Significant amounts
of hydrocarbon resources are left
behind after
primary and secondary recovery processes, necessitating the application
of enhanced oil recovery (EOR) techniques for improving the recovery
of trapped oil from subsurface formations. In this respect, the wettability
of the rock is crucial in assessing the recovery and sweep efficiency
of trapped oil. The subsurface reservoirs are inherently contaminated
with organic acids, which renders them hydrophobic. Recent research
has revealed the significant impacts of nanofluids, surfactants, and
methyl orange on altering the wettability of organic-acid-contaminated
subsurface formations into the water-wet state. This suggests that
the toxic dye methylene blue (MB), which is presently disposed of
in huge quantities and contaminates subsurface waters, could be used
in EOR. However, the mechanisms behind hydrocarbon recovery using
MB solution for attaining hydrophilic conditions are not fully understood.
Therefore, the present work examines the impacts of MB on the wettability
reversal of organic-acid-contaminated Khewra sandstone samples (obtained
from the outcrop in the Potwar Basin, Pakistan) under the downhole
temperature and pressure conditions. The sandstone samples are prepared
by aging with 10
–2
mol/L stearic acid and subsequently
treated with various amounts of aqueous MB (10–100 mg/L) for
1 week. Contact angle measurements are then conducted under various
physio-thermal conditions (0.1–20 MPa, 25–50 °C,
and salinities of 0.1–0.3 M). The results indicate that the
Khewra sandstone samples become hydrophobic in the presence of organic
acid and under increased pressure, temperature, and salinity. However,
the wettability changes from oil-wet to preferentially water-wet in
the presence of various MB solutions, thus highlighting the favorable
effects of MB on EOR from the Khewra sandstone formation. Moreover,
the most significant change in wettability is observed for the Khewra
sandstone sample that was aged using 100 mg/L MB. These results suggest
that injecting MB into deep underground Khewra sandstone reservoirs
may produce more residual hydrocarbons.