Architecture and Connectivity of Coal-Bearing Reservoirs: New Insights From Outcrop Analogues

Abstract

Predictive model for coal-bearing fluvio-deltaic successions in the subsurface are required to drive the effective and cost efficient hydrocarbon development of both unconventional coal-bed methane and conventional reservoir projects. The Eastern Kentucky and West Virginia road network provide world-class exposures of Upper Carboniferous coal bearing successions where the interplay between sand and shale intervals and intervening coals can be studied in detail. In this paper we present a summary of ongoing research recently carried out on the Pennsylvanian Hyden and Pikeville Formations where architecture and laterial facies variability can be observed and followed for several km thanks to exceptional outcrop quality and dense borehole data from coal mining operations. Coals, usually genetically associated with transgressive system tract, lies often on top of channel-fill sandstone and under shale dominated intervals the latter recording the transition from a flooded coastal plain to shallow to deep marine environment. However coals are found as well draping irregular topographic surfaces where wide and relatively deep (10–20 m) incisions can be recognised. In this situations coals are typically overlain by channel fill sandstone forming the stratigraphical unit above. In this cases, the coals are interpreted as forming during a low stand phase and thus possibly the true indicators of development of incised valleys. Five to ten meters-high inclined beds made of mixed heterolithic successions of sandstones and shales are associated with both fluvial-dominated mouth bars and point-bars develop in large meandering river systems often developed within estuarine environment. This study highlights the typical 3D features of these deposits allowing the definition of sedimentological and stratigraphical criteria to distinguish these tow systems in the subsurface. The Carboniferous succession of Eastern Kentucky is compared with the coeval succession in the North Sea (The Netherlands) to highlight the importance of outcrop based analogues studies to help understanding the overall distribution of subsurface geology by providing practical criteria for a) carrying out a well-to-well correlation and b) reconstruct the overall 3D reservoir architecture.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015