1st Research Conference - Gulf Coast Section SEPM

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Original primary porosity in False River reservoir sandstones, estimated at 42%, has been reduced by early mechanical compaction, followed by pressure solution, cementation, and finally by late mechanical compaction, followed by pressure solution, cementation, and finally by late mechanical compaction. Present porosities of 20-25% in many of the fine- to medium-grained sandstones are much higher than would normally be anticipated, in view of the porosity reducing processes that can be identified and the great depth of burial. Examination of thin sections and scanning electron photomicrographs reveal extensive partial and total leaching of 15% to 20% of the framework grains. Most of the leached grains probably had an original silicate mineralogy. Point count studies indicate that 20% of the total porosity may be attributable to this process. Porosity created in this manner is easily identified by the remnant shells of authigenic chlorite which remains after dissolution of the detrital grains. Subsequent to this grain leaching, or most likely concomitant with it, continued compaction of the reservoir sandstones occurred. This interpretation is supported by remnant chlorite shells that were compacted until the opposing shell walls are nearly in contact. The occurrence of euhedral quartz crystals and ferroan calcite within many of the collapsed or crushed chlorite shells represent a closing stage of diagenesis. Continued porosity reduction through pressure solution and cementation would have destroyed reservoir capacity if geopressuring of the Tuscaloosa interval had not occurred soon after grain dissolution. False River Field is an example of production from reservoir sandstones with a capacity greatly enhanced by secondary porosity. Mineralogical immaturity of the original Tuscaloosa sediment and geopressuring of sandstones that experienced a complex history of compaction, cementation, and dissolution are believed to be significant factors that have combined to produce this deep occurrence of unusually high porosity.
Sedimentology of the "19,800 Foot" Tuscaloosa Sandstone, False River Field, Pointe Coupee and West Baton Rouge Parishes, Louisiana Smith, G.W., Chevron USA, New Orleans, LA (p. 30-31) The "19,000 Foot" sandstone in False River Field has been cored in four of the productive wells and in two of the dry holes. Sedimentological studies of False River sandstones are based on these cores. From the total 994 ft of core, approximately 200 ft from the Chevron No. 1 W.A. Lorio, Jr and No. 1 Crochet have been selected for display to illustrate lithology, bed relationships, and sedimentary structures. Fine- to medium-grained moderately well to well sorted reservoir sandstones that tend to be massive, and occasionally friable, occur at the top of a gradational, coarsening upward sequence of shale, siltstones, and very fine- to fine-grained carbonaceous sandstone. Individual sandstones within the productive interval seldom exceed 40 ft. Wire-line log response can be generally be related directly to lithologic and grain-size changes. Sandstone composition, determined by X-ray diffraction, has been correlated with standard porosity and permeability measurements. Reservoir porosities frequently exceed 20% and permeability measurements. Reservoir porosities frequently exceed 20% and permeabilities exceeding 100 md are common. Permeability rarely exceeds 0.1md when the porosity is less than 15%. High porosity values are related to minor cementation of the grain framework and selective grain dissolution which contributes significant secondary porosity. Thin section and SEM micrographs illustrate distribution and paragensis of the cements and the primary and secondary pore systems. A depositional model based on the sedimentology and paleontology of the False River sandstones in the "19,800 Foot" interval proposes a possible interpretation of reservoir geometry and depositional environment.
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 and 18: Depositional Environment of Woodbin
Page 19 and 20: Origin of Porosity in Deeply Buried
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: Secondary Porosity in the "19,800 F
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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