DENVER, Aug 8 (Reuters) - U.S. oil producer Comstock Resources said it was facing about a 15% rise in oilfield costs, but was helping to offset inflation by switching to natural gas-powered equipment.

The company activated a BJ Energy Solutions natural gas-powered frack fleet in April to offset higher costs for diesel used to power oilfield equipment.

Comstock said it had saved between $12,000 to $20,000 per fracking stage after it activated the gas-powered hydraulic fracturing fleet and that cost reductions for those well completions were around 15%.

The company recently entered into a contract to activate a second natural gas-powered fleet owned by BJ, executives said at the Enercom conference in Denver, Colorado on Monday.

"Even though gas is expensive right now, diesel is really expensive," said Chief Finance Officer Roland Burns.

He said the fleet had eliminated the need for about 1.4 million gallons of diesel and helped it cut around 2,000 metric tons of greenhouse gas emissions. (Reporting by Liz Hampton in Denver Editing by Marguerita Choy)