Scale inhibitors are important additives in fracturing fluids to help prevent mineral scale depositions during hydraulic fracturing, shut-in, and flowback stages. The inhibition mechanisms rely heavily on the interactions of certain functional groups from the inhibitor molecules and the lattice metals on the scale crystal surface. In stimulation using crosslinked gel fluids based on metallic crosslinkers, such as zirconium (Zr), titanium (Ti), or aluminum (Al), these metals form strong covalent bonds with guar and guar derivatives and therefore significantly increase overall gel stability. When anionic liquid scale inhibitors are present, the crosslinker metals are susceptible to attack from scale inhibitors because of similar interactions, often resulting in lower viscosity and compromised fluid performance. For this reason, liquid scale inhibitors are usually pumped in prepads during many fracturing treatments. During these treatments, fracturing fluids from other stages and reservoirs that contact these fluids are not protected from scale deposition. Although this incompatibility issue is an important factor in designing fracturing fluid systems, the authors have not found sufficient prior literature providing valid solutions other than applications of time-released solid scale inhibitors.
This paper investigates the interferences of various types of liquid scale inhibitors on Zr-based crosslinkers. Their chemical compatibilities are evaluated in terms of crosslinked viscosity stability and scale inhibition efficiencies. Data presented in this paper indicate that two polymer-based liquid scale inhibitors can be added to selected Zr-crosslinked fluids with minimal impact on crosslinking performance. Scale inhibition efficiency can be maintained by adjusting the pumping flow rate to compensate for the effect of Zr-based crosslinkers.