Papers by Author: Guang Hui Zhao

Abstract: Coiled tubing (CT) injector head is a key part of CT unit. Friction between gripper blocks and CT offers axial force that runs and retrieves the CT into or out of the wellbore. The CT held by the gripper blocks is loaded by axial force, pressure of inner fluid and gripping force, and is in a complex forcing state. Here it was assumed that all stresses were invariable longitudinally and could be simplified as problem of plane strain. The gripping force acted on the outer surface of CT was set as sinusoidal function along circumference. Stress function was employed to deduce the stress state of CT in gripper blocks. The effects of gripping force, inner pressure and axial force on CT strength were studied, and yield limit curves of the CT were presented by Mises yield criterion. These results offer referring data for minimizes the risk of scarring or mashing the CT.

Abstract: Bottom hole assemblies (BHA) of oil drilling engineering were simplified as simply supported beam, and parametric resonances of BHA in mud drilling and air drilling were studied. Lateral vibration of BHA, which was induced by bit/formation interaction, was described and reduced into Mathieu equation by means of separation of variables and Galerkin method. Modified strained parameter method was adopted in stability analysis. The parametric resonance zones expressed by weight on bit (WOB) are presented here. It is found that drilling method, speed of rotation (SOR), material properties, and length of compression drillstring all can influence parametric resonance zones. So unstable responses can be avoided by adjusting these parameters.

Abstract: Drillstring in oil drilling is simplified as a half-infinite bar. Taking account of Peierls-Nabarro(P-N) force and viscous effect of solid, dynamic response is simulated under harmonic driving at the end of the bar. With the physical properties specified, periodic, quasi-periodic and chaotic motions would appear as a function of the amplitude of external driving. We find that all the particles of the bar have the same qualitative characters, while vibrating amplitude decreases along the bar. It appears that particles of the bar reach chaotic motion through quasi-periodic motion. Investigation of this half-infinite bar will provide references for design of drillstring to keep motion away from chaotic region.