Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Deposition and Diagenesis of Central Kansas Uplift Cambro-Ordovician Arbuckle Group Strata, Trego County, Kansas
(1) Geology, Wichita State University, Wichita, KS.
Arbuckle strata of the Central Kansas Uplift (CKU) largely consist of cyclic intertidal to shallow subtidal carbonates terminated by a regional unconformity (the Sauk-Tippecanoe sequence boundary) which formed in the late early Ordovician. These rocks contain karstic dissolution-collapse breccias that formed under the influence of meteoric water during the post-Sauk regression and additional prolonged periods of subaerial exposure up through the early Pennsylvanian. CKU Arbuckle reservoirs are still of economic importance as improved oil recovery efforts are underway. To develop a better understanding of CKU Arbuckle diagenesis and porosity evolution, core from the Keja #1-3 well in Trego County, Kansas was analyzed macroscopically as well as through thin section petrography. Six depositional facies have been identified including oolitic dolograinstones, dolowackestones/mudstones, clotted algal boundstones (thrombolites), laminated algal boundstones (stromatolites), breccias, and shale intervals. Initial diagenesis resulted in pervasive, non-fabric obliterative dolomitization with low porosity. The subsequent Mid-Ordovician lowstand exposed these rocks to meteoric alteration and produced regionally extensive karst. Breccia development occurred with the weakening and collapse of overlying rock. Three types of breccias are observed, and include cave roof crackle breccias, mosaic breccias, and chaotic breccias. Though karstification and brecciation have resulted in an increase in porosity through dissolution, secondary features such as vugs and fractures play an important role in reservoir development. Thin section petrographic studies detail multiple dolomite generations, leading to a decrease in permeability. Advanced studies using integrated cathodoluminescence petrography and O-C isotope analysis will better illustrate the depositional and diagenetic history of the dolomitized breccias and supporting matrix.