ENGLEWOOD, Colo. -- Although the Denver Broncos have made their two biggest acquisitions on defense this offseason via trades, they have spent the bulk of their free-agency dollars on offense thus far to help quarterback Drew Lock.

They continued that Saturday when they agreed to terms on a two-year, $5.7 million deal with tight end Nick Vannett, a source told ESPN, confirming multiple reports. That is to go with the four-year, $44 million deal with guard Graham Glasgow, a two-year, $16 million deal with running back Melvin Gordon and a two-year, $5 million deal with backup quarterback Jeff Driskel.

The Broncos also made trades for defensive tackle Jurrell Casey and cornerback A.J. Bouye since free agency opened.

Vannett is a player who has never had more than 29 receptions in any of his previous four years in the league. Last season, he finished with 22 catches overall for 166 yards as he was traded by the Seattle Seahawks in September to the Pittsburgh Steelers.

He ended up starting six games for the Steelers after the trade. The Broncos believe he can offer a quality complement, as both a blocker and a receiver, to Noah Fant at the position.

Vannett, at 6-foot-6, 261 pounds, is now easily the Broncos' biggest player at the position. He projects to be the second tight end in some of the one-back looks, as well as some of the goal-line personnel groupings, in Pat Shurmur's new offense.

Beyond Fant, the Broncos' other tight ends -- Jeff Heuerman, Jake Butt and Troy Fumagalli -- have all battled injuries at times, as Butt is trying to return from his third torn ACL. Heuerman, who was a teammate of Vannett's at Ohio State, has not played more than 14 games in any of his previous five seasons with the Broncos due to a variety of injuries.

The Broncos like Fant's potential in Shurmur's offense, and with an especially deep class of wide receivers in the draft, they had hoped to bolster the tight end spot in free agency.

When asked earlier this offseason what Fant's role in Shurmur's offense could be, coach Vic Fangio said: "I think he's a good fit. Noah's a good fit in anybody's offense ... He had a good season for us last year, but I expect him to even be better just from himself being more comfortable, more confident. He did get better as the season went on. I expect that to continue because he's got the right mindset. The guy's a worker, prideful. I think he would improve no matter what offense we have."

Vannett acknowledged his agreement with the Broncos on Saturday night, as he changed his Twitter profile to say: "Just a Denver Bronco from Westerville, OH.''