An Experimental Study of Effects of Chemical Additives to the Formulation of Fracturing Fluids in Altering Wettability for Enhanced Flowback of Treating Fluids
AL HINAI, Mohammed, AL NABHANI, Hamood, YU, Sung Yeup
Engineering Honours 2015
Australian School of Petroleum
University of Adelaide
It is widely known and acknowledged that hydraulic fracturing is almost always required to produce economically from unconventional reservoirs such as tight gas and shale gas formations. Fracturing involves pumping a vast amount of water into the formation which is highly detrimental to a gas producing reservoir. Therefore, the flowback process of fracturing fluids after hydraulic fracturing is a crucial step in recovering the injected water out of the fractured reservoir in order to enable higher gas returns from the fractured zones. The minimal amount of fracturing fluids left behind in the formation will minimize the water blocking and gas trapping phenomena within the reservoir.
Enhancing flowback of fracturing fluids can be approached in a number of ways. One of the most effective methods is altering the wettability of fractured pore surfaces in the reservoir. This method can be achieved by adding chemical additives to the formulation of the fracturing fluids. The injected chemical additives will adhere and coat the pore surfaces which will repel water and favour the non-water wetting phenomenon of the surface. By keeping the water unsaturated in the pore spaces, the water can be more easily pumped back out of the formation.
The chemical additives such as silane, fluorocarbon and talc were tested in experiments to measure their effectiveness as wettability altering agents. These chemicals have been proven to be more efficient at elevated pressure and temperature. The elevated level of pressure and temperature increases the collision energy of chemical particles onto the pore surfaces which is critical in ensuring considerable wettability alteration. However, a sensitivity analysis needs to be carried out in order to determine the optimum temperature, pressure, salinity and chemical concentration levels which will ensure that the optimal critical contact angle can be achieved without permanently altering the wettability of pore surfaces.
The experiments with chemicals found that the wettability and capillary pressure can be favourably manipulated with liquid Polytetrafluoroethylene (PTFE). The validation process of this phenomenon involved imbibition test and contact angle measurements. In particular, the water imbibition rate can be slowed down by treatment with PTFE. The imbibition rate was halved by treatment with PTFE, before the treatment core imbibed 20 grams of water in 10 hours and after treatment 20 grams of water in 20 hours both at standard pressure and temperature conditions. This strongly suggests that water was not the main wetting phenomenon within the core after the treatment. The contact angle were increased from 20 degrees to 170 degrees when core was treated with PTFE thus reinforcing the non-water wetting phenomenon of pores.