The Haima West reservoir in a mature field in south Oman showed severe production decline after initial encouraging results in re-development phase using horizontal injectors and horizontal producers. This sharp decline was due to rapid short- circuiting of injected water through possible presence of natural open fractures, induced fractures and/or thief zones. Further development of the reservoir was put on hold and an integrated well and reservoir management team was put in place to manage the waterflood with existing well stock and arrest production decline. The case study presents the successful implementation of a reservoir surveillance and optimization plan which could arrest production decline from the reservoir. Extensive data acquisition programme during this phase to reduce uncertainty in the next phase of development is discussed.


The field under discussion is located on the Eastern flank of South Oman salt basin (Fig.1). The field comprises a NE-SW trending anticline about 14 km long and 8 km wide. To date, more than 400 wells have been drilled in the field encountering oil producing reservoirs in the Mahwis formation (the Haima group of Cambro-Ordivician age) and the Al Khlata and Gharif formations (Haushi group of Carboniferous/Permian age) at depth ranges of 550–675 m sub-sea (ss). The case history presented in this paper focuses on the western culmination of the Mahwis formation in the field (known as Haima West Reservoir)

The Haima West reservoir crude has high viscocity (90 cp) and moderate to low API gravity (22 deg API oil). The reservoir has been on production since 1980 and currently has about 70 active wells of which 60 are oil producers and 10 are water injectors. The reservoir was initially developed using vertical wells on a 600 m spacing that was later reduced to 425 m spacing by drilling in-fill wells. To arrest rapid pressure decline, water injection using two five-spot patterns commenced in 1997. In 1999, a change in field development plan was initiated. The plan involved drilling of horizontal producers supported by long horizontal injectors.

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