Avalanche defenseman Ryan O’Reilly and defenseman Nick Bonino, who are both from Fort Wayne, Ind., were originally headed to Edmonton but decided to stay in Fort McMurdo, Alberta.
They will remain in Fort Wayne until their contracts are up in 2019-20.
O’Brien has been with the Avalanche since the start of the 2017-18 season.
Bonino joined the Avalanche after signing a two-year, entry-level contract in June 2017.
The Avalanche drafted Bonino in the fifth round of the 2016 NHL Draft.
They had O’Connor and O’Rourke on their final rosters last season.
Orenstein is a native of Calgary and a graduate of Fort Wayne High School.
He spent three seasons in the Calgary Hitmen organization.
In six seasons, he has scored 42 goals and 106 assists for 157 points in 705 games.
He has won two Calder Cups, four Stanley Cups and four Vezina Trophies with the Calgary Flames.
The 20-year-old has scored 20 goals and 37 assists for 55 points in 69 games this season.
He was a finalist for the Hart Memorial Trophy in the 2016 playoffs.
Oden was drafted by the Colorado Avalanche in the first round, 22nd overall, in the 2017 NHL Entry Draft.
He won the Hart Trophy in 2017 and is one of five players in NHL history to win the Hart Award in five different seasons.