Proceedings World Geothermal Congress 2005 Antalya, Turkey, 24-29 April 2005 1 Application of Modified Isochronal Test to Determine Output Curve of Wells at Kamojang Geothermal Field-West Java M. Achyar Karim, Aidil Hasibuan, Firman, Wawan Darmawan and Ali Ashat Pertamina Area Geothermal Kamojang, PO-BOX 120 GARUT, West Java, Indonesia (44101) achyar_karim@pertamina.com Keywords: production test, back pressure, modified isochronal, validate ABSTRACT Attempts were made at Kamojang Geothermal field, West Java, to apply Modified Isochronal Test to determine output curve from production test of KMJ-73 and KMJ-74 wells. In the past, wells at the Kamojang Geothermal field were tested using Back Pressure Method. The results of the test were satisfactory. However, the test was time consuming. Three months were spent testing a single well. The disadvantages of this test are high cost and delayed revenue gained from the wells. The result of the modified isochronal test has a good agreement with those obtained from back pressure test. The main advantage of modified isochronal test is duration of the test. Completion of modified isochronal test takes only 10 days. However, before it becomes an alternative method for testing dry steam wells, validation of this method is needed by applying it to other wells. 1. INTRODUCTION 1.1 Field Overview The Kamojang geothermal steam field is one of the world’s few developed dry steam reservoirs, located in an area of high elevation of 1500 masl, 40 km south east of Bandung, Indonesia. Since 1982, the field, which is operated by PERTAMINA- a state oil and gas company, has been producing steam to supply PLN’s 140 MW. An exploration was started under New Zealand government, and continued until 1974–1975 when five exploration wells were drilled down to 700 m throughout the Kamojang Area. LEGEND : Transmission line, 150 kV Installed Geothermal Power (Operator) Transmission line, 500 kV JAKARTA BANDUNG Sukabumi Bogor Cirebon Tasikmalaya Installed Thermal Power Installed Hydro Power Substation Cilegon 500 MW Suralaya 3 x 400 MW Muarakarang 4 x 125 MW Tanjung Priuk 4 x 57.5 MW G andul 500/150 kV Cibinong 500/150 kV Bogor Baru 150/20 kV Jatiluhur 6 x 25 MW Cirata 4 x 125 MW G. Salak (UGI) 330 MW Saguling 4 x 175 MW Darajat (AI) 125 MW Pangalengan 2 MW Bandung Selatan 500/150 kV W. Windu (MN) 110 MW N Ubrug Road Karaha Field Patuha KAMOJANG FIELD 140 MW Garut West Java Index MAP Figure 1: Location map of Kamojang, West Java Indonesia.