Transport and Adsorption Properties of Carboxylated Carbon Nanotubes for Enhanced Scale Inhibitor Squeeze Lifetime Performance

Scale formation in oil reservoirs is a primary challenge in the oil and gas industry. If not prevented, the formation of scale can cause the blockage of rock pores or safety valves, leading to reduced well production. One of the best methods to prevent scale formation is by injecting polymeric scale inhibitors into the reservoir; a methodology termed “squeeze treatment”. A significant problem with this current methodology is that a large amount of scale inhibitor does not adsorb effectively on the rock formation and it desorbs from the reservoir rock formation at a high rate. When the inhibitor concentration falls below the Minimum Inhibitor Concentration (MIC) the well will require another squeeze treatment. Consequently, it is highly desirable to enhance the retention of these inhibitors onto the rock formation in order to achieve a longer and more controlled desorption. In a previous study, Carboxylated Multi Walled Carbon NanoTubes (COOH-MWCNTs) demonstrated the ability to adsorb scale inhibitor (SI) more efficiently than rock. This finding was then conceptualised into a methodology that consists of treating reservoir rocks to bond with CNTs. In this case, the presence of the COOH-MWCNTs on the rock surface will provide more efficient adsorption of scale inhibitors. This novel methodology is called Nanotechnology Assisted Squeeze Treatment (NAST). The current work builds upon this previous research. The work herein aims to provide a better understanding of the behaviour of COOH-MWCNTs and their interactions with the scale inhbitor Poly Phosphino Carboxylic Acid (PPCA), with the goal to better understand the adsorption and desorption benefits of the NAST methodology in static and dynamic conditions. This research was also conducted for the purpose of understanding the transport and retention of CNTs in porous media and analyse its effects on porous media properties. The effects of brine and variation in pH values were studied and provided an understanding of the interaction of PPCA with COOH-MWCNTs. The study showed that the variation in mass-to-volume influenced scale inhibitor adsorption efficiency. Collected data were fitted to Freundlich adsorption isotherm, which provided important information on the adsorption of PPCA onto CNTs. Further characterisation is carried by the use of Phosphorus-NMR. Data from the transport studies provided a detailed quantitative analysis of the retention of COOH-MWCNTs in a silane-functionalised porous media. Furthermore, information about transport of COOH-MWCNTs across a range of typical rock permeabilities was obtained. It raised questions about permeability impairment issues because the physical properties of the rocks are modified to a point where a realistic application may be unacceptable. NAST squeeze treatment simulations were explored using coreflood and sand pack experiments; the results demonstrated outstanding performance compared to a conventional methodology.