The Geochemical Model of Tongonan Geothermal Field Prior to Full Commissioning of 450 MWe Power Plants

Abstract

Tongonan production field encompasses the five production sectors of Upper Mahiao, Mahiao, Sambaloran, South Sambaloran and Malitbog, Mamban and Bao sectors separate the Tongonan Mahanagdong field. This updated geochemical model of Tongonan Geothermal Field was based porn the baseline well chemistry during discharge tests and the present production chemistry after more than a decade of Mahiao-Sambaloran operations.

The upflow sector is inferred to be situated in Upper Mahiao, particularly in the vicinity of 407 and 410. Towards the south and southeast, that is in the general direction of Malitbog, mineralization, temperature and gas concentrations decrease. These directions are the major natural outflow of the system. Discharge tests and commercial production indicate the presence of secondary fluids in the periphery of Tongonan system. Cooler waters in northeast of Upper Mahiao characterize the well discharges of 4110, 4160 and 4170. Likewise, the 5RB wells in southwest of Malitbog exhibit less mineralized and cooler fluids. Northeast of Malitbog, however, there is a presence of sulfate-rich type of cooler waters as seen in the discharge of 505D. Acid fluids are also identified in 402, which appears to be confined only west of Upper Mahiao-Mahiao sectors. Notably, the exploitation of the Mahiao-Sambaloran sectors for over a decade has brought about the massive migration of reinjection fluids porn the southwest, which is the reinjection sink of Mahiao and Sambaloran.