Following failure of a ESP diverter valve in a dual podded subsea ESP completion, our client considered carrying out a through tubing punch operation to increase flow from the reservoir. While simple tensile strength calculations provided a level of confidence that the tubing could withstand the metal loss from the punching operation, FEA was used to determine the impact of localised stresses across the complex perforation pattern.
In order to improve productivity from an ESP completion in a subsea well our client considered perforating the pup joint above the ESP pod in order to by-pass a faulty diverter valve. Initial calculations based on pipe cross-sectional area and tensile strength indicated that the load could be sustained following the perforation operation. However, concerns around the cumulative effect of stress concentrations around the complex perforation geometry were assessed through the use of FEA (Finite Element Analysis).
LISA 8.0 was used to model, constrain and apply loads to the section of tubing to be perforated. As can be seen from the image below, while there are stress concentrations around the perforations horizontally, there are also stress ‘shadows’ above and below each perforation. The results of the analysis concluded that perforation of the joint could go ahead without failure of the pup-joint due to the anticipated loads.