Thermal Stability of Oilfield Aminopolycarboxylic Acids/Salts

Abstract

Summary 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 iminodiacetic acid, hydroxyacetic acid, and α-hydroxyglutaric acid. Studying the kinetics of aqueous solutions of NaH3GLDA, NaH2HEDTA, 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.

Novel chemical stimulation for geothermal reservoirs by chelating agent driven selective mineral dissolution in fractured rocks

“…The degree of permeability enhancement can be similar to or larger than that achieved from the injection-induced shear slip of fractures, depending on the distribution of biotite within the reservoir rocks. One concern related to this new chemical stimulation process is the thermal stability of the chelating agents 35 when a chelating agent is expected to be subjected to temperatures exceeding 200 °C during the stimulation of a reservoir of > 200 °C; however, it is not the primary target. Although we did not observe any adverse effects related to thermal stability in the present experiments at 200 °C, as expected from the reported thermal stability described in the introduction section, there is a concern that the thermal decomposition of the chelating agents and/or metal ions released due to the decomposition may generate deposits in such challenging applications.…”

“…This previous study reported that GLDA is as effective as other chelating agents and has the same degree of thermal stability as HEDTA 34 . A recent study regarding the thermal stability of major chelating agents, including GLDA and HEDTA, suggested that these agents can be used at temperatures of up to approximately 200 °C 35 . These previous studies have established the potential applications of environmentally friendly chelating agents to the chemical stimulation of geothermal reservoirs, especially for reservoirs with temperatures of up to 200 °C.…”

Chelating Agents in the Oilfield

“…Depending on the amount of nitrogen atoms that exist in the structure, chelating compounds can differ in their susceptibility to biodegradation. When compared to chelating compounds with numerous nitrogen atoms, those with a single nitrogen atom tend to be more biodegradable [107][108][109][110].…”

From initial treatment design to final disposal of chelating agents: a review of corrosion and degradation mechanisms

“…The thermal decomposition of GLDA was studied by several authors. 20,21,[94][95][96] GLDA exhibited similar thermal stability to HEDTA when heated for 4 hours at 149 C (300 F) and 177 C (350 F) and the decomposition products were cyclic GLDA and formic acid. 20 Sokhanvarian 95 examined the decomposition of GLDA at the same temperatures and a pH of 4 up to 12 hours.…”

“…Calcium ions (Ca 2+ ), which are common during limestone acidizing, were also found to stabilize GLDA. 96 Resonance stabilization of free carboxylate groups is thought to provide increased thermal stability in the presence of cations and higher pH. 95,97 Hydrated sodium salts of EDTA were found to be less stable at a much lower temperature than their aqueous form.…”