Experimental study of the effects of salinity on nanoparticle-surfactant foams for fracture stimulation application

Abstract

Liquid foams have been increasingly studied and used in hydraulic fracturing application to develop unconventional resources. In recent years, silica nanoparticles (SNP) have been commonly applied to improve foams' thermal stability and performance under reservoir conditions. While liquid foams are highly affected by salt concentration, the influences of salinity on the foams' characteristics have yet to be clearly understood. This paper investigates the effects of salinity on the properties of SNP-surfactant-stabilized foams. The key experiments included the zeta potential and particle size measurements of SNP in surfactant solutions and the foamability, stability, rheology and proppant suspension tests on the studied foams. The results showed that the increase in the NaCl salt concentration reduced the electrostatic repulsion and promoted the aggregation behaviour among the SNP. At higher salinity, the SNP-surfactant-stabilized foams were found to have lower initial volumes, shorter half-lives, reduced apparent viscosity and faster proppant settlement. Furthermore, it was observed that all the studied foams became extremely unstable with very low foamability and had limited proppant suspension capacity when the salinity was increased to 5%. This observation is critical to evaluate the compatibility of fracturing foams when interacting with the formation brine and to improve the process of recycling produced water as a base fluid to generate foams. The outcomes of this study enhance our understanding of the influences of salinity on the properties of liquid foams and contribute to developing a practical guideline for the foam-fracturing application under harsh reservoir conditions.