The Denver Unit, located in the Wasson Field of west Texas, is the world's largest Carbon Dioxide Enhanced Oil Recovery (EOR) project. Shell Western E&P Inc. initiated CO2 injection in the Denver Unit in 1983, utilizing CO2 from naturally occurring source fields in Colorado and New Mexico.

Production response to CO2 flooding has been impressive, with over half of the current daily oil production attributable to CO2 injection. In fact, oil production has substantially exceeded- original project performance predictions.

The project was- originally implemented with both a Continuous CO2 injection area and a Water-Altemating-Gas (WAG) CO2 injection area. A comparison of the performance of these two areas has clearly demonstrated the advantages of each injection method, and has led to the conversion of the the Unit to a "Denver Unit WAG" (DUWAG) injection process, which plays on the strengths of both injection schemes.

This paper will cover in more detail the observed production performance of the CO2 flood to date, present a comparison of the Continuous and Water-Altemating-Gas injection processes, and review the design and implementation of the Denver Unit WAG project. The paper will be of interest to companies who are either operating- or preparing to implement CO2 Floods.

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