Effective exploitation of the thin oil rim in the Amherstia / Immortelle 22 sand is particularly challenging because of the size of the overlaying gas cap, 2TCF, and the thickness of the oil rim varying between 31 to 46 feet gross pay interval. Since oil wells in the thin oil rim of the 22 sand did not justify well cost, the challenge, then, was to make the oil wells more attractive to facilitate early depletion of the oil rim.
Reservoir simulation work was undertaken and a joint team was formed to evaluate the reservoir performance and determine the best strategy for depletion. This team consisted of subsurface professionals from the Amherstia and Immortelle fields, and the bp Houston technology group. The performance of the two wells in the reservoir was history-matched and then the model was used to develop an improved strategy.
The reservoir simulation grid used was aligned with the major fault patterns and nested local grid refinement was utilized to better understand depletion of the oil rim. Sensitivity analysis conducted demonstrated that locating longer horizontal oil wells with larger size tubing in the upper third of the oil rim proved to be the best strategy for depletion of the oil rim. The strategy provided higher production rates with earlier accessibility to gas reserves while outrunning the aquifer.