Sandstone Acidizing Using A New Class of Chelating Agents

Abstract

Abstract The objective of stimulation of sandstone reservoirs is to remove the damage caused to the production zone during drilling or completion operations. Many problems may occur during sandstone acidizing with HCl/HF mud acid. Among these problems: decomposition of clays in HCl acids, precipitation of fluosilicates, the presence of carbonates can cause the precipitation of calcium fluorides, silica-gel filming, colloidal silica-gel precipitation. In this study, a recently introduced chelating agent, glutami-N, N-diacetic acid(GLDA), was used to stimulate sandstone cores. Berea sandstone cores with 8 wt% clays content were used in this study. Different GLDA solution pH values (1.7 - 13) were used in the coreflood experiments. The sandstone cores were scanned before and after the treatment to investigate the effect of GLDA on the core. The effluent samples were analyzed for calcium, magnesium, aluminum, and iron using the ICP to assess the ability of GLDA on the complexation of these ions. Coreflood experiments were run at temperatures of 200 to 300°F and the concentration of GLDA was determined after the treatment. The effects of injection rate, volume of GLDA, temperature, and GLDA initial pH value were investigated on the Berea sandstone cores in the coreflood experiments. Different correlations were used to determine the core permeability after the treatment, and the correlation that gave the minimum error was determined. GLDA showed a strong ability in chelating calcium, iron, magnesium, and it chelated small amounts of aluminum ions from the sandstone cores. At 300°F, GLDA at different pH values was able to enhance the core permeability. Decreasing the injection rate from 5 to 2 cm3/min increased the contact time between the fluid and the rock and increased the amount of dissolved ions. X-ray CT scan showed a porosity increase after the treatments at different conditions. The concentration of GLDA after the coreflood experiment was almost the same before the treatment showing a high thermal stability up to 300°F in the coreflood experiment. Labrid was found to be the best correlation to predict for the core permeability after treating Berea sandstone cores by 20 wt% GLDA solutions.