A lower stack assembly of a blowout preventer for a hydrocarbon extraction well includes a safety function that can be hydraulically activated to rapidly cut off a pipeline section. The assembly includes a first valve and a first fluidic connection connecting the first valve and the least one safety function, so that the first valve selectively cuts off a flow of fluid directed towards the safety function. The assembly further includes a port operatively connected to the first valve, cooperating with a remotely operated vehicle to transmit a pilot signal to the first valve, an accumulator housing pressurized fluid, and a second fluidic connection. By cooperating with the first valve, the accumulator supplies pressurized fluid to the safety function to activate it. The second fluidic connection connects the accumulator and the first valve, so that the second fluidic connection remains operative during the entire working life of the assembly.