A Mechanistic Model for Wettability Alteration by Chemically Tuned Waterflooding in Carbonate Reservoirs

Abstract

Injection of chemically tuned brines into carbonate reservoirs has been reported to enhance oil recovery by 5-30% original oil in place (OOIP) in coreflooding experiments and field tests. One proposed mechanism for this improved oil recovery (IOR) is wettability alteration of rock from oil-wet or mixed-wet to morewater-wet conditions. Modeling of wettability-alteration experiments, however, is challenging because of the complex interactions among ions in the brine and crude oil on the solid surface. In this research, we developed a multiphase and multicomponent reactive transport model that explicitly takes into account wettability alteration from these geochemical interactions in carbonate reservoirs.Published experimental data suggest that desorption of acidicoil components from rock surfaces make carbonate rocks more water-wet. One widely accepted mechanism is that sulfate (SO 2À 4 ) replaces the adsorbed carboxylic group from the rock surface, whereas cations (Ca 2þ , Mg 2þ ) decrease the oil-surface potential.In the proposed mechanistic model, we used a reaction network that captures the competitive surface reactions among carboxylic groups, cations, and sulfate. These reactions control the wetting fractions and contact angles, which subsequently determine the capillary pressure, relative permeabilities, and residual oil saturations.The developed model was first tuned with experimental data from the Stevns Klint chalk and then used to predict oil recovery for additional untuned experiments under a variety of conditions where IOR increased by as much as 30% OOIP, depending on salinity and oil acidity. The numerical results showed that an increase in sulfate concentration can lead to an IOR of more than 40% OOIP, whereas cations such as Ca 2þ have a relatively minor effect on recovery (approximately 5% OOIP). Physical parameters, including the total surface area of the rock and the diffusion coefficients, control the rate of recovery, but not the final oil recovery. The simulation results further demonstrate that the optimum brine formulations for chalk are those with relatively abundant SO 2À 4 (0.096 mol/kg water), moderate concentrations of cations, and low salinity (total ionic strength of less than 0.2 mol/ kg water). These findings are consistent with the experimental data reported in the literature. The new model provides a powerful tool to predict the IOR potential of chemically tuned waterflooding in carbonate reservoirs under different scenarios. To the best of our knowledge, this is the first model that explicitly and mechanistically couples multiphase flow and multicomponent surface complexation with wettability alteration and oil recovery for carbonate rocks specifically.

A critical review on fundamental mechanisms of spontaneous imbibition and the impact of boundary condition, fluid viscosity and wettability

“…The SI in cores with various wetting conditions is quite complex. The wettability of the cores not only has serious effect on the rate of oil production but also on the final oil recovery and the shapes of imbibition curves (Zhou et al, 2000;Qiao et al, 2015). The rate of imbibition in weakly water-wet cores can be extremely slower than strongly waterwet cores.…”

“…They supposed that three determining ions: Ca 2+ , Mg 2+ and SO 2+ 4 , have a significant effect on the wettability alteration of chalks from oil-wet to water-wet. Qiao et al (2015) developed a numerical model which considering the interaction among ions in the aqueous phase (Ca 2+ , Mg 2+ and SO 2+ 4 ), crude-oil acidity and solid surface to predict the wettability alteration and enhanced oil recovery for chemical flooding in mixedwet reservoirs. They reported that the concentration of sulfate have an important effect on wettability alteration, whereas the cations have relatively little effect on wettability alteration.…”

 Brine-Dependent Recovery Processes (Smart-Water/Low-Salinity-Water) in Carbonate and Sandstone Petroleum Reservoirs: Review of Laboratory-Field Studies, Interfacial Mechanisms and Modeling Attempts

“…The authors claimed that the decreased salinity decreased the oil-calcite BPS, which resulted in reduced oil adhesion and increased oil recovery, however diminishing returns was observed beyond ten times dilution. Qiao, et al [272] developed a multiphase multicomponent reactive transport model that captured the SCMs of surface reactions among carboxylic groups, cations, and sulfate. The model was used to interpret the oil recovery from SI experiment conducted on chalk by using brine with selective removal of non-active ions [140].…”

On Robust and Efficient Parallel Reservoir Simulation on Tianhe-2

“…This compositional model can be used to simulate a variety of problems including the black oil model, EOS compositional model and reactive transport models (Qiao et al 2014;Qiao et al 2015). The set of partial differential equation (PDE) and local algebraic equations are solved together.…”