Page 423 - Petrophysics 2E

ALTERATION OF WE'ITAElILITY 391

treated with various concentrations of the additives mentioned above
and dried once more at 1 10°C to fix the additive onto the surface of the
rock.
Wettability alteration must be conducted under carefully controlled
conditions because the final wettability depends on:

(1) the mineral composition of the rock;
(2) the cleaning procedure used;
(3) the type of additive used (silane, asphaltene, etc.);
(4) the concentration of the additive in the solvent used to permeate the
core; and
(5) the procedure used to evaporate the solvent and dry the core.

Completely uniform wettability throughout the core is not attained,
but this method has been used successfully to obtain systems at various
states of average wettability for examination of the effects of wettability
on production [75, 85-87].

ADDITION OF FLUID-SOLUBLE COMPOUNDS TO WATER AND OIL

Fractional wettability of unconsolidated sands and beads has been
achieved by solute/solvent treatments. Generally, a portion of the
cleaned, dry, sand is treated with a solvent containing the additive and
then dried. The treated sand is then mixed in various proportions with
untreated sand to produce different degrees of fractional wettability
[76, 88-90]. Graue et al. found that chalk cores attain fractional
wettability when they are aged for approximately 100 hours at 90°C
by immersion in crude oil [91, 921. The same method when used
with sandstone cores (including Berea sandstone from Amherst, Ohio)
did not produce consistent changes of wettability. They found that
various degrees of change of wettability from water-wet toward neutral,
or fractional, wettability are attained by immersion in different oils.
Wettability was determined using the Amott wettability index and the
imbibition-rate method.
Tweheyo et al. changed the wettability of sandstones from strongly
water-wet to neutral and oil-wet by adding organic acids (0-toluic acid)
and amines (dodecylamine and hexadecylamine) to the oil used to
saturate the cores [83]. The amines produced the largest changes from
water-wet to oil-wet. Waterfloods of the modified systems produced
results that have been reported previously:

(1) water-wet samples exhibit rapid and almost complete production
by the time water breakthrough occurs;