Effect of Water-Alternating-Gas Injection on Gas and Water Production Control in Carbonate Reservoirs

The viscous fingering during continuous gas flooding and water channeling during water flooding will reduce the sweep efficiency and ultimately affect the displacement efficiency. In this paper, extensive experiments with different injection modes were conducted to study their effect on production performance.

Experimentally, based on the geological characteristics and development conditions of the target carbonate reservoir, a laboratory physical model was established to study the migration characteristics and occurrence state of the injected gas and water. The effect of different injection modes, including continuous gas flooding, water-alternating-gas (WAG) flooding and water flooding, on water and gas production and oil-displacement efficiency was investigated. Experimental results indicated that the rising of water cut of WAG flooding was much lower than that of water flooding, presenting a good effect on delaying water production. WAG injection showed a relatively plateau period of gas-oil ratio, indicating injected water delayed gas channeling. WAG flooding achieved the highest oil recovery, followed by continuous gas flooding and water flooding.

This study provided an improved understanding of gas and water channeling behavior, and proposed schemes for delaying gas channeling and improving gas flooding.

Key words: gas flooding; water flooding; gas and water production; water-alternating-gas injection; physical simulation.