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Gas hydrate formation and corrosion within gas pipelines are two major flow assurance problems. Various chemical inhibitors are used to overcome these problems, such as monoethylene glycol (MEG) for gas hydrate control and methyl diethanolamine (MDEA) and film formation corrosion inhibitor (FFCI) for corrosion control. As an economical solution, MEG is regenerated due to the large volume required in the field. MEG regeneration involves thermal exposure by traditional distillation to purify the MEG. During this process, MEG is subjected to thermal exposure and so might be degraded. This study focuses on evaluating six analytical techniques for analyzing the degradation level of various MEG solutions consisting of MDEA and FFCI that were thermally exposed to 135 °C, 165 °C, 185 °C, and 200 °C. The analytical techniques evaluated are pH measurement, electrical conductivity, change in physical characteristics, ion chromatography (IC), high performance liquid chromatography–mass spectroscopy (HPLC-MS), and gas hydrate inhibition performance (using 20 wt % MEG solutions with methane gas at pressure from 50 to 300 bar). Most of the analytical techniques showed good capability, while electrical conductivity showed a poor result for solution without MDEA and IC showed poor results for solution exposed to 135 and 165 °C. The primary aim of this paper is thus to provide the industry with a realistic evaluation of various analytical techniques for the evaluation of degraded MEG solutions and to draw attention to the impact of degraded MEG on gas hydrate and corrosion inhibition as a result of the lack of quality control.

The key objective of this study is to investigate the efficiency of thermodynamic hydrate inhibition of monoethylene glycol (MEG) solutions collected from a MEG regeneration/reclamation pilot plant, simulating six scenarios of the start-up and clean-up phases of a typical gas field. The scenarios contain complex solutions of condensates, drilling muds/well completion fluids with high concentrations of divalent–monovalent ions, particulates, and various production chemicals, which can result in various system upsets in a MEG plant. MEG was regenerated and reclaimed at a recently constructed closed-loop MEG pilot plant that replicates a typical field plant. During MEG plant operation, feed-rich MEG is separated, cleaned, and heated so that water in it is evaporated and purified for reuse. In this study, equilibrium conditions of natural gas hydrates in the presence of 20 wt % of regenerated and reclaimed MEG solution at a pressure range of 65–125 bar were reported. The equilibrium data were measured in a PVT sapphire cell unit using an isochoric temperature search method. The measured data were compared with the literature and theoretical predictions to investigate the influence of regenerated/reclaimed MEG on gas hydrate inhibition performance. A better understanding of the efficiency of regenerated complex MEG solutions on hydrate phase equilibria forms a basis for improved system design, operations, and calculating required MEG dosages for hydrate inhibition.

Gas hydrate blockage and corrosion are two major flow assurance problems associated with transportation of wet gas through carbon steel pipelines. To reduce these risks, various chemicals are used. Monoethylene glycol (MEG) is injected as a hydrate inhibitor while methyl diethanolamine (MDEA) and film-forming corrosion inhibitor (FFCI) are injected as corrosion inhibitors. A large amount of MEG is used in the field, which imposes the need for MEG regeneration. During MEG regeneration, rich MEG undergoes thermal exposure by distillation to remove the water. This study focuses on analyzing the kinetics of methane gas hydrate with thermally exposed MEG solutions with corrosion inhibitors at 135−200 °C. The study analyses the hydrate inhibition performance of three different solutions at selected concentrations and pressures (50−300 bar), using a PVT cell and isobaric method. Results established that thermally degraded solutions cause hydrate inhibition drop. However, the inhibition drop was found to be lower than that of pure thermally degraded MEG, which is caused by the additional hydrate inhibition effects of MDEA and FFCI. In addition, hydrate phase boundaries and regression functions were reported to provide a deep insight into the operating envelope of thermally degraded MEG solutions.

New hydrate profile correlations for methane gas hydrates were obtained computationally (using three different hydrate prediction software packages) and experimentally (with three different MEG products from different suppliers). Methane gas with pure distilled water was the benchmark case used for the software comparison at pressures of 50 to 300 bar. In order to compare the hydrate inhibition performance of the MEG products, aqueous 10 wt% MEG solutions were tested using the isobaric method at a pressure range of 50 to 200 bar.Furthermore, the kinetics of MEG hydrate inhibition were studied experimentally for methane gas using a stirred cryogenic sapphire cell. Hydrate formation start, hydrate dissociation initiation and hydrate dissociation end points were identified and analysed. The results were correlated with the hydrate formation start points predicted by three well known selected hydrate prediction software packages (which all use the Peng-Robinson equation of state). Moreover, the hydrate inhibition performance of the three MEG products was evaluated to determine the superior MEG product that provides the best hydrate inhibition performance.Our analysis shows that the hydrate formation points predicted computationally are not identical to the hydrate formation start points measured in this work. Software ЉAЉ and software ЉBЉ predicted results matching with the average curve of the experimental hydrate formation start and hydrate dissociation start points, and with a deviation value of 0.06°C for software ЉAЉ and a deviation value of 0.03°C for software ЉBЉ. However, software ЉCЉ predicted results almost identical with the experimental dissociation start points, and with an average deviation value of 0.54°C.The methane gas hydrate profiles for the three different MEG products (X-MEG, Y-MEG and Z-MEG) indicated that X-MEG was the most efficient inhibitor as it shifted the hydrate curve most to the left; X-MEG shifted the hydrate formation curve by an average temperature of 2.07°C when compared to the benchmark curve (100% water); while Z-MEG shifted the curve by an average temperature of 1.81°C and Y-MEG shifted the curve by an average temperature of 1.71°C.We conclude that not all software packages predict the same results although they are all based on the same equation of state. Furthermore not all MEG products supplied have the same hydrate inhibition efficiency. Importantly, choosing the best MEG supplier will reduce the OPEX by reducing the amount of MEG used, and it will accommodate more relaxed operating conditions of lower temperatures and higher pressures.