Rheological study of CO₂ foamed chelating stimulation fluids under harsh reservoir conditions

Foamed acid is usually an HCl acid-based stimulation fluid applied to carbonate reservoirs. However, this study investigates the rheology of a CO₂ foamed chelating agent, L-glutamic acid-N, N-diacetic acid (GLDA), that acts as less corrosive, environmentally friendly, and more stable foamed acid. Foam rheometer and analyzer were used to study the foam rheology, quality, size and structure, and half-life. Five different commercial surfactants with different chemical structures were investigated. The study was conducted at 100 °C, 1000 psi, 3.5 pH level, and various water salinity, resembling harsh reservoir conditions. The general trend showed that the higher the water salinity, the higher the effective viscosity. It also showed that the chelating agent improved the effective viscosity of the high total dissolved solids (TDS) water samples. The highest viscosity (76 mPa⋅s) was attained by mixing GLDA with a cationic alkyl diamine derivative surfactant in formation water at a 100 1/s shear rate. The prolonged constant shear rate experiments revealed that some formulations are stable for more than 8 h. The study revealed that higher surfactant concentrations did not result in improved performance. For the first time, the study reveals that chelating agents could be used as a stable stimulation foamed fluid at harsh reservoir conditions.