Model and experimental study on jetting flow rate for installing surface conductor in deep-water

Jetting is preferentially adopted for surface conductor installation in deep-water oil and gas facilities. Surface conductor bearing capacity decreases due to soil disturbance, which is the main risk of jetting technology. A calculation model of the minimum jetting flow rate is established based on Bernoulli's theorem and soil mechanics. Jetting experiments are carried out to investigate the effect of jetting flow rate on the bearing capacity of surface conductor. Experiment results show that the bearing capacity of surface conductor decreases exponentially with flow rate. Considering the effect of flow rate both on hydraulic breaking soil capacity and the bearing capacity of surface conductor, a design method of jetting flow rate for installing surface conductor is proposed. This method ensures the successful implementation of jetting technology and has been successfully applied in more than 30 deep-water wells in the South China Sea and West Africa.     

Experimental investigation of jetting effect on spudcan extraction from soft clay

The jack-up unit may suffer difficult extraction from soft clay attributed to the large embedment and suction. To ease spudcan extraction, the jetting technique is extensively adopted. The jetting effect on spudcan extraction is investigated with a series of model tests. Firstly, the effectiveness of top jetting is investigated, and it is found that the top jetting is not effective in reducing extraction resistance. Secondly, the efficiency of different jetting procedures are studied. It is revealed that jetting prior to extraction reduces the suction by increasing the excess pore pressure at spudcan base. And the jetting after extraction begins reduces the suction by filling the gap formed under the spudcan with jetting water and eliminating cavitation. Finally, tests with different jetting times, jetting rates, jetting pressures, and jetting nozzle locations and numbers are conducted. It is found that the effect of jetting time converges as it increases. The flow rate of jetting prior to extraction has little effect on jetting efficiency, whereas the flow rate of jetting after the extraction begins has significant influences on the jetting efficiency. Jetting pressure also has great effect on jetting efficiency, and converges as it increases. The closer the nozzles are located to the spudcan edge, the sooner the post-peak extraction resistance decreases. And the jetting efficiency increases with the nozzle number. The findings from the experimental studies can serve as a reference for future studies on the operation and optimization design of a jack-up jetting system.