Preparation and performance evaluation of nanoemulsions for water control fracturing in tight gas formations

Key words:  orthogonal design  amino polysiloxane  nanoemulsion  water control  hydraulic fracturing  tight gas formation

Abstract:

With amino polysiloxane and one environmental-friendly surfactant fatty acid methyl ester sulfonate (MES), the optimal formation conditions of nanoemulsions were obtained by the orthogonal design experiments, which can be applied to water control fracturing in tight gas wells. The matching between the size distribution of droplet in nanoemulsions and pore throat in dense cores was analyzed. The effects of nano-droplets adsorbed on core surface on microstructure and interfacial properties were investigated. The water-flooding erosion resistance and water control performances were evaluated by core flooding tests as well. It is found that the optimal formation conditions of nanoemulsion are as follows:weight ratio of modified amino silicone and water 1∶2, the amount of emulsifiers MES, n-butanol, potassium amino are 40.0 ％, 20.0％, 5.0％ in that of modified silicone oil,respectively, and adjusted to pH 6.5 with acetic acid. The average median diameter of droplets in nanoemlsions is about 28.5 nm, which matches well with pore throat sizes in tight formation cores. And with the increase of nanoemulsions concentration, the surface morphology of core pore are gradually transformed from sharp groove shape to a uniform, smooth peak valley structure and the wettability also presents strong hydrophobic properties. Core flooding tests show that nanoemulsions possess good erosion resistance, reduce water phase relative permeability over 60％ and have little effect on gas permeability with 0.5％ nanoemulsions. These demonstrate that nanodroplets are firmly attached on the surface of cores through the physical or chemical adsorption of polar groups such as Si-O bond, Si-H bond and amino groups. And the hydrophobic silicon methyl groups in molecular chains alter the rock wettability properties, which results in greater impact on gas/water flow in porous media.