not sure if RST would detect behind pipe/casing flow of water, may be temperature log could be useful if reservoir is waterflooded (lower temp)?

can cross check where on the structure well located, i.e. is it possible to get water coning.

As suggested you can try identify if water is coming through thief zones with test or looking at log (permeability etc) and comparing with other wells in the similar location in regards to OWC...