Li Bo, Ye Yuan, Zhang Tingting, Wan Qingcui
State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China.
School of Resources and Safety Engineering, Chongqing University, Chongqing 400044, China.
Entropy (Basel). 2021 Jun 23;23(7):800. doi: 10.3390/e23070800.
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.
本研究的主要目的是通过数值模拟方法，研究祁连山DK-2场地多年冻土水合物矿层采用降压与热注入相结合方式时的能量回收性能。一种新型的具有五口水平井的多井系统被应用于大规模水合物开采。外部热量通过向中心水平井注水、井筒加热或二者结合的方式提供，而流体在恒压降压条件下从另外四口生产井抽出。注入的水能够通过热对流方式将热量更快地带入水合物矿层，同时也会显著提高局部压力，这对靠近中心井区域的水合物分解产生强烈的抑制作用。使用多井系统时，产水率始终可控。由于未分解水合物的阻力，储层中未观察到气体渗漏。与热水注入相比，电加热与常温注水相结合对气体回收的促进作用基本相同。虽然在纯电加热情况下水合物再生更严重，但气体水合物能更有效地吸收外部热量，与注水情况相比，产气效率最佳。因此，无水注入的纯井筒加热更适合于低渗透条件矿层的水合物开发。
