Shutting down an underwater fluid production well

A production control system for an underwater well, comprises: first electrically operated means (16) for supplying first hydraulic fluid, for opening a first control valve (18) of the well; second electrically operated means (22), for supplying second hydraulic fluid at a higher pressure than said first fluid, for opening a further control valve (23) of the well; electronic circuitry (SEM1) for providing electrical power for operating said first and second means; and means for controlling the sequence of closing said control valves as a result of a loss of electrical power from said electronic circuitry. The controlling means comprises: electrical power storage means (4); detection means (9) responsive to said loss of power from said electronic circuitry; and means (7, 8) coupled with said detection means for using electrical power from said storage means to keep said further control valve open for a period after closure of said first control valve and close it after said period.