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ABSTRACT: Fill'er Up, Tony ... and Check the Oil: Petroleum Migration into Pay Sands at the Mars Field, Deepwater Gulf of Mexico


Several oil pools at the Mars field are trapped adjacent to salt bodies that are inferred to have served as vertical migration pathways for oil generated by more deeply-buried source rocks. This geometric relationship can be intepreted as evidence that charging these pay sands required a `backfilling' mechanism (i.e., incremental charge entering at the crest of each pay zone had to displace an underlying buoyant oil column). For example, structural cross sections give the impression that backfilling occurred on both flanks of Mars. But a rigorous analysis of oil migration at Mars shows that backfilling mechanisms do not need to be invoked to explain how oil migrated into and through these turbidite reservoirs.

The traps at Mars combine several structural and stratigraphic elements. The general structure of the Mars field is that of an inclined, east-plunging trough lying within a salt embayment. The largest oil columns occur on the northern major limb of the trough. Smaller oil columns are found on the minor limb of the trough wrapping around the northern face of the Venus salt diapir (which probably provided a vertical entry `front' for oil charge into Mars).

Our key conclusions are that: (1) oil migrating up the plunge of the Mars trough along the Venus salt-sediment interface from structural lows on the minor limb spilled across the trough axis to fill traps on the major limb of the structure without requiring backfilling from structually-high charge entry points along both limbs of the trough; and (2) the suture between the Venus and Antares salt bodies, and stratigraphic complexities within turbidite deposits both played key roles focussing oil charge in and around the Mars field.

AAPG Search and Discovery Article #90941©1997 GCAGS 47th Annual Meeting, New Orleans, Louisiana