Abstract

The liquid-dominated system of the Dieng Geothermal Field in Central Java can be divided at least into three areas: the northwestern Sileri area, the central Sikidang-Merdada area, and the southeastern Pakuwaja area. A total of sixteen exploration and development wells have been drilled, with one well at Sileri, thirteen wells at Sikidang-Merdada, and two wells at Pakuwaja.

Interpretations of existing gravity, magneto-telluric and well data reveal that the Sikidang-Merdada area is separated from Sileri and Pakuwaja by zones of low permeability and low temperature. These low permeability barriers show up on the geophysics as regions of gravity highs and conductivity lows. A fumarolic area with an associated gravity anomaly known as the Siglagah prospect occurs in east of Sileri and represents a target for future exploration.

The total geothermal potential is estimated as 355 MW, of which 175 MW are located in Sikidang-Merdada. A 55 MW project is planned for Sikidang-Merdada to come on line in 1995/96. Modular units are recommended, consisting of 2×20 MW and 1×15 MW units. About ten megawatts of capacity currently exist at the wellhead and future development wells are expected to produce 55 tons/hr steam per well.

The reservoir at Sikidang-Merdada consists of a dome-shaped steam zone overlying a brine reservoir with 2000–3000 ppm chloride and 0.5 to 1.6% non-condensible gas by weight. The reservoir temperature is as high as 320°C.