Abstract: Aiming at low final oil recovery of steam stimulation for recovering heavy oil, the laboratory experiments and field tests of downhole aquathermolysis for in-situ upgrading heavy oil technology were conducted to study how to improve the situation. The experimental results show that the reservoir minerals have catalytic effects on aquathermolysis of heavy oil, among which the catalytic effect of clay minerals on oil viscosity reduction is better than that of rock minerals, reaching more than 30%. The higher the content of clay minerals is in the reservoir, the more oil reduction can be obtained in aquathermolysis. After nickel sulfate and tetralin are injected as a plug before steam, the final oil recovery is 8.8% more than that of pure steam stimulation, the oil viscosity reduction rate can be increased by 51.7% , the contents of saturates and aromatics increased by 38.0 mg/g and 26.3 mg/g and the contents of resins and asphaltenes reduced by 41.9 mg/g and 41.1 mg/g, respectively. The field test results demonstrate that downhole aquathermolysis technology for in-situ upgrading heavy oil can prolong production period of steam stimulation, increase daily oil production rate, control total water-cut, and increase oil/steam ratio and water recovery ratio. In the end, the development effect of steam stimulation will be largely improved.

Key words: Liaohe oilfield, heavy oil, steam stimulation, downhole aquathermolysis, enhanced oil recovery