Abstract: The gas cap reservoirs in Janajol filed in Kazakhstan are developed through isolating the oil and gas zones by injecting water as a barrier adjacent to the gas-oil interface. The oil ring is to be recovered first (by pattern water-flooding in the oil rig), then the gas cap in the later stage or the oil and gas be developed simultaneously after the water barrier has been formed. Taking South Б pool of the field as an example, in-depth analysis of the relationship between the water injection volume of the barrier and the incremental oil production by gas cap expansion is made, by which the feasibility of developing the gas cap reservoir is examined by integration of barrier-water injection with pattern water-flooding in the oil ring, timing reduction of the barrier water injection rate, making full use of the gas cap expansion energy to gain high economic benefits. In addition, reasonable annual injection-withdrawal ratio as well as proportion of the barrier-water injection rate and the pattern water-flooding volume in the oil ring is determined by using numerical simulation methods.

Key words: Kazakhstan, oil ring, water injection, numerical simulation