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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 63 (1979)

Issue: 9. (September)

First Page: 1599

Last Page: 1600

Title: Clasticity Index--Key to Correlating Depositional and Diagenetic Environments of Smackover Reservoirs, Oaks Field, Claiborne Parish, Louisiana: ABSTRACT

Author(s): Charles R. Erwin, David E. Eby, Virgil S. Whitesides, Jr.

Article Type: Meeting abstract


Oaks field is a stratigraphically trapped Smackover field which produces from at least three separate reservoirs. Individual reservoirs are shoaling-upward carbonate

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grainstone cycles. The three reservoirs are offlapping and are separated from each other by clastic facies rich in terrigenous matter. The two oldest reservoirs were deposited as well-defined barrier-island complexes up to 4 mi (6.4 km) long and less than ½ mi (0.8 km) wide. The youngest reservoir is less well defined and was deposited primarily as coalescing bars which were only occasionally emergent. All carbonate facies were deposited as mud-free oolitic and rhodolitic grainstones. Most porosity occlusion was by early cementation in the meteoric phreatic and mixed phreatic zones, paralleling depositional strike.

Ten of the 13 producing wells and all four dry holes were conventionally cored. Thin sections were made at 1-ft (0.3 m) intervals from perm plugs, corresponding with measured values of porosity and permeability. Detailed petrographic correlation of wells allowed the individual reservoirs to be subdivided into distinct mappable units on the basis of a plot of the diameter of the largest coated grain ("clasticity index") in each thin section. Clasticity index provides a simple, rapid tool for precise well correlation within individual reservoirs; the correlation is not possible by conventional log methods.

Prior to the incorporation of petrographic analysis in the development drilling program, the field consisted of seven producing wells and three dry holes. Combining clasticity plots and other petrographic information with porosity isopach values enabled the field size to be almost doubled with the successful completion of the next six holes.

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