Influences of depressurization rate on natural gas hydrate production characteristics in stepwise depressurization: Two-dimensional experimental study

The stepwise depressurization method offers substantial advantages in terms of mitigating the risk of pipeline blockages, ensuring production stability, and reducing environmental impact. This study employs a self-developed two-dimensional production simulation test system for natural gas hydrate. It enables precise control of depressurization rates through a servo system, allowing for stepwise depressurization within a single horizontal well at three different rates: high, medium, and low. The experiment investigates the temperature–pressure responses within the reservoir during the production, as well as gas production characteristics, including gas production and gas production rate. The results reveal that choosing a medium depressurization rate significantly increases gas production, achieving a gas production proportion of 59%. However, there is a considerable risk associated, with a peak gas production rate of 8.894 l/min, severely impacting reservoir stability and jeopardizing well control safety in the late-stage production. In the third depressurization stage, there is a relatively weak linear relationship between the normalized multiples of average gas production rate and depressurization rate, with the average gas production rate increasing to 5.78 times and 5.76 times the original rate when the depressurization rate is raised to 1.5 times and 3 times, respectively.