40 Years of Low-Salinity Waterflooding in Pervomaiskoye Field, Russia: Incremental Oil

Abstract

Low-salinity waterflooding (LSW) and its effect on oil recovery factor have been studied around the world during the last 30 years. Low-salinity/fresh water was used in the initial stage of waterflooding because of deficiency of produced water. The Pervomaiskoye oil field in Republic of Tatarstan is one of the examples. Waterflooding started in 1966. Water was taken from the nearest water source, the Kama River. After more than 40 years, about two PVI has been injected, and 30.1% of this injected water was low-salinity. This paper presents the results of laboratory study of double core flooding using high-salinity (formation) and low-salinity (river) water. Two plugs were taken with the clay content of about 0.8% and 0.1% and the permeabilities of 432 and 291 mD, respectively. Dead oil was used with the viscosity of 37.5 mPa.s. TDS values were about 252,738 ppm for high-salinity water and 848 ppm for low-salinity water. Dry and vacuumed plugs were saturated, first, with high-salinity water, then, with oil, to simulate connate water saturation; then, oil was displaced with the same water. After this, the cores wre restored to the connate water by a secondary oil flood, and finally, LSW was simulated. In both cases, oil recovery was recorded and fines release was analyzed. Processing of the low-salinity corefloods data by a numerical model shows a two-fold decrease of water relative permeability for the first plug and 1.5 times reduce of residual oil saturation for the second plug. Fines release and formation damage was observed in the first plug and wettability alteration in the second plug. Oil relative permeability didn't change. Also, the unusual behavior of water relative permeability in response to low-salinity waterflood was observed, namely, it decreased at water saturation values more than 0.4. To investigate the low-salinity EOR effect seven pilots on the Pervomaiskoye field were analyzed, with high-salinity waterflooding following LSW. Incremental oil recovery for these pilots, that has been achieved by now, is approximately 5-9%. Calculations of low-salinity EOR effect in the field show that LSW through 96 injectors ensures to date the incremental recovery factor of 3-4%. The reservoir 3D model of five-spot pattern for the Pervomaiskoye field for fines-assisted waterflooding gave incremental oil recovery by 5-11%. The laboratory relative permeabilities were used in the model. Incremental oil recovery depends on the number of the flooded layers.

Brine-Dependent Recovery Processes in Carbonate and Sandstone Petroleum Reservoirs: Review of Laboratory-Field Studies, Interfacial Mechanisms and Modeling Attempts

“…Little improvement in recovery was observed for both field cases because the low saline brine was injected below the water-oil contact. Meanwhile, Akhmetgareev and Khisamov [231] evaluated a historical injection of low saline water sourced from the nearest Karma river in the Pervomaiskoye oil field in the Republic of Tatarstan, Russia. They observed that more than one-third of the wells were not potentially effective, which is similar to conclusions made by Zeinijahromi et al [229].…”

“…Then, Tang and Morrow [13] proposed that the crude oil adsorbed onto fines-coated rock surface is mobilized with the detachment of mixed-wet fines during low saline brine injection rendering the mineral more water-wet due to exposure of the water-wet surfaces beneath the detached fines (see Figure 8). Bedrikovetsky and his colleagues [70,74] developed an analytical model based on torques balance and mass balance to describe the relationship between the static equilibrium of clay particles and salinity, which was also used in the study by Akhmetgareev and Khisamov [231]. The torque balance is distorted when the detaching torque of drag and lifting forces exceeds the attaching torque of electrostatic and gravity forces, resulting in fines detachment and migration during the arrival of low saline brine.…”

 Brine-Dependent Recovery Processes (Smart-Water/Low-Salinity-Water) in Carbonate and Sandstone Petroleum Reservoirs: Review of Laboratory-Field Studies, Interfacial Mechanisms and Modeling Attempts

“…Little improvement in recovery was observed for both field cases because the low saline brine was injected below the water-oil contact. Meanwhile, Akhmetgareev and Khisamov [203] evaluated an historical injection of low saline water sourced from nearest Karma river in Pervomaiskoye oil field in Republic of Tatarstan, Russia. They observed that more than one-third of the wells was not potentially effective, which is similar to conclusions made by Zeinijahromi, et al [201].…”

“…Then, Tang and Morrow [7] proposed that the crude oil adsorbed onto finescoated rock surface is mobilized with the detachment of mixed-wet fines during low saline brine injection rendering the mineral more water-wet due to exposure of the water-wet surfaces beneath the detached fines. Bedrikovetsky and colleagues [216,217] developed an analytical model based on torques balance and mass balance to describe the relationship between the static equilibrium of clay particles and salinity, which was also used in the study by Akhmetgareev and Khisamov [203]. The torque balance is distorted when the detaching torque of drag and lifting forces exceeds the attaching torque of electrostatic and gravity forces, resulting in fines detachment and migration during the arrival of low saline brine.…”

“…It was highlighted that induced-fines migration was more effective in improving sweep efficiency for large-scale heterogeneity with highly correlated flow paths. This model has been applied to interpreting and predicting fines-assisted waterflooding in many oil fields (such as Pervomaiskoye, Zichebashskoe, and Bastrykskoye fields) in Russia [201][202][203]. On the other hand, Borazjani, et al [216] extended this model by simultaneously accounting for wettability alteration and fines mobilization, migration, and straining, solved by using splitting procedure for hyperbolic system.…”