A 150m exclusion zone has been established around the rig as a precaution while engineers work on resolving the problem.
The incident occurred during drilling of the Argyle-162 well, about 25km southwest of Chinchilla, on a QGC-owned property.
Nobody has been hurt and QGC said the leak was not considered to pose any significant safety risk.
QGC said it had advised the Queensland Petroleum and Gas Inspectorate and neighbouring landholders.
The Brisbane Times quoted a company spokesperson as saying the leak would only take a couple of days to fix.