Numerical simulation of a new methodology to exploit challenging marine hydrate reservoirs without impermeable boundaries

The exploitation of challenging hydrate (CH)1 reservoirs without impermeable boundaries (CH–B)2 faces a series of challenges such as poor production, gas escape to the boundary layers, and possible ocean and air pollution. This paper presents a new methodology for the exploitation of CH–B with a five-spot diamond horizontal well system (FSD)3. In particular, the production performance of CH–B with FSD in the Shenhu area is simulated, and the significance level of the horizontal and vertical well spacing for gas production, gas recovery, and gas capture was investigated by variance analysis. The results show that the new multi-well system can maximise cumulative gas production by 80% and recovery efficiency by 30% under the same operating conditions, compared with the three-spot row horizontal well system. Moreover, variance analysis indicates that vertical well spacing plays a more significant role in production performance and gas recovery during the entire mining cycle compared to horizontal well spacing. The optimal horizontal and vertical well spacings of FSD for CH–B in the Shenhu area are 40–50 m and 20–30 m, respectively. Therefore, the new multi-well system could enhance gas production while avoiding gas escape and boundary water intrusion, providing a feasible and efficient scheme for the exploitation of CH–B.