The objective of matrix acidizing process is to create channels through the damaged zone in the near wellbore. Creating channels through the damaged zone yields a negative skin and improves the recovery in oil and gas reservoirs. The use of conventional matrix acidizing treatments with HCl is not effective in some cases due to corrosion and rapid acid spending at high temperatures. Previous studies have demonstrated the use of ethylenediaminetetraacetic acid (EDTA), hydroxy ethylethylenediaminetetraacetic acid (HEDTA), and DTPA (diethylenetriaminepentaacetic acid) as alternatives for HCl to stimulate carbonate reservoirs. These chelating agents were tested only on short cores (less than 5 in. length).
GLDA (L-glutamic acid-N, N-diacetic acid) chelating agent was introduced that can be used as an effective stimulation fluid for carbonate reservoirs. Unlike HCl, GLDA can be used at very low injection rates and can create wormholes without face dissolution problems or washout. Calcium carbonate cores 1.5 in. diameter of 6 and 20 in. lengths were used in this study. The optimum conditions for the formation of wormholes were studied using core flood experiments. These conditions were: flow rate, temperature, concentration and pH. Other factors such as rock permeability and core length were also examined.
GLDA was found to be very effective in creating wormholes at low injection rates and low to moderate pH values. Increasing temperature increased the reaction rate and more calcium was dissolved and larger wormholes were formed. Also, the optimum injection rate and GLDA concentration that should be used to minimize the volume of the fluid in the stimulation treatment were determined.