--> Seismic Stratigraphy and Depositional Model of the Kimmeridgian-Tithonian Dupuy Formation: Implications for Gorgon CO<sub>2</sub> Injection

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Seismic Stratigraphy and Depositional Model of the Kimmeridgian-Tithonian Dupuy Formation: Implications for Gorgon CO2 Injection

Abstract

The Kimmeridgian-Tithonian Dupuy Formation forms the reservoir for the Gorgon CO2 injection project. The injection project will be one of the largest in the world, reducing greenhouse gas emissions from the Gorgon Project by approximately 40 percent. The Project plans to inject between 3.4 and 4.0 million tonnes of reservoir carbon dioxide each year. The project involves CO2 injection, water production to manage reservoir pressure, water disposal into the overlying Barrow Group, and comprehensive reservoir surveillance. Understanding the reservoir architecture of the Dupuy Formation is a key aspect to ensuring the success of the injection program. The Gorgon CO2 Baseline survey (BWI3D) was acquired in 2009 to provide a 4D baseline for ongoing CO2 monitoring and to improve reservoir characterization. Mapping of the survey has been integrated with neighboring 3D and 2D seismic surveys, geophysical well logs, core, image log, and biostratigraphic data to characterize the reservoir architecture. The Dupuy Formation in the Barrow Island area is a locally thick (~500m), sand-prone system deposited in a variety of deep water environments at the base of an active, steep slope. The Dupuy Formation has been sourced from the southeast, via a Late Jurassic submarine canyon. Basin-ward of Barrow Island the Dupuy Formation forms a classical lobate geometry consistent with the size, age and orientation of the canyon. The injection area is outboard of the canyon mouth in the transition from a weakly confined to unconfined distributary system. Some intervals have been heavily modified via Mass Transport Complexes (MTC) that have degraded reservoir quality and imparted irregular bathymetry that has influenced subsequent deposition. The prevalence of slumping and disturbed bedding is anticipated to assist CO2 containment by increasing flow path tortuosity and formation exposure. Intra-reservoir baffles appear limited in extent and the absence of confined channels is anticipated to promote an even plume front. The work presented here is broadly consistent with previously published models for the Kimmeridgian-Tithonian of the Carnarvon Basin and confirms the Dupuy Formation beneath Barrow Island is a good target for the disposal of the Gorgon Field reservoir carbon dioxide.