Marine Natural Gas Hydrate Self-Entry Exploitation Device: Evaluation of Production Enhancement Measures

Test exploitation equipment and technology have progressed considerably in marine natural gas hydrate (NGH) exploitation, but many critical technical issues still need to be resolved before commercial production. Previous studies have proposed a non-drilling exploitation device—a self-entry exploitation device (SEED)—but reaching the NGH commercial exploitation threshold in its initial state is difficult. Consequently, we verified and evaluated some production enhancement measures to improve the exploitation system of the SEED. In this study, based on the geological data from the SHSC-4 site in the Shenhu sea and the material characteristics of the SEED, we carried out four production enhancement measures by numerical simulation. The results indicate that: (i) open-hole position adjustment can expand the contact areas between the device and NGH reservoirs; (ii) the effect of inner wall heating is limited but sufficient to achieve the goal of preventing clogging; (iii) it is necessary to select a reasonable spacing according to a combination of expected production cycle time and pressure when carrying out clustered depressurization; and (vi) when performing depressurization combined with thermal stimulation exploitation, factors such as permeability and thermal conductivity play a decisive factor in gas production.