Formation and rheology of CO2-responsive anionic wormlike micelles based clear fracturing fluid system

In recent years, a polymer-free fracturing fluid is under research to minimize the conductivity damage in formation and fracture during and after fracturing. Through extensive experiments, we prepared CO2-sensitive wormlike micelles (WLMs) based fracturing fluid system using anionic surfactant NaOA (Sodium Oleate-C18H33NaO2) and TMTAD (2,6,10-trimethyl-2,6,10-triazaundecane-C11H27N3). Rheological results from viscosity variation with steady shear rate using CO2/pH/time-response after CO2 bubbling confirm that the 3NaOA-TMTAD (3:1) was found as the best one in the properties of WLMs structure and the intermolecular interactions when comparing to 1NaOA-TMTAD and 2NaOA-TMTAD. Further, the surface tension after CO2 bubbling shows a good capability to decrease about 27.01 mN·m−1 at a CMC of 0.543 mM. The cryo-TEM test justifies the occurrence of spherical and WLMs in the fluid, before and after CO2 injection. The fluid system presents an outstanding sand suspension and gel breaking property, which are the positive features during the fracturing and flow back period; respectively. Good response with the alternative changes in CO2 pressures possesses an effective influence on shear viscosity using different temperatures (25 and 85 °C) and shear rates (20, 170, and 200 s−1). Also, the results of a linear relationship and low filtration coefficients verify that the fluid system has good filtration property. Such an easy and environmentally benign fluid system may be involved as a potential candidate in fracturing in unconventional hydrocarbon reservoirs, to reduce the formation damage which is usually very common in the polymer-based fracturing fluid.