The Volts resumed on 74 for five having dismissed Canterbury for a paltry total of 95.
Josh Finnie and Wells (104 not out) got the scoreboard moving. Finnie mixed patience and aggression in his knock of 60 and, together with Wells, the pair added 96 for the sixth wicket.
When Finnie offered a catch, Wells continued the resistance, reaching the milestone from 156 balls.
Nathan Smith and Christie Viljoen chipped in with cameos of 20 and 17 respectively to help Otago through to 291 nine.
Otago top-order batsman Ryan Duffy did not return to bat. He sustained a nasty knock on his forearm while batting on the opening day of the two-day game.
The in-form Carisbrook-Dunedin batsman had an X-ray and got
the good news there was no
fracture.
With the pitch flattening out, Canterbury was able to prosper in its second innings, reaching 152 for three by stumps. Opener Jack Boyle made 56.
Finnie grabbed two wickets with fellow spinner Anaru Kitchen claiming the other scalp. The game was drawn and the two side's will play another two day match beginning today.
