Breaking And Recovery Mechanism Of Shallow Formation Soil During Surface Conductor Jetting Process In Deepwater Drilling

Since features like low temperature and loose soil bodies are common in deepwater seabed,risks like both poor quality and stability of cementing and wellhead are existing in conventional drilling technologies.To solve these problems,the technology of running surface conductor by jetting was proposed and extended in worldwide deepwater wells.During conductor jetting process,soils in shallow formation are broken hydraulically and mechanically,and surface conductor hold steady by the recovery of lateral friction offered by soils after reaching into position.Therefore,a clear understanding on the break and recovery mechanism would be significant for this new conductor running method.Based on the principle of similitude,this research conducted a series of field simulation experiments on surface conductor jetting.There are two purposes of the experiments.One is to study the influence of weights on bit and displacement on the efficiency of breaking soil.The other is to explore the soil strength recovery mechanism by measuring the change of radial pressure and pore water pressure during conductor jetting process,and to achieve the time dependent change rule of lateral friction by testing the maximal pull over force in different standing time.By combining the methods of theoretical research,numerical simulation,field experiments and analyzing application examples,this paper firstly simulated the soil breaking process under the action water jetting,analyzed the soil breaking mechanism in shallow formation under and the influence of drilling parameters on running speed,explored the time dependent change rule of soil lateral friction and proposed an design method on safety operation time window.The research results can provide technical supports for increasing operation efficiency and reducing cost.