Dynamic competitive co-production behaviors between natural gas hydrate and higher-pressure shallow gas under wellbore interference: An experimental study

The commercial production of offshore natural gas hydrate (NGH) is currently hindered by low production rates, high fixed costs, and poor sustainability. The co-production of NGH and shallow gas (SG) may be a promising strategy for commercial NGH production. However, there remains a critical gap in understanding and improving co-production strategies involving NGH and SG reservoirs utilizing a single well. In order to address this knowledge gap, we compared the production behaviors of co-production of a hydrate-shallow gas reservoir (CPHSG) and production of a single hydrate reservoir (PSH) by depressurization utilizing a single vertical well in different three-phase saturations in the NGH reservoirs. The experimental outcomes showed that CPHSG outperformed PSH, with the average gas production rate increasing by 35.46 % - 51.10 %. Additionally, the study uncovered the dynamic competitive co-production behaviors between NGH and SG reservoirs under wellbore interference. The wellbore interference in CPHSG was due to differences in pressure, permeability, and gas occurrence forms between the NGH and SG reservoirs. Notably, the presence of SG in CPHSG played a crucial role in the hydrate reformation mechanism. It enhanced hydrate reformation in the stability zone by increasing the gas-water contact area, while simultaneously inhibiting it in the decomposition zone by reducing local pore pressurization and endothermic decomposition. Meanwhile, the competitiveness of each layer in the co-production process was determined by the permeability, production driving force, and hydrate decomposition rate. These findings not only deepen our understanding of CPHSG but also offer valuable insights for optimizing production strategies and promoting the sustainable exploitation of NGH resources.