Chelating agents such as GLDA, EDTA, and HEDTA have been used to stimulate calcite reservoirs as alternatives to HCl. HCl based stimulation fluids are very corrosive at high temperatures and should be loaded with many additives to reduce corrosion problems. In addition, the application of HCl can lead to face dissolution at low flow rates. GLDA chelating agent was used to stimulate calcium carbonate cores up to temperature of 300°F and at low rates without any face dissolution problems. The dissolution of dolomite by chelating agents has not been thoroughly investigated. Preliminary experiments with EDTA at ambient temperature revealed no significant dolomite dissolution. The dissolution mechanism is probably inhibited by the low stability of the magnesium chelate at that temperature.
In this study, we will investigate the ability of GLDA (glutamic -N,N- diacetic acid) to stimulate dolomite cores as well as calcite cores. GLDA with different pH (1.7, 3 and 13) was used for this study. Dolomite and Indiana limestone cores with dimensions of 1.5 in. diameter, 6 and 20 in. length were used. The coreflood experiments were run at different flow rates and temperatures to determine the optimum rate at which GLDA solutions can create wormholes in both dolomite and calcite cores. Complete fluid analysis for the coreflood effluent was done to study the reaction of GLDA with both dolomite and calcite cores.
GLDA was very effective in stimulating both dolomite and calcite cores at different pH levels over a wide range of temperatures (180, 250 and 300°F). There was no well defined optimum injection rate at which the amount of GLDA needed to create wormholes was minimum, instead a broad range of injection rates was found for which the amount of GLDA needed to breakthrough the core was minimum. Also, GLDA effectively chelated magnesium and calcium from dolomite cores. GLDA was stable up to temperatures of 300°F and the concentration of GLDA after the treatment was the same as that before the treatment, further confirming the thermal stability of GLDA at this temperature.