Influence of various cation valence, salinity, pH and temperature on bentonite swelling behaviour

A major issue for the oil and gas industry is the producing of high water from many fields due to massive water injection. Reducing the water production while improving oil recovery from these fields is a major challenge. Polymer gel has been widely used to shut off water-producing zones, but it is not suitable for high temperature reservoirs (> 100 °C). The aims of the present study were to investigate bentonite particles swelling properties and influence of specific ion type (monovalent/divalent) present in water in swelling behaviour, and hence their potential for plugging high water production zones. In this study series of free swelling tests were conducted on bentonite with varying salinity, pH and temperature. The study found that cation valence, salinities and pH had significant impacts on swelling performance of bentonite particles. Bentonite changed from highly swelled material to aggregate in high salinity. Test results showed that the free swelling of bentonite decreased with the increase of cation valence and concentration. Monovalent cations concentration greatly influenced the swelling volume of bentonite, whereas the influence of the increasing concentration of divalent cations was marginal. As the radius of the hydrated ionic increased, the free swell of bentonite in same valance cation solutions raised. Moderate swelling changes were obtained when the solution pH increased. Meanwhile, increases in temperature will increase the swelling of bentonite due to growth in frequency of interlayer cations and water molecules. Bentonite particles swelling could be controlled and inhibited by varying solution salinities and/or altering interlayer exchangeable cations. Thus, bentonite particles swelling will be triggered by low salinity, after it’s been injected and mixed with lower reservoir water salinity.