Subsea Production Control System (SPCS)
As illustrated in the SPCS generally can be divided into three main sections:
- The equipment installed on the surface;
- The umbilical and its terminations;
- The equipment installed on the subsea Christmas tree.
Because the components of a subsea production system are inaccessible for operator intervention and must work together in a coordinated manner, it is necessary to design an integrated control system that works remotely. That is the subsea production control system. The functions of an SPCS include the following:
- Opening and closing subsea Christmas tree production, annulus, and crossover valves;
- Opening and closing SCSSVs;
- Opening and closing subsea production manifold flowline valves and pigging valves;
- Opening and closing chemical injection valves;
- Adjusting subsea production chokes;
- Monitoring temperature, pressure, flow rate, and some other data from tree-mounted, manifold-mounted, or downhole instrumentation. Generally, there are four types of subsea production control systems:
- Direct hydraulic (DH) control system;
- Piloted hydraulic (PH) control system;
- Electrohydraulic (EH) piloted control system;
- Electrohydraulic multiplexed (EH-MUX) control system.
A DH control system is the simplest and cheapest production control system. It consists of a topside HPU with one dedicated control line for each remotely actuate valve on the subsea Christmas tree. This type of control system is recommended for a subsea production system with one or two well tie-backs that is located within 3 miles of the host platform. A PH control system is similar to a DH control system except that the valves that require fast closing times will have a pilot valve and will vent to the sea on closing. An EH piloted control system is used for medium-offset subsea tie-backs. It consists of a topside electrical and hydraulic control system tied to one or more service umbilicals to the field. Each subsea Christmas tree and manifold has an SCM that takes LP and HP supplies and directs them to local valves when commanded to do so by the topside equipment. An EH-MUX control system is used for medium- to long-offset subsea tie-backs. It consists of a topside electrical and hydraulic control system tied through a service umbilical to one or more subsea Christmas trees. Each tree and manifold has an SCM, which receives the multiplexed electrical control signals and LP and HP hydraulic supplies, which are directed to tree- or manifold-mounted valves or other equipment. This system is common in large multiwell deepwater developments. The main advantage is the use of a multiplexed electrical control signal over a single pair of conductors, resulting in a smaller control umbilical, which accommodates future expansion easily and reduces umbilical costs significantly.
 Society for Underwater Technology, Subsea Production Control, SUT, Subsea Awareness Course, 2008.
 B. Laurent, P.S. Jean, L. Robert, First Application of the All-Electric Subsea Production System Implementation of a New Technology, OTC 18819, Offshore Technology Conference, Houston, 2006.
 C.P. William, Subsea Control Module, U.S. Patent 6,161,618, 2000.
 International Electro-technical Commission, Functional safety of electrical/electronic/ programmable electronic safety-related systems, IEC 61508, 2010.
 J. Davalath, H.B. Skeels, S. Corneliussen, Current State of the Art in the Design of Subsea HIPPS Systems, OTC 14183, Offshore Technology Conference, Houston, 2002.
 International Organization of Standards, Petroleum and natural gas industries - Design and operation of subsea production Systems - Part 6: Subsea production control systems, ISO 13628, 2000.