--> ABSTRACT: Preservation of Anomalously High Reservoir Quality in Deeply-Buried, Chlorite-Coated Sandstones, by S. Bloch; #91021 (2010)

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Preservation of Anomalously High Reservoir Quality in Deeply-Buried, Chlorite-Coated Sandstones

BLOCH, SALMAN

On the Norwegian continental shelf, anomalously high porosity and permeability in normally-pressured, deeply-buried sandstones are often associated with well-developed and continuous chlorite coats. The nature of the association of high porosity and permeability with chlorite is highly complex. Although uncoated samples never display favorable reservoir quality, there is a wide range of porosity-permeability among chlorite coated samples.

A number of conditions have had to operate adequately and in conjunction to create high-quality sandstone reservoirs at deep burial depths (>15,000 ft). Preservation of significant porosity in the studied area occurred only when: (1) there was a source of ions necessary to precipitate chlorite; (2) the sand contained a high quartz abundance that provided a substrate for the coats and prevented collapse of preserved porosity; (3) sand deposition occurred in fluvially-influenced, high energy zones of near- shore marine environments; (4) the coated grains were of at least upper- medium size (mean grain size >0.45 mm), and (5) only limited amounts of carbonate cement, postdating chlorite-coats, precipitated.

Prediction of reservoir quality preservation in deep sandstones due to chlorite coatings is possible in extension exploration but not in rank wildcat exploration. 

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