Evaluation of Water Produced from a Steam Dominated System, a Case Study from Darajat Field

Abstract

Darajat is unusual as it is one of the few steam-dominated geothermal systems in the world. Current thinking indicates that the reservoir brine in this geothermal system is located deep and has not been accessed yet hence liquid is unlikely to be produced from existing production wells. DRJ-CA, drilled in early 2008 in the central part of the field, is an enigma because it produces liquid. Pressure-Temperature (PT), Pressure-Temperature-Spinner (PTS) and Tracer Flow Test (TFT) data showed that a maximum ~74 kg/s of liquid with an enthalpy of 916 BTU/lb is being produced from this well through both shallow and deep entries. Two permeable entries just below the production casing are the suspected sources of the liquid but the exact location liquid entry is quite difficult to delineate because of nature of these two feed zones. The deep liquid feed zone is at saturation temperature and is believed to flash to steam and very unlikely contribute liquid at the surface. To prevent liquid to be carried over into the steam pipeline, DRJ-CA is operated at high Flowing Well Head Pressure (FWHP). Geochemical analysis of Down Hole Samples (DHS) indicates that the liquid encountered by DRJ-CA is typical of steam-heated groundwater above or outside the reservoir with significant silica content. This suggests that there may be Marginal Recharge (MR) down flow in this part of the field. A complication with this hypothesis is that power plant condensate has been injected in both shallow and deep wells right at the center of the field. Three hypotheses are postulated to explain the source of the liquid in DRJ-CA, namely, injected condensate, MR entry into the reservoir or a combination of both. The recent strategy to move infield condensate injection to the northeastern edge of the field should help further narrow the source of the DRJ-CA liquid.