Date of Graduation

12-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Geosciences (PhD)

Degree Level

Graduate

Department

Geosciences

Advisor/Mentor

Liner, Christopher L.

Committee Member

Manger, Walter L.

Second Committee Member

Covington, Matthew D.

Third Committee Member

McGilvery, T.A. "Mac"

Fourth Committee Member

Zachry, Doy L.

Keywords

3D seismic; attributes; carbonate; paleokarst; well logs

Abstract

Paleokarst are characterized by epigene and/or hypogene processes in their formation and hold significant numbers of hydrocarbons and other natural resources. This dissertation examines worldwide seismic expression of paleokarst; and specifically, the characterization of paleokarst reservoirs developed across the Cherokee Platform, and in the Arkoma Basin, Oklahoma.

Worldwide subsurface paleokarst formations are of Precambrian to Miocene age and found at depths less than 200 m to as great as 8000 m. Karst can be are expressed on seismic records as sinkholes, paleocave collapse, and tower morphologies. Seismic modeling indicates that karst can be modeled and imaged to better understand its subsurface architecture. High variance, negative curvature, bright amplitudes/localized bright spots characterize karst. As part of this dissertation, a worldwide map of paleokarst locations was generated, and geophysical measurements for some of these locations were taken for further analysis.

In the Arkoma Basin, the Ordovician Viola Limestone, Mississippian Caney Shale, Pennsylvanian Jefferson Sandstone and Wapanucka Limestone were mapped on seismic data, and paleokarst sinkhole and pipe features were identified. Viola sinkholes can be recognized as structural depressions, characterized by higher seismic variance, and lower positive amplitude, and most-negative curvature. Wapanucka sinkhole features are subtle, show lower variance and higher positive amplitude, and no structural relief. The Ordovician sinkholes are coincident with the Pennsylvanian Wapanucka Limestone which are 610 m apart, with some of these sinkhole features occurring over vertical pipe features. The Viola sinkholes and pipe features are inferred to be a mature epigene karst system. The Wapanucka sinkholes are interpreted as an immature karst system with epigene and hypogene elements. This study indicates for the first-time evidence of pipe features that extend from the Ordovician into the Mississippian, and the presence of Wapanucka sinkhole features in the Arkoma Basin of Oklahoma.

In the Cherokee Platform, the term Chat designates residual chert which is either in place or transported, formed by an epigene process, and found above the Miss Lime. The tripolite is internal to the Mississippi Lime formed by in place alteration of the limestone by epigene and/or hypogene processes. I have classified and mapped Chat and tripolitic chert (tripolite) zones by seismic evaluation calibrated by well control with full-wave sonic log data. Chat and tripolite show clear separation on total acoustic impedance from Miss Lime, but no separation with VP /VS, and both exhibit total porosities greater than 20 % with an indication of fracture porosity. Sonic-based normal incidence wedge models for Chat bounded above by Pennsylvanian Shale and below by Miss Lime indicate two seismic expressions are probable: a strong negative amplitude when Chat thickness is above tuning and a weak or non-existent amplitude associated with small impedance contrast between Chat and overlying Pennsylvanian shale. This analysis suggests both the traditional Chat ‘strong response’ and a new ‘dim-out’ exploration approach. Tripolite response is consistently a negative amplitude event that strengthens with increasing tripolite thickness. This study provides an interpretive framework for characterizing Chat and tripolite zones associated with the Mississippian Lime in the US Midcontinent, which may be applicable to areas around the world.

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