Phase Equilibrium of Carbon Dioxide Hydrates Inhibited with MEG and NaCl above the Upper Quadruple Point

Abstract

Exploration of oil fields with high concentrations of carbon dioxide brings new challenges to the oil and gas industry. The high pressures reached in production pipelines can cause the condensation of the gas phase, characterizing the appearance of an upper quadruple point in the hydrate phase diagram. To prevent the formation of hydrates, the use of thermodynamic inhibitors, such as alcohols and glycols, is common in the industry. In addition, water from oil production is naturally inhibited with salts, such as NaCl. In this work, equilibrium data not previously reported for CO2 hydrates inhibited with MEG and NaCl were determined for pressures between 8.5 and 25 MPa using an isobaric experimental procedure. By the Clausius–Clapeyron relation and concepts of water activity, the consistency of the data was evaluated with promising results. A comparison of the measured data obtained in this work with prediction tools (Multiflash, PVTsim, and CSMGem) and the model by Sirino et al.30 [Fluid Phase Equilib.20184754563] was done.

Experimental Phase Equilibria of Carbon Dioxide and Methane Hydrates in the Presence of 2-Propanol and Sodium Chloride

“…(A) CO 2 hydrates equilibrium points with fresh water: experimental data of the present work (black circles) compared with literature data (pink diamond, green square, blue delta, and red left triangle) and (B) CH 4 hydrates equilibrium points with fresh water: experimental data of the present work (black circles) compared with literature data (blue delta, green square, pink left triangle, and red diamond).…”

“…In this region, CO 2 is in a liquid phase, having a density analogous to that of the hydrate and liquid water phases. Therefore, the identification of the dissociation through widths of the volume, pressure, or temperature point is a dare since these variations in equilibrium are minor …”

“…Phase equilibrium data results of CO 2 hydrates in 2-propanol + 5 wt % NaCl mixtures: fresh water (black circles), 5 wt % (green gradient), 10 wt % (red gradient) and 25 wt % (brown inverted delta), and NaCl 5 wt % (blue squares). , …”

“…Comparison between the model and experimental data referring to CO 2 hydrate systems in the presence of 2-propanol + 5 wt % NaCl mixtures: fresh water data (black circles), 2-propanol 5 wt % (green gradient), 2-propanol 10 wt % (red gradient), 2-propanol 25 wt % (brown gradient), NUEMhyd fresh water (dashed black lines), NUEMhyd 5 wt % 2-propanol + 5 wt % NaCl (dashed green lines), NUEMhyd 10 wt % 2-propanol + 5 wt % NaCl (dashed red lines), NUEMhyd 5 wt % 2-propanol + 5 wt % NaCl (dashed brown lines), NaCl 5 wt % (blue squares), , and NUEMhyd NaCl 5 wt % (dashed blue lines).…”

Experimental Study of the Effect of the Combined Monoethylene Glycol with NaCl/CaCl2 Salts on Sour Gas Hydrate Inhibition with Low-Concentration Hydrogen Sulfide

“…For example, the equilibrium temperature of CH 4 hydrate in the presence of a 10 wt % monoethylene glycol and 10 wt % sodium chloride mixture was 271.1 K and reduced to 261.6 K due to the monoethylene glycol concentration increase to 30 wt %, at a pressure of 4.33 MPa. Cordeiro measured the CO 2 hydrate equilibrium data in the presence of concentrations of 10, 20, and 30 wt % ethylene glycol, 5 and 10 wt % sodium chloride salts, as well as a mixture of 5 wt % sodium chloride and 10, 20, and 30 wt % ethylene glycol in the pressure range of 8.5–25 MPa, using the isobaric method . The results showed that sodium chloride and ethylene glycol had a synergistic effect on the inhibitory power of CO 2 .…”