Abstract: Formation fluid channeling caused by well casing damage occurred frequently in Bohai oilfield, and wells were closed.A new LHD chemical blocking agent was successfully developed, in which the active agent and solidified material reacted rapidly and fiber network structure was formed to withstand high pressure difference.In addition, micro-expansion increased the hardness and strength of transition layer.This chemical blocking agent was successfully applied to SZ36-1-C25hf horizontal multilateral well, oil production was up to 200 m³/d.The blocking agent is reliable and stable with broad application.