Study on Hydrate Production Behaviors by Depressurization Combined with Brine Injection in the Excess-Water Hydrate Reservoir

Abstract

Depressurization combined with brine injection is a potential method for field production of natural gas hydrate, which can significantly improve production efficiency and avoid secondary formation of hydrate. In this work, the experiments of hydrate production using depressurization combined with brine injection from a simulated excess-water hydrate reservoir were performed, and the effects of NaCl concentration on hydrate decomposition, temperature change, and heat transfer in the reservoir were investigated. The experimental results indicate that there is little gas production during depressurization in a excess-water hydrate reservoir, and the gas dissociated from hydrate is trapped in pores of sediments. The high-water production reduces the final gas recovery, which is lower than 70% in the experiments. The increasing NaCl concentration only effectively promotes gas production rate in the early stage. The final cumulative gas production and average gas production rate have little difference in different experiments. The NaCl concentration of the produced water is significantly higher than that which is in contact with hydrate in the sediments because the water produced by hydrate decomposition exists on the surface of undissociated hydrate. The high concentration of NaCl in the produced water from the reactor significantly reduces the promoting effect and efficiency of NaCl solution on hydrate decomposition. The injection of NaCl solution decreases the lowest temperature in sediments during hydrate production, and increases the sensible heat and heat transfer from environment for hydrate decomposition. The changes of temperature and resistance effectively reflect the distribution of the injected NaCl solution in the hydrate reservoir.

Theoretical investigation of threshold pressure gradient in hydrate-bearing clayey-silty sediments under combined stress and local thermal stimulation conditions

“…As widely acknowledged, the combination of depressurization and heat fluid injection [44][45][46][47][48][49] has been recognized as an effective approach for extracting gas from HBCSS. This method avoids the shortcomings of pure depressurization and thermal stimulation methods while capitalizing on their advantages.…”

Renewable Energy Desalination for Island Communities: Status and Future Prospects in Greece

“…However, such technologies are not yet introduced into commercial practice mainly because of the high cost. Other brine management methods have been developed and implemented including release in waste water, evaporation ponds, mixing with surface water, discharging in deep wells, releasing on land [21] and for field production of natural gas hydrate [22]. In more detail [21]):…”

Review of Heat Transfer Characteristics of Natural Gas Hydrate

“…Therefore, heat transfer affects hydrate decomposition and even the efficiency of gas hydrate extraction [9]. In this method, temperature control is the key factor, so we need to understand the heat transfer characteristics of natural gas hydrates, make more use of the sensible heat of the reservoir, and enhance the heat transfer to the environment to improve the production efficiency of hydrates [10,11]. On the other hand, natural gas hydrates are stable only in a specific temperature and pressure range, elucidating the danger of climate change.…”