Evaluation of Water Flooding to Increase Recovery of Oil |
Oilrecovery by low salinity water flooding in secondary and tertiary modes wasinvestigated in the present study. Cores from Berea outcrop sandstone andMinnelusa reservoir sandstone were used in the single phase and two phaseexperiments. Two types of Minnelusa crude oils were used in the two phaseexperiments. The single phase experiments provided the baseline for pH and pressurechanges in the two phase experiments. Setof experiments were performed by using low salinity brine for the tertiarywaterflood recovery method where oil saturated cores were first flooded withhigh salinity brine to simulate the secondary recovery method. In the secondset of experiments, oil saturated cores were directly flooded with the lowsalinity brine. Conductivity and pH analysis of effluent brines were performedin all the single phase and two phase experiments. Increasein oil recovery with low salinity brine as the invading brine was observed inboth secondary and tertiary modes (2-8% OOIP) with Berea sandstone. However,higher oil recoveries (5-8% OOIP) were observed when low salinity waterfloodingwas implemented as a secondary recovery method. Minnelusa reservoir cores hadlittle to no response to low salinity brine when it was used as a tertiaryrecovery method. However, Minnelusa cores showed an increase in oil recovery(10-22 % OOIP) with both types of crude oils when it was used as a secondaryrecovery method. An increase in pH of the effluent brine was observed duringthe low salinity brine injection in both Minnelusa and Berea cores. However,magnitude of the pH increase was smaller with the Minnelusa cores compared toBerea cores. Thelevel of investigation into the mechanism of low salinity incrementalproduction has sharply increased in the past two years. Most of the studiesfocus on core floods using the tertiary mode. Our work contributes systematiccoupled secondary and tertiary mode experiments that offer an expanded datasetfor all researchers to use in investigation of the mechanisms. Many countries in the world containsignificant heavy oil deposits. In reservoirs with viscosity over severalhundred mPas,waterflooding is not expected to be successful due to the extremely high oilviscosity. In many smaller, thinner reservoirs or reservoirs at the conclusionof cold production, however, thermal enhanced oil recovery methods will not beeconomic. Waterfloods are relatively inexpensive and easy to control; thereforethey will still often be employed even in high viscosity heavy oil fields. Thispaper presents experimental findings of waterflooding in laboratory sand packsfor two high viscosity heavy oils: 4650 mPasand 11500 mPas,at varying water injection rates. The results of this work show that capillaryforces, which are often neglected due to the high oil viscosity, are in factimportant even in heavy oil systems. At low injection rates, water imbibitioncan be used to stabilize the waterflood and improve oil recovery. Waterfloodingcan therefore be a viable non-thermal enhanced oil recovery technology even infields with very high oil viscosity.