1st Research Conference - Gulf Coast Section SEPM

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with less complete bedsets represent channel deposits while the thinner sandstones with more complete bed sets represent overbank deposits. Thinly bedded, non-bioturbated upper Woodbine sandstones are gradational upward into the thickly bedded, bioturbated sandstones. The non-bioturbated sandstones contain only turbidite bedsets reflecting overbank deposition. Ordered sequences are absent in the bioturbated upper Woodbine sandstones. A few relict ripple-laminated intervals suggest that the bioturbated sandstones were deposited by more persistent low flow regime, possibly geostrophic currents, rather than by turbidity currents. Woodbine clastic deposition is associated with a prograding shelf margin. Electric log correlation and seismic sections suggest that the lower Woodbine sandstones were deposited as a group of channel and overbank turbidites on the lower slope. Middle Woodbine sandstones were deposited in isolated feeder channels located farther up the slope and closer to the shelf break. The thick section of slope shale containing the lower and middle turbidite sandstones is overlain by thinly to thickly bedded upper Woodbine sandstones interpreted to be shelf margin sandstones that cap the prograding slope sequence. A turbidite origin for most Woodbine sandstones in the Seven Oaks producing area suggests that channel sandstones associated with submarine fans located farther downdip, possibly over the Sligo reef break, may form extensive diptrending reservoir bodies.
Origin of Porosity in Deeply Buried Tuscaloosa Sandstones, False River Field, Louisiana Franks, S.G., ARCO O&G, Dallas, TX (p. 20-21) Deeply buried Tuscaloosa sandstones in the False River Field, Pointe Coupee Parish, Louisiana, have unusually high porosity and permeability for their age (Upper Cretaceous), depth of burial (20,000 feet), and temperature (350 o - 400 o F). Permeabilities up to 1200 millidarcies and porosities as high as 27% have been reported. Petrographic analysis of Woodbine-Tuscaloosa sandstones, from the outcrop and from 24 wells ranging in depth from 2900 to grater than 20,000 ft, suggests that porosity in the deep Tuscaloosa of Louisiana is mostly of secondary origin. Present evidence indicates that the porosity is due to leaching at depth of early iron-rich calcite cement and basic rock fragments derived from an Upper Cretaceous volcanic terrain extending from central Mississippi into southern Arkansas. The interpreted diagenetic sequence is as follows: • Stage 1: Precipitation of authigenic smectite clay rims at shallow depths (converted to chlorite during burial). • Stage 2: Cementation of some sandstones by ferroan calcite, which postdates clay rims and replaces many framework grains. • Stage 3: Progressive silica cementation by quartz overgrowths in sandstones not cemented by early ferroan calcite (Stage 2). Sandstones with more than 10-15% volcanic clasts generally do not develop quartz overgrowths. • Stage 4: Dolomite cement post-dates silica cement and fills remaining porosity between quartz overgrowths. • Stage 5: Dissolution of iron-rich calcite and volcanic rock fragments produces abundant secondary porosity. • Stage 6: Following and accompanying dissolution, additional iron-rich chlorite and minor quartz overgrowths were precipitated. Depth of appearance and oxygen and carbon isotope data indicate that silica and dolomite cement formed at temperatures probably greater than 80 o C. Early carbonate cement has re-equilibrated isotopically and has values similar to that of the late dolomite cement. Leaching of the calcite cement probably is due to enrichment of the pore fluids in carbon dioxide evolved during maturation of the organic matter in the sediments. Some of this isotopically light carbon is incorporated in the late stage dolomite cement and in reequilibrated calcite.
Page 2 and 3: Cover Photographs Scanning electron
Page 4 and 5: GULF COAST SECTION SOCIETY OF ECONO
Page 6 and 7: BACK TO THE FUTURE: A NOTE FROM THE
Page 10 and 11: The Deep Tuscaloosa Gas Trend of So
Page 12 and 13: Park formations indicate that the s
Page 15 and 16: Fluid System Compositions: Drilling
Page 17: Depositional Environment of Woodbin
Page 21 and 22: The East Texas Field Halbouty, M.T.
Page 23 and 24: No. 1 Play in the U.S.A., South Lou
Page 25 and 26: sedimentary rock characteristics, i
Page 27 and 28: Local highs on aeroradioactivity ma
Page 29 and 30: Secondary Porosity in the "19,800 F
Page 31 and 32: Sedimentology of the "19,800 Foot"
Page 33 and 34: Preservation of Porosity in the Dee
Page 35 and 36: 21,194.5 - 95 0.9 14.4 20.2 29.9 21
Page 37 and 38: Environment of Deposition and Reser
Page 39 and 40: Seismic Stratigraphy of Seven Oaks

1st Research Conference - Gulf Coast Section SEPM

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