Stratigraphy and reservoir characterization of the Grundy Formation (Pennsylvanian, eastern Kentucky) in relation with the overlying Pikeville and Hyden Formations

Abstract

Pennsylvanian successions of eastern Kentucky are well known as excellent outcrop analogues for Carboniferous fluvio-deltaic reservoirs in coal-bearing strata. Well-established, high-resolution correlations and previous work on regional geology enable detailed studies of sedimentology and sequence-stratigraphic development. In addition, extensive roadcuts permit a direct, 3D analysis of architectural geometries and heterogeneities.

The Breathitt Group is a coarsening- and shallowing-upward succession of Lower to Middle Pennsylvanian shallow-marine and fluvial deposits, representing the infill of an elongated foreland basin developed during the Alleghenian Orogeny. It has been divided into eight formations, each bounded at base by a basin-wide marine unit. Stratigraphic cyclicity in the Breathitt Group is commonly attributed to high-magnitude glacioeustatic fluctuations driven by Gondwanan glaciations. The uppermost formations in the group (Pikeville, Hyden, Four Corners and Princess) have been extensively studied since the early 80's. However, lower formations are poorly or not exposed, and therefore accessible only through subsurface data. Since 2014, new outcrops of the Grundy Formation have been exposed by roadworks for the US 460 in the area of Elkhorn City. Here we compare sedimentology, architecture and stacking patterns of the Grundy Formation with the overlying Pikeville and Hyden formations, outcropping along the US 460, near Pikeville.

In this study we focus primarily on an extensive outcrop, approximately 1 mile wide and 500 feet thick, exposing most of the Grundy Formation and the basal part of the Pikeville Formation. Twelve sedimentary logs have been measured, and 50 rock samples extracted for quantitative porosity, permeability and QEMSCAN analyses aimed at an evaluation of reservoir properties for the main sandstone bodies. Previous authors established that the Pikeville and Hyden formations are generally formed by vertically stacked, erosively based transgressive depositional sequences of 1) river-dominated deposits and incised-valley fills, 2) transitional coastal to marginal-marine sediments, including coal beds and 3) regionally extensive, distal marine deposits. We aim at explaining the differences in the stacking patterns between the Grundy and overlying formations, especially the decreasing proportion of continental deposits and the lesser volume of incised-valley fills, as well as their different sedimentological expressions. In addition, this study aims to combine outcrop and subsurface data from the area into a geo-cellular, 3D facies and architectural model for fluvio-deltaic successions, thereby trying to link reservoir-rock properties to sequence-stratigraphic phase.

AAPG Datapages/Search and Discovery Article #90258 © 2016 AAPG Eastern Section Meeting, Lexington, Kentucky, September 25-27, 2016