Abstract:
Drilling tubulars typically function under large static and dynamic axial loads. The axial load causes curvature in the tubing and when loads are excessive, sections of tubing are forced in contact with the borehole wall. This causes excessive wear and fatigue and leads to failure of the tubing. The feasibility of inferring the incidence of curvature in the tubing and the increase in the attenuation level due to wall contact was investigated with pulse propagation tests on sections of drill tubing. Propagation speed and attenuation as a function of frequency were estimated from impulse response data using a nonlinear least-squares inversion technique. The changes in dispersion of phase speed and attenuation levels were used to identify changes in wall contact condition. Further, attenuation levels were also used to identify the presence of tubing curvature through the resultant coupling between axial and bending waves.