Abstract: Conventional packers are not reliable when they are set in big hole and irregular open hole.In this regard,the technology of water-swellable packer was studied.By testing the swelling rate and sealing capability of water-swellable rubber,an optimum formula of the special rubber was selected,namely,rubber D1+70% water absorbing polymer+20% reinforcing-agent A+40% reinforcing-agent C.The influences of temperature and salt solution on water-swellable rubber was analyzed in laboratory tests,indicated that the swelling rate went up with the temperature,but declined when the temperature was over 120 ℃,and the swelling rate decreased as the ion-strength of salt solution increased.Moreover,the sealing mechanism of the water-swellable packer was investigated,and the isolation behavior of such packer was analyzed by finite element method depending on swelling rate.It showed that the isolation capability was higher when the swelling rate of rubber element increases.Field applications showed that the water-swellable packer no longer has poor reliability that conventional packers have when they were set in big hole and irregular open hole.