A Novel Foamed Acid System Stabilized by Composite Material for Fracturing Applications

Abstract

Carbonate reservoirs hold 60% of the world's oil and 40% of the gas. Therefore, developing high-impact and innovative technologies for well stimulation, such as foamed acid fracturing fluids, is essential for restoring well productivity and enhancing commercial productivity for carbonate reservoirs. Acid fracturing treatment is associated with reactivity control, fluid loss control, and conductivity generation challenges. For overcoming some drawbacks associated with conventional acid fracturing, foamed acid fluid is applied to enhance retardation, reduce water consumption, improve acid diversion, remove water or emulsion blocks, and improve conductivity generation. In this study, a unique foamed acid system stabilized by composite material was studied to develop fracturing fluid at 275-350 °F. In addition, the foam stability, rheology, and morphology characteristics were investigated using several characterization tools at 275-350 °F. The composite material comprises nanosheet (NS), and surfactant (SURF) were added to either a pure-acid or acid system that contains several additives for developing stable NS/SURF-based foamed acid fluid. To evaluate foam rheological properties and thermal stability at dynamic conditions, foam loop rheometer experiments were conducted at 275-350 °F, 1050 psi, and 70 % N2 quality. A high-resolution optical microscope was also utilized to observe foam texture morphology and further assess foam stability. In addition, foam-decaying time was observed by determining the foam-half-life-time (foam volume altering as a function of time). The static and dynamic results illustrated that foamed acid fluid stability and thermal adaptability were improved after adding composite material at 275-350 °F. The viscosity of foamed acid increased by double and its viscosity was higher than 45 cP at a shear rate of 300 S-1 and 350 °F. In addition, the foam-structure of NS/SURF-based foamed acid displayed a small hexagonal bubbles size, which positively affected the stability of foam to reach up to three hours at 300 °F. In contrast, the stability of pure foamed acid was one hour. This result is attributed to the adsorption of composite material at the liquid-gas interface layer that enhances the mechanical strength of the foam-layer (lamellae film) and provides a more robust barrier between the gas bubbles and liquid phase, resulting in delaying the coalescence of the bubbles. The developed NS/SURF-based foamed acid possesses several advantages over the conventional acid fracturing fluids: long stability, adequate viscosity (obtained without adding gelling agent), low water consumption, and high efficiency at 275-350 °F.