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.