Dynamic Modeling and Vibration Analysis of Oilwell Drillstring During Backreaming Operation

摘要

Oilwell drillstring vibrations have been thoroughly studied due to their high damaging effects in the drillstring elements. The high costs involved in the oilwell drillstring operations have led scientists and companies to seek optimized parameters in the wellbore project or during the real time operation. This work presents a non-linear mathematical model for representing drillstring vibrations during backreaming operations, i.e. during the operation of pulling out the drillstring with fluid pumping and string rotation simultaneously. The proposed model focuses on the effects of lateral vibrations on the lower portion of the drill string, commonly known as Bottom Hole Assembly (BHA). The modeling approach is based on analytical, nonlinear and lumped parameters, which considers the effects of drilling fluid damping, stabilizer and drill collar contact with the borehole wall. The results of numerical simulations show the occurrence of abnormal lateral vibrations during the drill string withdrawal (backreaming), which can cause several problems during wellbore construction, e.g. BHA electronic equipment failure, falling rocks into the well, drillstring blockage.