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

The use of aminopolycarboxylic acids (APCAs) is increasing rapidly in several industries because of their unique properties of chelation and their effectiveness in high-temperature conditions. One of the major design considerations before their application is their thermal stability and their corrosivity to tubulars, especially the ones used in the oil and gas industry. Their disposal is also an active topic of discussion. The coordination bond formed between the chelator and metal ions is strong and thus can have long-lasting effects on the environment in terms of the metal's bioavailability. Therefore, its biodegradation and photodegradation must be considered. There is a lack of a single source of these major decision criteria for the selection of suitable APCAs and this paper provides an outlet for researchers and industry professionals to further their understanding of APCAs. Several types of APCAs including EDTA, DTPA, HEDTA, GLDA, NTA, MGDA, CDTA, HEIDA, EDDS, and ASDA were reviewed for their corrosion mechanisms and corrosion rates to the most common tubulars used in the oil and gas industry. In some cases, these chelating agents were implemented as corrosion inhibitors as well. The degradation of APCA was divided into three major categories: thermal-, bio-, and photo-degradation. The influence of temperature, microorganisms, and light play an important role during and post-treatment. To fully understand these degradation mechanisms, literature from several industries including medical, mining, toxicology, hydrometallurgy, materials, environmental sciences, mineral sciences, and electrochemical sciences was examined and elucidated. This paper provides a unique perspective of design considerations with the application of the frequently used APCAs. This review connects literature from several industries and can provide an important step-change in the overall understanding of APCAs from the initial design phase to their final disposal and treatment.

Insights on Potential Formation Damage Mechanisms Associated with the Use of Gel Breakers in Hydraulic Fracturing.

Hydraulic fracturing using water-soluble polymers has been extensively used to enhance the productivity of oil and gas wells. However, the production enhancement can be significantly impaired due to polymer residue generated within the proppant pack in the created fractures. This work describes an approach to establish a suitable fracturing fluid cleanup process by characterizing broken polymer residues generated from the use of different gel breaker types. Commonly used gel breakers such as inorganic oxidizers (bromate and persulfate salts), specific enzymes, and acids were evaluated in this work. The influence of each gel breaker was examined using High-Pressure/High-Temperature (HP/HT) rheometer, aging cells, zeta potential, Gel Permeation Chromatography (GPC), and Environmental Scanning Electron Microscope/Energy Dispersive X-ray Spectroscopy (ESEM/EDS). Experiments were performed on a carboxymethylhydroxypropyl guar (CMHPG) fracturing fluid at temperatures up to 300 °F. The developed GPC methodology showed that the size of the broken polymer chains was mainly dependent on the type of gel breakers used. Moreover, laboratory tests have revealed that some gel breakers may negatively influence the performance of polymeric clay stabilizers. Additionally, this work showed damaging precipitations that can be generated due to the interactions of gel breakers with H2S.

Micellar growth and network formation in acidic solutions of a sulfobetaine zwitterionic surfactant triggered by an inorganic salt.

Micellization (formation of wormlike structures) of 3-(N-erucamidopropyl-N,N-dimethyl ammonium)propane sulfonate (EDAS) in the presence of an inorganic salt, iron chloride (FeCl3), in acidic conditions is studied using static and dynamic rheological measurements and small-angle X-ray scattering (SAXS). Infrared spectroscopy, single crystal X-ray, and UV-visible spectroscopy are used to further investigate the mechanisms of viscosity and elasticity and the enhancement and formation of an elastic gel-like solution induced by Fe3+ in HCl. The nature of the interaction is characterized to be hydrogen bonding between the amide groups of EDAS and coordinated water in trans-[FeCl2(H2O)4]Cl structure. Such an interaction masks the repulsion forces between surfactant headgroups. This screening effect results in the formation of longer wormlike micelles in the solution. The chemical structure of FeCl3 in concentrated HCl was predicted in the literature through theoretical and experimental techniques; however, its crystal structure, including the exact geometry (e.g., cis or trans) and the non-coordinated chloride position is reported for the first time in the present study. The findings of this study show the sensitivity of a sulfobetaine zwitterionic surfactant to pH alteration and inorganic salt.