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Chelating agents are used to remove various inorganic scales, including sulfates and carbonates. They are also used as standalone stimulation fluids and as iron-control agents during acidizing treatments. The main chelating agents used in the oil field include ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), N-(hydroxyethyl)-ethylenediaminetriacetic acid (HEDTA), and glutamic acid diacetic acid (GLDA). (Note that the abbreviations for these chelating agents will be used throughout the rest of the paper.) One of the concerns with these chelants is their thermal stability at elevated temperatures. Chelant solutions (0.7 to 0.8M) of HEDTA, GLDA, NTA, EDTA, and their mono-/disalts were prepared. The aqueous solutions of these chelants were heated at various temperatures (300 to 400°F) and times (2 to 12 hours). The concentration of chelant was measured with a titration method that uses FeCl3 solutions. The products of thermal decomposition of chelants were determined with mass spectrometry (MS) and gas-chromatography/MS techniques. Most chelants decomposed at temperatures greater than 350°F. At 400°F and after 12 hours of heating, diammonium salt of GLDA degraded more quickly than diammonium salt of EDTA chelant. Analyses of NH4H3GLDA with MS techniques after heating highlighted that the decomposition products included iminodiacetic acid, hydroxyacetic acid, and α-hydroxyglutaric acid. Studying the kinetics of aqueous solutions of NaH3GLDA, NaH2- HEDTA, and (NH4)2H2EDTA showed that their thermal-degradation kinetics followed a pseudo first-order reaction. The Arrhenius equation can be used to predict the activation energy that is necessary for the degradation mechanisms of chelants. [ABSTRACT FROM AUTHOR]

Chelating agents are used to remove various inorganic scales, including sulfates and carbonates. They are also used as standalone stimulation fluids and as iron-control agents during acidizing treatments. The main chelating agents used in the oil field include ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), N-(hydroxyethyl)-ethylenediaminetriacetic acid (HEDTA), and glutamic acid diacetic acid (GLDA). (Note that the abbreviations for these chelating agents will be used throughout the rest of the paper.) One of the concerns with these chelants is their thermal stability at elevated temperatures. Chelant solutions (0.7 to 0.8 M) of HEDTA, GLDA, NTA, EDTA, and their mono-/disalts were prepared. The aqueous solutions of these chelants were heated at various temperatures (300 to 400°F) and times (2 to 12 hours). The concentration of chelant was measured with a titration method that uses FeCl3 solutions. The products of thermal decomposition of chelants were determined with mass spectrometry (MS) and gas-chromatography/MS techniques. Most chelants decomposed at temperatures greater than 350°F. At 400°F and after 12 hours of heating, diammonium salt of GLDA degraded more quickly than diammonium salt of EDTA chelant. Analyses of NH4H3GLDA with MS techniques after heating highlighted that the decomposition products included iminodi-acetic acid, hydroxyacetic acid, and a-hydroxyglutaric acid. Studying the kinetics of aqueous solutions of NaH3GLDA, NaH2-HEDTA, and (NH4)2H2EDTA showed that their thermal-degradation kinetics followed a pseudofirst-order reaction. The Arrhenius equation can be used to predict the activation energy that is necessary for the degradation mechanisms of chelants. [ABSTRACT FROM AUTHOR]

