Hybrid low salinity water and surfactant process for enhancing heavy oil recovery

Combining low salinity water (LSW) with surfactants has an enormous potential for enhancing oil recovery processes. However, there is no consensus about the mechanisms involved, in addition to the fact that several studies have been conducted in model systems, while experiments with rocks and reservoir fluids are scarce. This study presents a core-flooding experiment of LSW injection, with and without surfactant, using the core and heavy oil samples obtained from a sandstone reservoir in southeastern Mexico. The effluents and the crude oil obtained at each stage were analyzed. The study was complemented by tomographic analysis. The results revealed that LSW injection and hybrid process with surfactants obtained an increase of 11.4 percentage points in recovery factor. Various phenomena were caused by LSW flooding, such as changes in wettability and pH, ion exchange, mineral dissolution, detachment of fines and modification of the hydrocarbon profile. In the surfactant flooding, the reduction of interfacial tension and alteration of wettability were the main mechanisms involved. The findings of this work also showed that the conditions believed to be necessary for enhanced oil recovery with LSW, such as the presence of kaolinite or high acid number oil, are not relevant.

A critical review of carbonate reservoir wettability modification during low salinity waterflooding

The nature of carbonate reservoirs promotes the adsorption of oil onto the rock surface hence making oil recovery a challenge even with the interventions of varied chemical EOR methods.Recently,low salinity water flooding has become of great interest since it is cost-effective and environmentally friendly.Although low salinity waterflooding has been highly investigated in sandstone reservoirs,it is not the same for carbonate reservoirs due to its complexities.Nonetheless,it has been proposed as a favourable technique to mobilise the trapped oil in carbonate reservoirs.Wettability alteration is regarded as the most accepted mechanism for low salinity flooding but has not been well understood making field scale applications doubtful.In this paper,we present a detailed review of the wettability alteration mechanisms in carbonate reservoirs during low salinity waterflooding.Parameters influencing wettability alteration in carbonates and the interactions that occur at the rock/brine/oil interface are also presented.The different methods utilised for wettability measurements during low salinity waterflooding are also reviewed including their drawbacks and advantages and recommendations.This will provide an improved understanding of the low salinity flooding application in carbonate reservoirs.

Evaluation of sour gas-low salinity waterflooding in carbonate reservoirs-A numerical simulation approach

Although significant amount of H_(2)S(sour gas)rich natural gas is estimated globally,but not much attention has been given to the application of H_(2)S in the oil recovery process.Recent studies on the use of H_(2)S in oil recovery processes showed that H_(2)S has the potential of improving the oil recovery,and it can be even more effective than using CO_(2) in some processes.H_(2)S can equally dissolve in the water,react with the reservoir rock to change its surface charge,porosity,and permeability.However,previous in-vestigations on H_(2)S oil recovery attributed the improved oil recoveries to the higher miscibility of H_(2)S in the oil,and the reduction in the oil viscosity.Therefore,there is limited understanding on the H_(2)S-oil-brine-rock geochemical interactions,and how they impact the oil recovery process.This study aims to investigate the interactions between H_(2)S,oil,and carbonate formations,and to assess how the combi-nation of H_(2)S and low salinity water can impact the wettability and porosity of the reservoirs.A triple layer surface complexation model was used to understand the influence of key parameters(e.g.,pressure,brine salinity,and composition)on the H_(2)S-brine-oil-rock interactions.Moreover,the effects of mineral content of the carbonate rock on H_(2)S interactions were studied.Thereafter,the results of the H_(2)S-oil-brine-rock interactions were compared with a study where CO_(2) was used as the injected gas.Results of the study showed that the seawater and its diluted forms yielded identicalζ-potential values of about 3.31 mV at a pH of 3.24.This indicates that at very low pH condition,pH controls the ζ-potential of the oil-brine interface regardless of the brine's ionic strength.The study further demonstrated that the presence of other minerals in the carbonate rock greatly reduced the calcite dissolution.For instance,the calcite dissolution was reduced by 4.5%when anhydrite mineral was present in the carbonate rock.Findings from the simulation also indicated that CO_(2) produced negative ζ-potential values for the car-bonate rocks,and these values were reduced by 18.4%-20% when H_(2)S was used as the gas phase.This implies that the H_(2)S shifted the carbonate rockζ-potentials towards positive.The outcomes of this study can be applied when designing CO_(2) flooding and CO_(2) storage where the gas stream contains H_(2)S gas since H_(2)S greatly influences the dissolution of the carbonate mineral.

Effect of multi-component ions exchange on low salinity EOR:Coupled geochemical simulation study

The mechanism(s)of Low salinity water flooding(LSWF)has been extensively investigated for 15 e20 years,as a cost-effective and environmentally friendly technique for improved oil recovery.However,there is still no consensus on the dominant mechanism(s)behind low salinity effect due to the complexity of interactions in the Crude oil/Brine/Rock(COBR)system.While wettability is most agreed mechanism of low salinity EOR effect.Nevertheless,the mechanism(s)behind the wettability change is debated between multi-component ion exchange(MIE)and double layer expansion(DLE)in sandstone reservoirs.This paper aims to investigate the effectiveness of MIE with a coupled geochemical-reservoir model using published experimental data reported by Nasralla and Nasr-El-Din[1].We created core-scale numerical models with parameters identical to those used in the experiments.We simulated the low salinity effect using a commercial reservoir simulator,CMG-GEM,by coupling three chemical reactions:(1)aqueous reaction,(2)multi-component ion exchange,and(3)mineral dissolution and precipitation.We modelled the adsorption of divalent cations on the surface of the clay minerals during low salinity water injection.Simulation results were compared with the experimental results.Simulation results show that the fractional adsorption of divalent cations(Ca^2+)increased almost 25%by injecting a 2000 ppm NaCl solution,compared to initial 10,000 ppm NaCl.Injecting a 2000 ppm of CaCl2 solution,however,significantly increased the adsorbed Ca^2+from 0.1 to 1,which implies the complete saturation of mineral surface with divalent cations.Moreover,injecting 50,000 ppm of CaCl2 solution also demonstrated the same effect as the 2000 ppm CaCl2 solution but with a faster rate.Upon combining the simulation and experimental results,we concluded that the multicomponent ion exchange is not the sole mechanism behind low salinity effect for two reasons.First,almost 10%additional oil recovery was observed from the experiments by injecting the 2000 ppm CaCl2 compared with 50,000 ppm CaCl2 solutions.Even though in both cases the surface is expected to be fully saturated with Ca^2+according to the geochemical modelling.Second,6%incremental oil recovery was achieved from the experiments by injecting 2000 ppm NaCl solution compared with that of 50,000 ppm NaCl.Although 25%incremental adsorption of divalent cations(Ca^2+)were presented during the flooding of the 2000 ppm NaCl solution.Therefore,it is worth noting that the electrical double layer expansion due to the ion exchange needs to be taken into account to pinpoint the mechanism(s)of low-salinity water effect.