The Department of Environmental Protection says in the report a contract worker with no oil field experience worked on the well, contrary to company policy, but did not identify a specific cause for the fire.
The report also says Chevron's well site managers did not always provide enough oversight to contractors at the site about 50 miles south of Pittsburgh.
The blast killed 27-year-old Ian McKee, a field service technician for Houston-based Cameron International. DEP previously said Chevron improperly restricted state access to the well site for the first two days. A Chevron spokesman says they are reviewing the DEP report.