Compositional reactive-transport modeling of engineered waterflooding




Sanaei, Alireza

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It is widely accepted that oil recovery during waterflooding can be improved by modifying the composition of the injected brine in a process known as low salinity/ engineered waterflooding. In recent years, several studies, ranging from laboratory corefloods to field trials, have shown the positive effect of engineered waterflooding on oil recovery; however, a few studies have shown no benefit gain from this approach. The inconsistency in responses is because the main mechanism underpinning this recovery method is not fully understood. Several mechanisms have been proposed as the dominant mechanism of engineered waterflooding. Although wettability alteration is believed to be the principal mechanism of engineered waterflooding, the main mechanism leading to wettability alteration is not yet agreed upon. In this research, we follow a systematic approach to develop a model that can be used to evaluate the efficiency of the engineered waterflooding process at different length-scales. We hypothesize that wettability alteration, as a consequence of changes in surface charges at oil/brine and brine/rock interfaces, is the underlying mechanism of engineered waterflooding. We perform surface complexation modeling and contact angle calculation to explain the mechanism of the process at small length-scales. We then implement the developed model into UTCOMP-IPhreeqc, a compositional reactive-transport simulator, developed at The University of Texas at Austin. We conduct coreflood history-matching on carbonate and sandstone cores to validate the model and interpret the underlying mechanism of the process. Finally, we employ the model to assess the applicability and efficiency of engineered waterflooding in field-scale scenarios. Most of the experimental and modeling studies performed in the area of engineered waterflooding neglect the effect of CO₂ dissolution in the aqueous phase. However, the presence of CO₂ in the reservoir can alter the geochemical equilibrium state and the performance of engineered waterflooding. To address this problem, we implement four-phase flash equilibrium calculations into UTCOMP-IPhreeqc. We use the developed model to investigate the effect of CO₂ dissolution in the aqueous phase on the performance of engineered waterflooding. To reduce the computational time of reactive-transport simulations, we implement the geochemical modules of UTCOMP-IPhreeqc into a parallel reservoir simulator framework. Moreover, we develop a new speedup scheme which can reduce the computational time of geochemical equilibrium calculations up to 80%. Carbonated Water Injection (CWI) is another promising enhanced oil recovery technique that takes advantage of both CO₂ and water flooding processes. In this method, CO₂ is added to the injected brine and transported in the reservoir by flood water. While there are several laboratory experiments reported on this process, simulation studies in this area are scarce. In this research, we use UTCOMP-IPhreeqc to understand the mechanisms of the CWI process and investigate the effect of carbonated brine injection on petrophysical properties of the reservoir. We verify the developed model against an analytical model and apply our simulation approach to match carbonate and sandstone corefloods. Finally, we design a synthetic field-scale case study and evaluate the efficiency of CWI on oil recovery. Alkaline-Surfactant-Polymer (ASP) flooding is another EOR method that usually yields significant incremental oil recovery compared to waterflooding. One major concern for high pH ASP flooding is the possibility of inorganic scale formation near the wellbore and in the production facility. To address this problem, we perform batch and 1D single phase geochemical calculations to identify the possibility and extent of scale formation during ASP flooding. Moreover, we use UTCHEM-IPhreeqc, a coupled chemical flooding simulator and geochemical tool, and design a synthetic field-scale model to study scale formation due to ASP injection in a carbonate reservoir


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