Review of WAG Field Experience

Jes Reimer Christensen, Erling Halfdan Stenby, A. Skauge

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

In recent years there has been an increasing interest in water-alternating-gas (WAG) processes, both miscible and immiscible. WAG injection is an oil recovery method initially aimed to improve sweep efficiency during gas injection. In some recent applications produced hydrocarbon gas has been reinjected in water-injection wells with the aim of improving oil recovery and pressure maintenance. Oil recovery by WAG injection has been attributed to contact of unswept zones, especially recovery of attic or cellar oil by exploiting the segregation of gas to the top or the accumulating of water toward the bottom. Because the residual oil after gasflooding is normally lower than the residual oil after waterflooding, and three-phase zones may obtain lower remaining oil saturation, WAG injection has the potential for increased microscopic displacement efficiency. Thus, WAG injection can lead to improved oil recovery by combining better mobility control and contacting unswept zones, and by leading to improved microscopic displacement.

This study is a review of the WAG field experience as it is found in the literature today,(1-108) from the first reported WAG injection in 1957 in Canada to the new experience from the North Sea. About 60 fields have been reviewed. Both onshore and offshore projects have been included, as well as WAG injections with hydrocarbon or nonhydrocarbon gases. Well spacing is very different from onshore projects, where fine patterns often are applied, to offshore projects, where well spacing is in the order of 1000 m.

For the fields reviewed, a common trend for the successful injections is an increased oil recovery in the range of 5 to 10% of the oil initially in place (OIIP). Very few field trials have been reported as unsuccessful, but operational problems are often noted. Though the injectivity and production problems are generally not detrimental for the WAG process, special attention has been given to breakthrough of injected phases (water or gas). Improved oil recovery by WAG injection is discussed as influenced by rock type, injection strategy, miscible/immiscible gas, and well spacing.
Original languageEnglish
JournalS P E Reservoir Evaluation and Engineering
Volume4
Issue number2
Pages (from-to)97-106
ISSN1094-6470
DOIs
Publication statusPublished - 2001
Event1998 SPE International Petroleum Conference and Exhibition of Mexico - Villahermose, Mexico
Duration: 1 Jan 1998 → …

Conference

Conference1998 SPE International Petroleum Conference and Exhibition of Mexico
CityVillahermose, Mexico
Period01/01/1998 → …

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