Grand Isle 43 is an oil and gas field in the Gulf of Mexico that was discovered in 1955. This field is currently being re-evaluated in the context of depositional system and sequence stratigraphic analyses. These analyses, which are largely well log and, to a lesser extent core based, have been integrated with cumulative production histories and have led to the identification of bypassed or underexploited reservoir compartments, and consequently additional drilling locations.

This study focuses on the Middle Miocene JR sandstone, one of 93 pay sands in Grand Isle 43. Reservoir compartments in this field are delineated primarily by flooding surfaces overlain by fine-grained transgressive deposits, and maximum flooding surfaces, lying within fine grained transgressive to highstand deposits. At initial discovery, a common oil/water contact was observed in the JR sand. Recent drilling, however, has shown there to be multiple oil/water contacts as some compartments have been drained and others not.

The depositional model suggests that the producing sandstones are part of a shingled, offlapping shelf-edge lowstand systems tract progradational shoreface/deltaic succession. Several orders of permeability barriers have been identified. These include first order barriers comprising shales deposited as part of the transgressive to highstand system tract. Second order barriers are shales deposited in response to lobe switching and minor depocenter shifts within a given lowstand. Third order barriers comprise shales deposited within a given progradational event and are associated with a shingling architecture. Careful analysis of production history and perforation strategy, combined with analysis of recent drilling results within a tightly constrained sequence stratigraphic framework has revealed that significant bypassed pay remains in this 40-year old field.

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