The blast occurred midday at a Husky Energy site near the town of Edson, some 140 miles west of Edmonton, the Canadian Broadcasting Corp. reported.
The injured sustained trauma and burn injuries, but none were life-threatening, officials told Global TV.
A spokesman from the provincial Energy Resources Conservation Board said there were no environmental hazards created by the explosion that involved so-called sour gas.
An official with a subcontracting firm working at the site told the CBC employees were preparing to start a process of fracturing rocks to access the gas deposits when the blast happened.
The incident was the third energy-related accident in the region in a week, Global TV said. A sour gas fire was reported at another site Friday and a woman was killed in an industrial accident at an oil processing plant Saturday, the report said.