Abstract: A system includes a primary wellbore and a plurality of secondary wellbores. The primary wellbore includes a substantially vertical portion extending from a terranean surface to a predetermined location above a first target subterranean formation; a curved portion coupled to the substantially vertical portion and extending through the first target subterranean formation above a second target subterranean formation containing at least one of oil or gas; and a substantially horizontal portion coupled to the curved portion and extending through the first target subterranean formation and adjacent the second target subterranean formation. The plurality of secondary wellbores are coupled to the primary wellbore and extend angularly downward into the second target subterranean formation.