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Lean Salt Architecture in the Northern Gulf of Mexico

Abstract

Allochthonous salt, such as associated with Roho system domain in the northern Gulf of Mexico have been defined by early deep water exploration more than 3 decades ago and their gravity/load driven evolution are well captured. However, the variability in individual salt body dimensions appear less clearly defined. Recent seismic reprocessing efforts offered the opportunity to analyze and hence better image those salt systems. This study focuses on the dimensions of Roho salt bodies and their evolution from previous allo- and/or autochthonous salt on the Louisiana shelf near the late Miocene to middle Pliocene shelf edge. Recent analysis reveal that most Roho systems are smaller in size than the well-studied Eugene Island and Rum Roho systems, though these systems exhibit the classic Roha attributes: (i) up-dip extensionial low angle detachment fault patterns; (ii) translation along a detachment surface; and (iii) down-dip compression shown by thrust faults and folded section. Mapped Roho mini basins appear to occur in a stacking pattern and are often converging or interference. They also demonstrate variability in areal size, expression of down-dip compression, presence/absence of internal salt rollers, translation distance, linearity of individual basin trajectories, and relative volume of evacuated salt. The occurrence of Roho mini basins appears to coincide with the regional sediment input following an East to West trend for the late Miocene to middle Pliocene and support the conclusion that these are localized gravitational instabilities triggered and/or amplified by enhanced sedimentary depositions. Timing, frequency and rate of sediment input appears to correlate with the areal size, linearity, and convergence of individual Roho mini basins as well as with the volume of evacuated salt.

The complexity in Roho mini basins formation has not been completely captured for a variety of reasons including limited 2D/3D seismic data. As a result, subsurface models commonly reveal grossly over-inflated salt budgets, which in turn resulted in less than optimal seismic imaging. However, improved imaging technology and salt model building workflows result in seismic images suitable for petroleum system assessment and identifying reservoir opportunities, particularly in sub-salt settings.