Simulation of gas condensate reservoir is described for water injection and gas injection, with the objective of improving hydrocarbon recovery. A compositional simulator was used for the studies conducted. The methods investigated were Continuos and Simultaneous Gas Cycling with Water Injection (CSGW) and Continuous Gas Cycling with Alternating Water Injection (CGAW).
Numerous injection-production strategies involving water injection and hydrocarbon production with gas cycling, were examined. Fluid saturation distributions were studied for a three-layer reservoir. These shoved that gravity segregation plays an important role in all three processes. On the whole, CSGW recovered 4.6% more oil initially in place than conventional gas cycling. CGAW performed no better than conventional gas cycling.
The detailed results show that the water injected supplemented reservoir energy, improved the mobility ratio, and helped to maintain a reasonable gas-oil ratio. Implications of field application are discussed.
As traditionally defined 1, there are three methods of recovering gas condensate fluids from a reservoir. One method of recovery is Gas Cycling (GC) from the beginning of the operation. A second method is Gas Cycling delayed until part of the reservoir fluid has been removed by means of natural depletion and is known as Partial Gas Cycling (PGC). The third method, Natural Depletion (ND), does not return gas to the reservoir at any stage of the operation. Gas Cycling from the beginning of the operation displaces 50 percent, more or less, of the original fluid from a reservoir by injecting residue gas (dry gas), after being separated at the surface in a separator, into the formation. The original reservoir pressure is usually not fully maintained, but the condensation that occurs in the reservoir is only a fraction of that which would result without pressure maintenance. The second method is less efficient than the first for most of the time, and depends on the stage of operation at which the residue gas is being injected. Since gas cycling starts after part of the fluid has been removed without pressure maintenance, the original reservoir pressure can never be maintained. Consequently, the condensation occurring in the reservoir is much greater than that in the first method.
Natural depletion involves only production. No residue gas is injected back into the formation. Liquid recovery is efficient only at the beginning of operations when the reservoir fluid produced contains the full original content of liquefiable hydrocarbons. As the reservoir is depleted and the pressure declines below the dew point, the retrograde condensation process begins. Butane and heavier hydrocarbons in the gas condensate will be condensed in the formation. The actual percentage condensed will vary with the composition of the fluid. Recovery of part of this percentage by evaporation at lower pressures is not fully assured. Recently, two other methods have been used in the recovery of gas condensate: Waterflooding (WF) and Water- Alternating-Gas (WAG). Variations of these methods include Immiscible WAG (ImWAG) and Simultaneous WAG (SWAG).
In this study a new method is tested. Continuous and Simultaneous Gas Cycling with Water Injection (CSGW) consists of injecting water and gas simultaneously and continuously right from the beginning of operations.
