Idemitsu is an operator for a block, offshore Vietnam (300 km away from shore with approximate water depth of 120 m) and has drilled 4 exploration wells with semi-submersible rigs in this block. In this symposium, challenges and the lessons learned in the last two wells, Well-A of HPHT condition drilled at 2012-2013 and Well-B drilled at 2014 were presented.