Hi,
the comment about damage from logs comes from an estimate of invasion profile from mud during drilling - this assumes you have contracts in resistivity between the formation and drilling fluids. It really applies to new wells - this sounds like a well that has bene on production for some time, but if not, and there is resistivity contrast, then you shoul dbe able to determine the invasion depth. The premise is that the mud invasion blocks the formation permeability, while perforating might reach beyond the damaged zone (nothing stopping you perforating the open hole, by the way).

Water coning occurs when the drawdown at the well exceeds the pressure difference required between the oil and water density and the vertical permeability pressure drop due to flow at the wellbore (assuming flow of water is not due to communication through poor cement!). So instead of keeping the water in the formation to provide reservoir drive, you are producing it, which costs money and reduces the oil production. You can check this by producing the well at different rates and run TDT logs - if you see the water contact receed, you can identify coning, and you can check the oil and water productivity to see if it changes. If you have a cement channel, then you will still produce the same water productivity (rate over drawdown). Ideally, with active water drive, you use a horizontal well in the upper part of the reservoir, or other methods to minimize the drawdown at the wellbore.