This paper shows the leading role of geology in the choice of a well test interpretation model and in the selection of the best solution; at the same time the results coming from well test interpretation contribute to improve the geological model. Three field cases are discussed:

  • The first case evidences the need of a good sedimentological analysis, in order to choose among the different reservoir models that match properly the derivative plot: Radial Composite, Homogeneous with two parallel or three boundaries. Geology indicates that the reservoir was deposited in the median part of a deep-sea fan, and that the perforated interval belongs to a channel layer. The model retained is therefore the homogeneous reservoir with two parallel boundaries, which gives a channel width of about 400 meters, in accordance with sedimentology.

  • The second case deals with a shaly formation with few sandbodies. Regional geological knowledge allows to divide this formation into two main units with different sandstone sedimentological origin: fluvial or lacustrin. Interpretation of the well tests performed in the different sandbodies emphasizes the differences between the two sedimentological units, and allows to locate their limit

  • In the case of the fractured reservoir some input parameters were affected by a high degree of incertitude, and interpretation led to a too big range of possible values for the output parameters (permeability, vertical permeability anisotropy). Geological studies allow to decrease the incertitudes.

A multidisciplinary approach with repeated information exchanges between geologist and reservoir engineer seems to be the best way to deal with well test interpretation problems.

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