Research focus

Hydraulic fracturing

“Hydraulic fracturing (“fracking”) is applied on oil & gas wells as a common stimulation technique since 1947 to enhance hydrocarbon production. More recently, fracking has been performed extensively on shale and coalbed reservoirs. In operation, a fracturing fluid is pumped downhole and into the rock at a sufficiently high pressure to fracture the formation and increase its permeability to values which allow oil and gas flow to the borehole. The fracturing fluid (“frac gel”) needs to exhibit high viscosity to transport large amounts of proppants (e.g. sand) into the fractures. Proppants prevent the fractures from collapsing after the pressure has been subsided. Reservoirs containing thick crude oil require exceptionally viscous frac gels for the creation of wide fracs and the transportation of large size proppants into those fracs. For more information on the fracking process and the chemicals used in the frac fluid please watch this video.



Frac gels typically contain guar gum, a natural galactomannan harvested from Cyamopsis tetragonolobus. Titanium or zirconium complexes are commonly utilized as crosslinkers to enhance the viscosity yield from guar.

In our research we focus on the mechanism underlying this crosslinking process. We could demonstrate that the crosslinking effect of titanium or zirconium complexes relies on their hydrolysis and condensation to MO2 nanoparticles which induce the formation of a 3D network through the formation of hydrogen bonds between the OH functionalities present on the MO2 surface and the guar gum. Furthermore, we found out that the crosslinking ability of MO2 nanoparticles increases with ascending electropositive character of the metal in MO2 (Ti > Sn >> Si) and decreases with the size (surface area) of the MO2 nanoparticles.
 

Fig. 1: Crosslinking mechanism occurring between MO2 nanoparticles and guar gum.