Numerical study of gas production from fine-grained hydrate reservoirs using a multilateral horizontal well system

Natural gas hydrate is prevalent in ultralow-permeability fine-grained sediments with substantial reserves. However, effective and safe gas production from fine-grained hydrate reservoirs remains a global challenge. Here, a multilateral horizontal well system is innovatively employed to improve production efficiency in finegrained hydrate reservoirs. A three-dimensional (3D) numerical model of a real gas hydrate reservoir is constructed, and the influences of well configuration, deployment location, depressurization pressure, and reservoir properties on production are systemically and quantitatively evaluated. The spatial distributions of the physical properties of the 3D reservoirs during gas production are clearly revealed. The results indicate that the production efficiency of multilateral horizontal wells improves with increasing branch number and length, particularly when the ratio of branch length to reservoir width exceeds 0.15. Branch interference and perforation length positively affect production enhancement when multilateral horizontal wells are deployed in hydrate reservoirs with specific ultralow permeabilities; these discoveries are revealed for the first time. Multilateral horizontal wells with helically and vertically distributed equal-length branches yield high production efficiencies, and their optimal locations are in the lower sections of the reservoirs, particularly within high-isotropicpermeability reservoirs. Moreover, uniformly low depressurization pressure in helically distributed branches facilitates gas extraction; gas recovery efficiency increases by 8% when production pressure decreases by 1 MPa. This study suggests that the use of a helical multilateral well system is a promising strategy for achieving commercial gas production from fine-grained hydrate reservoirs.