Response of Bao-Banati thermal area to development of the Tongonan geothermal field, Philippines

Abstract

During the first six years of commercial operations at Tongonan-1, the chloride contents, flow rates, and quartz geothermometer temperatures of the Bao-Banati springs generally declined. Geysering ceased, and some springs were reduced to non-flowing pools. The total flow decreased from 85 (1983) to 10 kg/s (1992), due to a reduction in the contribution of deep reservoir fluids to the surface discharges resulting from an exploitation-induced decline in reservoir pressures. There was no reinjection fluid breakthrough from Tongonan-1 to the springs during this period. In 1982–83, test reinjection into well 5RD1 in the Malitbog sector resulted in increased thermal activity of the springs, but a tracer test had negative results. A further reinjection test in 1983 caused a brief increase in chloride content and flow rate, but these resumed their decline after the test ended. Similar responses occurred during pre-commissioning trials for the Malitbog plant in 1996. Activity increased again when the plant was commissioned in 1997. A tracer test, using Na-fluorescein, confirmed communication between 5R1D and the hot springs.