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The Effects of Mineral Fractionation by Turbidity Currents on Previous HitReservoirNext Hit Quality: A Study From the Aspen Field, Northern Gulf of Mexico

Abstract

Turbidites are prolific hydrocarbon reservoirs, yet numerous studies document that Previous HitreservoirNext Hit quality (Previous HitporosityNext Hit and permeability) prediction is a difficult challenge. In this study, we examine core from the Aspen Field, northern Gulf of Mexico to test how sedimentation processes by turbidity currents impacts Previous HitreservoirNext Hit quality in turbidite reservoirs. Strata in Aspen Field consist of a series of interbedded, Upper Miocene Previous HitsandstoneNext Hit and mudstone intervals that are interpreted to reflect deposition in a distributive channel-lobe system. Five facies are identified, which differ by interpreted sediment-transport mechanism and interpreted flow type. The vertical succession of facies in core is interpreted to record the compensational stacking of 5 lobe elements, resulting in the vertical juxtaposition of the axes, off-axes, and margins of the lobes. X-ray diffraction analysis documents axis-to-margin variations in the composition of turbidite lobes, particularly with regard to the amount of volcanic glass and its diagenetic byproduct, clinoptilolite, resulting in abrupt vertical variations in Previous HitporosityNext Hit and permeability. Clinoptilolite, which results from the devitrification of volcanic glass, is enriched in finer-grained, argillaceous facies, resulting in increased cementation and reduced Previous HitporosityNext Hit and permeability. The argillaceous facies are interpreted to be from the lateral and distal margins of turbidite lobes. We propose that because volcanic glass is highly angular and has a relatively low density relative to the other mineral grains in the Aspen Field, turbidity currents preferentially fractionate the glass grains to the lateral and distal margins of lobes, where they alter to clinoptilolite during diagenesis. Understanding how fractionation of mineral grains relates to spatial changes in Previous HitporosityNext Hit and permeability has implications for Previous HitpredictingNext Hit vertical changes in Previous HitreservoirTop quality in a variety of turbidite-hosted reservoirs. Results of this study can be used to infer similar patterns in other turbidite systems that contain a diverse mineral assemblage with variable settling velocities.