Numerical Investigation into the Gas Production from Hydrate Deposit under Various Thermal Stimulation Modes in a Multi-Well System in Qilian Mountain.

Bo Li,Tingting Zhang,Yuan Ye,Qingcui Wan

doi:10.3390/e23070800

Abstract

The primary objective of this study was to investigate the energy recovery performance of the permafrost hydrate deposit in the Qilian Mountain at site DK-2 using depressurization combined with thermal injection by the approach of numerical simulation. A novel multi-well system with five horizontal wells was applied for large-scale hydrate mining. The external heat is provided by means of water injection, wellbore heating, or the combinations of them through the central horizontal well, while the fluids are extracted outside from the other four production wells under constant depressurization conditions. The injected water can carry the heat into the hydrate deposit with a faster rate by thermal convection regime, while it also raises the local pressure obviously, which results in a strong prohibition effect on hydrate decomposition in the region close to the central well. The water production rate is always controllable when using the multi-well system. No gas seepage is observed in the reservoir due to the resistance of the undissociated hydrate. Compared with hot water injection, the electric heating combined with normal temperature water flooding basically shows the same promotion effect on gas recovery. Although the hydrate regeneration is more severe in the case of pure electric heating, the external heat can be more efficiently assimilated by gas hydrate, and the efficiency of gas production is best compared with the cases involving water injection. Thus, pure wellbore heating without water injection would be more suitable for hydrate development in deposits characterized by low-permeability conditions.

Highlights

With the rising desire for new energy and solving the global problem of climate change, natural gas hydrate has received more and more attention as the most promising energy source in recent years
We considered three heat injection approaches to figure out the most suitable thermal stimulation regime: electric heating, hot water injection, and electric heating combined with normal temperature water flooding
Gas recovery behaviors of hot water injection and electric heating combined with normal temperature water flooding are basically the same

Summary

Introduction

With the rising desire for new energy and solving the global problem of climate change, natural gas hydrate has received more and more attention as the most promising energy source in recent years. Natural gas hydrate (NGH) is an ice-like compound generated by the combination of water and small gas molecules when they are situated at high pressure and low temperature conditions. Studies have shown that natural gas hydrates are largely preserved in frozen terrestrial areas and marine sediments [1]. It is characterized by high energy density, wide distribution range, large-scale, and shallow burial. Mountain permafrost in China has favorable formation conditions of natural gas hydrate, a drilling project was carried out in 2008–2009 with the purpose of hydrate exploration, and rock samples containing natural gas hydrate were resoundingly acquired [2]. Thereafter in 2011, the first hydrate mining test was carried out in the permafrost areas of Qilian

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Conclusion