The dryness of superheated steam is 100% and it exists in the form of pure steam whose properties are like ideal gas. When the steam has a large degree of superheat, it may take a relatively long time to cool, during which time the steam is releasing very little energy and transmitted long distances. The heating radius of superheated steam in the formation is 5-10m larger than saturated steam. In the heating area of superheated steam, the comprehensive effects by superheated steam (crude oil viscosity reduction, improved flow environment, changes in rock wettability and improved oil displacement efficiency, etc.) is much higher than that of saturated steam. Superheated steam stimulation in Kenkyak high water cut heavy oil reservoir pilot test results showed that the average daily oil production of single well by superheated steam stimulation was 2-4 times than that of saturated steam stimulation. Superheated steam is more effective to heat water-invaded oil reservoir than saturated steam.

With superheated steam, there is no direct relationship between temperature and pressure, Therefore, at a particular pressure it is possible for superheated steam to exist at a wide range of temperatures higher than that of its saturated steam. The heat transfer coefficient is 1/150-1/250 as much as that of saturated steam during heat transferring, and it takes a relatively long time to cool, during which time the steam is releasing very little energy and transmitted long distances. The mechanisms of superheated steam stimulation are mainly pointed to the performance of crude oil viscosity reduced, flow environment improved, rock wettability changed, oil displacement efficiency improved. Physical simulation shows that oil displacement efficiency by superheated steam is 6-12% higher than that of saturated steam at the same temperature, and under the condition of carrying the same heat, superheated steam enlarged the heating radius by about 10m, oil steam ratio increased by 0.7. Superheated steam stimulation was put into Kazakstan’s heavy oil reservoir after two cycles of saturated steam stimulation. The average daily oil production was 2-4 times that of saturated steam stimulation, which improved heavy oil production effectively. The secondary heavy oil thermal recovery by superheated steam stimulation applied in marginal heavy oil reservoirs achieved satisfactory effect.