Despite the old and extensive use of water flooding as a secondary oil recovery scheme, the actual performance of a given water flood is still often difficult to predict even in the most homogeneous of reservoirs. This performance is heavily dependent on the injection pattern, fluid mobilities, as well as reservoir heterogeneity. For this reason, it is essential that the actual performance of a water flood be measured in order to be able to optimize that performance. This is best accomplished through the combined use of reservoir saturation and production logging tools.

The Reservoir Saturation Tool (RST) provides cased hole reservoir saturation using the water salinity-dependent Sigma capture cross-section measurement as well as a salinity-independent measurement of oil saturation using carbon-oxygen ratio. The latter is especially useful in fresh water and mixed/unknown salinity environments, such as might be expected in a water-injection environment. Production logging, on the other hand, provides information on zonal fluid contributions, fluid typing, as well as clues to fluid movement inside and outside the well bore. The use of shut-in as well as flowing surveys adds a third (time) dimension to the picture.

This paper presents a case of water flood performance monitoring from the Younis Field, operated by the Gulf of Suez Oil Company of Egypt, and illustrates the data analysis cycle involved. The role of the analyst is to piece all the measurements together and come up with a hypothesis to explain what may be happening. This hypothesis is then tested against production data, injection data, and other reservoir data. It is then refined and fine-tuned until a satisfactory explanation is found for all the observed phenomena. The resulting conclusions are highly valuable for the assessment and subsequent optimization of the injection pattern.

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