If you had a signed written agreement regarding this well and your neighbor is not complying with the agreement, you can sue him for breach of contract arising from the written agreement.
If you did not have a signed written agreement, you can sue your neighbor for trespass to land, conversion, and nuisance for encroaching on your property. You could also include a cause of action for injunctive relief to require him to abandon the well and return your land to its original condition.
You will want to seek the advice of a Real Estate attorney in your area. To do that, in Google, type in your city and state; and real estate attorney.
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