Thus paper discusses the application of a compositional model to develop an optimum exploitation scheme for the C Pool gas condensate reservoir. Performance predictions of a straight blowdown and Performance predictions of a straight blowdown and three cycling schemes involving different replacement ratios have been obtained. Considerable emphasis was placed on predicting the reservoir rock properties in placed on predicting the reservoir rock properties in a highly heterogeneous reservoir such as the Kaybob Beaverhill Lake C Pool, and on the phase behavior of data derived from laboratory studies. Also, a productivity loss factor that results due to productivity loss factor that results due to condensate accumulation in the vicinity of the wellbore was incorporated in the model. These special features were necessary to increase the reliability of model predictions while cycling.
Results of the model study indicated that a good match of phase behavior was developed, thus ensuring a reliable prediction of gas cycling. Predictions indicated that cycling technically was feasible and that recovery of an additional 2 million bbl of hydrocarbon liquids trill occur compared with a straight blowdown scheme. The economic evaluation performed for the simulated schemes indicated that a performed for the simulated schemes indicated that a partial cycling scheme provides the best economics to partial cycling scheme provides the best economics to initiate the exploitation of the C Pool. This simulation study formed the basis of an application filed with the Energy Resources Conservation Board of Alberta requesting approval to implement a gas cycling scheme in the Kaybob Beaverhill Lake C Pool.
The Kaybob Beaverhill Lake C Pool, discovered in 1961, is located approximately 180 miles northwest of Edmonton, Alta., as shown in Fig. 1. Exploitation of the pool will be performed through five wells located in Townships 63, 64, and Range 18 West of the Fifth Meridian.
Originally it was believed that this gas condensate reservoir was in communication with an oil reservoir northwest of the Kaybob Beaverhill Lake area. However, reservoir fluid analyses from Wells 12-24-63-18 and 10-4-64-18 as well as pressure surveys in Wells 2-4, 10-4, and 4-10-64-18 led to the conclusion that the East Kaybob Beaverhill Lake area consisted of a saturated volatile oil reservoir and a gas condensate reservoir that do not communicate. This was confirmed further with the drilling of Well 11-3-64-18, which encountered the early postulated permeability barrier. The well postulated permeability barrier. The well subsequently was abandoned.
Production from this gas condensate reservoir under a straight blowdown could be detrimental to hydrocarbon liquids recovery because of retrograde loss during depletion, so gas cycling can be carried out to maintain the reservoir pressure and minimize retrograde loss by simultaneously changing the reservoir fluid composition.
The Kaybob Beaverhill Lake C Pool is part of the Swan Hills reef limestone development. The reservoir dips toward the south and west as indicated by the structure contour map of the bottom of the pool shown in Fig. 2. Maximum net pay thickness pool shown in Fig. 2. Maximum net pay thickness based on the reef section encountered in Well 12-24 is 195 ft (6875 to 7070 ft subsea). The hydrocarbon pore volume distribution is shown in Fig. 3. Based pore volume distribution is shown in Fig. 3. Based on this mapping, the total hydrocarbon pore volume was calculated to be 7676 acre-ft, resulting in an original gas-in-place of 82 Bcf. The computational grid for the simulation model is presented in Fig. 4. The original reservoir pressure at a datum of 7040 ft subsea is 4315 psia. This pressure is about 240 psia above the dew-point pressure of 4075 psia at 237 deg. F. The reservoir fluid has a total propane-plus fraction of 18.08% with the heptane-plus fraction in the amount of 6.64%. Based on this composition the initial hydrocarbon liquid content of the gas is estimated at 190 bbl/MMcf.
