Experimental Study on Permeability of Methane Hydrate Clayey Interbedded Sediments Considering Effective Stress and Hydrate Dissociation

Abstract

Owing to the heterogeneity of methane hydrate reservoirs in the South China Sea, hydrate and silty clay particles mostly exist in the form of interbedded reservoirs. Permeability is a decisive factor for the efficiency of interbedded methane hydrate deposits. Therefore, using montmorillonite as the simulated sediment material, permeability measurements of interbedded sediments with different methane hydrate distributions and effective stresses were carried out for the first time in this study. By comparing with homogeneous sediments, the permeability evolution of interbedded sediments under different hydrate distributions and effective stresses is explored, and the effect of methane hydrate dissociation on the permeability of interbedded sediments is analyzed. The results show that the permeability of interbedded sediments with different hydrate saturation levels has little difference and is almost the same as that of pure soil sediments. With the increase of effective stress, the porosity of methane hydrate interbedded sediments decreases and permeability damage is caused, but the final permeability damage is less obvious than that of homogeneous hydrate sediments. In addition, the gas slip effect exists in methane hydrate interbedded sediments. Moreover, the dissociation of methane hydrate causes clay swelling, which leads to the decrease of interbedded permeability, but the degree of permeability damage is lower than that of homogeneous sediments. The results of this study provide a theoretical basis for the development and utilization of interbedded methane hydrate sediments in the South China Sea.

Permeability Anisotropy of Hydrate-Bearing Sediment during Consolidation Process: Insights from CT Scanning and Pore Network Modeling

“…When σ 31 ′ is 1 MPa, the number of pores and throats is minimum. As σ 31 ′ reaches 2 and 3 MPa, the number of pores and throats gradually increases; this is due to the rise of σ 31 ′, which makes the pore space compressed and the pore structure more complex, and the displacement of the compression process is larger at this time and shows a strong nonhomogeneity . When σ 31 ′ attains a magnitude of 4 MPa, it is unfeasible to reduce the radius of the local pores and throats, and the cutoff phenomenon appears, which makes the quantity of pores and throats increase greatly.…”

“…As σ 31 ′ reaches 2 and 3 MPa, the number of pores and throats gradually increases; this is due to the rise of σ 31 ′, which makes the pore space compressed and the pore structure more complex, 63 and the displacement of the compression process is larger at this time and shows a strong nonhomogeneity. 36 When σ 31 ′ attains a magnitude of 4 MPa, it is unfeasible to reduce the radius of the local pores and throats, and the cutoff phenomenon appears, which makes the quantity of pores and throats increase greatly. On the other hand, the pore and throat quantities in the unconsolidated process remained basically unchanged compared to 4 MPa in the consolidation process, indicating that the effective stress of 4 MPa had already caused the HBS to enter the plastic phase, and the particle positions would not be recovered after the effective stress reduces.…”

“…To elucidate dynamic evolution of water relative permeability ( k rw ) and gas relative permeability ( k rg ) throughout the process in hydrate depressurization for exploitation, most researchers have used experiments and simulations to study the process. − For experimental studies, Johnson et al investigated the two-phase seepage properties at different hydrate saturations ( S h ) based on a modified relative permeability measurement rig, which is capable of performing multiphase fluid permeability experiments and maintaining its thermodynamic stability. Ahn et al demonstrated the change rule of k rw and k rg curves based on artificially remodeled cores and explained the reason from the pore scale.…”

Formation and Production Characteristics of Shallow Marine Hydrates Considering Overlying Water Erosion

“…In recent years, the huge exploitable resource potential of marine hydrates has attracted worldwide attention. − Among them, shallow hydrates usually occur on the seabed surface and near seabed sediments. The buried depth of shallow hydrate is generally less than 120 m below the seafloor, which has the characteristics of high hydrate purity and large reservoir thickness .…”