Mechanism of fines migration in low-salinity waterflooding and its development effect

In recent years, low-salinity waterflooding has become the focus of research in the petroleum industry owing to its enormous advantages, including high efficiency in displacing oils, ease of injection into oil-bearing formations, easy access and operation of water, and low investment and pollution, all of which are more cost-effective compared to other enhanced oil recovery methods. Numerous experimental studies and field trials of sandstone and carbonate rocks have proven that low-salinity waterflooding can enhance oil recovery effectively due to various mechanisms, including fines migration and mineral dissolution, increased pH effect and reduced interfacial tension, multicomponent ion exchange, and double-layer expansion. As an important mechanism of low-salinity waterflooding, fines migration induced by lowering injected water salinity can effectively change reservoir quality and injection profile, thereby achieving equilibrium displacement and enhance oil recovery. Several models and mathematical equations that describe particle release and capture have been proposed by many scholars in previous studies, and the maximum retention concentration function of fine particles is considered to be the most effective method for describing fines migration. Based on the Derjaguin-Landau-Verwey-Overbeek theory and electric double-layer theory of colloid stability, the effect of injected water salinity and ion valence on the clay particle force and particle migration concentration were analyzed from the microcosmic view in this paper, and the relationship between the particle migration concentration and the permeability impairment was established through maximum concentration of attached fine particles. Aiming at the problem of interlayer interference in vertically heterogeneous reservoir, the numerical simulation of low-salinity waterflooding was carried out in high water-cut stage. Force analysis and numerical simulation results show that the high-permeability layer with high injected water flow rate will cause the hydration, expansion, migration, and clogging of a large amount of clay particles, leading to a marked permeability decline in the high-permeability layer. More injected water is diverted into low-permeability and middle-permeability layer with low sweep efficiency. The injection profile and interlayer interference is relieved. Therefore, the production degree of reservoirs and cumulative oil recovery improve by approximately 3% beyond conventional seawater flooding.