Geochemical Evaluation of the Reservoir Response to Exploitation of the Mindanao-1 Geothermal Production Field, Philippines

Abstract

Mindanao-1 production field has been operating commercially for almost two years. Nine (9) production wells were tapped to supply steam for the 52 MWe power plant. Significant changes in the physical and chemical characteristics of the producing wells were observed and are attributed to the response of the reservoir to continued exploitation. Variations in the geochemical parameters of the producing wells from its initial production were used to describe the effects of continued exploitation. Decline in discharge enthalpy with corresponding increase in waterflow were observed in wells along the Marbel Corridor. Slight increase of reservoir chloride and apparent decrease in TSiO2 were also experienced and are likely due to dominance of the liquid-saturated bottom feed zone in the discharge and the likely ingress of the reinjection fluid. The declining output of APO-1D, APO-3D and SP-4D is attributed to calcite deposition. To avert the ingress of reinjection fluid and calcite deposition in the production wells, reinjection load at present sink should be reduced and diverted farther north of the field and antiscalant injection system is being progressively installed in the affected production wells.