Investigation of Drill Bit Heave Response to Drill Rig Heave Excitation

摘要

Managing bottom hole pressures within acceptable limits when drilling from a floating drill rig has become one of the facing challenges for the Managed Pressure Drilling (MPD) in deep waters. When adding a new segment to the drill string, the drill string is set on the slips and the entire drill string moves vertically with the heave of the rig. This can cause high surge and swab pressures in the borehole and may lead to lost circulation of drilling fluid or an influx of formation fluid. The drill string is very long (up to several thousand meters) and is surrounded by the drilling fluid. In addition to the material properties of the drill string, the frictional drag along the string, as well as the reaction of the fluid to the motion of the drill bit at the borehole, will have significant influence on the vertical motion response of the drill bit to the heave of the drill rig. This paper presents an investigation on the vertical motion of the drill bit to the heave motion of the floating drill rig using a simplified elastic string model. The computer software RIFLEX and SIMO are employed in conducting the nonlinear dynamic response analysis of the drill string dynamic system and sensibility study of the important factors (parameters) on the response of the drill string. The drill bit heave Response Amplitude Operator (RAO) curves obtained would reveal the relation between the motion of the drill bit and the heave motion of the floating rig.