High-amplitude reflection packets (HARPs) of the Mississippi Fan, Gulf of Mexico

Abstract

Examination of seismic data from the deep-water Gulf of Mexico reveals the presence of High-Amplitude Reflection Packets (HARPs). An analog study conducted by the Ocean Drilling Program Leg 155 identified and described Amazon Fan HARPs as a stacked, relatively unconfined series of graded turbidites overlain by a channel-levee. HARP seismic facies thin laterally and onlap antecedent bathymetry (preexisting submarine topography). HARP areal extent is controlled by antecedent bathymetry and turbidity flow sediment volumes. Mississippi Fan HARP deposition can be described by three depositional models: the "avulsion" model, the "fill and spill" model, and the "transition" model. The "avulsion" depositional model, developed by Flood et al. (1991), describes avulsion of submarine channel-levees by turbidity flows. Subsequent turbidity flows exit the channel-levee at the avulsion point and are deposited as unchannelized HARPs. The "fill and spill" model, developed by Satterfield and Behrens (1990), describes turbidite deposition in the Gulf of Mexico salt province. Initial stages of the "fill and spill" model accurately describe the seismic geometries of HARPs confined by adjacent salt structures. The "transition" model was developed in this study to describe the Gulf of Mexico HARP seismic geometries seen in the transition zone from the salt province to the abyssal plain. The HARPs described by the "transition" model contain an upslope segment confined by salt structures and a downslope segment confined by antecedent bathymetry. Utilizing seismic data from the Gulf of Mexico and core and well-log data from the Amazon Fan, this study has determined that HARPs and related channel-levees have hydrocarbon play potential. HARP sheet sands, internal HARP channel fill, overlying channel-levee fill, and overbank levee sands are potential reservoir units. Detrital carbonate and hemipelagic shale source rocks are in place in the deep-water Gulf of Mexico. In addition, structurally derived migration pathways combine with percolation as potential migration processes. This study integrates identification and description of HARP seismic facies relationships, current and newly developed depositional models, interpretation of stratigraphic controls, HARP internal reservoir architecture, and determination of HARP hydrocarbon potential in order to predict HARP deposition in the Mississippi Fan and other mud-rich fans worldwide.