Use the hot spring’s Chloro-Alkaline Index (CAI) for the low enthalpy prospect of the Rawadanau geothermal field

Abstract

Abstract The emergence of hot springs along the volcanic shelf in Indonesia is a feature of geothermal manifestations. The geothermal system is affected by heat sources, reservoir rocks, cap rocks, and meteoric water that fills and escapes as hot springs through fractures. The Rawadanau geothermal field in Serang Banten is low enthalpy prospects. Geothermal maintenance is defined by the chemical composition of the hot springs, one of which can be determined by the ion exchange rate, namely the chloro-alkaline index (CAI) method. There are 16 hot spring samples, with temperatures (31.2 - 54.6 °C), pH (6.2 – 7.3), and EC (1190 – 4460 μS/cm), respectively. The water types encountered are Na-Cl in the southern and Mg-Ca-HCO3, and Na-Mg-Ca-HCO3-Cl in the northern and western, respectively. Generally, samples taken in the rainy show negative CAI and positive CAI in the dry, while Cl-type is positive in two seasons. Based on water type and CAI show that the Na-Cl type tends to be positive in the two seasons. While the Ca-Mg-HCO3 type is positive in the dry and negative in the rainy, and the Mixed-type shows a negative CAI. The results of this study provide information for the maintenance of geothermal fields as they are developed.