Injector-Well Completion Designs for Selectively Waterflooding Up to 18 Zones in a Multilayered Reservoir: Experiences in the Cerro Dragon Field

摘要

The Cerro Dragon asset, located in the highly mature area of Golfo San Jorge Basin, Argentina, has around 30 producing structures; each one containing from 20 to 50 separate, highly heterogeneous, reservoir horizons, from 6 to 30 feet thick. From 1999 to 2005 proved reserves increased threefold and non proved reserves increased fourfold, moreover, oil production grew from 48,000 BOEPD to over 116,000 BOEPD, largely due to optimization and expansion of waterflood projects. The aim of these projects was to increase the water injection rate from 248,000 BWPD to 714,000 BWPD along with the 1999 average of 5 reservoirs accessed per injector-well to an average of 12, with a maximum of 25, in 2005, keeping at the same time the highest possible control over the injected-water flow rate on each layer. In an experimental process started in 2000, injector-well completions were designed and tested in several wells with different reservoir properties. The experience acquired with the analysis of these completions was used to improve them as well as to develop new ones. Today, this process continues, testing and enhancing new designs to fulfill the needs of the upcoming waterflooding projects. This paper shows the experience acquired from 401 injector- well completions over the past 6 years, discuss the successes and problems encountered with each completion design under different reservoir conditions (i.e. differential pressures between layers). In addition, it contains information about the procedures and technology used to reduce the completion set up cost and to extend its useful life by solving leakage problems without replacing the completion installation. The mayor achievement at this point of the process have been successfully running an injector-well completion of a total of 19 packers and 18 injector mandrels (with an average of 12 packers and 12 mandrels out of 48 completions ran on the first half of 2005). The objective of this paper is to serve as a reference guide for injector-well completion designs in multilayered fields where a vertical expansion of the waterflooding projects is intended.