BP Trinidad and Tobago LLC ("bpTT") operates offshore, along the east coast of Trinidad in predominantly retrograde gas condensate fields, some of which contain reservoirs with thin oil rims. As part of the company's surveillance philosophy, saturation logs have historically proven to be a key method to define the fluid saturations after primary production.

In recent years, as the technology behind saturation logging improved, the tools are more capable of measuring fluid saturations across more complex and varied completions. This has led to higher reservoir recovery through increased understanding of the reservoir energy and drive mechanism and ultimately supporting the identification of remaining resources and new opportunities within reservoirs Offshore Trinidad.

Routine saturation logging campaigns have allowed further insight into the movement of all fluid contacts in the reservoir with time, be it from gas cap expansion seen in some of the thin oil rim reservoirs, or aquifer encroachment as observed from the gas-water and oil-water interfaces. This knowledge of the strength and direction of water movement supports more accurate production forecasting for base well stock by assisting with predicting the time to water breakthrough in reservoirs reducing one of the more significant subsurface uncertainties.

An improved understanding of the sweep efficiency is also gained from the saturation logs, which enables more accurate prediction of the overall recovery factor. Furthermore, the saturation logging campaigns have led to the definition of new reservoir opportunities, and validation of existing options for both oil and gas production. As such, this type of surveillance is highly recommended for most mature reservoirs to help validate the predicted contact movement and help optimise brown-field developments. This relatively inexpensive surveillance method can help enhance well planning elements such as well placement and completions design.

This paper summarises case studies from four reservoirs, focusing on the development of the cased hole saturation log, its uses and production benefits.

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