Fabric Development and Pore-Throat Reduction in a Mass-Transport Deposit in the Jubilee Gas Field, Eastern Gulf of Mexico: Consequences for the Sealing Capacity of MTDs

Mass-transport deposits (MTDs) are important stratigraphic elements in many deepwater basins. MTDs have traditionally been identified as seals but can also act as migration pathways. Studying the character of deposits within a MTD from proximal to distal, in a framework of seismically identifiable morphologies provides a template for using seismic character to predict the petrophysical properties of such deposits. During failure and subsequent transport, MTDs are exposed to shear deformation and remolding that can enhance clay alignment and destroy large pore-throats thus creating potential seal quality facies. Deformation in the various MTD morpho-domains can be quantified by measuring the degree of clay-fabric alignment. In this study we investigate a MTD acting as the top-seal in the Jubilee gas field, Gulf of Mexico, by integrating 3D-seismic, core, and well-log data to characterize clay fabrics. X-ray-texture goniometry analysis was performed using core material from the top-seal MTD to determine the degree of clay fabric alignment. Final results indicate that samples have an anomalously high clay-fabric orientation not correlated with burial depth or diagenesis. We conclude that these zones with high clay-fabric alignment in the MTD are the result of shear deformation as the gravity flow moved downslope. Recognition of zones with enhanced microfabrics has important implications for shallow geohazards as well as sealing potential evaluation. This technique—although in its infancy—could be used to identify sealing MTD facies in core samples and outcrop studies.