Numerical investigation of marine challenging gas hydrate extraction using multibranched horizontal wells

Natural gas hydrate in the Shenhu Area is deposited in low-permeability clayey-silty sediments and is known as challenging hydrates because of the most difficult to exploit. Herein, multibranched horizontal well technology for hydrate reservoir stimulation is proposed, and the production behavior including hydrate dissociation, and gas-water production was investigated using a three-dimensional numerical model. The results indicate that the well control drainage area of a single horizontal section is very limited under the inhibition of boundary water intrusion as well as the extremely low effective permeability. However, side-drilling multiple branches greatly enlarged the well control drainage area, resulting in a substantial hydrate dissociation zone. With the increase of branch length and the decrease of branch spacing, the hydrate decomposition rate and gas production rate gradually increase. At a branch spacing of 20 m and a branch length of 60 m, the cumulative gas production over 3600 days reached 453 × 10⁴ STm³ , which is 2.09 times higher than that of a single horizontal section. Additionally, the final gas-to-water ratio was also substantial. Consequently, the proposed multi-branched horizontal wells significantly enhance the efficiency of hydrate extraction, which provides a valuable reference for marine challenging hydrate development.