Effects of expansion rate on plasticity and structural integrity of downhole tubular

Abstract

The current work presents an investigation of the effects of expansion rate on plasticity and structural integrity of down-hole solid tubular. Down-hole tubular has proven itself to be a promising technology in oil well applications by providing optimum solutions for many issues. One of the challenges still facing researchers and field engineers in implementing and making down-hole tubular technology cost effective is to conserve structural integrity of tubular. Cold expansion affects mechanical properties and induces residual stresses in tubular, hence reduces its collapse, burst, and fatigue ratings. The knowledge of properties variation is required in correctly predicting life span of tubular under given operational conditions. In present work, cold expansion of tubular under down-hole conditions is experimentally and numerically investigated at different strain rates. Strain rates are varied by changing the velocity of mandrel that is used to expand the tubular. Firstly, different tubular expansion experiments are performed to achieve 16%, 20%, and 24% expansion ratio. Secondly, finite element model of tubular expansion is developed in commercial finite element software ABAQUS. Simulation results are found to be in good agreement with experimental observations. Finally, further simulations are performed to thoroughly analyze the effects of expansion rate on the deformation behavior of tubular. It is found that there is variation in contact pressure at tubular-mandrel interface, effective stress, equivalent plastic strain, and thickness reduction during expansion process. These variations ultimately influence post-expansion properties of tubular particularly collapse and burst strengths, and hence its structural integrity. However, length shortening has marginally affected by expansion rates.