Print this pagePreservation 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.