The synthetic effect of traditional-thermodynamic-factors (temperature, salinity, pressure) and fluid flow on natural gas hydrate recovery behaviors

Highlights: • Radial-interface dependence of MH dissociation dominated by water flow are verified. • MH dissociation rate has an obvious dependence on temperature under low flow rate. • Saturation and distribution of MH in sand sample dominate the water injection volume. • Promotion effect of multi-thermodynamic-factors on dissociation is the most obvious. The commercial exploitation of natural gas hydrates (NGHs) has been a growing research focus due to its features of enormous reserves and clean fuel. To guarantee the safe and efficient production of NGHs, we have proposed a novel strategy of water flow erosion to promote methane hydrate (MH) decomposition based on the tremendous seawater resource and the fundamental process of water-gas flow during NGHs exploitation. In this study, the synthetic effects of traditional-thermodynamic-factors (temperature, salinity, pressure) and fluid flow on MH decomposition characteristics, which is known little about yet, are comprehensively analyzed via in-situ magnetic resonance imaging (MRI). The temporal-spatial behaviors of MH decomposition are visually investigated. The results indicate that the pressure, salinity, temperature and water flow synergistically increased MH decomposition efficiency. Additionally, the propagation of the decomposition front along the interface between MH and ambient phase shows that the water flow rate and heat transfer are two crucial factors for accelerating MH decomposition. The higher water flow rate also efficiently complements the insufficient decomposition driving force due to the heat loss during MH decomposition process. The highest average decomposition rate (1.1%/min) and the relatively less water injection volume (320 mL) can be archived in this study. Furthermore, the decomposition rate has a significant dependence on temperature under lower water flow rate.