Interaction between drill bit and subsea soil during deepwater drilling pipe ejection

In order to analyze the interaction between the drill bit and subsea soil during the pipe ejection and lowering, the mechanical model of drill bit during the pipe lowering has been established. According to the analysis of jet flow theory and soil mechanics, the calculation method for nozzle jet flow force and critical destruction force of soil layer is gained. According to the research results, the interaction force between drill bit and subsea soil may be divided into direct acting force and jet flow acting force. The drill bit pressure directly acting on the stratum exists only when the jet flow force is small. The displacement is a main factor affecting the acting force. After the calculation of actual cases on site, the jet flow force and anti- erosion force of soil layer during the construction, and the height from drill bit to downhole during the ejection are figured out. Such research results are capable of analyzing the drill bit and drill string stress during the ejection based on the subsea soil characteristics in the specific sea areas, and providing a theoretical basis for the drilling parameter design of pipe ejection of deepwater drilling.