Darajat Edgefield Evaluation

Abstract

One of the main objectives of the West Darajat Edgefield Evaluation was to gain a better understanding of the southwest, west and northwest portions of the Darajat reservoir by using information from newly drilled wells and combining them with recent reservoir interpretations. Three step-out and edgefield wells in southwest and west Darajat were drilled during 2009-2011, and these wells offered new information about these portions of the reservoir. The long-term objective of this study is to assist in the strategic field development, specifically, whether to build a new pad in the northwest from which to drill additional production wells. Recent analyses indicate that the upflow of the Darajat geothermal system is located in the northwest based on consistent high CH4 (since initial production), heavier stable isotopes, high initial steam deliverabilities, low production decline rates and high initial reservoir pressures and temperatures. The results of the edgefield wells in the west indicate the possible extent of the commercial reservoir in this area although further evaluation of the productivity and permeability of both wells F1 and F2 is still incomplete. Meanwhile W3, the southwest step-out well, shows non-commercial permeability and encountered low temperatures. Re-interpretation of the MT/TDEM data shows thickening and deepening of the clay cap in the southwest, west and northwest outside the current production area, and may eventually represent a limit to commercial permeability as well. This hypothesis is corroborated by the MEQ clusters during blind drilling of the step-out and edgefield wells. The Kendang Fault appears to be the geologic boundary of the Darajat geothermal system in the west and southwest based on results of wells F1, F2 and W3 wells. Similar thickening and deepening of the clay cap and MEQ swarms in northwest Darajat suggest that this fault may also be the boundary of the reservoir in this part of the field. However, the presence of young domes and the upflow in this area makes northwest Darajat interesting. A step out well towards the northwest could validate this hypothesis.