Improve the Performance of CO2-based Fracturing Fluid by Introducing both Amphiphilic Copolymer and Nano-composite Fiber

Abstract

Abstract Liquid CO2 fracturing is an outstanding stimulation treatment for unconventional reservoirs, such as coal-bed methane reservoir and shale gas reservoir. However, the viscosity of liquid CO2 is extremely low, only 0.03 ~ 0.10 cp under reservoir conditions, resulting a very poor proppant-carrying capacity. Meanwhile, liquid CO2 is a kind of Newtonian fluid, its friction is very large. All these properties greatly reduce the stimulation results. A novel copolymer composed of CO2-philic fluoride and CO2-phobic partly sulfonated styrene is synthesized. Computer simulations show that these copolymers can create the macromolecular structures via non-covalent association, thus will greatly thicken CO2. Experimental tests showed that this copolymer can increase the solution viscosity 100-fold relative to neat carbon dioxide at 333K and 28 Mpa with a concentration of 1 wt %. A new kind of nano-composite fiber is also introduced to further improve the performance of the CO2-based fracturing fluid. This nano-composite fiber is synthetized by introducing nano-particles in the conventional polyester fiber. A novel CO2-based fracturing fluid with both the amphiphilic copolymer and the nano-composite fiber added was then developed. A series of evaluation tests were performed in laboratory. The results showed that this fiber can disperse easily in the fluid and an addition of very small amount (0.5%) can enhance the proppant-carrying capacity drastically. At 263K and 28MPa, friction can be cut by 17% via adding 0.5% nano-composite fiber under the shear rate of 5000s−1. Meanwhile, nano-composite fiber can prevent backflow of proppant effectively. Leak-off of fluid can also be mitigated significantly. The addition of both the amphiphilic copolymers and the nano-composite fibers can significantly improve the performance of liquid CO2 fracturing fluid, thus may greatly enhance the stimulation results of the liquid CO2 fracturing.