Adsorption of polyphosphinocarboxylic acid (PPCA) scale inhibitor on carbon nanotubes (CNTs): A prospective method for enhanced oilfield scale prevention

A scale inhibitor 'squeeze' treatment is used in the oil and gas industry as a control measure to reduce the risk of mineral scale precipitation and deposition in the near-wellbore rock formation and associated installations. One of the determining factors in a successful squeeze job is the potential of formation rock to adsorb scale inhibitor (SI); the higher the adsorption, the better the treatment. This paper investigates the potential of employing carbon nanotubes (CNTs) to increase the adsorption of a common SI (polyphosphinocarboxylic acid, PPCA) on formation rock as part of a new methodology forming a 'Nanotechnology-Assisted Squeeze Treatment' (NAST). The focus here is assessing the adsorption potential of PPCA on CNTs for the purpose of creating a longer-lasting squeeze treatment. Analyses using various techniques including Transmission Electron Microscopy (TEM), Inductively Coupled Plasma Mass Spectrometry (ICP-MS), Thermogravimetric Analysis (TGA) and Raman Spectroscopy are presented, and results indicate that up to 180 mg/g of PPCA adsorbed on CNTs, with strong bonding, which is significantly higher than the 1 mg/g adsorption of PPCA on crushed formation rock. Adsorption of PPCA decreases with increasing temperature of the solution, indicating an exothermic reaction. The impact of water salinity on adsorption is also considered, with calcium producing a positive effect on adsorption and sodium the opposite. It is also illustrated that a good dispersion of CNTs in the solution can dramatically increase the adsorption due to the exposure of higher surface area to PPCA in the solution. The influence of using CNTs on adsorption of SI onto internal surface of sandstone rock were evaluated using coreflood tests with simplified brines. The results demonstrate the potential of employing CNTs to increase adsorption of SI in squeeze treatments and possibly to improve the squeeze treatment lifetime.