Vortex induced vibration suppression of the drill pipe for the long-term borehole monitoring system installation

This study proposes a Vortex Induced Vibration (VIV) suppression method for the Long-Term Borehole Monitoring System (LTBMS) installation in areas of strong ocean currents such as Kuroshio. One of the primary challenges in realizing LTBMS was to install high-precision, sensitive sensors into the borehole without damaging them. Two field tests were performed using accelerometers attached on instrument carrier and/or drill pipes to investigate the characteristics and causes of drill pipe VIV. This test demonstrates that the reduction of the drag on circular drill pipes and tubings and the vortex suppression can be achieved by the suppression ropes and the drill collars. They were suggested to be attached on the drill pipe above the sensor assembly for the actual LTBMS installation. From the VIV monitoring during the installation over a period of several days, the following three points can be drawn for the further VIV suppression: 1) The bottom hole assembly should be lowered in the low current area, with the relative current speed being as low as possible, 2) the drifting speed should be kept well below 1 knot, and 3) the drifting angle between drifting direction and sea current should be kept as small as possible (definitely less than 45°). The results show the VIV amplitude was further reduced to less than 0.5G, which led to the success of the first LTBMS installation.