Pressure effects on the elastic properties of hydrate-bearing sediments based on laboratory observation

Abstract Investigating the role of confining pressure in affecting hydrate-sediment properties is crucial for improving the accuracy of hydrate content assessment. Experiments investigated how different confining pressures affected ultrasonic velocities during hydrate formation. The results showed that as confining pressure and hydrate saturation increased, ultrasonic velocities also increased, but at different rates. A comparison between the experimental result and theoretical model indicated that confining pressure significantly influences hydrate morphologies within the sediment. At a confining pressure of 10 MPa, hydrates predominantly adopted cementing morphologies, whereas at 14 MPa they primarily assumed pore-filling morphologies. The confining pressure also altered pore structure, leading to the closure of soft pores. A theoretical model was applied to calculate the variation in soft pore content with pressure, revealing a close correlation between hydrates morphology and soft pore content. At lower confining pressure, the samples exhibited a higher content of soft pores, resulting in hydrates mainly existing cementing morphologies. Conversely, at higher confining pressure, the reduction in soft pore content led to a predominance of pore-filling morphologies. These findings showed new insights of the relationship between hydrate morphology and pore structure, providing a valuable foundation for the quantitative assessment of hydrate reservoirs.