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The development of technologies for the accelerated formation or decomposition of gas hydrates is an urgent topic. This will make it possible to utilize a gas, including associated petroleum one, into a hydrate state for its further use or to produce natural gas from hydrate-saturated sediments. In this work, the effect of water content in wide range (0.7–50 mass%) and the size of quartz sand particles (porous medium; <50 μm, 125–160 μm and unsifted sand) on the formation of methane and methane-propane hydrates at close conditions (subcooling value) has been studied. High-pressure differential scanning calorimetry and X-ray computed tomography techniques were employed to analyze the hydrate formation process and pore sizes, respectively. The exponential growth of water to hydrate conversion with a decrease in the water content due to the rise of water–gas surface available for hydrate formation was revealed. Sieving the quartz sand resulted in a significant increase in water to hydrate conversion (59% for original sand compared to more than 90% for sieved sand). It was supposed that water suction due to the capillary forces influences both methane and methane-propane hydrates formation as well with latent hydrate forming up to 60% either without a detectable heat flow or during the ice melting. This emphasizes the importance of being developed for water–gas (ice–gas) interface to effectively transform water into the hydrate state. In any case, the ice melting (presence of thawing water) may allow a higher conversion degree. Varying the water content and the sand grain size allows to control the degree of water to hydrate conversion and subcooling achieved before the hydrate formation. Taking into account experimental error, the equilibrium conditions of hydrates formation do not change in all studied cases. The data obtained can be useful in developing a method for obtaining hydrates under static conditions.

Clathrate hydrates of carbon dioxide represent a subject of considerable interest in both fundamental science and the development of promising technologies. The phase behavior of CO2 hydrate in the presence of concentrated aqueous solutions remains poorly understood. In this study, we conducted a comprehensive investigation into the impact of magnesium chloride (0–24 mass%) and methanol (0–40 mass%) on the thermodynamic stability of CO2 hydrate. New experimental data on the three-phase gas–aqueous solution–gas hydrate equilibrium in the temperature range 243–283 K and pressure range 1–4.5 MPa were obtained. A correlation is proposed for the precise representation of equilibrium pressure–temperature lines. A comparison of the anti-hydrate effect, as indicated by the parameter ∆Th, of these substances demonstrated that ionic MgCl2 exhibits a stronger thermodynamic inhibitory effect on CO2 hydrate formation than nonionic MeOH. The results of measuring the melting point of ice at 0.1 MPa for aqueous solutions of MgCl2 and MeOH confirmed the thermodynamic consistency of the hydrate equilibrium data. A detailed comparison of the anti-hydrate effect of MgCl2 and MeOH in a wide concentration range was performed on hydrates of different gases (CO2 and CH4). The phase composition of CO2 hydrate samples obtained from water and aqueous solutions of MgCl2 and MeOH was examined using powder X-ray diffraction (PXRD) at 133 K. The PXRD results indicate the formation of sI CO2 hydrate with a cell parameter of 11.86 ± 0.04 Å in all cases.

The design of new dual-function inhibitors simultaneously preventing hydrate formation and corrosion is a relevant issue for the oil and gas industry. The structure-property relationship for a promising class of hybrid inhibitors based on waterborne polyurethanes (WPU) was studied in this work. Variation of diethanolamines differing in the size and branching of N-substituents (methyl, n-butyl, and tert-butyl), as well as the amount of these groups, allowed the structure of polymer molecules to be preset during their synthesis. To assess the hydrate and corrosion inhibition efficiency of developed reagents pressurized rocking cells, electrochemistry and weight-loss techniques were used. A distinct effect of these variables altering the hydrophobicity of obtained compounds on their target properties was revealed. Polymers with increased content of diethanolamine fragments with n- or tert-butyl as N-substituent (WPU-6 and WPU-7, respectively) worked as dual-function inhibitors, showing nearly the same efficiency as commercial ones at low concentration (0.25 wt%), with the branched one (tert-butyl; WPU-7) turning out to be more effective as a corrosion inhibitor. Commercial kinetic hydrate inhibitor Luvicap 55 W and corrosion inhibitor Armohib CI-28 were taken as reference samples. Preliminary study reveals that WPU-6 and WPU-7 polyurethanes as well as Luvicap 55 W are all poorly biodegradable compounds; BODt/CODcr (ratio of Biochemical oxygen demand and Chemical oxygen demand) value is 0.234 and 0.294 for WPU-6 and WPU-7, respectively, compared to 0.251 for commercial kinetic hydrate inhibitor Luvicap 55 W. Since the obtained polyurethanes have a bifunctional effect and operate at low enough concentrations, their employment is expected to reduce both operating costs and environmental impact.

