Excessive
water production from natural gas reservoirs is a main
challenge facing the industry nowadays. Polymeric gelants have been
widely applied to seal the water production zones, leading to a more
feasible production operation. Nevertheless, conventional treatments
fail in reservoirs characterized with the presence of sour gases.
In this paper, aluminum-based salts are investigated as potential
replacement for the conventional chromium acetate as crosslinkers
for polyacrylamide (PAM), where aluminum has the advantage of being
more environment-friendly besides its abundance. The investigation
covers the whole pH range and examines the rheological behavior of
the mature gels in the temperature range between 25 and 100 °C.
While chromium acetate was proven to be sensitive to the presence
of sour gases, namely, CO
2
and H
2
S, because
of the inability to produce a stable gel at the acidic conditions,
this paper presents aluminum-based crosslinkers that are more tolerable
toward high acidity. Unlike the conventional crosslinkers, the gelation
rate in aluminum acetate and aluminum aminoacetate systems was found
to decrease with the increase in pH. Both the crosslinkers succeeded
in producing a strong gel with a storage modulus of more than 2000
Pa. Moreover, this study relates the physical stability of the colloidal
aluminum crosslinkers with the viscoelastic behavior of the mature
gel. The results reveal that aluminum acetate, among the screened
salts, has a controllable gelation time at pH conditions between 3.5
and 8.5 and is the most stable in the temperature range 25–100
°C. PAM/
AlAc
system has a gelation time of around
50 min at 75 °C making it suitable for near-wellbore treatments,
while the gelation time increased to 80 min upon increasing the pH
of the system from 4.1 to 4.6. Moreover, the system showed good stability
in saline conditions with NaCl concentration of up to 50,000 ppm.
Scanning electron microscopy of freeze-dried samples proved the uniform
distribution of colloidal crosslinkers and showed sheets wrapping
around the colloidal particles. The performance of the new crosslinker
is compared with available commercial crosslinkers.