Abstract

Diagenetic history and petrophysical properties of the Corcoran and Cozzette sandstones are closely related to depositional environment. Coarsening-upward shoreface-beach sequences and fining-upward tidal-inlet sequences display the same diagenetic phases: (1) compaction and deformation, (2) overgrowth of quartz, (3) cementation by carbonate, (4) dissolution of feldspar and carbonate, and (5) precipitation of kaolinite. Development of the phases differs according to vertical position within the sequences. Finer grained (3ϕ-4ϕ) shoreface and upper tidal-inlet deposits contain abundant pseudomatrix. Poorly developed quartz overgrowths and little secondary porosity indicate that pseudomatrix and carbonate restricted fluid movement during phases 2 and 4. Abundant overgrowths and pervasive secondary porosity in coarser (2ϕ-3ϕ) beach and lower tidal-inlet deposits suggest freer movement of diagenetic fluids apparently in the absence of much pseudomatrix. Kaolinite is best developed in coarser sandstones and occurs as local replacement and ubiquitous pore-filling phases, but its abundance varies with abundance of feldspar and prekaolinite porespace. Lower tidal-inlet sandstones containing 8-13% feldspar display both replacement and ubiquitous pore-filling kaolinite. Beach sandstones with less feldspar (3%) contain only local replacement kaolinite. Lower tidal-inlet deposits present a paradox: well-developed secondary porosity but abundant diagenetic kaolinite has reduced permeability. Permeability is greatest in high-energy beach deposits where the least pseudomatrix and diagenetic kaolinite occur; these are the best targets for exploration.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not currently have access to this article.