| Summary: | Natural gas hydrates have garnered worldwide attention as an important potential non-conventional fossil fuel resource. When extracting natural gas from gas hydrate deposits via depressurization, problematic ice generation and hydrate reformation can occur under conditions of fast depressurizing and low production pressures, due to insufficient heat transfer in the surrounding sediments. In this work we conduct in situ magnetic resonance imaging (MRI) visualization and analysis of hydrate decomposition behavior for different depressurization modes; we visually determine the volumetric and spatial characteristics of the hydrate decomposition during depressurization induced gas production operation. Our results indicate that fast depressurization rate can result in a fast hydrate decomposition rate, therefore, a rapid gas production rate. In addition, the radial extension behavior of the decomposition front confirms that ambient heat transfer is a critical factor driving hydrate decomposition into free gas and liquid water. Obvious hydrate reformation and ice generation phenomenon, seen in some of the sudden depressurization experiments, can be effectively avoided using piecewise and continuous depressurization methods. The findings of this study clearly demonstrate how production pressures affect the gas production behavior from hydrate deposits and provide further insight for establishing optimal production techniques for utilizing hydrate resources in the field. Natural gas hydrates; Depressurization; Production pressure; Ice generation; Heat transfer;
|
|---|