Gas Hydrate in Oil-Dominant Systems: A Review

Kinetic and Thermodynamic Influence of NaCl on Methane Hydrate in an Oil-Dominated System

This experimental study reports the kinetic and thermodynamic inhibition influence of sodium chloride (NaCl) on methane (CH4) hydrate in an oil-dominated system. To thoroughly examine the inhibition effect of NaCl on CH4 hydrate formation, kinetically by the induction time and relative inhibition performance and thermodynamically by the hydrate liquid-vapor equilibrium (HLwVE) curve, enthalpy (ΔHdiss) and suppression temperature are used to measure the NaCl inhibition performance through this experimental study. All kinetic experiments are performed at a concentration of 1 wt % under a pressure and temperature of 8 MPa and 274.15K, respectively, whereby for the thermodynamic study, the concentration was 3 wt % by using the isochoric T-cycle technique at the selected range of pressures and temperatures of 4.0-9.0 MPa and 276.5-286.0K, respectively; both studies were conducted using a high-pressure reactor cell. Results show that kinetically, NaCl offers slightly to no inhibition in both systems with/without oil; however, the presence of drilling oil contributes positively by increasing the induction time; thermodynamically, NaCl contributes significantly in shifting the equilibrium curve to higher pressures and lower temperatures in both systems. In the oil system, the contribution of the THI to the equilibrium curve increases the pressure with a range of 0.04-0.15 MPa and reduces the temperature with a range of 1-3 K, which is due to the NaCl presence in the systems that reduces the activity of water molecules by increasing the ionic strength of the solution. At a high pressure of 9 MPa, the NaCl inhibition performance was greater than that at lower pressures <5.5 MPa because, at the high pressure, NaCl increases the activity of water, which means that more water molecules are available to form hydrate cages around gas molecules.

Polysaccharides Are Effective Inhibitors of Natural Gas Hydrate Formation

This review covers the types and applications of chemical inhibitors of gas hydrate formation in the oil and gas industry. The main directions of the development of new types of highly effective and environmentally safe “green” kinetic hydrate inhibitors (KHIs) based on biopolymers are analyzed. The structure, physicochemical properties, efficiency of gas hydrate formation inhibition, and commercial prospects of polysaccharides in preventing and controlling the formation of gas hydrates are considered. The criteria for their selection, current experimental data, and the mechanism of inhibition are presented. Recent research in the development of cost-effective, efficient, and biodegradable KHIs for industrial applications in the oil and gas industry is also presented.

Combined Approach to Evaluate Hydrate Slurry Transport Properties through Wetting and Flow Experiments

A condensate oil system was evaluated with respect to its hydrate properties by two experimental methods, namely, the wetting index (WI) procedure and a flow loop called the wheel flow loop. The WI was used to initially indicate the efficiency of a gas hydrate antiagglomerant (AA), while the wheel flow loop was used for evaluating the transport properties of systems without and with AA. The results provide new insight into the effect of water cut and flow properties on the risk of hydrate plugging. The test case used in the study was a relevant field from the Vega gas condensate asset on the Norwegian continental shelf. This asset is currently producing using continuous monoethylene glycol (MEG) injection as a hydrate prevention philosophy. The wettability of the hydrate particles was determined for uninhibited, underinhibited (10% MEG), and AA-inhibited systems, and the results indicated favorable wettability of the AA-protected system by changing the emulsion inversion point to higher water cuts. Furthermore, the wettability data were then confirmed by flow tests utilizing SINTEF's wheel flow loop. Moreover, both uninhibited and underinhibited systems led to plugging upon hydrate formation, indicating the need for optimized AA concentrations for a given fluid system and water cut. The overall results show that the WI combined with the wheel flow loop or similar equipment is an effective method for better selection and description of the plugging potential and transport properties for gas hydrate systems.

Experimental investigation and modelling of synergistic thermodynamic inhibition of Diethylene Glycol and glycine mixture on CO2 gas hydrates

In this experimental and modelling study, Diethylene glycol (DEG) and Glycine (Gly) mixtures are introduced to hinder carbon dioxide hydrate formation by pushing the phase boundaries on the lower temperature side. The mixture of DEG and Gly with the ratio of 1:1 is experimented at 15, 10, and 5 wt% concentrations and the pressure vary from 2.5 to 4.0 MPa. The T-cycle method is employed to assess the effect of the studied blends on the CO₂ hydrate by evaluating the hydrate dissociation temperature. Varied compositions of pure DEG and Gly as well as their mixtures are used to compute the synergistic effect. The studied system's thermodynamic hydrate inhibition (THI) influence is a concentration-driven phenomenon. Higher concentration can shift the hydrate liquid vapor equilibrium (HLVE) curve to lower temperatures and high-pressure regions. The outcomes depict that mixture of DEG and Gly at 15 wt%. Shows comparatively better results than the mixtures at 5 and 10 wt%, respectively. The obtained 10 wt% mixture results have also been compared with the conventional hydrate inhibitors and other THIs systems and provide a significant hydrate average suppression (ΔT) of 2.4 K. Furthermore, the freezing point-based Dickens and Quint Hunt model was also applied to predict the HLVE data of CO₂ hydrates and satisfactory agreement found with maximum mean absolute error (MAE) of 0.498 K. A better inhibitory performance was seen when diethylene glycol and glycine were combined, demonstrating the potential of amino acids as synergistic inhibitors in the exploitation of hydrates, transportation of oil and gas, and flow assurance.