--> Sequence Stratigraphic Architecture at the Reservoir Scale in St. Louis Carbonates, Kansas, by T. R. Carr and C. Lundgren; #90986 (1994).

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Abstract: Sequence Stratigraphic Architecture at the Reservoir Scale in St. Louis Carbonates, Kansas

Timothy R. Carr, Carl Lundgren

The St. Louis Limestone in Kansas is a prolific reservoir that has been viewed as a blanket-like deposit with random changes in facies resulting from processes such as migrating shoals. Integrated detailed analyses of facies, well logs, cores, and reservoir data within the framework of a high-resolution stratigraphy, based on surfaces, provides a new model of stratigraphic and reservoir geometry. Thin subtidal grainstone reservoir units represent a series of transgressive deposits at the bases of individual sequences. The reservoir facies onlap and pinch-out against a long-term exposure surface at the top of the underlying nonporous siliciclastic-rich limestones (eolianites), and interfinger and downlap basinward with muddy carbonates deposited in open shelf environments. Continued se -level rise led to the drowning of the shoal facies and deposition of deeper shelf wackestone over the grainstones forming the reservoir top-seal.

Features indicative of long-term exposure are visible in core at the top of St. Louis eolianites (e.g., paleocaliche and eolianite breccias). Distinctive spectral gamma ray response, consisting of relative uranium enrichment at these surfaces, provides additional evidence for relatively long-term exposure at the top of the eolianite facies, and a criterion for recognition of subaerial exposure surfaces in the absence of core. The contact between the subtidal grainstone shoals and the overlying muddy carbonate and shale facies is sharp and is interpreted as representing a drowning surface. This surface has a distinctive spectral gamma ray response with a relative enrichment of potassium.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994