Systematic analysis of reservoir properties on gas recovery from natural gas hydrate by multi-branch vertical wells: Examples from the Shenhu Sea of China

Available studies indicate that a multi-branch vertical well (MVW) may be the most appropriate well type for natural gas hydrate (NGH) exploitation, and the effect of branch parameters on gas production has been extensively explored. However, there is still a lack of systematic research and organization on how reservoir properties like reservoir types, porosity, and thickness affect gas production indexes. Consequently, we established Class 1-3 reservoir models and designed a series of cases to analyze the effect of reservoir properties on the exploitation with MVW. Results indicate that (i) MVW may be suitable for short-term production in Class 1 and Class 2 reservoirs and long-term production in the Class 3 reservoir, and the main well of MVW accounts for about 19% of gas production. (ii) It is preferable to locate the branches as close to the top of the reservoir as possible while maintaining reasonable spacing to capture the dissociated gas escaping from the lower reservoir. In addition, in Class 1 reservoirs, branches below the main well can capture free gas in the mixed layer. (iii) Reservoir parameters, including saturation, porosity, permeability, and thickness, make a significant difference in gas production, which provides an essential basis for further research by correlation analysis and polynomial fitting.