Steve Metcalf, Joel Boles and Richard Wheeler, BJ Services Company, USA
One of the most effective methods of carbonate stimulation is acid fracturing. Development of fracture geometry sufficient to allow etched penetration to provide economic production increases is dependent upon several factors, one of which is pump rate. High rates and/or lower hydraulic horsepower requirements can be critical to success to one of these projects. Many times wells lack the integrity or flexibility to be treated down casing. Treating down tubing affords highly viscous fluid's opportunity for rate restrictions due friction pressure. In addition, fluids of high viscosity based on the crosslinking of polymers using zirconium are known to have shear limitations, and, therefore, high rates have been unattainable. Laboratory testing and case histories are presented regarding the evaluation and usage of zirconium crosslinked hydrochloric acid systems in the acid fracturing of several carbonates utilizing a variety of tubulars from 2-3/8 to 4-1/2 inch.