Regular Pore Network Model to Study Dynamic Permeability Evolution in Hydrate-Bearing Sediments

Abstract

Permeability is a key parameter to characterize fluid flow in hydrate-bearing sediments. Figuring out dynamic permeability evolution is of great importance for the effective development of hydrate-bearing deposits. In this paper, a grain-coating hydrate-bearing regular pore network model with complex pore throat cross-sections is first constructed. Afterward, the dynamic permeability evolution regularity is calculated. After the validation, the effects of initial aspect ratio, coordination number, and pore throat cross-sections on dynamic permeability evolution are investigated. The results show that hydrate narrows the effective flow space, which results in the exponential decrease of dynamic permeability with the increased hydrate saturation. The larger initial aspect ratio aggravates the heterogeneity of the pore network, resulting in a faster permeability decline rate. However, hydrate weakens the effect of initial aspect ratio on dynamic permeability evolution since the physical hydrate thickness in large pore bodies and throats is larger. The high initial coordination number reduces the dynamic permeability decline rate with the increased hydrate saturation since the higher coordination number increases the topology of the network, while hydrate compresses or blocks the effective pore throat space. Pore throat cross-sections have nothing to do with dynamic permeability evolution, but they dramatically influence the absolute permeability values. This study provides a novel insight into dynamic permeability evolution in hydratebearing sediments.

Reservoir Stimulation Technologies for Natural Gas Hydrate: Research Progress, Challenges, and Perspectives

“…29−31 Creep during the exploitation of natural gas hydrate deposits is also a cause of geological disasters. 32 The mechanical stability analysis of the reservoir was mainly used to study the mechanical properties and morphological changes of the samples during the decomposition of hydrates. Hydrate-bearing sediment samples prepared in the laboratory can reflect the strength and deformation characteristics of an actual sediment reservoir to a certain extent.…”

Experimental Study on the Permeability of Hydrate-Bearing Silty-Clayey Sediments with Grain-Cementing and Pore-Filling Hydrate Morphologies

“…A series of investigations were undertaken by scholars to characterize hydrate-bearing sediments considering multiple factors from the perspective of permeability. One crucial recognition is that hydrate content is scattered in the pore space of sediments, which is rendered with negative correlation to permeability. , Furthermore, the decreasing tendency of effective permeability with increasing hydrate saturation is validated experimentally to be diverse with the functions of the pore-scale environment, such as sediments’ particle size, porosity, suffered effective stress, and hydrate morphology. − Typically, hydrate morphology is a vital permeability-related factor in view of hydrate reservoir formation and NGH exploitation, in which two typical forms represented by grain-cementing and pore-filling morphologies are introduced to hydrate permeability models, including the Parallel Capillary Model, Kozeny Grain Model, and Hybrid Model, and their modification. − However, the correlation between permeability and hydrate morphology is mostly established by model calculations based on computed tomography imaging or theoretical hypothesis, − and there are few laboratory experiments taking this into account. For in situ NGH deposited in natural hydrate-stabilized zones, massive references point out that pore-filling or fracture-filling hydrate-bearing silty-clayey sediments (HBSCSs) below the seabed occupy vast reserves in contrast to other hydrate reservoirs. − To this end, determining the seepage characteristics of HBSCSs with different hydrate morphologies in laboratory pore scale is essential for gaining insight into the numerical simulation and model verification of hydrate reservoirs, as well as provides gas and water recovery prediction over long-term hydrate production.…”