Sedimentologic Control on Diagenesis and Petrophysical Properties in a Skinner Sandstone Reservoir in Southeastern Kansas
David J. Bouquet, Anthony W. Walton
Depositional environment and detrital composition exert the major control of diagenetic history and petrophysical properties of sandstones in the Strauss field. The sandstones can be divided into four distinct lithofacies: (A) conglomerate, (B) cross-bedded and structureless sandstone, (C) ripple-bedded sandstone, and (D) interlaminated sand, silt, and shale. An upward-fining sequence of lithofacies A-D is interpreted to have been deposited in a distributary channel, whereas an upward-coarsening sequence of lithofacies D and C represents deposits of a crevasse splay or small distributary mouth bar.
The effects of diagenesis and the resulting petrophysical properties vary with lithofacies. The following diagenetic sequence was noted: (1) compaction, (2) formation of pyrite, siderite, and rare chlorite grain coatings, (3) quartz and feldspar overgrowth cementation, (4) dissolution, (5) iron-magnesium-calcium carbonate cementation, (6) kaolinite precipitation, (7) authigenic illite formation, and (8) oil emplacement. Lithofacies A, the conglomerate, is characterized by a pore-occluding siderite cement, which inhibits later diagenesis and results in low porosity and permeability. The finer grained lithofacies, C and D, are composed mostly of quartz and plagioclase with abundant soft rock fragments and mica grains. Early compaction results in the deformation of ductile rock fragments and mica grains forming a pseudomatrix, which reduces porosity and permeability. Therefore, later diagenesis is inhibited, as noted by the lower percentage of late diagenetic phases in lithofacies C and D. The coarser grained lithofacies B sandstones are composed mostly of quartz and plagioclase, but lack the abundant soft rock fragments and mica grains found in lithofacies C and D. As a result, lithofacies B sandstones have higher porosity and permeability, and a greater percentage of later diagenetic phases such as iron-magnesium-calcium carbonate cements and kaolinite.
We can model the distribution of these various facies by understanding the depositional environment, and thus, locate the better quality reservoir rock and preferred flow paths through the reservoir.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.