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Influence of Depositional Dynamics on the Internal Architecture and Facies Continuity of the Eagle Ford Formation, TX, USA


Hydrocarbon production in the Eagle Ford Formation primarily targets the organic-rich Lower Eagle Ford, which was deposited below storm-wave base, under the influence of bottom currents. Sediments include calcitic planktonic organisms, whose abundance was driven by episodes of increased primary productivity driven by volcanic ash deposition productivity, and clay minerals derived from continental weathering. Bottom currents deposited and reworked these sediments, resulting in discontinuous beds and lenses of pelagic grainstones and ash beds interbedded with organic-rich globigerinid argillaceous wackestones. This study investigates and quantifies the internal heterogeneity and complex internal architecture of the Lower Eagle Ford. Datasets include outcrop along Highway 90, Val Verde Co. and Big Bend National Park Brewster Co. West Texas and vertical and horizontal subsurface cores. Outcrop observations show that the lateral continuity of pelagic grainstone bodies depends on the direction of paleocurrents; the lateral continuity of these beds is lowest along the progradation direction, reaching at most 50%. Only five of 35 traced grainstone horizons were continuous over a 170 m long outcrop. Ash bed continuity is controlled mainly by thickness and erosional processes: ash beds thicker than 1 cm display 72% continuity. Thinner ash beds display much lower continuities. Preliminary study of small scale facies variations a long horizontal core reveals similar patterns of discontinuity. This suggests that facies continuity may be similar at all scales.