Abstract:Due to the high heterogeneity of reservoir space, the kick and blowout accidents are easy to occur in the fracture-cave formation. As a downhole well control tool, the main function of the downhole BOP(Blow Out Preventer) is to close the inner and outer annulus of the drill pipe above the dangerous bottom layer and realize safe well control when there are abnormal conditions such as kick or blowout. In view of the application of downhole blowout preventer in fracture-cave formation, in order to meet the requirements of open-hole large annulus sealing, the downhole blowout preventer with a single compression long barrel is proposed as the sealing unit by improving the structure and material of the barrel. The structure of the downhole blowout preventer is characterized by the long rubber barrel and the expansion ratio is over 40% to ensure the sealing of the annular. Through the laboratory performance test, the aging and erosion of the rubber cylinder pressure up to 35MPa. Downhole blowout preventer torsional strength in the overall performance tests of up to 36100 N?m, with tensile strength of 1500kN, meets the requirements of normal engineering application. Finally, an experimental well was selected in the fracture-cave formation to take functional experiments on the packer. The experimental well results show that the sealing and unsealing functions of the downhole BOP can be realized, with the pressure keep stabilization in sealing processes. After tripping out, the overall component function is normal, and the reliability of downhole BOP is good.