THE MUNDU FORMATION: EARLY PRODUCTION PERFORMANCE OF AN UNCONVENTIONAL LIMESTONE RESERVOIR, EAST JAVA BASIN - INDONESIA

摘要

The Maleo and Oyong fields are situated in the South Madura Basin, part of the larger East Java Basin, and have been on production for three and a half and two and a half years respectively. The reservoir in both fields is a Pliocene aged, foraminiferal rich limestone of the Mundu and Paciran sequences. This reservoir is unique and there were no currently producing analogues prior the start-up of Maleo and Oyong.The fields are south of Madura Island and are located over the southernmost part of the Rembang-Madura-Kangean inversion zone, which has been active since the end of the Early Pliocene. The reservoir facies are dominated by fossils of Globigerina foraminifera. The foraminiferal rich reservoir consists of a detrital, bioclastic limestones varying from high porosity, high permeability grainstones to poorer quality wackestones.This reservoir has both inter and intra-test porosity, which results in very high porosities. The permeability varies from several milli-Darcies to over 1 Darcy. The shallow depth of burial and lack of cementation resulted in a soft, friable rock that made reliable SCAL data difficult to obtain.During the development planning for Maleo and Oyong, significant consideration was given to assess the nature of the reservoir and predicting how it would perform under production. A key issue was compaction and assessing the affect this would have on well productivity over time.Production performance was predicted by creating static geological and dynamic simulation models that encompassed the range of uncertainties associated with this reservoir. All available data were incorporated in these models. Nevertheless prior to the fields coming on-stream a degree of uncertainty still existed on the ability of the reservoir to deliver.A surveillance programme has been established for both fields and continuously implemented since the commencement of production. Data from daily production monitoring and six-monthly pressure surveys were used to gain better understanding of reservoir behaviour and optimize hydrocarbon recovery.The production from Maleo and Oyong has proven the reservoir to be a reliable producer. The decisions arising from the pre-development, conceptual work have been vindicated by the performance of the two fields.