Water use characteristics and water footprints of China's oil and gas production

•Presented novel water footprint assessment method for China's oil and gas production.•Proposed unconventional water use factor to measure nontraditional water use.•Blue water decreased and unconventional water increased in oil and gas production.•Natural (esp. unconventional) gas exploitation may challenge China's water protection.•Total blue water footprint of oil and gas production in China may rise by 43% by 2030.