Equip some kind of knockback (perhaps a physical utility) and knock them out of the wells. Otherwise, sit outside and attack with your longbow until the wells are gone. Preferably, stay further than 600 range so that Life Blast does minimal damage. The whole purpose of the wells is to create an area that is advantageous for them – and if they’re using wells, it’s also pretty much their only “gimmick.” The cooldowns on the most of wells are pretty long.
A necromancer specced into “wells and might stacking” probably won’t be specced for condition damage (necromancer might stacking = one 10-might utility skill and gaining might on Life Blast autoattacking, which is power-based), so any bleeds they apply aren’t really worth removing aside from maybe the 2 long-lasting bleeds from Blood is Power. Use condition removal against them on things like immobilize and chill.
As you have discovered, one of the weaknesses of a well-based necromancer is simply moving away from the fight. Due to the static nature of wells and the way death shroud drains over time, forcing them to waste cooldowns and life force is a viable tactic.
If the necromancer is using an axe, dodge during Ghastly Claws (channeled attacked) to prevent them from gaining life force. If the necromancer is using a dagger, their melee attack will be their source of life force. And if for some reason they’re using a focus, dodge Reaper’s Touch (flying black scythe). A necromancer who specializes in might will want to use Life Blast, so you want to deny him from gaining life force.
Either way, a warrior condition build isn’t going to fare well against a necromancer because they have a large amount of removals and transfers. Burst damage or especially crowd control work much better. Consider using a build that incorporates a shield, mace, or hammer to deal with necromancers.
The best solution, however, is to fight the necromancer 2v1, because their ability to deal with being outnumbered is next to none outside of their elite skills (which just bide for time until they end in such a situation).
