Abstract: The invention provides a method of separating at least two production zones in a well (P) using the following method and apparatus. The method is a method of making a sealing ring (18) in situ in an annular space (5) lying between a well (P) and casing (T) in the well, with the sealing ring being made adjacent to a production zone in the well, and with the method comprising the following stages:the annular space (5) to be occupied by the sealing ring (18) is delimited; anda sealing substance (11) is injected into the annular space.The apparatus comprises two confinement membranes (2--2) for sealing off the annular space (5); andseparator membrane (8, 13) for separating the substance to be injected (11) from the fluids that normally exist between the well (P) and the casing (T), said separator membrane also serving to eject said fluids from said space (5). The invention is applicable to the drilling industry, and in particular to the oil industry, and the like.