A gravity well is used to draw water from which type of aquifer?

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Gravity wells draw water to the surface by gravity, which works best when the aquifer is unconfined. In an unconfined aquifer, the water table is open to the surface and the pore water pressure at that surface is atmospheric, so water entering the well can rise and discharge simply under gravity. In contrast, a confined aquifer is overlain by a confining layer and water there is under pressure; tapping such a system can produce flow due to artesian pressure rather than gravity alone, which makes it a different scenario. So the gravity well is used for an unconfined aquifer.