The paper reviews the current practice of optimising the performance of hydraulic sub-systems e g pumps, to the exclusion of the rest of the system. A system is defined and a proposal is made to take a more holistic approach to considering subsea production controls. This considers the complete production control system from the surface hydraulic power limit to the down-hole equipment as the system boundary, with each item equipment as components within the system. Each component will have an impact on the overall reliability performance of the subsea production control system. The paper questions what is the impact on the system if new components are introduced e g changes in materials of construction, or if the external environmental changes e g contamination by seawater, change in reservoir flowing well temperatures. Examples are discussed which include the lesson learned.
A system is an assembly of components connected together in an organized way
The components are affected by being in the system and the behaviour of the system is changed if any components leave the system or are changed in some way
This organized assembly of components has or performs a function
This assembly has been defined as being of particular interest
Every system has a boundary, this is dependent on the perspective of the individual defining the system of interest. In the area of subsea production control an operator may see the production control system as including everything from the surface hydraulic power unit to the subsea X-Mas Tree as the system with sub-systems such as an umbilical. However a pump designer may consider the pump to be the system with the housing to be a component. The perspective of the system definer should always be stated to make this clear
A system can be made up of several different types of components
Elements, these are items that (from the perspective taken of the system) do not need to be separated into smaller parts For example, a regulator may be considered an element in a HPU system.
Sub-Systems, these are items that (from the perspective taken of the system) can be separated into smaller constituent parts. For example, a control pod could be considered sub system with the directional control valve an element within it. Note this is an example and it is not an absolute definition, it is only illustrating that the perspective taken is critical, and must be defined to all parties involved.
The boundary is defined by the level & perspective from which the system is viewed. This determines what lies inside and outside the system boundary. This is of obvious importance whencomponents are included or excluded from the system as a result of boundary definition as the behaviour of the system will change. Defining different levels of system boundary has been coined the helicopter view Fig 1 below illustrates the wider boundary seen from the higher position 1 Although the boundary seen at level two is smaller the components within the system maybe considered in more detail.