The Hydrological Model of the Mahanagdong Geothermal System

Abstract

The Mahanagdong sector of the Leyte Geothermal Power Project (LGPP) is committed to supply I80 MWe of steam by mid-1997. An updated hydrological model was carried out based on available geoscientific and reservoir engineering data Pam a total o/ 34 wells drilled in the area. The Mahanagdong resource is derived from a fracture-controlled and volcano hosted geothermal system characterized by neutral to slightly alkali chloride fluids with reservoir temperatures exceeding 295oC. A major upflow region was identified in the vicinity of MG-3D, MG-14D and MG-5D. Fluids outflowing in the north possibly encountered an acid body originating from condensed magmatic HCI-rich vapors or a sulfur-rich body producing acid CI-S04, fluids. Isochemical contours indicate ouflowing fluids with temperatures of 27O-275oC to the south and west. Its southwesterly flow is restricted by the intersection of the impermeable Mahanagdong Claystone near MG-IOD, which delimits the southern part of the resource. Low chloride, shallow inflows are evident at the west near MG-4D and MG-I 7D wells which act as a cold recharge in this sector.