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

Abstract

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.

Confined Compressibility of Fine-Grained Marine Sediments with Cavities after Complete Dissociation of Noduled Natural Gas Hydrates

“…Compression wave velocity of the specimen is monitored by using a pair of acoustic transducers connected to an HS-CS4EL acoustic tester (Xiangtan Tianhong Electronics Research Institute, Xiangtan, China), and the penetration depth of each acoustic transducer is 1 mm. This seismic wave monitoring system has been used in previous studies to measure the wave velocity of hydrate-bearing sands [43,44].…”

Review and Outlook of Visual and Geophysical Detections for the Pore-Scale Morphology of Gas Hydrates

“…Several laboratories have developed devices for simultaneous visual observations and geophysical measurements. For example, the Qingdao Institute of Marine Geology, China Geological Survey, has developed a joint X-CT and acoustic/electrical detection device. − Bu et al conducted a joint X-CT and P-wave velocity/resistivity test. They found that the sample’s P-wave velocity did not increase linearly with the increase of hydrate saturation but presented stage characteristics related to the change of the hydrate morphology.…”

“…Variation in hydrate morphology of CT images and P-wave velocity (a) or resistivity (b) characteristics of hydrate-bearing sand with hydrate saturation (S h ). (a) Adapted from open access ref . (b) Adapted with permission from.…”