Evaluation of the Hottest Identified Area in the Salak Geothermal Field

Abstract

Downhole Pressure-Temperature-Spinner (PTS) surveys from Awi 9-7 and Awi 9-8, recently drilled in the southwestern part of the Salak (Awibengkok) geothermal field, show some of the deepest, hottest fluid entries in the field. Flowing temperature measurements as high as 600¢ªF were measured in Awi 9-7 while static temperatures up to ~585¢ªF were found in Awi 9-8. These high temperatures were measured even though spent brine has been injected into other wells on the same well pad for the past 19 years, causing considerable cooling of producers in the vicinity. Geologic interpretation of logs and cuttings shows that the hot entries in these wells occur within the Lower Andesite and Mixed Volcanic and Sedimentary (MVS) rocks at similar elevation. Image logs show that small-scale fractures are well developed within andesite lavas and andesite lithic tuffs in Awi 9-8 with a dominant strike orientation of NW-SE and NNW-SSE. XRD results from Awi 9-7 indicate a predominant alteration assemblage of neutral pH minerals illite, mica, chlorite, and calcite, and the high temperature mineral diopside. This data confirm the interpretation that the deep Salak up-flow is located near the southwestern edge of the field, and thick lower temperature outflow flows across the field to the east.