Didier,

you can use 'Assign' - 'Database' - IDW with only one neighbor - 'Load
time-constant' data. Hit 'Start' and choose 'interactive' in the
pop-up dialog. Then hit F2 on the keyboard. The wells will be put in
the exact location refining the mesh around. However, you cannot
directly set a target element size. Before you import the wells, you
can use 'Options' - 'Wells' to set a distance between the input point
and the nearest node from which refinement shall be stopped. The lower
the value, the finer the mesh.

Peter Schätzl
Product Manager FEFLOW