Enhancement of Fracture Conductivity Using CO₂-Foamed Acid for Elevated Temperature Wells

Conventional acid fracturing systems experience challenges during flowback, especially in depleted and gas reservoirs. Additionally, limited acid penetration is observed because of the low fluid efficiency and high reactivity at elevated temperatures. To overcome these challenges, foamed acids have emerged as a promising alternative. This study investigates the potential of seawater-based CO₂-foamed acid in enhancing the fracture conductivity under harsh reservoir conditions. Three foamed acid systems were formulated: foamed CO₂, CO₂ foamed Glutamic diacetic acid (GLDA)-based, and CO₂ foamed hydrochloric acid (HCl)-based. A core flooding system was used to perform acid fracturing treatments at 100 °C and 1,200 psi, where the conductivity was measured at different confining pressures. A high-resolution surface analyzer assessed the etching profile and surface roughness. Moreover, the rock strength before and after treatment was measured with a Brinell hardness tester. The viscosity and stability of foamed CO₂ were measured via a high-pressure, high-temperature foam flow loop rheometer. The liquid solution consisted of synthetic seawater with a salt mixture totaling 57.707 g/L and a 3 wt % foaming agent. The outcomes of the foam rheometer indicated that the foamed CO₂ produced a viscosity of 82 cP at a shear rate of 100/s and a temperature of 100 °C. Fracture conductivity is significantly influenced by surface roughness. Higher roughness presented higher fracture conductivity. CO₂-foamed-HCl-based materials demonstrated substantial improvements in fracture conductivity, exhibited turbulence etching pattern, and reduced the rock strength by 30%. The outcomes suggested that the HCl-based system was the optimum for maintaining long-term fracture conductivity. Nevertheless, the GLDA-based system improved the fracture conductivity remarkably and showed a wide channel etching pattern with shallow depth due to the acid-controlling reaction. This research provided valuable insight into the applicability and effectiveness of using CO₂-foamed acid in acid fracturing under high-temperature reservoirs.