An Efficient, Durable, and Practical High-Temperature Novel Viscoelastic Surfactant (VES) for Acid Stimulation

Acid stimulation is extensively utilized as a technique to enhance the productivity of oil wells, either through matrix acidizing to mitigate near-wellbore permeability impairment or via acid fracturing to improve connectivity between wells and reservoirs. In carbonate reservoirs, acid stimulation enhances near-wellbore permeability by creating deeply penetrating fluid pathways, termed wormholes. This process involves injecting acid at pressures above or below the fracturing threshold, ensuring the dissolution of the rock matrix without inducing large fractures, better leak-off control, and diversion of acid to low-permeability regions for uniform stimulation. The efficacy of stimulation is contingent upon the length and width of these wormholes. Increasing the viscosity of the acid stimulation fluid is a common practice in carbonate reservoirs to facilitate acid penetration into low-permeability regions. Three primary types of acids are utilized: self-diverting acids, cross-linked acids, and viscoelastic diverting acids (VDA). The selection of acidic fluid is influenced by factors such as reservoir rock characteristics and desired stimulation outcomes. Self-diverting acids increase viscosity upon reacting with carbonate, temporarily obstructing flow to enable acid penetration into other regions. Cross-linked acids exhibit higher viscosity than gelled acids, aiding in viscous fingering within porous carbonate reservoirs. Viscoelastic diverting acids comprise a viscoelastic surfactant, acid, solvent, and other additives, with fluid viscoelasticity varying with shear rate to optimize flow pathways and enhance productivity. In this work, we are focusing on the novel viscoelastic surfactant that has been developed in the laboratory. In this study, we have identified a novel viscoelastic surfactant (VES) exhibiting prolonged stability under harsh conditions, including very low pH and temperatures exceeding 300°F. Notably, the VES maintains increased viscosity post-reaction with carbonate rock, even under such extreme conditions. Laboratory tests demonstrated the VES's stability over two years at ultra-low pH. The novel VES's chemistry resists hydrolysis in hydrochloric acid (HCl) solutions, unlike conventional VES, which decompose under high temperature and acidic conditions due to hydrolyzable moieties. Comparative laboratory testing of the novel VES and conventional VES at 6% loading in 15% HCl and calcium carbonate revealed that conventional VES lost thickening properties under high temperature due to decomposition. Conversely, the novel VES maintained significantly higher viscosity across a broad temperature range, up to 300°F. These properties suggest enhanced fluid efficiency, improved wormhole formation, better leak-off control, and more effective zonal coverage in high-temperature carbonate reservoirs.