Impact of the injected water salinity on oil recovery from sandstone formations:Application in an Egyptian oil reservoir

In the last decade,there has been an increasing interest in understanding the effects of changing injected water salinity on the performance of oil reservoirs.This paper aims to investigate the effects of injected water salinity on oil recovery of an Egyptian oil reservoir(Bahariya formation).An experimental work program has been performed using 25 core plugs and 5 different water salinities to study the effects of changing water salinity during both secondary and tertiary stages of waterflooding.The objectives of the experimental work were to(1)investigate the effects of the low water salinity on oil recovery and(2)identify the optimum water salinity and the main reservoir parameters for application of low salinity waterflooding project(LSWF)in Bahariya formation.The results revealed that there is an optimum salinity for waterflooding in the secondary flooding stage.However,for the tertiary flooding stage,the results showed that the controlling factor is not decreasing the salinity,but rather changing the salinity(e.g.either increasing or decreasing).It was also clear that applying the optimum salinity in the secondary recovery stage is more effective than applying it in the tertiary recovery stage.Furthermore,the results showed that the positive impact of LSWF may be expected in reservoirs with high amount of kaolinite,high values of CEC,and low amounts of plagioclase feldspar.This study is an original contribution to develop guidelines for designing optimum salinity waterflooding projects in sandstone reservoirs.

Role of the injected water salinity and ion concentrations on the oil recovery in carbonate reservoirs

Low salinity water flooding(LSWF)was initially considered using water with a low concentration of dissolved salts and was later extended to include modifying the ionic content of injected brines.This work investigates the effects of changing water salinity and composition along with the concentration of sulfate and iodide ions on oil recovery in carbonate reservoirs during the tertiary recovery stage.An experimental study was carried out using crude oil of 29°API,8 core samples extracted from the Eocene carbonate reservoir(Egypt),and 6 different water salinities.The results showed additional oil recovery up to 5%of the original oil in place(OOIP)in the tertiary recovery stage with changing water salinity and water composition.Injection of high salinity(HS)and low salinity(LS)brines with high sulfate concentrations increased the incremental oil recovery by a value ranging from 1.7 to 3.8%of the OOIP.On the contrary,injection of HS and LS brines with low sulfate concentrations showed insignificant incremental oil recovery(less than 1%of the OOIP).Furthermore,injection of water with potassium iodide(KI)after injection of water with high sulfate brines showed additional oil recovery of about 1.7%of the OOIP.On the other hand,injection of water with KI after injection of water with low sulfate concentration showed insignificant incremental oil recovery(less than 0.4%of the OOIP).The concentration of sulfate in the injected water appeared to be key parameter to achieve effective waterflooding(WF)projects in carbonate reservoirs.Moreover,the results revealed that the multi-component ion exchange(MIE)mechanism seems to be the primary recovery mechanism for LSWF in carbonate reservoirs.The results and conclusions of this study can be used to develop guidelines for designing waterflooding projects in carbonate reservoirs with optimum salinity.