Formation and Dissociation Kinetics of Methane Hydrate in Aqueous Oilfield Polymer Solutions (Polyacrylamide, Xanthan Gum, and Guar Gum) and Their Performance Evaluation as Low-Dosage Kinetic Hydrate Inhibitors (LDHI)

摘要

Hydrate formation and deposition during drilling offshore oil and gas wells has been one of the major challenges faced by the oil and gas industry. The use of low-dosage hydrate inhibitor (LDHI), such as water-soluble polymers, has become an established technique to prevent hydrate plugging during drilling and transportation. Commonly used oilfield polymers, such as polyacrylamide (PAM), xanthan gum (XG), and guar gum (GG), have not yet been clearly investigated individually and compared for their possible role as LDHI. The present study aims to investigate the performance evaluation of various water-soluble oilfield polymers as LDHI by performing hydrate formation and dissociation kinetic experiments. Two different molecular weights and varying concentrations of polymer in water were considered for the investigations. These are PAM (Mw: 1.1 X 10(6) g/mol-PAM-1 and 1.5 x 10(5) g/mol-PAM-2); XG (Mw: 6.4 X 10(5) g/mol-XG-1 and 2.4 X 10(5) g/mol-XG-2); and GG (Mw: 1.7 X 10(6) g/mol-GG-1 and 6 X 10(5) g/mol-GG-2), with 100, 200, and 500 ppm. These are referred to as high molecular weight polymers (PAM-1, XG-1, and GG-1) and relatively low molecular weight polymers (PAM-2, XG-2, and GG-2). The experiments were performed at an initial pressure of 8 MPa and a constant temperature of 274.15 K (i.e., at 10-11 degree of subcooling conditions). The hydrate nucleation (induction) time, gas consumption and its rate, gas-to-hydrate and water-to-hydrate conversion during formation experiments, and moles of gas released and its rate during hydrate dissociation were reported. The growth kinetics of gas hydrate were studied and reported up to 20 h after hydrate nucleation, while the dissociation kinetics were investigated for few selected polymers. From the study, it was observed that the molecular weight and concentration of polymer does play a major role in hydrate growth (consumption of gas) and the rate of gas consumed. PAM-1 exhibits excellent kinetic hydrate inhibition properties among the polymers studied. Other polymers such as XG-1 and GG-1 at 500 ppm also performed well as LDHI. Low molecular weight polymers, such as PAM-2, XG-2, and GG-2, did not result in much hydrate inhibition as compared to relatively high molecular weight polymers (PAM-1, XG-1, and GG-1). These observations have special significance for flow assurance, safer offshore drilling, and drilling fluid design and analysis particularly during degassing operations.