Houston's contingent will be assigned to the Peoria Javelinas in Peoria, Ariz., with play beginning Oct. 12.
Clemens, the son of seven-time Cy Young Award winner Roger Clemens, is hitting .246 with 24 homers and 80 RBIs at Double-A Corpus Christi this year.
"He's had a good year and we'll continue to get him at-bats," said Astros assistant general manager/director of player development Ricky Bennett. "One thing I want him to do is work on using the whole field. At times this year he got pull happy, and I want him to use the whole field and work on his swing and going the other way."
Urckfitz, who is 4-3 with a 4.13 ERA at Class A Lancaster, will be used primarily out of the bullpen. Steele is a fleet-footed outfielder who appeared in only 67 games at Double-A Corpus Christi because of an injury. The Astros want him to get about 100 at-bats in Arizona.
Nevarez, who is 2-1 with a 3.53 ERA at Corpus Christi, will be sent to Arizona to work on his mechanics, and Perez will need extra innings after injuries slowed him at Corpus Christi and Triple-A Round Rock. Greenwalt is 8-6 with a 5.92 ERA in 25 starts at Lancaster, and Shuck hit a combined .300 at Double-A and Triple-A.