Effect of reservoir fluid type on the stimulation of carbonate cores using chelating agents

Different fluids have been introduced in the oil industry to be used as alternatives to HCl. Chelating agents such as EDTA (ethylenediaminetetraaceticacid), HEDTA (hydroxyethylenediaminetriaceticacid), and GLDA (L-glutamic acid-N,N-diacetic acid) have been introduced to be used as stand-alone stimulation fluids. These fluids can be used to stimulate water injectors, oil, or gas producers, therefore, the effect of the type of reservoir fluid on the stimulation process should be investigated. In this study, 0.6M concentration of GLDA, EDTA, and HEDTA were used in the coreflood experiments on carbonate rocks at 300°F. The cores were saturated with water, oil, or gas to determine the effect of reservoir fluid type on the performance of the chelating agents with the carbonate cores. The different chelants were injected into the calcite cores saturated by oil and gas after flooding the water into the cores until the residual saturations were reached. The effect of using 10 vol% mutual solvent (ethylene-glycol-monobutyl-ether) in the preflush on the stimulation process was examined. CT was used to scan the cores after the treatments, and the 2D images were used to characterize the wormhole and face dissolution. GLDA at pH of 4 stimulated calcite cores better than HEDTA at 300°F at different injection rates. No face dissolution was observed at low injection rate and high temperature in the case of GLDA. The results obtained with carbonate cores saturated with nitrogen gas were almost similar to those obtained when the cores saturated with water. Using mutual solvent as a preflush in the oil-saturated cores removed most of the oil from the core and water-wet the calcite allowing reaction of chelants with calcite, similar to the case of water-saturated cores.