Abstract: A modular liquid/liquid gravity separation device for separating the aqueous phase and the oil phase of a crude oil at the sea bottom. The device has a plurality of separation modules coupled to a common manifold device. Each separation module has a fluid delivery pipe coupled to at least one gravity separation pipe by a tubular bend device. The common manifold device has a first tank fed with crude oil by a feed pipe resting on the sea bottom via a first inlet orifice, a plurality of first outlet orifices feeding crude oil to said delivery pipes. The aqueous and oil phases are separated within the separation pipes before being delivered into a second tank via second inlet orifices of the second tank to which the separation pipes are coupled. The oil phase is conveyed to the surface from the second tank via a first removal pipe. The aqueous phase is conveyed to the sea bottom.