The wellbore storage effect has been extensively studied during the last 40 years, highlighting its effects on the early time build-up data and on the resulting hurdles or mismatching tendency during the interpretation process. Although these phenomena, mainly due to the compressibility of the fluids1 , can be reduced using a down-hole shut-in tool, they are not completely eliminated and most of the information related to the near wellbore area remains inaccessible. However, it appears that the interpretation inaccuracy is greatly influenced by how fast the production is shut down before the build-up test. An instantaneous down-hole shut-in action reduces the masking effect due to the wellbore storage. Therefore, during the build-up early time, it will provide more valuable data, useful for an accurate characterisation of the near wellbore region and its heterogeneities.

The following paper shows the effects of the shut-in time on the data acquisition at early time and its interpretation. Simulations have been performed in typical well configurations and reservoir types (near wellbore permeability reduction, fractured well, layered reservoir). The results illustrate clearly the benefits of an instantaneous production shut-in action to characterise near wellbore reservoir. Oilfield data have been acquired during an oil well test using a fast shut-in tool which allows shutting down the production within 2 seconds. A slight deflection in pressure build-up can be observed in the first minutes. This deflection has been interpreted as a reduction of the fluid mobility close to the well. Numerical simulations performed using the resulting model matched on this data set, demonstrate that the mobility reduction could not have been detected using a slow action shut-in tool.

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