Methane Hydrate Dissociation in Quartz Sand by Depressurization Combined with Microwave Stimulation

Abstract

Depressurization combined with thermal stimulation is a promising method for gas hydrate production. Owing to its advantages of rapid uniform heating, microwave radiation is an efficient source of heat. However, the mechanisms of hydrate decomposition under depressurization combined microwave stimulation are currently unclear. In this study, methane hydrate was synthesized under 6 MPa and 2 °C, with hydrate saturation of approximately 42% in natural quartz sand. We then compared hydrate decomposition via rapid depressurization and piecewise depressurization, with or without microwave stimulation at 2.45 GHz and 400 W. When using the depressurization method alone, the hydrate decomposition rate increased with the depressurization amplitude. However, in the last stage of hydrate decomposition, the external flow of gas was hindered by the Jamin effect, especially under larger depressurization amplitudes; therefore, extremely low production pressure is not justified. When combined with microwave stimulation, both depressurization methods resulted in increased reservoir temperature within a few seconds, and microwave heating provided an extra driving force for hydrate decomposition. Furthermore, microwave heating was more effective when larger amounts of undecomposed hydrate remained after depressurization. When depressurization was combined with microwave stimulation, the average gas production rate at 100% gas production was 0.269−0.601 L/min, which was significantly higher than that for depressurization alone. However, the energy efficiency ratio was approximately 1, which has no practical value. Conversely, the average gas production rate at 90% gas production was 0.452−2.945 L/min and the energy efficiency ratio was 2.9−17.6. Under the combined method, gas hydrate decomposition at a production pressure of 1.9 MPa achieved the subtle balance between the average gas generation rate and energy efficiency. Thus, optimizing the gas production pressure and microwave stimulation time can improve the average gas production rate and energy efficiency ratio according to the reservoir hydrate conditions.

Constructing Amorphous‐Crystalline Interfacial Bifunctional Site Island‐Sea Synergy by Morphology Engineering Boosts Alkaline Seawater Hydrogen Evolution

“…[30] Thus, we further verify the origin of the activity on PdCo- The key reaction steps of the alkaline HER and the optimal configuration of relevant species on Co 3 S 4 (220) and PdCo-Co 3 S 4 are shown in Figure 6c as well. As discussed in previous reports, [31] the sluggish kinetics of the HER in alkaline solution can be attributed to the initial adsorption and dissociation of water molecules on the catalyst surface. As shown in Figure 6c, the Gibbs free energy change associated with the formation of H─OH intermediates in the water dissociation step (ΔG H─OH ) was found to be energetically favorable for both Co 3 sites and Co sites, suggesting a rate-limiting role, and hence it was applied as an activity descriptor.…”

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

“…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. The main controlling factors of the gas production rate of hydrate dissociation are the pressure propagation and heat supply rates.…”

Production Characteristics of the Methane Hydrate Sediment under Ionic Liquid Injection

“…And for the combined approach of depressurization and microwave heating, Li et al 25 preliminarily suggested that the hydrate dissociation phenomenon occurred rapidly under microwave stimulation compared with the water bath heating method, and the increasing microwave power could increase the hydrate dissociation rate. Zhu et al 39 believed that compared with other mining approaches, the hydrate reservoir temperature would rise quickly under microwave stimulation. Moreover, the optimal production pressure existed when the combined approach of depressurization and microwave stimulation was used.…”