An effective stimulation fluid for deep carbonate reservoirs: A core flood study

Matrix acidizing is used to remove near wellbore damage and create channels or wormholes in carbonate formations to improve well performance. The use of conventional matrix acidizing fluids with HCl is not effective in some cases because of the rapid acid spending. Previous studies have demonstrated the use of chelates such as ethylenediaminetetraacetic acid (EDTA) and N-hydroxyethylenediaminetriacetic acid (HEDTA) as alternatives for HCl to stimulate carbonate reservoirs. A recently introduced chelating agent was examined to stimulate deep carbonate reservoirs. This chelating agent can be used at very low injection rates to avoid fracturing the target zone during the treatment, which may occur if HCl is used at high flow rates. The chelating agent used in this study was glutamic acid-N,N-diacetic acid (GLDA). Two sets of calcium carbonate cores were used one with 1.5 in. diameter and 20 in. length and the other set was 1.5 in. diameter and 6 in. length. Calcium carbonate cores such as Indiana limestone cores were used in this study. A dolomite core 1.5 in. diameter and 6 in. length was used to investigate the ability of this chelating agent to stimulate dolomite cores. The cores were treated with GLDA at various pH (1.7-13) and temperatures (180-300°F). The concentrations of dissolved calcium, magnesium, and GLDA in the core effluent were measured for material balance determination. GLDA was found to be highly effective in creating wormholes over a wide range of pH (1.7-13) in calcite cores. Increasing temperature enhanced the reaction rate, more calcite was dissolved, and larger wormholes were formed for different pH with smaller volumes of GLDA solutions. In addition, GLDA was very effective in creating wormholes in the dolomite core as it is a good chelate for magnesium. GLDA was found to be equally effective in creating wormholes in short and long cores.