Sullivan, 30, will compete for the fifth outfield spot with Alex Romero, Jason Bourgeois and Yordany Ramirez, among others. Michaels re-signed last month and has the inside track for the fourth outfield spot behind starters Carlos Lee, Michael Bourn and Hunter Pence.
Sullivan is a career .276 hitter with 10 homers and 93 RBIs in 419 games. He's a career .233 hitter as a pinch-hitter and has batted .277 against right-handers in his career.
"He's an experienced guy," Wade said. "He's left-handed and can play all three outfield positions. At the very least, we can put him into the competition for the fourth and fifth outfield spots and see where it goes."
Wade said the Astros discussed signing Sullivan last year but never got the finish line.
"He's a guy that could potentially fill the need we think exists out there," he said. "Cory's experience serves him well."
Sullivan started 32 games last year, seeing time in right field, center field and left field. Michaels also started games at all three outfield positions last year for the Astros.
"In our league, with a four-man bench plus a backup catcher -- to me, versatility serves you pretty well," Wade said. "It's important for guys to do as many things as possible and give the manager more options. In the case of Michaels and Sullivan, they can play more than one outfield position.
"Look at the guys who are in the mix in the infield. Geoff Blum is going to play a lot and can play everywhere, and Keppinger can play everywhere and [Edwin] Maysonet can play everywhere, too. Equally important for Cory is he hits from the left side and serves another purpose for us to be one of those guys that [manager Brad Mills] can call upon when he needs a left-handed bat."
Bourgeois, who was designated for assignment last week, was invited to Major League Spring Training on Wednesday after clearing waivers and accepting his assignment to Triple-A Round Rock. Bourgeois, 28, hit .189 in 24 games with Milwaukee last year, but played the majority of the season with Triple-A Nashville, hitting .316 with 41 RBIs and 36 steals.
The Astros acquired him from Milwaukee on a waiver claim Oct. 26. A Houston native, Bourgeois has played in two Major League seasons with the Chicago White Sox (2008) and Milwaukee ('09) and owns a career .200 average.
The Astros have now invited 16 non-roster players to Major League Spring Training.