INITIAL RESPONSE TO EXPLOITATION OF THE MT. APO GEOTHERMAL RESERVOIR, COTABATO, PHILIPPINES

Abstract

Large scale exploitation of the Mt. Apo geothermal reservoir commenced after the commissioning of the Fluid Collection and Disposal System (FCDS) of Mindanao 1 Geothermal Production Field (MI GPF) in October 1996. The first 52 MWe power plant was commissioned in December 1996 and baseload operation started in March 1997. The Mindanao 1 is
utilizing nine production vvells located in the outflow sector of geothermal field. The separated brine and steam condensate from the power plant are reinjected to five reinjection wells. A second 50 MWe power plant, scheduled for commissioning by mid-1999, will utilize the production wells drilled in the Mindanao 2 Production Field.

The first year of continuous exploitation resulted to a steady rise in the fieldís average enthalpy of MlGPF. The most noticeable increases were on wells APO-1D and SP-4D. Four production wells, SK-2D, SK-3D, SK-5D and SK-6D, exhibited increases in their mass flows. However, the steam well SK-1D showed a decreasing mass flow. APO-ID and SP-4D
experienced calcite blockage in their liners after prolonged commercial operation. This resulted to a substantial decrease in their mass flows. The decline in the mass flows of the three wells, however, was offset by a corresponding increase in the mass flow of four other production wells. In the reinjection sector pressurization was observed in the Kullay
sector.

At this present stage, the reservoir responds distinctively to exploitation relying largely on the location of the feedzones of the wells in the
production field.