Uncertainties in finding an underdeveloped Hydrocarbon Play in a mature Basin: Case study based on contrasting two Carbonates play from East Java Basin, Indonesia

Abstract

The idea of a play concept demonstrates that hydrocarbon accumulations with similar geological characteristics occur in groups within a basin. Such fields have similar hydrocarbon characteristic either gas or oil, reservoir age, sealing lithologies and structural style. When we identify these characteristic, and understood the geology, we may be able to delineate hypothetical play trends where other similar fields exist. This study using example from offshore East Java Basin, Indonesia. The basin contains 6 formations which has been penetrated by 482 exploratory well with only 25% overall proven success. As we recorded, the exploration phase on East java Basin already begins since early 18th centuries and by the overall exploration creaming curve, could be categorized as mature basin. However, with appropriate classification we could isolate unique play type contains proven opportunities. By mapping the play and specifically analyze the; reservoir, seal, charge, trap and put it all on a play based exploration context, we are able to drill one discovery on a mature working permit. The successful case belongs to Mundu carbonate formation. Mundu carbonate of East Java Basin prove to be a prolific oil and gas reservoir target. Based on the play based exploration analysis, Mundu carbonate associated with 18 discovered structures and seven dry holes. These carbonate reservoirs consist of more than 85 % foraminifera bioclast, and worth 3.5 Trillion Cubic Feet of Gas from all 18 developed field. Statistic numbers from discovered gas volumes (Field Size) gives ranges of 25 Billion to 650 Billion Cubic Feet of Gas could found from a single structure. While analysis from porosity and permeability gives average 45 % porosity with permeability ranges could reach 1 – 3 Darcy. This information is very valuable when placed on a Yet-to-Find perspective upon an exploratory campaign to search for remaining exploratory targets. By contrasting the Mundu carbonate play with the well-known Kujung carbonates in the area we could carefully approach the suitable play type for our exploration targets. This study clearly demonstrates play based exploration method to identify targets with 72% success by using historical exploratory data combined with appropriate dry holes analysis and strong understanding of geology of an area. Methods used to analyze the Mundu targets may also be proven elsewhere in various basin. In conclusion, result of this study placed the Mundu play as unique play type which still contains moderate amount of undrilled hydrocarbon.

AAPG Datapages/Search and Discovery Article #90354 © 2019 AAPG Asia Pacific Technical Symposium, The Art of Hydrocarbon Prediction: Managing Uncertainties, Bogor, (Greater Jakarta), Indonesia, August 7-8, 2019