Structural Uncertainties Concerning Fault and Caprock Sealing along the Rosedale Fault System, Gippsland Basin

Swierczek, Ernest¹; Holford, Simon P.²; Backe, Guillaume³; Mitchell, Andy²
¹CO2CRC - Australian School of Petroleum, University of Adelaide, Adelaide, SA, Australia.
²Australian School of Petroleum, University of Adelaide, Adelaide, SA, Australia.
³BP, London, United Kingdom.

One of the main risks associated with storing carbon dioxide underground is the possibility of its leakage from the reservoir through the sealing formation. Permeable fault systems and highly fractured caprocks are the most likely pathways for fluid migration. Therefore, understanding of geometrical relationship of fault segments and their sealing properties is important in order to assess the long-term storage in fault dependent reservoirs.

We present results from a structural analysis of the Rosedale Fault System (RFS) in the Gippsland Basin, Victoria, which is undergoing assessment for CO2 storage. Conventional structural mapping of high fidelity 3D seismic data has been supported by seismic attributes (curvature, dip, coherence, variance, etc.) mapping using the dip-steering method. Coupling of seismic attribute analysis with fault kinematic analysis of the RFS has enabled us to define 3D geometry and connectivity of the RFS and to delineate its associated damage zone. The RFS is a long-lived anastomosing normal fault system that displays lateral changes in the degree of late Miocene-onwards reverse reactivation affecting reservoirs in the Latrobe Group (Late Cretaceous to Eocene) and older units. Our analysis reveals an extensive small-scale fault-system locally occurring in the mud-dominated sealing formation - Lake Entrance Formation (Oligocene) - indicating that this component of the stratigraphy is structurally decoupled from older pre-Latrobe sedimentary section. We describe the results of 3D stress simulations aimed at detecting fault segments that are potentially at high risk for reactivation, and obtaining optimal natural fracture and induced fracture distribution. Our results show that some segments of the RFS are highly stressed under present-day stress conditions, allowing for migration of fluids through caprocks.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012