High pressure rheometer for in situ formation and characterization of methane hydrates

Integration of Pore-Scale Visualization and an Ultrasonic Test System of Methane Hydrate-Bearing Sediments

The acoustic characteristics of hydrates are important parameters in geophysical hydrate exploration and hydrate resource estimation. The microscale distribution of hydrate has an important influence on the acoustic response of a hydrate-bearing reservoir. Although microscale hydrate distributions can be determined using means such as X-ray computed tomography (X-CT), it is difficult to obtain acoustic parameters for the same sample. In this study, we developed an experimental system that integrated pore-scale visualization and an ultrasonic testing system for methane-hydrate-bearing sediments. Simultaneous X-CT observation and acoustic detection could be achieved in the same hydrate sample, which provided a new method for synchronously monitoring microscale distributions during acoustic testing of natural gas hydrate samples. Hydrate formation experiments were carried out in sandy sediments, during which the acoustic characteristics of hydrate-bearing sediments were detected, while X-ray computed tomography was performed simultaneously. This study found that hydrates formed mainly at the gas–water interface in the early stage, mainly in the pore fluid in the middle stage, and came into contact with sediments in the later stage. The development of this experimental device solved the difficult problem of determining the quantitative relationship between the microscale hydrate distribution and the acoustic properties of the reservoir.

Advances and challenges in the high-pressure rheology of complex fluids

Complex fluids and soft materials are ubiquitous in nature and industry. In industrial processes, these materials often get exposed to high hydrostatic pressures. Some examples include polymer melts, crude oils, gas hydrates, food systems, foams, motor oils, lubricants, etc. In spite of the relevance and utilization of hydrostatic pressure in many industrial applications, the role of pressure on the rheological properties has not been examined extensively in the literature. We review the high-pressure rheometric systems and present advantages and drawbacks of various kinds of rheometers such as capillary rheometer, sliding plate rheometer, falling ball viscometer, and rotational rheometer. By outlining the design complexities, precision, low-torque resolution limits and the inherent error sources of each type are critically evaluated. Furthermore, the high-pressure rheology data, chosen to cover a broad range of pressures and material class ranging from simple Newtonian fluids (incompressible), complex non-Newtonian fluids and compressible fluids featuring various key applications from different industries, are reviewed. The literature suggests, while effect of pressure on the rheological behavior is vital for many applications, compared to the effects of temperature on the rheological behavior, knowledge of the effect of pressure is still in its infancy.

Gas hydrates in sustainable chemistry

This review includes the current state of the art understanding and advances in technical developments about various fields of gas hydrates, which are combined with expert perspectives and analyses.

Oil Droplet Size Distributions in Deep-Sea Blowouts: Influence of Pressure and Dissolved Gases

To date, experimental investigations to determine the droplet size distribution (DSD) of subsea oil spills were mostly conducted at surface conditions, i.e. at atmospheric pressure, and with dead, i.e. purely liquid, oils. To investigate the influence of high hydrostatic pressure and of gases dissolved in the oil on the DSD, experiments with a downscaled blowout are conducted in a high-pressure autoclave at 150 bar hydrostatic pressure. Jets of "live", i.e. methane-saturated, crude oil and n-decane are compared to jets of "dead" hydrocarbon liquids in artificial seawater. Experiments show that methane dissolved in the liquid oil increases the volume median droplet diameter significantly by up to 97%. These results are not in good accordance with state-of-the-art drop formation models, which are based on oil-only experiments at atmospheric pressure, and therefore show the need for a modification of such models which incorporates effects of hydrostatic pressure and dissolved gases for the modeling of deep-sea oil spills and blowouts.

High pressure rheology of gas hydrate formed from multiphase systems using modified Couette rheometer

Conventional rheometers with concentric cylinder geometries do not enhance mixing in situ and thus are not suitable for rheological studies of multiphase systems under high pressure such as gas hydrates. In this study, we demonstrate the use of modified Couette concentric cylinder geometries for high pressure rheological studies during the formation and dissociation of methane hydrate formed from pure water and water-decane systems. Conventional concentric cylinder Couette geometry did not produce any hydrates in situ and thus failed to measure rheological properties during hydrate formation. The modified Couette geometries proposed in this work observed to provide enhanced mixing in situ, thus forming gas hydrate from the gas-water-decane system. This study also nullifies the use of separate external high pressure cell for such measurements. The modified geometry was observed to measure gas hydrate viscosity from an initial condition of 0.001 Pa s to about 25 Pa s. The proposed geometries also possess the capability to measure dynamic viscoelastic properties of hydrate slurries at the end of experiments. The modified geometries could also capture and mimic the viscosity profile during the hydrate dissociation as reported in the literature. The present study acts as a precursor for enhancing our understanding on the rheology of gas hydrate formed from various systems containing promoters and inhibitors in the context of flow assurance.