# Properties and Model of Pore-Scale Methane Displacing Water in Hydrate-Bearing Sediments
## 1 Introduction  
The world's energy consumption structure is transitioning from fossil fuels to clean energy sources [1]. Over the past 20 years, the primary energy consumption structure has shown a decreasing trend in the proportion of traditional fossil energy sources like oil and coal, while the share of clean and renewable energy has significantly increased [2]. Natural gas hydrate (CH\({}_{4}\)-nH\({}_{2}\)O) has remarkable characteristics such as wide distribution, large reserves, high density, and high calorific value [3], and the development of the natural gas hydrate industry serves as a bridge to promote the transformation of the energy consumption structure from high-carbon fossil energy to low-carbon/non-carbon new energy sources [4]. Submarine gas hydrates account for more than 90% of the total amountof gas hydrates in the world and are primarily stored in the seafloor sediments at the edge of the continental shelf, distributed at water depths between 300 and 3000 m [5]. Submarine gas hydrates have garnered significant attention due to their vast energy potential, but the rapid decline in gas production is a crucial factor that hinders the commercial exploitation of submarine gas hydrates [6; 7]. Seafloor hydrate extraction typically utilizes a range of methods (thermal method, depressurization method, carbon dioxide replacement, etc. [8]) to disrupt the in situ pressure state of seafloor sediments and convert solid natural gas hydrates into gaseous methane and liquid water. The pores of the seafloor hydrate deposits are filled with a significant amount of water. The released methane propels the flow of saturated water to the production wells under differential pressure [9]. This process is manifested as a gas-liquid two-phase flow state within a porous medium [10], and the periplasmic flow process during mining is illustrated in Figure 1. Influenced by the geometry, physical properties, and two-phase flow behavior of the sedimentary layer, the effective gas-producing channels are diminished, leading to a decrease in the conductivity of the sedimentary layer [11]. Therefore, an in-depth study of the gas-liquid two-phase flow law in pore medium is of great significance for the efficient development of natural gas hydrate resources and ensuring a clean energy supply [12]. Clarifying the characteristics of gas-driven water flow in the pore scale of seafloor hydrate sedimentary layers is crucial for advancing the stable testing of marine natural gas mining and the marine economy [13]. Indoor tests typically involve using simulated reservoir conditions of hydrate aquifers to examine the differential pressure changes within the reservoir [14; 15]. This is performed to investigate the flow patterns of methane and water. [PERSON] et al. [16] developed a series of multi-dimensional hydrate mining simulation test systems, conducted direct pressure drop mining tests, established the relationship between gas production per unit of pressure drop and the average gas production rate, and explained the mechanism behind the difference in peak gas production rate between vertical and horizontal wells. [PERSON] et al. [17] used nuclear magnetic resonance (NMR) technology to monitor the distribution characteristics of water flooding in deep-sea sandstone reservoirs. They quantified the repulsive capacity of the aqueous phase in the pore-scale medium, explored the mathematical model of repulsive efficiency concerning porosity, and analyzed the sensitivity of reservoir geometry to permeability properties. [PERSON] et al. [18] carried out high-pressure microfluidic visualization experiments, realized the visual observation of gas hydrate generation and decomposition phase transitions at the pore scale, investigated the evolution of bubble size over time, and examined how the warming rate affects the variation of methane bubbles at the pore scale. Limited by the conditions for conducting indoor experiments, many scholars have investigated the pore-scale gas-liquid two-phase flow through numerical simulation. [PERSON] et al.