Depressurization is considered to be one of the realistic production methods of methane gas from methane hydrate (MH). However, there is a concern about this method: flow blockage takes place inside the pipe, as MH forms on the surface of methane bubbles rising within a riser pipe. The objective of this study is to develop a numerical simulation method that can analyze the behavior of rising bubbles covered with MH in the water within a riser pipe. For this purpose, we measured the cohesion force of MH, considering that the bubbles come into contact with each other. The results, however, suggested that there is little force between 2 MH samples for them to detach in the water. We then numerically simulated the behaviors of rising methane bubbles in the water within a contracting pipe and found that the bubbles may clog the neck of the contraction, depending upon the contact angle at the pipe wall in the water.