Preparation and Performance Study of Carbon Nanotube Crosslinker for Guar Gum Fracturing Fluid System

As the exploration and development of oil and gas resources continue to develop into ultra-deep and high-temperature reservoirs, the demand for high-temperature resistant fracturing fluids is increasing. Guar gum fracturing fluids is one of the most commonly used types of water-based fracturing fluids, and increasing the size of the crosslinker and the number of crosslinking sites can enhance the performance of the fracturing fluid. In this study, the surface amination modified of hydroxylated carbon nanotubes with KH550, and a nano-crosslinker (CNC) with larger sizes and more crosslinking sites were prepared by combining them with organoboron crosslinkers. The B-N characteristic peak in the FTIR and XPS test curve proved the successful synthesis of the nano-crosslinker. Meanwhile, the thermogravimetric analysis showed that both the modified carbon nanotubes and the nano-crosslinker had good thermal stability. The fracturing fluid formed by crosslinking carbon nanotube crosslinker with 0.3 wt.% hydroxypropyl guar gum (HPG) showed good temperature and shear resistance. The residual viscosity is higher than 50 mPa·s after shearing 120 min at 130 °C and 170 s−1 shear rate. During the formation of a gel by CNC and HPG base solution, the guar molecules form a continuous membrane structure from the original linear structure, thus forming a macroscopic gel that can be picked up. In addition, the presence of carbon nanotubes enhances the strength of the guar gum continuum membrane structure and the tightness between membranes in the fracturing fluid. Therefore, the CNC crosslinked guar gum fracturing fluid has stronger water retention capacity and temperature and shear resistance. This research simplifies the synthesis method of nano-crosslinkers, and the prepared colloidal carbon nanotube crosslinkers can reduce the dosage of guar gum, which has good prospects for application.