Where we started from: the existing formulations. There are several types of fracturing fluids, but in most cases the formulations are composed by: base fluid, proppant, and additives [1]. Water-based fluids are applied in approximately 80% of the xxxxx and they can use as water source fresh water, seawater, brine, or a saturated brine, depending on the well conditions or on the drilled interval of the well [2,3]. The compounds added to the frac-fluids fulfil three main functions: enhance the fluid performances, improve the capability to carry the proppant and minimize formation damage [4]. The additives commonly used include: thickening agents, crosslinking agents, temperature stabilizers, pH- control agents, gel breakers, scale inhibitors, corrosion inhibitors, biocides, and surfactants. In order to formulate green and environmentally friendly frac-fluids, we pursued two different strategies: one based on biopolymers and another one on viscoelastic surfactants. More precisely, we investigated Guar Gum (GG), Sodium Hyaluronate (SH) and HydroxyPropyl Cellulose (HPC) as polysaccharides. These fluids were tested in model solvent (pure water) and in the presence of high amount of salt. We investigated the effect of both salt concentration and nature on the formulation properties. Then we studied specific additives like surfactants in order to optimize the multifunctional performances of the formulation. Simultaneously, we also explored as multifunctional components for unconventional fracturing fluids two ViscoElastic Surfactant (VES) systems, one based on Sodium Oleate (NaOL) plus KCL and the second one based on cetyltrimethylammonium bromide (CTAB) combined with sodium salicylate (NaSal). The proposed formulations are designed to cover a wide range of viscosities and rheological behaviours, thus ensuring their applicability in various basins characterized by different rock composition and where different fluid properties may be required.
