Abstract: Using synthetic fluids of separate oil and gas samples from Ma36-5-5 well compounded according to gas oil ratio 24.7 m3/t, flooding experiments are conducted upon two groups of long real formation cores from Xinxia23and Xinxia24-5of Ma36 well block to research flooding efficiencies by nitrogen alternating foam water injection. Results show that the recovery enhanced by nitrogen alternating water injection with the core of Xinxia23is 6% or so and enhanced by nitrogen alternating foam water injection is 10% or so. And with the core of Xinxia24-5,the recovery enhanced by nitrogen alternating water injection is 3% or so, while enhanced by nitrogen alternating foam water
injection is 8% or so. It is also demonstrated that the displacement efficiency by foam water alternating injection is more obvious, and the enhanced recovery is higher, but it needs longer injection time and bigger injection volume, and the injection pressure also rises quickly.

Key words: Ma36 well block, lab research, nitrogen/wa-ter alternating, nitrogen/foam water alternating, recovery