The challenges in exploration and development of unconventional oil and gas resources are enormous. The complex reservoir characteristics, and oil and gas flow regimes introduce difficulty in predicting the oil and gas in-place, recovery and production profiles, and wells placement, design and completion. Horizontal drilling and completion using centuries-old manufacturing process of tube forming resulted in producing oil and gas from large areas with smaller footprint on the surface. Though expensive but it optimizes the recovery. The in-situ diametral expansion of tubular using a solid mandrel causes permanent deformation in which the system experiences large frictional forces at mandrel/tubular interface resulting in stick-slip phenomenon. It results in varying tubular thickness and diametral eccentricity which causes structural instability in wells leading to premature failure.
A finite element model describing the dynamics of stick-slip phenomenon in down-hole tubular expansion was developed. Three different set of equations; one each for stick, slip and transition phases were derived using equilibrium equations, time-dependent static friction model and velocity-dependent kinetic friction model. A switch model utilizing the zero velocity interval criterion was used to define stick, slip and transition phases. The newly developed model was implemented in the finite element model by means of two user-defined subroutines namely VFRIC and VDLOAD in commercial finite element software ABAQUS. Experimental and simulation results agree well for expansion force, wall thickness reduction and tubular length shortening. It was found that the thickness variation is the most critical parameter due to its effect in lowering collapse strength of expanded tubular. Parametric study investigations showed that the effect of this phenomenon may possibly be minimized by manipulating mandrel geometry, contact conditions, and/or mandrel speed.
