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.