Oil Recovery Efficiency and Mechanism of Low Salinity-Enhanced Oil Recovery for Light Crude Oil with a Low Acid Number

Abstract

Low salinity waterflooding (low salinity-EOR) has attracted great interest from many giant oil producers and is currently under trial in some of the oil fields of the United States, Middle Eastern countries, and North Sea reservoirs. Most of the reported studies on this process were carried out for medium to relatively heavy oil with significant polar contents. In this work, we have investigated low salinity waterflooding performance for light paraffinic crude oil with a low acid number. This study has been performed using crude oil from an Indian offshore oilfield and Indian offshore seawater. Oil recovery efficiencies of seawater and its diluted versions (low salinity seawater) were evaluated through core-flooding experiments performed on a silica sand pack containing small amounts (2 wt %) of bentonite clay saturated with crude oil. Interfacial tension and wettability studies were performed to understand the associated low salinity effects on the crude oil/brine/rock properties. Effluent brine produced during the flooding experiments was also analyzed to obtain a clearer insight into the low salinity-enhanced oil recovery (EOR) mechanism. The results showed that injection of low salinity seawater can significantly increase the waterflood recovery in comparison with high salinity seawater injection. Interfacial tension and contact angle studies revealed that there is an optimum dilution level at which the interfacial tension and wettability are the most favorable for enhanced oil recovery even in the case of light paraffinic crude. These results are in line with the results obtained from the core-flooding experiments. The possible reason behind recovery improvement based on the interfacial tension and wettability studies in conjugation with the effluent brine analysis has been discussed in detail. In this study, we have observed that the enhanced oil recovery efficiency could be achieved by applying low salinity seawater flooding even in the case of light paraffinic oil with a low acid number.

Low Salinity Polymer Flooding: Effect on Polymer Rheology, Injectivity, Retention, and Oil Recovery Efficiency

“…The increasing oil recovery during secondary water flooding from HSPF to LSPF #3 clearly indicates the oil recovery potential of low salinity water flooding. Data reported in our previous study indicated that a reduction in oil–water interfacial tension and a change in reservoir rock wettability are the primary mechanisms of low salinity enhanced oil recovery . It was also observed that the oil recovery was a maximum in the case of 25% seawater, as interfacial tension and wettability states were most favorable at this salinity.…”

“…Data reported in our previous study indicated that a reduction in oil−water interfacial tension and a change in reservoir rock wettability are the primary mechanisms of low salinity enhanced oil recovery. 88 It was also observed that the oil recovery was a maximum in the case of 25% seawater, as interfacial tension and wettability states were most favorable at this salinity. A lower interfacial tension at low salt concentration is due to the surface excess of aqueous ions which preferentially move to the oil−water interface by dipole-induced dipole interaction.…”

“…Along with decomplexation of organo-metallic species, the expansion of the electrical double layer at elevated pH also plays a vital role in making the reservoir rock surface more water-wet. A more elaborate discussion on this mechanisms has been provided in our previous publications. − …”

Pressure Attenuation Law of Low-Frequency Pulse Pressure Flooding and Its Influence on Oil Recovery

“…With the development of science and technology, the range of vibration intensity (increasing) and frequency (decreasing) of a hydraulic vibrator is gradually expanding and improving. 24 At the same time, with the aid of automation technology, acidizing, hydraulic fracturing, and other enhanced stimulation measures, the near-well treatment effect of this method has been further strengthened. 25 …”

Modeling of surfactant adsorption on coated quartz crystal surfaces during surfactant flooding process

“…Low salinity water flooding is a quite new technique, implemented to adjust the salt content in sea water before injection to the reservoir. Therefore it has been considered by various research groups as one of the most inexpensive techniques of EOR [5,6] and has been reported for both laboratory core floods and field tests [7][8][9][10]. The combination of low salinity water injection and surfactant flooding (LSW-SF) is considered to be an economically attractive EOR approach, as high oil recovery and low surfactant retention was reported in core flooding tests [11].…”