--> ABSTRACT: Sandstone Exhumation Effects on Velocity and Porosity: Perspectives from the Ferron Sandstone, by R. D. Jarrard and S. E. Erickson; #91021 (2010)
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Sandstone Exhumation Effects on Previous HitVelocityNext Hit and Porosity: Perspectives from the Ferron Sandstone


The fluvial-deltaic sediments of the Cretaceous Ferron Sandstone, Utah, were buried to 3000-3400 m, with associated compaction and cementation, then uplift exhumed different portions of the Ferron by 0 to >3400 m. Previous HitVelocityNext Hit and density-based porosity logs for 24 wells, plus petrophysical analyses of outcrop plugs, show the petrophysical responses of Ferron exhumation.

Exhumation here is accompanied by an acceleration of carbonate leaching, probably because of increasing groundwater flux at shallower depths. Previous HitVelocityNext Hit logs show a Previous HitvelocityNext Hit decrease that is even greater than expected based on this secondary porosity development. Ferron logs deeper than 550 m, as well as high-pressure measurements of plug Previous HitvelocityNext Hit, fit the time-average Previous HitvelocityNext Hit-porosity relationship, whereas shallower logs are much slower than predicted from this transform, and outcrop-plug velocities are even slower. We attribute this Previous HitvelocityNext Hit plunge to reduction of framework modulus, caused mainly by exhumation-induced pressure release but enhanced in outcrop by freeze-thaw.

Acceleration of carbonate leaching with exhumation, as seen in the Ferron, may be anticipated only where meteoric water flux, rather than hydrocarbon migration, controls carbonate dissolution. Previous HitVelocityNext Hit rebound caused by pressure release probably is a pervasive companion to exhumation. For exhumed formations, undetected leaching or rebound can cause errors in the following analyses: estimating amount of exhumation from Previous HitvelocityTop/depth or porosity/depth trends, extrapolating outcrop-based petrophysical relationships to the subsurface, calculating reservoir porosity from seismic velocities for depths of <550 m, and estimating accretionary prism fluid flux using seismic velocities.

AAPG Search and Discovery Article #91021©1997 AAPG Annual Convention, Dallas, Texas.