Improving Wormholing Efficiency in Carbonates with a Novel System Based on Hydrochloric Acid

Abstract

Abstract This paper presents a single-phase alternative to widely used emulsified acid systems. The performance of the new single-phase acid was evaluated for both fracturing and matrix operations and benchmarked against hydrochloric acid and emulsified acid. Wormhole experiments were performed in Indiana limestone cores up to 300°F. The rate of wormhole propagation was used a measure to compare the performance of the acid systems. Diffusion constants were measured with a rotating disk experiment (RDE) at different temperatures. Laboratory measurements characterized the viscosity and friction pressure of each of the acid systems. Two single-phase retarded acid concepts were evaluated. In wormhole experiments with Indiana limestone, the best single-phase retarded acid possesses lower pore volume to breakthrough (PVBT) than unmodified HCl across all injection rates. The PVBT are substantially decreased for the single-phase retarded acid at low injection rates, meaning that when HCl enters the conical wormhole regime, the single-phase retarded acid is still efficiently forming dominant wormholes. At many injection rates, the single-phase retarded acid possesses similar PVBT to emulsified acid. These observations are confirmed up to 300°F. Diffusion coefficients obtained from the RDE are up to 10 times lower for the single-phase retarded acid at 220°F. Friction reducers hydrate quickly and show low friction pressures in the single-phase retarded acid. The new single-phase system matches the performance of emulsified acids while eliminating issues that confront them.