Fines migration as an EOR method during low salinity waterflooding

Abstract

This study presents a novel mechanism of enhancing oil recovery by fines migration during low salinity waterflooding. Formation damage is isolated from other low salinity mechanisms in the experimental tests performed in this work. Therefore, the reduction in residual oil saturation is attributed to fines migration mechanism only that is caused by improved microscale sweep efficiency via water flux diversion due to fine particles straining. Corefloods were performed on Berea cores with high clay content, Bentheimer cores with low clay content, and artificial clean sand cores with no clay to investigate the effect of clay presence on residual oil saturation. HSW and LSW took place after drainage displacements that resulted in the same initial conditions of connate water saturation and oil relative permeability. Non-polar oil is used to ensure water-wetness in the cores and to avoid possible wettability alteration by low salinity waterflooding. Single phase corefloods were also performed to study the effect of piecewise decreasing salinity on permeability. The results show a permeability decline with low salinity water injection in the single phase tests of clay-rich cores accompanied by fine particles production and pH increase. The same effect is observed in the two phase tests. In addition, incremental oil production is observed along with the permeability decrease and fines production. This is due to detachment of clay particles by weakened attraction as a result of LSW, which leads to fines migration and straining in water filled pores. Therefore, water flux diversion into trapped oil pores takes place, which displaces the residual oil in these pores. A relationship between formation damage, βΔσ, and residual oil saturation has been introduced and it can be applied in reservoir simulation for LSW.