Marussia dropped the experienced Timo Glock shortly before the start of testing for financial reasons.
It will begin the year as the only team with two F1 novices in its cockpits.
The Brazilian acknowledged that he and Chilton faced a tough task, but did not think Marussia would suffer for its choice.
"I would say we are going to have some tough times but no problems," he told reporters at Jerez.
"For the team, it was a tough decision.
"I think we just need to get there together and work through all the difficulties we have and eventually we'll come up with good stuff.
"There are some circuits we don't know and a lot of stuff is new to us so we need to get into the rhythm.
"GP2 drivers get into the rhythm quite quickly."
Razia is determined to prove that he is worthy of an F1 place, but admits the last-minute nature of his deal could be an initial handicap.
"I've been pushing all my life to this point and eventually I got the opportunity," he said.
"It's a great opportunity to show and to prove - to me before anybody else - that I belong in this place.
"First of all I need to work hard because it's quite late that I got into the team.
"I need to catch up with everybody and move through all the things I can do in the car."