Depositional Facies and Hydrocarbon Reservoir Compartmentalization of the Mississippian Aux Vases Formation at King Field, Jefferson County, Illinois

Abstract

King field has produced over 4 million bbl of oil from the Mississippian Aux Vases Formation along a north-south-trending anticlinal structure 3 mi long and 1.5 mi wide. The porous and permeable quartz sandstone, which comprises the principal hydrocarbon reservoir, can grade laterally into nonporous calcareous sandstone, siltstone, shale, or limestone within one well location (660 ft). The Aux Vases Formation at King field was deposited in an intertidal to subtidal, mixed siliciclastic-carbonate environment, and the resulting mosaic of depositional facies significantly affects reservoirs continuity. Impermeable to only slightly permeable siltstones, shales, and limestones of the various offshore facies, and shales and siltstones of the tidal-flat facies separate the producing sandstones of a tidal channel-offshore bar facies into distinct reservoir compartments. This reservoir heterogeneity results in an oil-water contact at various depths across the field. Lateral compartmentalization of the reservoir has allowed large sections of the Aux Vases reservoir to remain unswept by waterflooding. Volumetric analyses suggest that untapped reservoir compartments may contain an additional 1-2 million bbl of oil recoverable by primary and waterflood methods.