Research on Natural Gas Production Behavior Using Stepwise Depressurization with a Horizontal Well

Abstract

The commercial development of natural gas hydrates (NGH) is important for addressing the future energy requirements due to the depletion of conventional sources. Analyzing and understanding the effectiveness of different production methods under various well configurations are essential for the exploitation of NGH. According to the typical physical properties of hydrate reservoirs in the South China Sea, a simulation model was established. The natural gas production behavior was compared and analyzed via one-time rapid depressurization and stepwise depressurization using a horizontal well. The results showed that the heat and mass transfer capacities in a horizontal well configuration are enhanced due to gravity, and the water yield is decreased. For a horizontal well, stepwise depressurization is more advantageous than the one-time rapid depressurization method. Stepwise depressurization can significantly reduce water production and increase external energy input, which heats up the reservoir quickly. In addition, the horizontal well configuration with stepwise depressurization has a wider application range and can be used in various hydrate reservoirs with different physical properties. Although the average gas production rate during stepwise depressurization with a horizontal well configuration is lower, the gas−water ratio, thermal efficiency, and comprehensive exploitation economy are higher.

Impact of Varied Depressurization Rates on Gas Production and Heat Supply in Hydrate Dissociation

“…It is worth noting that the pressure propagation rate depends on the pressure difference between the production well and far-field reservoir, ,, as well as the permeability of the reservoir. − The pressure difference is not constant, which results in a variable depressurization rate during hydrate production . Some researchers have studied different depressurization schemes, including linear continuous depressurization, intermittent depressurization, cyclic depressurization, and stepwise depressurization. − Hydrate dissociation is pressure-oriented at the site scale, while the depressurization rate dominates the dissociated gas flow and strongly affects the recovery . Although the hydrate dissociation rate increases with the depressurization amplitude, extremely low production pressure is not justified due to ice and hydrate reformation, and the Jamin effect hinders the gas flow.…”