"As far as hyphenation is concerned, the general stylistic principle is that if the adjectival compound is placed attributively (i.e. it comes before the noun), it should be hyphenated (a well-intentioned remark) but that if it is placed predicatively (i.e. standing alone after the verb), it should not be hyphenated (her remarks were well intentioned)."

Anna-uk has a good point, and my answer would be that the hyphen is NOT needed. 'Well' is an adverb, and therefore cannot directly refer to the noun. Hyphens are only needed when there is a compound adjective (i.e. adj. + noun used adjectivally) because without them, you wouldn't know whether the adj. belonged to the adjectival noun or the main noun (e.g. two(-)year-old children; deep(-)blue water).

Having said which, while it's not 'needed' with 'well', it does no harm, and if it keeps your editor happy, there are more important things in life.