--> ABSTRACT: Petrography and Diagenesis of Reservoir and Non-Reservoir Sandstones in Shattuck Member of Queen Formation, Northwest Shelf of Permian Basin, by A. Malicse, J. Siegel, and J. Mazzullo; #91030 (2010)

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Petrography and Diagenesis of Reservoir and Non-Reservoir Sandstones in Shattuck Member of Queen Formation, Northwest Shelf of Permian Basin

A. Malicse, J. Siegel, J. Mazzullo

The Shattuck Member is a thick (6-20 m) sandstone that defines the top of the Queen Formation (Permian, Guadalupian) and is a major hydrocarbon reservoir on the Northwestern shelf of the Permian basin. The Shattuck was deposited in desert dune and interdune, dry and wet sand sheet, and sandy sabkha environments during a lowstand of sea level. The desert dune, interdune, and dry sand sheet deposits constitute the producing horizons in the Shattuck, whereas the wet sand sheet and sabkha deposits are generally non-productive. The purposes of this study are to examine the petrographic characteristics of the producing and non-producing horizons with petrographic and scanning electron microscopes, and to determine their provenance and diagenetic history.

The reservoir and non-reservoir horizons in the Shattuck are both composed of well-sorted, rounded to subrounded fine to very fine-grained sand with a detrital composition of 70 to 85% quartz, 15 to 30% feldspar, and traces of mica and opaque iron oxide grains. Generally, the quartz grains are monocrystalline and have Boehm lamellae, bubble trains, and undulose extinction, and the feldspar grains are potassic and variably weathered. The texture and roundness of the grains are attributed to their eolian transport history, whereas the detrital composition indicates their derivation from plutonic and sedimentary rock sources.

The reservoir and non-reservoir horizons in the Shattuck shared three successive phases of early diagenesis: (1) dissolution and alteration of feldspar and Fe-Mg grains; (2) precipitation of grain-lining feldspar, hematite, and hematitic smectite; and, (3) precipitation of pore-filling anhydrite, calcite, and dolomite cements. The Shattuck reservoirs were created by the subsequent partial dissolution of the pore-filling anhydrite, calcite, and dolomite cements and any remaining unstable grains, and the reduction of the grain-lining hematite and hematitic clay prior to the introduction of hydrocarbons.

Presently, the reservoir horizons in the Shattuck have average porosities of 15 to 20%, and permeabilities between 5 and 500 md. They are distinguished by their tan and brown color, which is attributed to the dissolution of hematite during the formation of their secondary porosity. The non-reservoir horizons have average porosities of 0 to 5%, and permeabilities between 0 and 5 md. They are distinguished by their reddish-brown color, which is attributed to the abundance of hematite, hematitic clays, and oxidized Fe-Mg grains.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.