Ouellet, with 54 goals in 187 NHL games with Pittsburgh and Tampa Bay, was already in the AHL with Norfolk after clearing waivers last week. Ouellet, with a salary of $1.3 million this season, will be sent to Vancouver's farm team in Manitoba.
O'Brien fills a defensive spot created when the Canucks lost Nathan McIver to a waiver wire claim from the Anaheim Ducks over the weekend. O'Brien has 37 points and 330 penalty minutes in 158 NHL games.
Krajicek missed most of last season with a shoulder injury that required surgery and slipped down the depth chart with the emergence of Canucks rookie Alexander Edler and the additions of Rob Davison and Lawrence Nycholat.
Simek was the Canucks sixth-round pick in 2006, and has yet to play an NHL game.
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