Phase Equilibrium of Methane Hydrate in Aqueous Solutions of Polyacrylamide, Xanthan Gum, and Guar Gum

Abstract

The use of water-soluble polymers as natural gas hydrate inhibitors has gained interest in recent years. Variety of polymers have been studied for their kinetic performance in methane hydrate inhibition in the past; however, thermodynamic hydrate inhibition by water-soluble polymers is not fully understood and needs further investigation. This study investigates the effect of molecular weights and concentrations of aqueous solutions of various oilfield water soluble polymers on phase equilibrium of methane hydrate. Water-soluble polymers, such as polyacrylamide (PAM), xanthan gum (XG), and guar gum (GG) with two different molecular weights and varying concentrations, have been considered for the investigations. These are as follows: PAM (Mw: 1.1 × 106 g/mol, PAM-1 and 1.5 × 105 g/mol, PAM-2), XG (Mw: 6.4 × 105 g/mol, XG-1 and 2.4 × 105 g/mol, XG-2), and GG (Mw: 1.7 × 106 g/mol, GG-1 and 6 × 105 g/mol, GG-2), with varying concentrations of 100, 200, and 500 ppm each. 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 have been conducted in the pressure and temperature range of 8.63–5.50 MPa and 284.6–279.8 K, respectively. The results indicate that the water-soluble polymers have shown thermodynamic hydrate inhibition with an average temperature depression ranging from 0.25 to 1.05 K. The molecular weight and the concentration of polymers have been shown to affect the hydrate inhibition tendency. We have also proposed a hypothesis for hydrate inhibition based on the mobility of the polymer chain in the solution with a desired functional group in relation to nonelectrolyte/electrolyte thermodynamic hydrate inhibitors. The presented study on methane hydrate phase stability in the presence of various oilfield polymers is vital for their use in the design and development of hydrate inhibitive drilling fluids for offshore wells, hydrate-bearing formations, and studies related to the recovery of methane from hydrate-bearing sediments using polymer injection.

Polymer-Assisted Chemical Inhibitor Flooding: A Novel Approach for Energy Recovery from Hydrate-Bearing Sediments

“…Although PAM_200 ppm is not a good thermodynamic hydrate inhibitor, it has a better viscosity. 48 The effect of adding the polymer is quite encouraging, which has resulted in 31.3% of methane recovery even with lower methanol concentration (M1). This clearly shows that the polymer present in an aqueous solution helps in sweeping the methane produced from the hydrate reservoir.…”

“…Polyacrylamide has been used as it has been shown in our previous study that polyacrylamide can act as a better kinetic hydrate inhibitor. 47,48,50 Polyacrylamide is also often used for the chemical enhanced oil recovery process in the upstream oil industry, so its potential use for methane recovery from hydrate reservoirs can be extended. In total, seven different simultaneous formation and hydrate dissociation experiments were performed for the chemical inhibitor + polymer injection study.…”

“…It has been found that these polymers acted as a thermodynamic hydrate inhibitor. In addition, molecular weight and the concentration of polymers did affect the hydrate inhibition. , These water-soluble polymers (viz., polyacrylamide, xanthan gum, guar gum, and PEG) are also observed to act as kinetic hydrate inhibitors, , while the conventional hydrate inhibitors such as methanol and EG are known to act as thermodynamic hydrate inhibitors. Combinations of thermodynamic and kinetic hydrate inhibitors for methane recovery from hydrate reservoirs have not yet been explored in detail.…”

Phase Equilibrium of Methane Hydrate in Aqueous Solutions of Clay Stabilizers

“…However, the influence of clay stabilizers on the hydrate phase equilibrium may in turn affect the formation or decomposition of hydrates in wellbores and pipelines, leading to their blockage or to softening of the well wall, thereby posing a threat to safe production. 11 Furthermore, in the process of hydrate mining, due to the fact that hydrate reservoirs involve hydrate phase transitions, high-concentration clay stabilizers are likely to affect the hydrate phase equilibrium and thereby influence the mining. Therefore, a basic understanding of the phase equilibrium of methane hydrates in the presence of clay stabilizers should be established to understand their influence on different stages of the mining process.…”

“…Therefore, clay stabilizers are already common additives in oil and gas exploitation. , Because natural gas hydrate reservoirs contain high clay contents and present soft textures, they are more prone to wellbore safety problems and reservoir damage, and so the required clay stabilizer content for inclusion in the chemical additives is also quite high. However, the influence of clay stabilizers on the hydrate phase equilibrium may in turn affect the formation or decomposition of hydrates in wellbores and pipelines, leading to their blockage or to softening of the well wall, thereby posing a threat to safe production . Furthermore, in the process of hydrate mining, due to the fact that hydrate reservoirs involve hydrate phase transitions, high-concentration clay stabilizers are likely to affect the hydrate phase equilibrium and thereby influence the mining.…”