A second monitor 4D seismic was recently acquired over a deepwater field in Nigeria. The acquisition was completed on time and without any Health Safety Security or Environmental incident. This survey used steerable streamers, advanced current prediction techniques, and a dedicated time-lapse data acquisition expert onboard the vessel to guide the sail-lines selection. These improvements contributed to a final 4D dataset with better geometric repeatability than the first seismic monitor acquired four years prior. Early results of the 4D seismic interpretation of the results from fast-track processing in the different reservoirs reveal two predominant sweep patterns: (a) localized channeling indicative of limited movements within sinuous channels and meander belts; and (b) broad flood-front movement associated with the more lobate, amalgamated systems. This interpretation has provided another level of detail in the understanding of reservoir architecture within the field. Areas of bypassed oil can be identified on 4D seismic and are being used in locating potential additional infill wells. In addition, there has been an improvement in the mapping of the flooded areas of the reservoirs and the seismic-derived flood patterns have provided additional constraints to enhance the quality of the history-matches, resulting in improved static and dynamic subsurface models.

In producing assets, the drive to reduce production deferments is increasing the interests in injection fall-off (IFO), as against pressure build-up, tests for reservoir characterisation. The IFO, which entails the measurement and analysis of pressure transients due to the shut-in of an injector after a period of continuous injection, provides estimates of important subsurface parameters such as static pressure, transmissibility and, where applicable, induced-fracture characteristics. This paper documents the application of IFO in selected cases from an oil-producing deepwater field. The pressure fall-off curves obtained for two water injectors in the subject deepwater field are analysed. Particular attention is paid to the analysis of the fall-off curves and the identification of the various flow regimes. The estimation of key subsurface parameters such as skin factor, transmissibility, and boundary characteristics is detailed.To reduce interpretation uncertainties, an integrated application of geoscience data has been employed to constrain the possible range of IFO interpretations. In addition, the IFO results have been used to rationalise the declining injectivity indices observed in the subject injectors, while providing clues for these observations at the pore scale. In essence, this work reechoes the credentials of IFO, as a credible and cheaper alternative to pressure build-up tests, for the characterisation of subsurface systems.