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Book Chapter

Build-and-Fill Sequences: How Subtle Paleotopography Affects 3-D Heterogeneity of Potential Reservoir Facies

By
Jason R. Mckirahan
Jason R. Mckirahan
Department of Geology, University of Kansas, 1475 Jayhawk Blvd., Lawrence, Kansas 66045-7613, U.S.A. Present address: ConocoPhillips Company, Westlake 3-6002, P. O. Box 2197, Houston, Texas 77252-2197, U.S.A. e-mail: jason. mckirahan@conocophillips. com
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Robert H. Goldstein
Robert H. Goldstein
Department of Geology, University of Kansas, 1475 Jayhawk Blvd., Lawrence, Kansas 66045-7613, U. S. A. e-mail: gold@ku. edu
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Evan K. Franseen
Evan K. Franseen
Kansas Geological Survey, 1930 Constant Ave, Lawrence, Kansas 66047-3724, U. S. A. e-mail: evanf@kgs. ku. edu
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Published:
January 01, 2003

Abstract

This study analyzes the three-dimensional variability of a 20-meter-thick section of Pennsylvanian (Missourian) strata over a 600 km2 area of northeastern Kansas, USA. It hypothesizes that sea-level changes interact with subtle variations in paleotopography to influence the heterogeneity of potential reservoir systems in mixed carbonate-siliciclastic systems, commonly producing build-and-fill sequences. For this analysis, ten lithofacies were identified: (1) phylloid algal boundstone-packstone, (2) skeletal wackestone-packstone, (3) peloidal, skeletal packstone, (4) sandy, skeletal grainstone-packstone, (5) oolite grainstone-packstone, (6) Osagia-brachiopod packstone, (7) fossiliferous siltstone, (8) lenticular bedded-laminated siltstone and fine sandstone, (9) organic-rich mudstone and coal, and (10) massive mudstone. Each facies can be related to depositional environment and base-level changes to develop a sequence stratigraphy consisting of three sequence boundaries and two flooding surfaces. Within this framework, eighteen localities are used to develop a three-dimensional framework of the stratigraphy and paleotopography.

The studied strata illustrate the model of “build-and-fill”. In this example, phylloid algal mounds produce initial relief, and many of the later carbonate and siliciclastic deposits are focused into subtle paleotopographic lows, responding to factors related to energy, source, and accommodation, eventually filling the paleotopography. After initial buildup of the phylloid algal mounds, marine and nonmarine siliciclastics, with characteristics of both deltaic lobes and valley fills, were focused into low areas between mounds. After a sea-level rise, oolitic carbonates formed on highs and phylloid algal facies accumulated in lows. A shift in the source direction of siliciclastics resulted from flooding or filling of preexisting paleotopographic lows. Fine-grained siliciclastics were concentrated in paleotopographic low areas and resulted in clay-rich phylloid algal carbonates that would have made poor reservoirs. In areas more distant from siliciclastic influx, phylloid algal facies with better reservoir potential formed in topographic lows. After another relative fall in sea level, marine carbonates and siliciclastics were concentrated in paleotopographic low areas. After the next relative rise in sea level, there is little thickness or facies variation in phylloid algal limestone throughout the study area because: (1) substrate paleotopography had been subdued by filling, and (2) no siliciclastics were deposited in the area. Widespread subaerial exposure and erosion during a final relative fall in sea level resulted in redevelopment of variable paleotopography.

Build-and-fill sequences, such as these, are well known in other surface and subsurface examples. Initial relief is built by folding or faulting, differential compaction, erosion, or deposition of relief-building facies, such as phylloid algal and carbonate grainstone reservoir facies, or siliciclastic wedges. Relief is filled through deposition of reservoir-facies siliciclastics, phylloid algal facies, and grainy carbonates, as well as nonreservoir facies, resulting in complex heterogeneity.

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SEPM Special Publication

Permo-Carboniferous Carbonate Platforms and Reefs

Wayne M. Ahr
Wayne M. Ahr
Department of Geology and Geophysics, Texas A&M University, College Station, Texas 77843-3115, U.S.A.
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Paul M. (Mitch) Harris
Paul M. (Mitch) Harris
ChevronTexaco E&P Technology Company, 6001 Bollinger Canyon Road, San Ramon, California 94583-0746, U.S.A.
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William A. Morgan
William A. Morgan
ConocoPhillips, Inc., P.O. Box 2197, Houston, Texas 77252-2197, U.S.A.
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Ian D. Somerville
Ian D. Somerville
Department of Geology, University College - Dublin, Belfield, Dublin 4, Ireland
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SEPM Society for Sedimentary Geology
Volume
78
ISBN electronic:
9781565763340
Publication date:
January 01, 2003

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