Comparative Analysis on the Evolution of Seepage Parameters in Methane Hydrate Production under Depressurization of Clayey Silt Reservoir and Sandy Reservoir

Abstract

Gas hydrates are likely to become an important strategic resource with commercial development prospects. It is therefore of great significance to realize the long-term and efficient production of methane hydrate reservoirs. Previous studies have shown that the lithological characteristics of hydrate reservoirs have a significant impact on reservoir productivity by influencing the evolution of seepage parameters in the process of hydrate production. The porosity (Φ) and initial hydrate saturation (SH) affect the amount of hydrate decomposition and pressure transfer, and also indirectly affect the reservoir temperature field. The permeability (k) directly affects the rate of pressure-drop transmission and methane gas discharge. Due to the differences in seepage parameters caused by different reservoir lithology, a sandy hydrate reservoir (SHR) in Japan and a clayey silt hydrate reservoir (CHR) in China were found to have different gas production rates and the spatial evolution characteristics of the temperature and pressure fields varied in gas hydrate production tests. Therefore, to ensure the long-term and efficient production of the CHR in China, two models were established for a comparative analysis based on a numerical simulation. The two models were depressurizing models of the CHR of the W11 drilling site in the Shenhu Sea area of the South China Sea and the SHR of the AT1 drilling site in the Eastern Nankai Trough of Japan. Both models considered the heterogeneity of seepage parameters, and the TOUGH+HYDARATE (T+H) code was used in subsequent calculations. Four key results were obtained: (a) The order of the significance levels of the lithological parameters on productivity was k > SH > Φ in the CHR and SH > k > Φ in the SHR. (b) The heat conduction and heat convection in the CHR were weaker than in the SHR, which made it difficult to recover the low-temperature area caused by hydrate decomposition. (c) The exploitation of a high k hydrate reservoir should be given priority when the other initial conditions were the same in both the CHR and SHR. (d) The exploitation of both the CHR and SHR should not only rely on the hydrate content or seepage capacity to determine the reservoir exploitation potential, but the combined effect of the two parameters should be fully considered.

Study on Gas Hydrate Reservoir Reconstruction for Enhanced Gas Production in the Shenhu Area of the South China Sea Based on a 3D Heterogeneous Geological Model

“…29,30 Due to the high sedimentation rate of the Cenozoic Layer, rich oil and gas resources, and active deep fluid activities in the area, the hydrate accumulation system unique to the South China Sea has been formed, which has become a key target area for marine hydrate exploration and development in China. 31,32 From April to June 2007, China started GMGS1 drilling campaigns in the Shenhu sea area in the north of the South China Sea for the first time, drilling and coring eight sites according to the bottom simulating reflector. Research shows that the hydrate sample was obtained from the area near SH2, SH3, and SH7 sites; other sites show the hydrate occurrence based on seismic, logging, and geochemical data but have not got the hydrate samples.…”

“…The Shenhu Sea area is located near the southeast area of Shenhu Shoal in the middle part of the northern continental slope of the South China Sea and belongs to the northern continental margin of the South China Sea (Figure ). The area is bordered to the north by Shenhu Uplift and Panyu low Uplift and to the south by southeastern Uplift and belongs to the ZhuII depression in the Pearl River Mouth Basin in the structural area. , Due to the high sedimentation rate of the Cenozoic Layer, rich oil and gas resources, and active deep fluid activities in the area, the hydrate accumulation system unique to the South China Sea has been formed, which has become a key target area for marine hydrate exploration and development in China. , …”

Production Behavior of Hydrate-Bearing Sediments with Mixed Fracture- and Pore-Filling Hydrates

“…They are distributed in coarse-grained sediments, such as the Mackenzie Delta in Canada [12], Nankai Trough in Japan [13], and Northern Slope of Alaska in the United States [14]. Although the Shenhu area of the South China Sea is a fine-grained clayey silt sediment, a large number of pore-filling hydrates with high-saturation are found there due to the abundant foraminiferal shells and calcareous micro-fossils [15,16]. Fracturefilling hydrates refers to NGH occurring in sediment fractures and are blocky, layered, nodular, vein-like, etc.…”

Sensitivity Analysis of Multi‐phase Seepage Parameters Affecting the Clayey Silt Hydrate Reservoir Productivity in the Shenhu Area, South China Sea

“…Natural gas hydrates (NGH) include clathrate, ice-like compounds under specific high pressure (p) and low temperature (t); they are widely distributed in continental permafrost regions and deep-sea sediments (Li et al, 2022a;Wang et al, 2022). The energy density of NGH is high, under standard t and p conditions, when 1 m 3 NGH is completely decomposed, 164 m 3 methane gas and 0.8 m 3 water can be generated (Xiao and Zhang, 2021;Li et al, 2023a).…”