Evaluating Structural Controls on the Formation and Properties of Carboniferous Carbonate Reservoirs in the Northern Midcontinent, U.S.A.
Published:January 01, 2008
W. Lynn Watney, Evan K. Franseen, Alan P. Byrnes, Susan E. Nissen, 2008. "Evaluating Structural Controls on the Formation and Properties of Carboniferous Carbonate Reservoirs in the Northern Midcontinent, U.S.A.", Controls on Carbonate Platform and Reef Development, Jeff Lukasik, J.A. (Toni) Simo
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During the Carboniferous a carbonate shelf covered areas of the central U.S, including Kansas, with the outer shelf and shelf margin intermittently extending through southern Kansas and northern Oklahoma. The regional setting resulted in deposition of relatively laterally continuous carbonate and siliciclastic facies belts. Areally sparse subsurface well data and surface exposures have led to the interpretation that most structures on the craton are simply shallow draped anticlines and associated synclines primarily reflecting general aspects of regional structure and depositional and erosional heterogeneity. Models that assume a broad continuous shelf relegate local structure to being minor or non-existent. However, our recent examination of subsurface data, 3-D seismic, and rock properties for oil fields from the Middle Mississippian shelf margin, Middle Pennsylvanian mid-shelf, and Late Pennsylvanian lower shelf indicate that regional- and kilometer-scale structures (e.g., faults, fractures, lineaments) segmented the shelf and shelf-margin areas in Kansas, primarily along Precambrian structures that were reactivated throughout the Phanerozoic. Movement on faults resulted in segmentation expressed as rhombic-shaped structural blocks (1-10s km) with subtle variations in relief (generally meter to ~ 70 m) and slope (near zero to upwards of 2-3 m/km). Regional, down-to-basin block faulting produced linear shelf edges and segmentation of the ramp and shelf profile repeatedly during the Carboniferous. The association of stratal packages and rock properties with structural elements argues that structure exerted continued, but episodic, influence and affected sediment accommodation, depositional patterns, paleotopography, weathering intensity, diagenesis, and later fluid movement, including hydrocarbon emplacement. Results from our study of the “stable” shelf carbonates of the Midcontinent indicate that tectonic events may have had far-reaching effects and caused structural deformation in the interiors of cratons. Sedimentologic and stratigraphic analyses in such settings can benefit by evaluating the possible influence of subtle faulting and fault reactivation on depositional and diagenetic patterns that can significantly influence rock properties and reservoir development.
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Controls on Carbonate Platform and Reef Development
Carbonate platforms and reefs emerge, grow and die in response to intrinsic and extrinsic mechanisms forced primarily by tectonics, oceanography, climate, ecology and eustasy. These mechanisms, or controls, create the physical, biological and chemical signals accountable for the myriad of carbonate depositional responses that, together, form the complex depositional systems present in the modern and ancient settings. If we are to fully comprehend these systems, it is critical to ascertain which controls ultimately govern the “life cycle” of carbonate platforms and reefs and understand how these signals are recorded and preserved. Deciphering which signals produce a dominant sedimentological response from the plethora of physical and biological information generated from superimposed regional to global-scale controls is critical to achieving this goal. With this understanding, it may be possible to extract common time- and space-independent depositional responses to specific mechanisms that may, ultimately, be used in a productive sense. Extensive research on a wide variety of carbonate platform and reefal systems in the past few decades has provided the foundation and understanding necessary to take carbonate research to a new level. With assistance from rapidly advancing computer software and an increasing use of cross-disciplinary integration, carbonate research is shifting from description and morphological analysis towards a science that is more focused on the assessment of process and genetic relationships. The aim of this special publication is to present a cross section of recent research that shows this evolution from a variety of perspectives and scales using examples distributed throughout the Phanerozoic.