Abstract: The study aims to investigate the impact of stepwise depressurization on the production characteristics of natural gas hydrate reservoirs to enhance the efficiency and controllability of hydrate production. A self-developed large-scale two-dimensional simulation test system was utilized to conduct stepwise depressurization experiments on a single vertical well of natural gas hydrate at three varying rates. The research focused on analyzing the effects of different depressurization rates on pressure response, temperature response, gas production, instantaneous gas production rate, and average gas production rate at the reservoir’s planar scale. The results indicate that abnormal peak phenomena in pressure change rate are closely associated with the back-pressure valve. The duration ratio is approximately inversely proportional to the depressurization rate. With the same depressurization magnitude, a lower depressurization rate results in a longer duration, enhancing external heat transfer and promoting greater hydrate decomposition during depressurization. This leads to a higher total gas production ratio. A decrease in depressurization rate delays the peak gas production rate in the second stage and shifts the time for maximum hydrate decomposition rate.

Key words: natural gas hydrate, stepwise depressurization, depressurization rate, temperature-pressure response, gas production characteristics