geothermal resource is bounded in the southwest by Asia Splay Extension based on declining temperature trends towards well PT-3D. The northwestern margin, on the other hand, is likely defined by Dinagaan Fault as suggested by cooling temperatures going to well PT-6D. This reservoir model agrees with geophysical surveys which also identified the upflow region in Pataan sector, possibly extending further southeast towards Sumaguan area. The heat source of the present geothermal system is likely related to the oldest eruption vent of Mt. Canlaon, the Hardin Sang Balo volcanic center which lies southeast of Pataan.
To complete steam requirement for the 40 MWe Northern Negros geothermal power plant, at least one more production well needs to be drilled in Pataan sector. On the other hand, three injection wells drilled in the northwestern sector of Pataan are already sufficient for disposal of spent brine from production wells. Expected commissioning of the Northern Negros power plant in 2006 will help meet growing electricity demand in Central Philippines.