Illitic sandstone reservoirs are sensitive to hydrochloric-acid (HCl) -based fluids. When HCl contacts illite, it breaks down and causes fines migration and formation damage. The migration of fines through the porous media will block the pores, reduce permeability, and decrease the production rate of oil and gas wells. A thorough literature review showed that all clay minerals are essentially unstable in HCl at temperatures greater than 300°F. In turn, there is a need to search for stimulation fluids other than HCl to stimulate deep sandstone reservoirs. Alternative fluids to HCl/hydrofluoric (HF) mud acids were introduced to stimulate and remove the damage from illitic sandstone reservoirs. These fluids are chelating agents such as hydroxyl ethylene diaminetriacetic acid (HEDTA) and glutamic acid-N,N-diacetic acid (GLDA). In this study, sandstone cores with different illite contents were examined. Illite contents of 1, 10, 14, and 18 wt% of the sandstone cores were used in the core-flood experiments at 300°F. Different combinations of GLDA/HF were tested to determine the optimum ratio of chelate/HF. Computed tomography scans and permeability measurements before and after the treatment were used to assess the effectiveness of each fluid in removing the damage and in the stimulation of the sandstone cores. The results show that 15 wt% HCl caused severe damage to sandstone cores with different illite contents. GLDA and HEDTA solutions showed a good compatibility with the illitic sandstone cores, with up to 18 wt% at 300°F. Permeability measurements showed that GLDA performed better than HEDTA at a pH of 4 and at the same molar concentration. The optimum ratio of GLDA/HF concentration was found to be 20 wt% GLDA/1 wt% HF, which gives the maximum increase in core permeability. No deconsolidation was noted with the two chelates tested. The results obtained from this study will significantly improve the outcome of acid treatments in illitic sandstone reservoirs at high temperatures. [ABSTRACT FROM AUTHOR]

Matrix acidizing of high-temperature gas wells is a difficult task, especially if these wells are sour or if they are completed with high-chrome-content tubulars. These harsh conditions require high loadings of corrosion inhibitors and intensifiers in addition to hydrogen sulfide scavengers and iron control agents. Selection of these chemicals to meet the strict environmental regulations adds to the difficulty in dealing with such wells. Recently, a new environmentally friendly chelating agent, glutamic acid-diacetic acid (GLDA), has been developed and extensively tested for carbonate and sandstone formations. Significant permeability improvements have been shown in previous papers over a wide range of conditions. In this paper, we evaluate the results of the first field application of this chelating agent to acidize a sour, high-temperature, tight gas well completed with high-chrome-content tubulars. Extensive laboratory studies were conducted before the treatment, including corrosion tests, coreflood experiments, compatibility tests with reservoir fluids, and reaction-rate measurements using a rotating disk apparatus. The treatment started by pumping a preflush of mutual solvent and water-wetting surfactant, followed by the main stage consisting of 20 wt% GLDA with a low concentration of a proper corrosion inhibitor. Following the treatment, the well was put on production, and samples of flowback fluids were collected. The concentrations of various ions were determined using ICP. Various analytical techniques were used to determine the concentration of GLDA and other organic compounds in the flowback samples. The treatment was applied in the field without encountering any operational problems. A significant increase in gas production that exceeded operator expectations was achieved. Unlike previous treatments where hydrochloric acid (HCI) or other chelates were used, the concentrations of iron, chrome, nickel, and molybdenum in the flowback samples were negligible, confirming low corrosion of well tubulars. Improved productivity and longer-term performance results confirm the effectiveness of the new chelate as a versatile stimulation fluid. [ABSTRACT FROM AUTHOR]

The article presents a study observing different chelating agents that are used as alternatives for hydrochloric acid (HCI) in matrix acidizing in the creation of wormholes in carbonate formations. It highlights the use of calcite cores in determining the optimum conditions of where the glutamic acid-N,N-diacetic acid (GLDA) can penetrate through the core and form wormholes. Concluded is that GLDA has been found to be very effective in creating wormholes at different injection rates.

The article focuses on the reaction between calcite and L-glutamic acid, N, N-diacetic acid (GLDA), a polyacidic chelate used for the acid treatment of deep wells. It says that GLDA is less corrosive and dissolves calcium carbonate (CaCO3) effectively. It compares GLDA with other chelates such as the hydroxyethylethylenediaminetriacetic acid (HEDTA) and ethanoldiglycine (EDTA). It concludes that GLDA inhibits higher solubility and thermal stability than HEDTA, and a lower toxicity.