The main functions of the IWOCS are as follows:

File:Illustration of an IWOCS in Tree Mode.png
Illustration of an IWOCS in Tree Mode
  • Control and monitor subsea equipment during installation, retrieval, and workover.
  • Control and monitor downhole equipment during completion, flow testing, and workover.
  • Log data during completion, flow testing, and workover operations.
  • Test manifolds and/or PLEMs during installation, if applicable. Because the IWOCS is used for intervention of subsea wells, certain safety features are required:
  • Emergency shutdown (ESD): It must be possible to initiate emergency shutdown. The shutdown shall be automatically sequenced such that the system is shutdown safely and release of hydrocarbons is prevented. ESD panels are provided on different panels located on board the rig to enable ESD even if there is a fire or release of hydrocarbons on the drill floor.
  • Emergency Quick Disconnect (EQD): It must be possible to disconnect the lower riser package (LRP) within a certain time delay from initiation. An ESD must automatically be executed prior to disconnection of the LRP. The IWOCS usually consists of the following components:
  • HPU;
  • Main control panel (on HPU);
  • Remote control panel (on the drill floor);
  • Emergency shutdown panels (at main escape routes);
  • Umbilicals on reels;

Primary tools controlled by IWOCS are the tubing hanger running tool and the tree running tool/tree cap running tool. To control these tools, a riser system is utilized that may consists of various riser joints, LRP, etc. As with the SPCS, the IWOCS also has four types: direct, piloted, electrohydraulic, and electrohydraulic multiplexed.


[1] Society for Underwater Technology, Subsea Production Control, SUT, Subsea Awareness Course, 2008.

[2] 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.

[3] C.P. William, Subsea Control Module, U.S. Patent 6,161,618, 2000.

[4] International Electro-technical Commission, Functional safety of electrical/electronic/ programmable electronic safety-related systems, IEC 61508, 2010.

[5] 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.

[6] 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.