Page 365 - Reservoir Formation Damage

Inorganic Scaling and Geochemical Formation Damage 345

contain considerable detrital clay minerals and carbonate clasts, along with
quartz, plagioclase, and minor volcanic rock fragments and ^-feldspar
grains. Observed accessory minerals were muscovite, glauconite, horn-
blende, zircon, and pyrite. Authigenic minerals are dominated by carbon-
ate cements and filamentous lathes of pore-lining and pore-filling illite.
Some authigenic chlorite and overgrowths of quartz and feldspar are also
present." He reports that the formation porosities and permeabilities are
in the ranges of 10-20% and 0.5 to several mD, having consider-
able natural fracture permeability in certain regions and possibly some
systematic fractures. He reports that this sandstone formation contains
6-10 volume % illite, 1-2 volume % chlorite, and negligible amounts of
kaolinite (Scott, 1988).
Typical minerals present in porous rocks and subject to dissolution
in contact with aqueous phase include the various types of carbonates
such as calcite, CaCO 3, magnesite, MgCO 3, dolomite, CaMg(CO 2) 2,
strontianite, SrCO 3, witherite, BaCO 3, and siderite, FeCO 3, and various
types of sulfates such as anhydrite, CaSO 4, gypsum, CaSO 4 • 2H 2O,
celestine, SrSO 4, and barite, BaSO 4 (Schneider, 1997).
Schneider (1997) points out that the kaolinite compositions remain
close to the Al 2Si 2O 5(OH) 4 formula, but the illite and chlorite formulae
may vary as indicated by Aja et al. (1991a,b). He considered the typical
mean compositions of the Bothamsall (Pennsylvanian), Rotliegendes
(Permian), and Gulf Coast illites given, respectively, by (Warren and
Curtis, 1989; Kaiser, 1984):

M A/ (13-40)
^0.80 ( 8 0. 13^0.07 1.80 ) (^0.60^3. 3.40

(13-41)

(13^2)

Schneider considered the typical mean compositions of the Gulf Coast
(Kaiser, 1984) and the North Sea (Curtis et al., 1984, 1985) chlorites
given, respectively, by

Mg 23Fe 23Al L4(Al lASi 2. 6)O w(OH\ (13-43)

M Fe Al Al S H (13-^4)
82.l5 2.25 \.5( \30 h.lo)°\o(° \