ABSTRACT

In this research, a numerical model is adopted to study the multi-field variations under different original reservoir pressure. According to the exploration cases, the basic properties of hydrate-bearing layers are predesigned and the trial-calculation is carried out. The results indicate that the real-time pore pressure reaches phase equilibrium requirements earlier under the lower original reservoir pressure, although that of higher one decreases faster at first. The gaps between them narrow with the depressurization, and all the results tend to overlap at last. Original reservoir pressure difference can accelerate the hydrate dissociation. The permeability variations are basically consistent with hydrate saturation.

INTRODUCTION

With the shifting of current energy structure, natural gas hydrate attracts attention all over the world as a huge green energy resource (Shao, 2020). The exist exploration cases said that it is widely distributed in both the sediments of the permafrost and ocean under high pressure and low temperature (Klauda, 2005; Wang, 2011; Guo, 2012), and successfully extracted by several trial-production projects based on depressurization, thermal stimulation, CO2 replacement and solid fluidization (Sloan, 1998; Yin, 2022; Chen, 2018).

Up to now, depressurization is believed to be the most popular method for marine natural gas hydrate development due to simple process, low cost and convenient operation (Ye, 2020; Zhang, 2014; Zhang, 2012). However, the critical commercial threshold is still hard to reach (Wu, 2021). On the one hand, there are certain engineering risks, like blowout, collapse and landslide, etc., should be addressed. On the other hand, the production efficiencies should be improved to cover the high costs of trial-production.

Pressure and temperature are the most important factors determining the hydrate phase transitions. It is necessary to learn the impacts of pressure on hydrate-bearing layers, especially during depressurization. In this research, a numerical model mentioned in our previous work (Chen, 2022) is selected to study the multi-field variations under different original reservoir pressure.

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