Safety evaluation on the casing strength of reactivated old wells after secondary and tertiary perforation

In order to reactivate old wells, it is necessary to conduct secondary and even tertiary perforation on the original wellbore to increase penetration depth and shot diameter, so as to improve the fracturing stimulation effect. one old well in Jidong Oilfield was taken as an example to study the remaining casing strength after multiple perforation. Firstly, the enhanced MISES yield criteria was defined for casing model by using the finite element software, and the grids at the edge of shot were refined by 10 times. Then, the remaining strength of casing after multiple perforation was analyzed by means of grid independence test. Finally, the adverse distribution modes of old and new shots were compared, e.g. axial tangency, circumferential tangency and conchoidal tangency. It is indicated that axial tangency is the most unfavorable distribution that decreases the remaining casing strength after multiple perforation. The remaining strength of?139.7×9.17 mm P110 casing and?139.7×10.54 mm P110 casing is decreased by 21% and 22%, respectively after secondary perforation of 16 shots/m. After?139.7×9.17 mm P110 casing is perforated three times at the density of 32, 32 and 16 shots/m successively, its remaining strength is decreased by 36%. The remaining strength of?139.7×10.54 mm P110 is decreased by 30% after perforation at the density of 16 shots/m for three times. In this way, the decreasing amplitude of remaining casing strength after multiple perforation is preliminarily quantified. It can provide the reference for the wellbore safety evaluation on the reactivation of old wells and recommend the way for the safety evaluation of casing in reactivated old wells after multiple perforation.