Effect of Crosslinkers on the Performance of Calcium Sulfate Scale Inhibitors at High Temperature: Impact of Zirconium

Abstract

Abstract With the increased desire to fracturing treatments using seawater based-fluid, the formation of calcium sulfate scale becomes a challenging problem. This is due to the presence of high concentration of calcium ions released from the reservoir after fracturing treatment and high sulfate content in the seawater. Preventing calcium sulfate formation is imperative in order to maintain conductive flow channels after the treatment. The challenge basically lies in finding an efficient scale inhibitor that works at high calcium and sulfate concentrations and high temperature without compromising the efficiency of the fracturing fluids. Zirconium is widely used in the fracturing fluid as a crosslinker for guar-based gels to increase the elasticity and proppant transport capability. Using these materials makes each crosslinker have unique reaction conditions and behavior. Unfortunately, no systematic study has been conducted to investigate the influence of zirconium on calcium sulfate scale inhibitor performance at high temperatures. This work is intended to 1) evaluate the efficiency of six different types of commercial-grade scale inhibitors for calcium sulfate (anhydrite) at high temperature and super saturation; 2) to determine the impact of zirconium on the performance of common scale inhibitors used in the oilfield. Extensive experiments have been conducted at 149°C (~300°F), pH 6.8, and 1.0 M NaCl solution at different concentrations of zirconium and with various organic and polymeric scale inhibitors. The induction time and the performance of inhibitors were detected by using an in-house developed laser technique. It was found that the presence of zirconium adversely reduced the performance of calcium sulfate scale inhibitors. The level of impact varies based on zirconium concentration, solution conditions and type of scale inhibitor present.