Laboratory Investigation of Low Salinity Waterflooding for Carbonate Reservoirs
- Amira Al Harrasi (Petroleum Development Oman) | Rashid Salim Al-maamari (Sultan Qaboos University) | Shehadeh K. Masalmeh (Shell Technology Oman)
- Document ID
- Society of Petroleum Engineers
- Abu Dhabi International Petroleum Conference and Exhibition, 11-14 November , Abu Dhabi, UAE
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 5.8.7 Carbonate Reservoir, 5.6.5 Tracers, 5.2 Reservoir Fluid Dynamics, 5.2.1 Phase Behavior and PVT Measurements, 5.4.1 Waterflooding, 5.3.4 Reduction of Residual Oil Saturation, 1.6.9 Coring, Fishing, 4.3.4 Scale
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Low sa linity waterflooding (LSF) research has been gaining more momentum in recent years for both sandstone and carbonate reservoirs. Published laboratory data and field tests have shown an increase in oil recovery by changing injected brine salinity, especially for sandstone reservoirs. It is widely accepted that low salinity water alters the wettability of the reservoir rock from less to more water-wet conditions, oil is then released from rock surfaces and recovery is increased. The main objectives of the current study are to: test the potential of increasing oil recovery by LSF of a carbonate reservoir and to investigate the factors that control it. The impact of LSF on oil recovery was investigated by conducting coreflood and spontaneous imbibition experiments at 70 oC using core samples from a carbonate reservoir, crude oil and synthetic brine (194,450 ppm) which was mixed with distilled water in four proportions twice, 5 times, 10 times and 100 times dilution brines. Moreover, both crude oil/brine interfacial tension measurements (IFT) and ionic exchange experiments were carried out at room temperature (25 oC).
The results of the study show higher oil recovery as a result of reducing injected water salinity in both coreflood and spontaneous imbibition experiments. Coreflood experiments showed an increase in oil recovery by 3 to 5 % of OOIP, while spontaneous imbibition experiments showed an increased by 16 to 21 %. Additionally, spontaneous imbibition experiments provide direct evidence of wettability change by the LSF. The study also shows that the increase in oil recovery was obtained at much higher water salinity than the one observed in the case of sandstone rock.
The concept of low salinity water flooding (LSF) was tested in the laboratory more than 50 years ago, see Bernard (1967). The study concluded that cores containing clays will produce more oil with a fresh waterflooding than with brine and if the fresh water flood does not develop a high pressure drop then no additional oil is produced. The subject attracted significant interest since Tang and Morrow (1997) reported an increase in oil recovery by low salinity waterflooding. The LSF is preferred over other EOR techniques as it requires lower capital and operating costs and is easier to handle.
The influence of injecting different dilution slugs of brine into sandstone cores was studied by many researchers, see Morrow and Buckley (2011) and references therein. The results of these studies showed that LSF in sandstones is effective in both tertiary and secondary modes. LSF was also reported by McGuire et al. (2005) in a single well chemical tracer tests (SWCT) in Alaska and by Webb et al. (2004) in a log-Inject-log test (LIL) which was carried out in the Middle East. According to the SWCT, remaining oil saturation was reduced by 6 to 12 % OOIP when flooding with LSF. LIL test showed reduction of 25 to 50 % in waterflooding residual oil saturation. Moreover, evidence of LSF on improving recovery in a multi-well field scale was observed using historical data from several fields in the Powder River basin of Wyoming which has been flooded with LSF (Robertson, 2007).
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