Doug Walser & Enrique Lopez, BJ Services Co.
Polyacrylamides hydrated in hydrochloric acid and crosslinked with iron-based ions have been utilized for a number of years as in-situ divertors in the stimulation of extended-length carbonate zones. A significant improvement to this process has been developed, field-tested, and placed into general use. Crosslinking the polyacrylamide with a zirconium-based metallic ion has proven to be an alternative with a number of advantages over existing systems. Dependency of the system on iron derivatives for crosslinking is eliminated, the precipitation of ferric or ferrous compounds that can cause sludging or stabilize oil/water emulsions is minimized, and viscosity degradation of the in-situ crosslinked acid is not completely dependent upon the rising pH of the acid as it spends. An external breaker is added to the system as an aid in apparent viscosity reduction. Case histories are briefly reviewed. Treatment design data, including fluid friction pressure curves and rheologies are presented for use by the practicing engineer. Input parameters suitable for the most common 3-dimensional fracturing and matrix stimulation modeling simulators are included.