Cased-Hole logging is carried out to understand post-production well saturation profiles, and subsequently, to infer the reservoir fluid distribution, especially when multiple wells dispersed across the reservoir is logged. This process promotes further oil and gas development (proper well placement). It is also used for reserves booking and production optimisation from the existing completions. The concept can also be used to conduct saturation monitoring on a routine basis to observe wells and to ensure that field statuses adhere to the Wells and Reservoir Management (WRM) minimum standards and to proper reservoir management practices.

Effective strategic mapping of reservoir fluid distribution using post-production saturation logs, either from open hole and/or cased hole data has led to an improved understanding of reservoir fluid dynamics in Shallow offshore field of Niger Delta. Saturation logs have been used to update the dynamic models in the field. The general direction of water ingress in the reservoirs can now be predicted; hence the need for saturation logging is only carried out on an exception-basis.

In accordance with Exception-Based Surveillance (EBS) concept, data should be acquired on a ‘need only basis’. This is a departure from the traditional routine acquisition. According to the EBS concept, the main issue is to determine when data gathering is needed. Clearly, data requirements will differ from reservoir to reservoir or from well to well. This also underscores the view that data acquisition on a routine basis may not address some specific reservoir/well peculiarities.

The focus of this paper is to describe how the proposed saturation monitoring process, can be managed via EBS for a Shallow offshore field of Niger Delta, using five monitoring wells.

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