Elastic Pipe Control and Compensation for Managed Pressure Drilling Under Sea Wave Heave Conditions

Abstract

Managed pressure drilling (MPD) was developed as a group of technologies to more precisely control the annular pressure profile for which accuracy of the estimation of the bottomhole pressure is important. Particularly, under severe wave heaves in deepwater environments, the estimation based on static state pipe movement models can result in underestimation/overestimation of bottomhole pressures. The purpose of this study is to investigate the dynamic axial response of the drillstring with friction to applied heaving velocity, with particular interest to the effect at the bottomhole pressure. The paper presents an efficient and accurate method for solving the dynamic axial drillstring with friction and it allows it to be applied to heave velocity at the surface. The model that couples the pipe motion solves the full balance of mass and balance of momentum for pipe and annulus flow, considering the compressibility of the fluids, the elasticity of the system, and the dynamic motions of pipes and fluids. Also considered are surge pressures related to fluid column length below the moving pipe, compressibility of the formation, and axial elasticity of the moving string. Fluid properties are adjusted to reflect the effects of pressure and temperature on the fluids. The modeling takes into account the pipe elasticity under different combinations of heave and pipe velocities. Furthermore, the realtime torque and drag models are calibrated to actual hole conditions in realtime using survey, temperature, pressure, and downhole tool data to calculate friction factors in a wellbore. It has been observed that different conditions exist, some resulting in velocity reversal; thus causing surge or swab pressures. It has also been observed that heave amplitude has significant influence on bottomhole pressure. The different conditions observed for periodic or time function of displacements include (1) surface pipe velocity attributed to wave heave is in phase with the bottom movement of the string; (2) surface velocity of the pipe is out of phase with the bottom velocity of the pipe; (3) wave velocity and surface pipe velocity can be out of sync, and the bottom pipe velocity can be in phase with the surface velocity; and (4) wave velocity and surface pipe velocity can be out of sync, and the bottom pipe velocity can be out of phase with the surface velocity. The results of these calculations can be coupled to a realtime hydraulics model to determine a setpoint pressure for the MPD choke system. (SPE 173|005)