A Jetting Flow Rate Design Method for Conductor Installation through Jetting in Deepwater Drilling

When conductors are installed in deepwater drilling through jetting, it is necessary to design jetting flow rate appropriately based seabed parameters so as to guarantee the proper installation of conductors and rational recovery time of conductor capacity. A computation model of minimum jetting flow rate for rock breaking was established according to the submerged water jet theory and the unconsolidated seabed failure criteria. Then a pilot simulation test was carried out on conductor (φ339.7 mm) installation by jetting to analyze the influential rules of jetting flow rate on seabed breaking and surface conductor capacity. It is shown that the lowering velocity of conductors would be slow when jetting flow rate is less than a minimum certain value. On the other hand, the lowering velocity of conductors would increase quickly with the increasing of the jetting flow rate. The conductor bearing capacity decreases exponentially with the increasing of the jetting flow rate and reaches the lowest when jetting flow rate is over 1.2 times of the minimum value. Based on the calculation model and simulation of minimum jetting flow rate, the jetting flow rate design method is established under the constraint of hydraulic seabed breaking capacity and conductor bearing capacity. It has been applied in 22 deepwater wells in the South China Sea and the installation efficiency of conductors from jetting is increased and conductor stability is guaranteed.