Minimization of Pop-Out Phenomenon Effect in Down-Hole Tubular Expansion

Abstract

In published literature, Solid Expandable Tubular (SET) is defined as a down-hole cold work process to expand a tubular to attain desired inner diameter. Tubular expansion process is a complicated process and a number of challenges are associated with its usage. However, proper planning before execution may lead the operators for more options that can affect important parameters such as; tubular length after expansion, hole diameter, expansion force, tubular structural integrity, post expansion properties, suitable material for tubular, selection or design of associated tools for expansion, and optimal selection of system components based on formation type, to name a few. Further studies are needed to overcome the challenges of these problems. Most of the published materials in this area mainly present the experience of using the technology without pointing directly to the technical challenges and understanding the fundamentals behind it. The successful expansion process shall make sure of no fracture, burst, collapse or any damage in the tubular; constant tubular diameter along the tubular; and the structural integrity of tubular and tubular connections. In general, expansion process involves placing a cone inside tubular and through the application of force at one end of the cone tubular expands. The sudden release of energy, at the end of expansion process, acts as a dynamic excitation to the tubular-fluid-formation system, which may affect tubular material properties and geometry, and is termed as pop-out phenomenon. The dynamics of problem is solved by considering inner/outer fluids and tubular itself. The forward and backward movement of pressure waves in inner and outer fluid and the stress wave in tubular is solved analytically as a coupled problem. It is assumed that the three mediums are uniform in nature, formation is isotropic, damping is negligible, fluid velocity behind cone is low and wave lengths are large compared to borehole diameter. It was found that the fluctuating stress levels at the fixed end of the tubular causes permanent ripples, which will increase tubular diameter beyond allowable limit and/or will cause converging and diverging sections within the tubular resulting from constructive or destructive interference of stress wave originating after pop-out. In order to limit the number of runs for computer simulation, particular type of tubular and well are chosen, hence keeping the geometrical parameters constant for all simulation. Other parameters are changed and their effects on pop-out phenomenon are determined. The results show that changing the formations, inner and outer fluid densities have no effect on the inner fluid pressure and axial stress for specific tubular materials. However, significant variations occur in outer fluid pressure. Among all tubular materials high Mn steel alloy experiences lower stress values. The current study can be used to aid in selection of reliable materials for SET system to minimize the affect of pop-out phenomenon. Also, formations variation varies outer fluid pressure. In addition, all expansion ratios follow the same pattern in parameters variation.