Brittle fracture of cement sheath,induced by perforation and stimulation treatments,can cause cross flow of formation fluid and increase casing damage.A novel agent XL was developed for solving the problem.Experimental results showed that the toughness of the set cement containing XL was improved remarkably.The engineering properties of the slurry containing XL,drag reducer USZ (0.2% BWOC),filtrate loss additive F17B (1.2% BWOC) and crystalloid expanding agent F17A (3% BWOC) could meet technical requirements of cementing operation.After perforation,good quality cement sheath enhanced with XL was observed by CBL/VDL logs in a deep well.