An unconventional method to improve sweep efficiency in highly stratified or naturally fractured gas condensate reservoirs has been explored through simulation studies. The alternating water and gas injection process (WAG) has not been heretofore seriously considered in gas cycling projects for fear of losing ultimate production. For the base case study presented here, however, WAG is shown to improve sweep efficiency and ultimate recovery by 862 at one pore volume injection over that of dry gas injection alone into a prototype gas condensate reservoir containing a single, high permeability thief zone. The increase in sweep efficiency occurs primarily because the high viscosity water tends to block the thief zone, thus forcing following injection gas to invade the reservoir matrix. The principal factors governing the process are the contrast between thief zone and matrix permeabilities, the viscosities of injected gas and water, and the residual gas saturation to water. Varying the relative permeability curves and water/gas slug sizes and ratios had smaller effects on the results. Since only relatively small amounts of water are required to obtain large increases in recovery, expected detrimental effects from gas trapping and premature abandonment are limited. An additional economic benefit arises because the water occupies space which must otherwise be occupied by make-up gas.

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