Numerical Simulation of the Effect of Porous Media Permeability on the Decomposition Characteristics of Natural Gas Hydrate at the Core Scale

Abstract

As a new type of clean energy, natural gas hydrates are widely distributed in ocean and permafrost. Moreover, it is important to understand the gas production characteristics of gas hydrate resources for the commercial exploitation in the future. The natural gas produced from hydrate bearing sediment is influenced by heat transfer, multiphase flow, and hydrate decomposition phase transition in the reservoir. This paper investigates the impact of permeability on the decomposition characteristics of hydratebearing sediments at laboratory scale by using a validated two-dimensional axisymmetric model. The results showed that in the initial depressurization stage for the low-permeability hydrate core the pressure-lowering end and right boundary exhibit a relatively large pressure difference; as the decomposition advances, the effective thermal conductivity within the reservoir decreases. Subsequently, the Joule−Thomson effect and hydrate decomposition phase change absorb sensible heat in the reservoir, contributing to a further decrease in the center temperature of the core; in areas far from the pressure-lowering end, the hydrate decomposition rate is slower than that in cores with high-permeability hydrates. The hydrate decomposition can lead to an increase in permeability, and hydrate cores with high permeability exhibit faster instantaneous gas production rate than hydrate cores with low permeability, which peak at 12 min. The variation of the effective thermal conductivity has a relatively minimal influence on the gas production characteristics of the hydrate core by depressurization. The gas production of the hydrate core under different conditions exhibits relatively small differences; for the low-permeability hydrate core, hydrate decomposition with thermal injection and the depressurization method exhibits obvious improvement in gas production, and for the higher permeability hydrate core, the acceleration effect is weaker.

Virtual Special Issue of Recent Research Advances in China: Unconventional Gas

“…There are six reviews covering a wide range of aspects related to methane hydrates targeting resource potential, production methods (depressurization and CH 4 /CO 2 exchange), exploration activities, sand management, and hydrate properties . The original research articles pertaining to the topic of hydrates cover a wide spectrum of areas, from numerical modeling, ,,, hydrate properties and characterization, ,,,, hydrate equipment ,,, to fluid production analysis, ,− ,, etc.…”

Seepage and Thermal Conductivity Characteristics of Fractured Hydrate-Bearing Sediments

“…In the evaluation of NGH reservoir productivity, seepage and thermal conductivity parameters are the most critical technical parameters. − This is mainly because they can respectively reflect the gas production efficiency and decomposition rate , to a certain extent. According to previous studies, in terms of permeability, Kumar et al measured the absolute permeability of filled porous media under different hydrate saturations and found that the presence of a hydrate phase will significantly reduce the intrinsic permeability of sediments, pointing out that in addition to traditional oil and gas storage, the study of permeability characteristics of HBS reservoirs should be regarded as an independent direction.…”

Mechanical Characteristics of Underconsolidated Methane Hydrate-Bearing Clayed-Silty Sediments

“…Natural gas hydrates (cage compounds) are transparent or translucent solid compounds formed by hydrogen bonding of guest molecules such as methane gas or carbon dioxide with water. − In the natural environment, gas hydrate exists stably in the form of methane and water crystallization under low-temperature and high-pressure conditions, which is also widely distributed in offshore areas and permafrost zones. − Under the background of the exhaustion of traditional fossil resources and continuously increasing energy demand, − as a clean and efficient unconventional fossil energy with wide distribution and large reserves, natural gas hydrate can provide critical support for solving the energy shortage problem. , However, the geological characteristics of hydrate-bearing sediments are complex and the sedimentary environment is sensitive, , and the exploitation of hydrate is accompanied by the decomposition of hydrate. , The decomposition of hydrate will reduce the sediment strength, which will lead to landslide, deposition, and another marine geological disaster. − Therefore, the study of the mechanical characteristics of methane hydrate-bearing sediment (MHBS) under triaxial stress is of great importance to the safety and stability exploitation and commercialization of hydrate engineering …”