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Current workflow for Seismic Facies Identification and Characterization in the Miocene Carbonates of the Gulf of Papua and the Eastern Fold Belt of Papua New Guinea

Abstract

The characterisation of reservoir facies represents one of the greatest challenges when exploring the Oligo-Miocene Carbonate play in Papua New Guinea. The heterogeneity in reservoir quality is a key part of the challenge as it incorporates (1) the initial depositional rock fabric (its primary porosity and permeability), (2) the subsequent impact of early diagenetic effects prior to burial, and (3) later diagenesis during and post burial (can be destructive or accretive to porosity). Based on seismic mapping integrated with data from well penetrations in the offshore Gulf of Papua (GOP) and onshore in the Eastern Papuan Basin (EPB), the authors have developed a systematic and structured, seismic-based approach to reservoir facies identification. This workflow is a systematic scorecard methodology that has been modified from Burgess et al (2013). Using this approach, three seismic facies are recognised: High Energy Platform and Reef (HEPR) facies; Low Energy Platform (LEP) facies; and Pelagic-Puri facies: • The HEPR facies, based on petrographic studies, have better initial porosity as they grew in shallow marine (0-20m water depth) conditions, characterised by high wave energy in the upper euphotic zone. Such bodies are well positioned when sea level drops (lowstand event) and subaerial exposure ensues. The introduction and movement of meteoric fluids typically results in extensive secondary porosity development (through carbonate dissolution and dolomitization). These facies have been penetrated in reef margins at Borabi 1, Pandora 1, Uramu 1, Ini 1 and Antelope 1 and are evident on the associated seismic lines. • The LEP facies in contrast are deposited in an intermediate marine setting (20m-100m water depth) associated with ‘oceanic’ platform conditions growing in the lower euphotic zone. Such units have been able to benefit from lowstand related secondary porosity enhancement and represent the LEP facies which has been penetrated at the Triceratops platform, Dibiri platform, the lower platform facies at Antelope 1 and Bobcat 1, these facies typically have significantly lower reservoir quality than the HEPR facies but have significantly better porosity than the Pelagic-Puri facies described below. • The Pelagic-Puri facies are a finer-grained deeper marine (>100m water depth) carbonate that accumulated in basinal areas. They are penetrated at Muabu 1, Ipigo 1, Puri 1, Elk 1 and Raptor 1 and have the poorest reservoir properties of the three facies. A seismic facies atlas of the GOP and EFB’s drilled carbonate units was prepared to provide reference imaging and geometries upon which the authors were able to create a consistent scoring methodology. The aim of this project was to develop a robust, systematic methodology to support exploration target risking and resource estimation; through application this approach has been shown to be auditable, defendable and repeatable.