Modular undersea oil production plant

A modular undersea oil production plant having at least one satellite unit and a central structure, a collector pipe conveying satellite products towards said central structure, said central structure having operating modules grouped together, means for removing said product from said operating modules within said central structure, the improvement wherein said satellite unit has a wellhead linked by a connector to the upper portion of a pipe in a drill hole, a raisable individual auxiliary module, said auxiliary module containing control and operation components, said satellite unit comprising a template bearing two distinct cavities whose shape is complementary to that of said wellhead and said auxiliary module, said cavities receiving said wellhead and said auxiliary module with their sidewalls in juxtaposition and facing each other, and wherein the sidewall of said auxiliary module is in juxtaposition and faces the end of said collector pipe, said wellhead being linked by a connector internally thereof to an upper portion of a pipe in a drill hole beneath said template, and said auxiliary module containing control and operation components and being connected firstly to said wellhead by a first connector through said juxtaposed sidewall of said wellhead and said auxiliary module and secondly directly to said one end of said collector pipe by a second connector through said auxiliary module sidewall, and means carried by said auxiliary module controllable from the surface for controlling solely at said auxiliary module, the disconnection of said auxiliary module from the collector pipe and from the wellhead and for removing it from the template.