This paper introduces a novel apparatus and the analyzing method for hydrate blockage detection in natural gas pipeline using the ultrasonic focused testing technique. The apparatus mainly consists of three parts: an ultrasonic focused transducer, a supporting guide track and a positioning ruler for the transducer. It can be installed by fixing the guide track onto the pipe outer wall, and the distance of the transducer to the pipe wall can be adjusted with the positioning ruler. The reflection signals of hydrate surfaces can be then received and recorded by an oscilloscope. The hydrate thickness thus can be calculated by multiplying the ultrasonic velocity with the time difference between two reflections. A calibrating test using this apparatus certified that it can provide an accurate measurement of both the pipe wall thickness and the hydrate blockage thickness from outside of the pipe. A maximum hydrate thickness of 50 mm can be measured due to the high penetrability of the ultrasonic. The feasibility of applying this apparatus to the metal pipeline was verified with a carbon steel cylinder with ice attached on the inner wall. A 360° blockage profile around the cylinder was obtained with a step angle of 5°. The accuracy of measured thickness and cross‐sectional area of the blockage can reach 96% and 91%, respectively. Finally, an application test was conducted on a full visible flow loop of 35 mm inner diameter and 49 m length. The test results showed that the hydrate blockage contour measurement can be achieved with this apparatus despite the gas and water flow in the loop. This hydrate blockage detection apparatus can be applied to gas‐dominated pipelines in which hydrate mainly forms on the wall. Early warning of hydrate blockage can be further studied based on the measurement results using this apparatus.

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Deepwater oil and gas development is extremely difficult and challenging. One of the most critical challenges stems from hydrate deposition, aggregation, and the eventual blocking of the deepwater oil and gas transportation system. The low-temperature and high-pressure environment in the deepwater oil and gas field causes the combination of gas molecules and water molecules to form hydrate, thus affects the hydrocarbon transportation. In this Perspective, to discuss the commonly faced safety issues for deepwater oil, gas, and gas hydrate development, the following three critical problems are comprehensively summarized and analyzed. First, the mechanisms of phase transition, aggregation, and blockage of the hydrate in the multiphase transport system have been investigated from the microscopic perspective to macroscopic characteristics. Second, based on different theoretical models, the algorithms are discussed to introduce an online monitoring technique for hydrate blockage, which can detect the safety risks and provide early warnings. Furthermore, for hydrate blockage prevention and control, the active methods based on chemical injection and the passive methods based on the modification of physicochemical properties of pipeline surfaces are reviewed. Finally, an outlook is provided for the future development of deepwater oil and gas and for the schemes to mitigate hydrate blockage.

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Safety issues are always a major concern in the oil and gas transportation facilities. Equipment damages are frequently encountered due to solid deposition such as gas hydrate deposition. A fast and efficient detection of the location, length, and rate of the accumulating blockage will significantly help relieve the potential risk. Most existing pressure wave‐based models suffer the difficulty to properly predict the blockage percentage arising from the ignorance of the wave attenuation. In the present work, an attenuation model to describe the transportation of the pressure pulse wave in gas is developed; the effects of waveform distortion and absorption as a result of the nonlinear effect and viscous dissipation are collectively considered for the first time. A simplified procedure to couple the wave attenuation in the model is proposed. The results show that the model can remarkably improve the prediction accuracy of blockage percentage by reducing the errors from −9.0% to −4.2%. Moreover, the attenuation process of the pressure pulse wave is determined to consist of three stages. The effect of waveform distortion on amplitude mainly occurs in the second stage, when our proposed model shows an improved prediction. The performance of the proposed model will help the early warning of the blockage in the pipelines and effectively avoid the potential injury and financial loss.

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In oil and gas exploitation and transportation, it is essential to avoid hydrate blockage in the wellbores and pipelines. Using kinetic inhibitors in composite with thermodynamic inhibitors can reduce the operational expenditure for oil and gas pipelines under high water content conditions. The phase equilibria of pure water natural gas system, oil–water natural gas system, and oil–water monoethylene glycol (MEG) natural gas system were first investigated by experiments and combined with software predictions in this study. The results showed that both mineral oil and MEG shifted the phase equilibrium of the system to high‐pressure and low‐temperature directions. The oil phase increased the effective temperature range of the compounding inhibitor. Then the hydrate inhibition performance and natural gas hydrate generation characteristics of the composite formulation of Luvicap 55w and MEG in oil–water emulsions and natural gas mixtures were investigated. With the increased subcooling, the induction time decreased sharply, and the gas consumption increased. The induction time increased with increasing MEG concentration, which verified the synergistic effect of MEG in oil–water emulsion for Luvicap 55w. The hydrate generation characteristics did not change much with increasing Luvicap concentration at the same temperature. In contrast, the hydrate induction time rose from 142.8 to >3500 min as the MEG concentration increased from 10 to 20 wt%.

The first prerequisite for the efficient and safe exploitation of gas hydrate resources is to accurately analyze the primary mechanical performance of hydrate-bearing sediments (HBSs). The mechanical performance of HBSs is complex and affected by many factors, including the reservoir environment in situ (temperature, pore pressure, salinity). Several published studies have demonstrated a correlation of the mechanical behavior of hydrates with temperature and pressure (T-PP). However, the research on the effect of salinity on the mechanical properties of hydrates or HBSs is still a relatively blank field. This study found that the strength of HBSs decreased with increasing salinity. This phenomenon can be attributed to the influence of salinity on the phase equilibrium state of hydrates. NaCl changed the relationship between the phase equilibrium curve of the hydrate and the T-PP conditions. The distance between the T-PP conditions and equilibrium curve was reduced with increasing salinity, which in turn led to a decline in sample strength. Moreover, the effect of the phase equilibrium of hydrates on the mechanical performance of HBSs was further explored. NaCl was added to HBSs to regulate the phase equilibrium state of the hydrate. When the T-PP conditions were on the phase equilibrium curve, the strength behaviors of HBSs showed a high degree of consistency.