Low Salinity Waterflooding in Low Permeability Sandstone: Coreflood Experiments and Interpretation by Thermodynamics and Simulation

Abstract

In recent years, low salinity waterflooding (LSWF) has been a promising technique to recover oil in sandstone reservoirs. In view of research results for the last decade, it is acknowledged that substantial oil recovery beyond conventional waterflooding from sandstone is wettability alteration. However, the major contributor to wettability alteration is still uncertain. Therefore, this paper investigates this major mechanism and shows how it is involved in the process of IOR. Rock and oil surface chemistry were tested to explain the influence of zeta potential on the disjoining pressure. Coreflood experiments with permeability less than 1mD were carried out and the impact of different wettabilities ranging from strong water-wet to slight water-wet on LSWF recovery was investigated with combination of thermodynamic theory. Relative permeability curves were obtained by history matching the corefloods experiments for both slight water-wet and strong water-wet cores with consideration of salinity effect. Thermodynamics of wettability by low salinity waterflooding was analyzed to characterize the surface forces between the surfaces of oil/water and water/rock. Zeta potential results showed that decreasing divalent cations and salinity makes the electrical charges at both oil/brine and brine/rock interfaces become strongly negative, which results in elevation of the repulsive forces between oil and rock, and as a result the rock turns more water-wet, which was confirmed by thermodynamics characterization. Corefloods experiments showed that a high potential in slight water-wet reservoirs can be achieved by low salinity waterflooding due to the double layer expansion. The relative permeability curves obtained by history matching showed that LSW improves oil recovery by accelerating oil production (relative perm changes) and reducing residual oil saturation in slight water-wet rock but not in strong water-wet rock. Thermodynamics of wettability analysis indicated that the mechanism of low salinity waterflooding might be interpreted by disjoining pressure calculation. In conclusion, double layer expansion caused by highly negative zeta potential as a result of lower salinity and divalent cation plays a major role in recovering additional oil. The low salinity waterflooding EOR-Effect might be interpreted by disjoining pressure calculation. These findings can help in composition design of low salinity water to maintain higher potential to recover oil in oil field.

Nonmonotonic Elasticity of the Crude Oil–Brine Interface in Relation to Improved Oil Recovery

“…In the past 15 years the research on low salinity water injection in relation to improved oil recovery has accelerated. In some petroleum fluids there is substantial increase from injection of low salinity brine, but in others there is no effect of salt content in the injected brine on improved oil recovery . Some authors are of the opinion that even after some 500 published papers, the mechanisms of low salinity water injection remain largely unknown .…”

“…In some petroleum fluids there is substantial increase from injection of low salinity brine, but in others there is no effect of salt content in the injected brine on improved oil recovery. 12 Some authors are of the opinion that even after some 500 published papers, the mechanisms of low salinity water injection remain largely unknown. 13 In all the past work, the molecular structure of the fluid−fluid interface has been neglected except in a recent paper by Alvarado et al 14 The formation of organized molecular structures at fluid− fluid interfaces increases interfacial viscoelasticity.…”

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

“…Several oil companies, such as BP [34], Shell [35], Saudi Aramco [36], and PetroChina [17,18,21,37] have conducted numerous lab experiments, i.e., Log-Inject-Log, Single Well Chemical Tracer Test (SWCTT), and field scale trials. Their results have shown that, while in some cases LSWF has achieved an additional 5-25% oil recovery, in other cases, only minor incremental oil recovery was observed [38].…”

Flow Dynamics of Sulfate-Modified Water/Polymer Flooding in Micromodels with Modified Wettability

“…The concept of smart/modified water flooding was first proposed by Morrow et al [1]; leading to further investigations with regards to the impact of injected water composition on oil recovery [2][3][4][5][6][7][8][9]. In simple words, smart/modified water flooding deals with either the addition of active ions/salts or removal of in-active ions/salts from the injection brine.…”