MECHANISMS AND CHALLENGES OF LARGE-SCALE EXPLOITATION OF NATURAL GAS HYDRATE IN THE SOUTH CHINA SEA

This study systematically reviews gas hydrate extraction mechanisms and the challenges associated with large-scale development in muddy-silt reservoirs of the South China Sea. Research indicates that hydrates in this region occur predominantly in unconsolidated muddy-silt sediments, which exhibit complex mineral composition(rich in clay, quartz, carbonates, etc.),pore structures dominated by micro-to nano-scale biogenic fossil pores and clay interparticle pores, extremely low permeability, and strong heterogeneity. The phase transition behavior of hydrates is governed by temperature and pressure fields with notable hysteresis effects, while clay minerals play a dual role—thermodynamically inhibiting and kinetically promoting phase transitions. During depressurization-based extraction, multiphase flow in the decomposition zone is constrained by the"water blocking" effect, leading to a sharp decline in gas-phase permeability. For reservoir stimulation, techniques such as hydraulic fracturing, thermal injection(e.g.,low-frequency electrical heating), and chemical methods(e.g.,CO₂ replacement)have been applied to enhance flow capacity. Notably, a calcium oxide-based in-situ thermal compensation and pore-filling method achieved a maximum reservoir temperature increase of 21.3 ℃ in field tests through synergistic thermal compensation and pore structure modification. The development of numerical simulators has focused on thermo-hydro-mechanical-chemical multi-field coupling, though further integration of chemical and biological processes is still required. Productivity simulations show that horizontal wells combined with fracturing significantly enhance gas production, though fracture parameters must be optimized to balance output and formation stability. Future work should deepen the understanding of phase interface evolution in nanoscale pore throats, advance multi-technology collaborative stimulation strategies, and establish fully coupled intelligent simulation platforms.