posted on 2024-03-18, 16:34authored byOluwafemi
P. Oyenowo, Hao Wang, Abouzar Mirzaei-Paiaman, Omar A. Carrasco-Jaim, Kai Sheng, Ryosuke Okuno
This paper presents new data on core-scale wettability
alteration
of carbonate porous media with FM concentrations up to 30 wt % in
NaCl brine. Experimental data from Amott tests, core floods, calcite
dissolution experiments, and zeta potential measurements were analyzed
to mechanistically understand the wettability alteration observed
in the experiments. Static calcite dissolution tests showed that the
degree of dissolution increased with increasing FM concentration in
NaCl brine, even with an initially neutral pH. For example, the calcium
concentration in the 30 wt % FM solution was 15.9 times greater than
that in the NaCl brine with an initial pH of 7.0. Furthermore, reducing
the initial solution pH from 7.0 to 6.1 for the 30 wt % FM solution
caused the calcium ion concentration to increase by a factor of 3.2.
Geochemical modeling and Raman analysis indicated that increased calcite
dissolution was caused by interactions between calcium and FM ions.
The 30 wt % FM solution with an initial pH of 6.1 yielded 4.7 times
greater oil recovery than the NaCl brine in the spontaneous imbibition.
The resulting Amott index indicated the wettability alteration to
a water-wet state by the FM solution. The 30 wt % FM solution with
an initial pH of 7.0 yielded only 30% greater oil recovery than the
brine in the spontaneous imbibition; however, it reached nearly the
same total oil recovery (spontaneous and forced) as the 30 wt % FM
solution with an initial pH of 6.1. A numerical model was calibrated
using core flood data, based on which the relative permeabilities
indicated the core-scale wettability alteration by FM solutions. Results
showed that increasing the FM concentration in the injection brine
rendered the initially oil-wet core to a more water-wet state and
that the in situ solution pH played an important role in wettability
alteration by FM solution in carbonate media.