Integrated 3-D seismic, well log, and petrophysical analyses of mature gas reservoirs in Vermilion Block 50 and nearby Tiger Shoal fields established a firm genetic context from which reservoir-specific attributes could be derived for locating additional resources. The 10,000-ft study interval, within which as many as 36 potential gas and oil reservoirs occur, shows minor faulting and represents about 15.5 m.y. of deposition - nearly the entire Miocene Series.
The overall regressive succession comprises more than 30 fourth-order (~0.5-m.y.) sequences. Paleontologic data indicate that third-order cycle tops coincide with those of published basinwide coastal-onlap curves. Systems tracts are increasingly dominated by more landward facies upsection. Arial patterns from net-sand maps, 3-D stratal slices of seismic data, and log-facies analysis indicate that the succession represents nearly an entire basal-slope (bottom-lower Miocene) to proximal-shelf (top-upper Miocene) depositional tract. Sequences lower in the section, 200 to 600 ft thick, contain few but thick (200-ft) incised valleys (IV) filled with shaly estuarine deposits and upper-slope-canyon fills. Local lowstand wedges onlap the upper slope surface. Conversely, upper sequences, 100 to 200 ft thick, partly comprise blockier fluvial-dominated IV fills and proximal deltaic sands.
Untapped and producing gas reservoirs occur primarily in five facies within the two fields. In Vermilion block 50, slope-fan, lowstand (LS)-wedge, LS-IV, transgressive-bayhead-deltaic, and late-highstand (HS)-deltaic sands of early to middle Miocene age predominate. In Tiger Shoal, reservoirs occur in generally stratigraphically and structurally higher mid-to-late-HS-deltaic and LS-fluvial, IV sands in the middle to upper Miocene section.
2000 AAPG Annual Meeting
Marching into Global Markets -- A World of Resources