A Water-Alternating-Gas (WAG) scheme is a proven enhanced oil recovery (EOR) method. The first WAG project was reported in 1957 and until today more than sixty (60) field experiences can be found in the literature. Most of the published experiences report 5-10% additional oil recovery over waterflood. WAG injection can lead to improved oil recovery by combining better mobility control, improved microscopic displacement, and better sweep efficiency.

This study presents a recent field experience where a miscible WAG injection has been designed and implemented with the objective of enhancing oil recovery in a heterogeneous, low dipping, and tight carbonate reservoir. The project has been performed on close-spaced slanted wells and utilizes rich hydrocarbon gas. Since the beginning of the injection, an integrated surveillance program has been applied to determine whether the miscible flood is working efficiently. This program involves observation wells, time-lapse saturation logging, well testing, tracer injection, and i-field technology along with numerical simulation.

This paper presents a review of the main findings, issues and lessons learned during eight (8) years of EOR-WAG injection. The paper discusses the project design, the integrated surveillance program and the WAG mechanisms to enhance oil recovery. It also summarizes worldwide WAG experiences based on published field observations.

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