INTERPRETATION METHODS IN THE EXPLORATION OF OLIGOCENE-MIOCENE CARBONATE RESERVOIRS, OFFSHORE NORTHWEST MADURA, INDONESIA

摘要

Exploration offshore northwest Madura by Kodeco Energy over a five-year period from 2000-2005 has resulted in a series of oil and gas discoveries within Oligocene to early Miocene Kujung Formation carbonate reservoirs. These discoveries are attributed to the use of certain seismic interpretation techniques combined with a commitment to exploration. Seismic methods include use of isochrons, amplitude, variance images, amplitude versus offset (AVO), acoustic impedance, seismic facies and detailed velocity estimation as part of a pre-stack depth migration processing flow. Hydrocarbon discoveries have been made in both Kujung Ⅰ carbonate reefal buildups, as well as deeper Kujung Ⅱ-Ⅲ platform carbonates. Simple structure and isochron information initially resulted in Kujung Ⅰ discoveries of the KE-23B and KE-40 fields in the year 2000, and the KE-24 and KE-30 fields in 2001. This was followed by the discovery and testing of the Kujung Ⅲ interval in the KE-40 field in 2002. Amplitude analysis resulted in five further Kujung Ⅰ discoveries during 2002-2003. Dipole sonic logs taken in two of these wells combined with AVO analysis have confirmed the likelihood of additional carbonate buildups containing hydrocarbons.rnTwo additional discoveries were made during 2004 in the South Poleng and KE-7 areas. Previous Poleng and KE-7 wells were drilled underneath late Miocene Wonocolo Formation carbonate buildups, and so accurate velocity estimation was the key to both subsequent discoveries. South Poleng, which is the largest discovery made in the five-year period,rninvolved the combined use of acoustic impedance, isochron analysis, seismic facies, velocity estimation and an understanding of regional paleogeography. A novel approach is used to extract seismic attributes in depth using a standard 3-D time volume. The South Poleng discovery is also remarkable in that it has approximately doubled the estimated size of the Poleng accumulation, over 30 years after its initial discovery.rnThe exploration well success rate has been 67% (and 65% including delineation wells) over the five-year period, highlighting the potential for future hydrocarbon discoveries.