Thin Oil Rim Development in the Amherstia / Immortelle Fields, Offshore Trinidad

Abstract

Abstract 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. Introduction Located 30 to 40 miles off the south - east cost of Trinidad in 235 feet of water (Figure 1), the Immortelle/ Amherstia field complex consists of a number of stacked reservoirs, the largest of which is the 22 sand. This field complex consists of two major NE plunging anticlines; the Immortelle platform lies on the northern-most anticline while the Amherstia platform is perched on the southern-most anticline. A number of faults intersect these two anticlines. The largest of these is the A4 fault. The reservoir consists of a coarsening upward clastic sequence interpreted to be a shore face or delta front environment. Some of the deeper reservoirs, inclusive of the 22 sand, are continuous across the Amherstia / Immortelle field complex.