Effects of Crosslinking Chemistry on Proppant Suspension in Guar Networks

Abstract

Abstract Dynamic proppant suspension behavior of carboxymethyl hydroxypropyl guar (CMHPG) crosslinked with labile (reversible) and inert (irreversible) crosslinkers are quantified and compared in this work. In reversibly crosslinked CMHPG by borate, particle settling slows with increased imposed orthogonal shear rate and proppants remain suspended for long periods above a critical shear rate. On the contrary, in irreversible zirconium crosslinked CMHPG, particle settling is negligible at low shear rates, dramatically accelerating above a critical shear rate. Local flow field data was obtained to provide insight into the dramatically different particle settling behavior. It was observed that the slowing of particle settling with increased shear rate in borate crosslinked CMHPG originates from shear-induced gelation, which leads to significant increases to both viscosity and elastic stresses. For zirconium crosslinked CMHPG sheared at low shear rates, the local velocity profile is flat, indicating that the network remains intact with negligible flow in the bulk. Above the critical shear rate, the velocity profile becomes sloped, indicating breakup of the network. Therefore, reversibly crosslinked polymers suspend proppant better at high shear rates with an upper critical shear rate for proppant suspension, whereas irreversibly crosslinked polymers suspend proppant better at low shear rates with a lower critical shear rate for proppant suspension. These findings provide valuable guidance in terms of optimizing fracture fluid design to help maximize proppant transport into fractures.