Isothermal nucleation of gas hydrates in two-layer water–organic liquid systems was studied with the use of Sapphire Rocking Cell RCS6 with six transparent sapphire cells by thermal analysis under gas pressure. The experiments were conducted at constant supercooling (about 20.2 °C). Decane (both with and without surfactants Surfynol 420 and Span 80) and crude oils were used as organic liquids. It was observed that gas hydrate nucleation occurred at water–stainless steel–gas and water–sapphire–organic liquid three-phase contact lines rather than at water–gas or water–organic liquid interfaces. The empirical survival curves were constructed for the entire set of data. Two series of experiments for the system of water–decane–Surfynol 420–methane with the same sample were also conducted. The series of experiments differed with cell angle relative to the horizontal (45° and 14°). Comparison of the observed thermal effects with data of visual examination for this system allowed nucleation rates of methane hydrate on the different nucleation sites to be determined.

This article investigates the phase behavior of n-octacosane (C28H58) in the form of an aqueous dispersion with a particle size of about 100 nm. Samples of stable dispersions were prepared by ultrasonication without the addition of surfactants. Studies at various concentrations of n-alkane were performed by differential scanning calorimetry (DSC), powder X-ray diffraction, and light scattering methods. At low n-alkane concentrations, the sensitivity of DSC is not sufficient to detect the paraffin phase transitions. The light scattering method allows determining the phase transition temperatures (melting, crystallization, rotator phases) of n-alkane even in the 10−4 mass% dispersion.

Precise data on the non-variant equilibrium of the four phases (vapor–aqueous solution–ice–gas hydrate) in P–T coordinates are highly desired for developing accurate thermodynamic models and can be used as reference points (similar to the triple point of water). Using the two-component hydrate-forming system CO2–H2O, we have proposed and validated a new express procedure for determining the temperature and pressure of the lower quadruple point Q1. The essence of the method is the direct measurement of these parameters after the successive formation of the gas hydrate and ice phases in the initial two-phase gas–water solution system under intense agitation of the fluids. After relaxation, the system occurs in the same equilibrium state (T = 271.60 K, P = 1.044 MPa), regardless of the initial parameters and the order of crystallization of the CO2 hydrate and ice phases. Considering the combined standard uncertainties (±0.023 K, ±0.021 MPa), the determined P and T values agree with the results of other authors obtained by a more sophisticated indirect method. Validating the developed approach for systems with other hydrate-forming gases is of great interest.

Polymeric models of the core prepared with a Raise3D Pro2 3D printer were employed for methane hydrate formation. Polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), carbon fiber reinforced polyamide-6 (UltraX), thermoplastic polyurethane (PolyFlex), and polycarbonate (ePC) were used for printing. Each plastic core was rescanned using X-ray tomography to identify the effective porosity volumes. It was revealed that the polymer type matters in enhancing methane hydrate formation. All polymer cores except PolyFlex promoted the hydrate growth (up to complete water-to-hydrate conversion with PLA core). At the same time, changing the filling degree of the porous volume with water from partial to complete decreased the efficiency of hydrate growth by two times. Nevertheless, the polymer type variation allowed three main features: (1) managing the hydrate growth direction via water or gas preferential transfer through the effective porosity; (2) the blowing of hydrate crystals into the volume of water; and (3) the growth of hydrate arrays from the steel walls of the cell towards the polymer core due to defects in the hydrate crust, providing an additional contact between water and gas. These features are probably controlled by the hydrophobicity of the pore surface. The proper filament selection allows the hydrate formation mode to be set for specific process requirements.