Compositional Simulation to Develop an Optimnum Gas Cycling Scheme At The Kaybob Beaverhill Lak C Pool, Alberta
Authors: Flores J. 
Published: March 2010

This 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 three cycling schemes involving different replacement ratios have been obtained. Considerable emphasis was placed on predicting the reservoir rock properties in a highly heterogeneous reservoir such as the Kaybob Beaverhill Lake C Pool, and on the phase-behaviour matching of data derived from laboratory studies. Also, a productivity loss factor which results from 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.

During the development of the compositional model, a good match of phase behaviour of the reservoir fluid was obtained and so ensured a reliable prediction of gas cycling. Predictions indicated that cycling was technically feasible and that recovery of an additional two million barrels of hydrocarbon liquids will occur when compared to a straight blowdown scheme. 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.

Introduction

The Kaybob Beaverhill Lake C Pool, discovered in 1961, is approximately 180 miles northwest of Edmonton, Alberta (Map 1) It is a gas condensate or dew-point reservoir having a hydrocarbon liquid content of approximately 190 bbl/MMcf. The volumetric original raw gas-in-place is estimated at 82 Bcf. Exploitation of the pool is expected to commence early in 1979 through five wells located in Townships 63 and 64, Range 18 west of the Fifth Meridian.

Originally, it was believed that this gas condensate reservoir was in communication with an oil reservoir toward the 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 [he East Kaybob Beaverhill Lake area consisted of a saturated volatile oil reservoir and a gas condensate reservoir which do not communicate(1). This was further confirmed with the drilling of 11-3-64-18 well, which encountered the early postulated permeability barrier. The well was then subsequently abandoned.

Because production from this gas condensate reservoir under a straight blowdown could be detrimental to hydrocarbon liquids recovery due to retrograde liquid loss during depletion, gas cycling can be carried out to maintain the reservoir pressure and minimize retrograde loss by simultaneously changing the reservoir fluid composition.

Data for the Model Study

Reservoir Description & Fluid Properties

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 (Map 2). Maximum net pay thickness, based on the reef section encountered in the 12–24 well, is 195 feet (6875–7070 ft subsea). The hydrocarhon-porosity-foot.ge distribution is shown in Map 3.