Document Type : Original Article
Petroleum Engineering Group, Science and Research Branch, Islamic Azad University, Tehran, Iran
Research Institute of Petroleum Industry, Tehran, Iran
Today underbalanced drilling has attracted much attention to itself. Among low density drilling fluids, foam has better ability to carry drilling cuttings, and to suspense them while drilling is stopped. Of foam properties, which has important role in controlling bottomhole pressure and carrying cutting, are foam stability and foamability. Mixture of nanoparticle and surfactant was used to stabilize foam. Nanoparticles could not solely generate foam. With adsorption of cationic surfactant molecules on nanoparticles, they change from complete hydrophilicity to partial hydrophobicity, and make nanoparticles as a surface active material.
The surface tension of nanoparticle-surfactant mixture was measured in domain of surfactant concentration, nanoparticle concentration, salinity and pH. Measurement revealed that surface tension experienced a minimum which is related to maximum adsorption of surfactant on nanoparticles. Also, surface tension decreased with an increase in nanoparticles and a decrease in salinity.
Nanoparticle-surfactant stabilized foam was prepared through Ross-Miles method, and foamability and foam stability was investigated. With respect to reduction in the surface tension, the domain of surfactant concentration divided into two characteristic section, namely, high adsorption and low adsorption, respectively related to high IFT reduction and low IFT reduction. It was found out that foamability has the most resistance in high adsorption region.
In high adsorption region (about 1 CMC), due to reaching to the maximum hydrophobicity, nanoparticles act as a surface active material and obtain the more stability than surfactant stabilized foam and nanoparticle-surfactant stabilized foam at low adsorption region.