Depth Clause Wording

I would like to know if anyone can see anything unusual about the wording of this Depth Clause: Upon the expiration of the primary term, this lease shall automatically terminate as to all rights lying one hundred (100) feet below the base of the stratigraphic equivalent of the deepest penetrated common source of supply in any well drilled on the leased premises or on lands pooled therewith; provided however, if Lessee is then engaged in operations on the leased premises or on lands pooled therewith, this lease shall remain in full force and effect as to all depths so long as no more than ninety (90) days elapse between said operations.

This was the depth clause wording of my original Indultado well lease. I am interested in the opinion of those with more experience than myself. Tks, N