Effect of chemical additives on the stability and performance of suspended-emulsion fracturing fluid formed by associative thickener

Using suspended-emulsion is one of the important methods to achieve the online-mixing of fracturing fluid. In order to solve the practical problems that the conventional suspended-emulsion fracturing fluid is limited to online mixing and needs additional additives to endow it other function during construction, in this paper, the effect of different chemical additives on the suspended stability, bulk viscosity and other performances of suspended-emulsion fracturing fluid were investigated by different measurements, and the long-term suspension-stability mechanism was revealed by optical microscope analysis. The results show that both the stability and the bulk viscosity of the suspened-emulsion gradually increase with the addition of emulsifier, suspension stabilizer and dispersion stabilizer, whereas the addition of emulsifier APEO can cause the decrease of the viscosity releasing rate. Adding 6.0wt% mixture of OBS with APEO (3:1 mass ratio), 3.0% YJT-180 and 2.4% PAE-2, a suspended-emulsion system with no significant stratification after 90 days, moderate bulk viscosity (321 mPa·s) and high viscosity releasing rate can be formed, in which the fine-dense microscopic morphology with uniform distribution can be vividly seen. Moreover, the addition of APEO and OBS not only can greatly promote the suspension stability, but also can obviously improve the thickening property and temperature-shear resistance of the fracturing fluid through the synergistic interaction, and can positively change the surface tension and contact angle of the gel-breaking liquid because of the high surface activity. It can be concluded that the addition of APEO and OBS to the suspended-emulsion can directly give it the functions of increasing viscosity and assisting discharge, which can provide important guidance for the design of multi-functional and online-mixing fracturing fluids.