The enhancement of
oil recovery (EOR) through low-salinity waterflooding
(LSWF) and the emerging hybrid with a polymer (LSP) has proven to
be effective at microscale investigations and cost-effective with
ease of operation at field-scale tests. Their application in carbonate oil reservoirs, which typically
occur oil-wet, presents a particularly essential capacity given that
over half of the global oil reserves are hosted in carbonate formation.
However, modeling the mechanisms involved to predict and evaluate
the performance of low salinity-based EOR at a large scale is complex
and requires the integration of geochemistry in reservoir simulation
to upscale the interfacial interactions of crude oil, brine, and rock
observed at the micrometer scale. This study presents an integrated
approach that combines MRST’s polymer model with PHREEQC geochemical
modeling to simulate LSWF at the reservoir scale. Using single-phase
and multiphase experimental flooding data for validation, the coupled
model was shown to accurately predict effluent ionic and oil recovery
profiles. The simulation of LSWF and LSP both exhibited additional
tertiary oil recovery, with LSWF and LSP showing 3 and 2%, respectively,
which are consistent with previously reported field and core flooding
results. Furthermore, the sequential application of formation water
(FW), LSWF, and LSP flooding in secondary mode showed a high increase
in oil recovery, with oil recovery percentages of 61, 20, and 19%,
respectively. However, the FW results were 50% lower compared to regular
core flooding due to upscaling limitations. The modeling of vertical
and anisotropic permeability heterogeneity effects showed a positive
synergy with low-salinity floodings, resulting in a 4% drop and 3
and 1% increase in FW, LSWF, and LSP, respectively. These findings
demonstrate the potential of the coupled MRST-PHREEQC model in accurately
simulating hydrogeochemical interactions during LSWF/LSP at the reservoir
scale, providing valuable insights for the optimization of low salinity-based
EOR strategies in carbonate reservoirs.