Cannot build an oil well with a neutronium nearby.

Of course it works with every other material. But neutronium can not be digged by dupes. So a plan can not be placed there.

An oil well occupies a 4x4 grid where the bottom 1x4 positions must be over the top of an oil well.  In your screenshot, the upper left tile of your oil well is blocked by a tile of neutronium.  Since neutronium can not be dug through, it can not be removed.  This means that you do not have an available 4x4 grid to place your oil well.

This is not a bug.  Due to the random placement of such features, it is possible for one to be positioned such that it is difficult or impossible to fully access.  While I haven't seen this happen very often, the edges of the map are the most likely place for this to occur.  Other examples include overlapping POIs, such as a neural vacillator blocking a cool steam vent.

The bug here is in map generation, which should not place POIs in ways that overlap like this.