Investigation on the Multiparameter of Hydrate‐Bearing Sands Using Nano‐Focus X‐Ray Computed Tomography

Abstract

In this study, a nano‐focus X‐ray computed tomography (X‐CT) is used to observe the formation of methane hydrate in sands on pore scale and to quantify hydrate saturation, pore structure parameters, and permeability of hydrate‐bearing sands. A new analytical technique is developed to improve the identification of water‐hydrate boundary. Three hydrate accumulation habits (i.e., floating, contacting, and cementing) in pore spaces are observed. When there is no methane bubble, hydrate distribution evolves from floating to contacting and then to cementing as hydrate saturation increases. In contrast, only contacting and cementing distribution patterns appear in the pores with methane bubbles. Based on the surface extraction and defect detection from 3‐D images, both the gas/water/hydrate distributions and the pore structure characteristics are investigated. The results show that the porosity, the maximal pore volume, and maximal diameter decrease as hydrates accumulate in the pores. However, the maximal pore surface, the total pore number, and the large pores (>100 voxels) number increase gradually until the hydrate saturation reaches 35%, when they turn to decrease rapidly. The pore structure parameters show detailed changes of hydrate and water on pore scale. The incompressible Navier‐Stokes equations are used to calculate absolute permeability of hydrate‐bearing sands based on X‐ray computed tomography digital images. It indicates that the microdistribution of the hydrate has a significant effect on the permeability calculation. The fluid streamlines obtained through simulation are used to track the water transport paths.

Pore‐Scale 3D Morphological Modeling and Physical Characterization of Hydrate‐Bearing Sediment Based on Computed Tomography

“…From Figure 9, the absolute permeabilities K h calculated via the FVM methods and PNM methods are quite similar in sediments with the same hydrate saturation, showing that both methods were equally reliable. Moreover, Figures 9a and 9b show that the absolute permeability K h decreases exponentially with increasing hydrate saturation for both models, which is similar to the results of previous experimental studies (Ji et al, 2020; Kuang et al, 2019; Wu et al, 2018) and simulation studies (Chen et al, 2018; Dai & Seol, 2014; Li, Liu, et al, 2019). This is primarily because the generation of hydrate blocks the flow channels.…”

Pore Fractal Characteristics of Hydrate‐Bearing Sands and Implications to the Saturated Water Permeability

“…This leads to the grayscale level of methane hydrate in Figure c lying in the middle position between grayscale levels of methane gas and NaCl solution. This kind of grayscale level distribution for methane gas, methane hydrate, and solution is quite consistent with those reported by Lei et al () and Li et al ().…”

Cementation Failure Behavior of Consolidated Gas Hydrate‐Bearing Sand

“…Yang et al (2015, 2016) and Zhao et al () visualized the gas hydrate morphology in various host materials without loading. Li et al () studied the changes in pore and gas hydrate morphologies along with hydrate saturation by X‐ray CT images. Waite et al () used X‐ray CT technology to track the gas hydrate morphology changes in hydrate‐cemented sands owing to depressurization/repressurization.…”