Publications

Alas Tua West (ATW), discovered by Mobil Cepu Ltd in 2011, is a carbonate gas field located in Cepu KKS, East Java Basin. It is an Oligo-Miocene isolated carbonate build-up with a crestal depth of ~1600m TVDSS. The reservoir is comprised of ~500m of good quality shallow water carbonates reservoir with a porosity range of 7-22%. One exploration well (A-1) has been drilled to date. The current dataset used for the ATW reservoir characterization includes moderate quality 2011 3D J-AT PSDM seismic data, good quality logs from A-1 (GR-RES-NEU-DEN-SON), sidewall cores, cuttings and pressure data. Full diameter core, image logs and well test data were not acquired. Based on 3D seismic data interpretation, three distinct seismic facies are identified within the ATW carbonate buildup: (1) parallel, (2) mounded - chaotic, and (3) clinoform. The parallel seismic facies represent the early stages of the carbonate platform (basal carbonate). Mounded-chaotic seismic facies are interpreted, based on the A-1 well, as platform margin or platform interior. The clinoform seismic facies can be interpreted in two ways: (1) detrital carbonate comprised of eroded, shallow water carbonate mixed with deepwater material or (2) a progradational carbonate platform. This paper will discuss the observations and evidence (seismic data, outcrop and subsurface analogues) supporting each of the clinoform facies interpretations. Integrated geological analysis of subsurface data conclude that most of the evidences are leaning towards supporting the clinoform as a progradational carbonate platform. This interpretation will impact reservoir distribution and quality in the Alas Tua West carbonate structure.