A list of the most useful and common equations when drawing/formulating any Control Systems.Full description
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control notesFull description
L8 - SUBSEA CONTROL SYSTEMS & UMBILICALS •
SYSTEMS
•
TYPES
•
ELECTRO-HYDRAULIC MULTIPLEXED SYSTEMS
•
TOPSIDES & SUBSEA COMPONENTS
•
OPERATIONS
•
UMBILICALS
•
CHEMICAL INJECTION
PRINCIPAL COMPONENTS OF SUBSEA PRODUCTION CONTROL SYSTEM ARRANGEMENT FOR TIE_BACK TO HOST PLATFORM
CONTROL SYSTEMS FUNCTIONS The control of the components of a production system is managed by the subsea production control system. Control functions include : y Opening and closing subsea tree production, annulus and crossover valves. y Opening and closing the SCSSV. y Opening and closing subsea production manifold flowline valves and pigging valves. y Opening and closing chemical injection valves. y Adjusting subsea choke position. y Monitoring pressure, temperature and other data from treemounted, manifold mounted or downhole instrumentation.
CONTROL SYSTEM / DESIGN ISSUES Key design issues that must be considered when specifying or designing the subsea control system: y Offset distance. Distance affects signal strength, hydraulic pressure loss, response time and cost. y Valve control requirements: The number of valves, types of valves, types of actuators, size of valves, failure position of valves. y Chemical injection requirements. Valve operation, umbilical sharing. y Instrumentation requirements: Pressure or temperature monitoring, pig detection. y Installation and workover requirements and interface with the IWOC system. y Redundancy requirements / availability y Expandability. Future wells, future flowline tie-ins
CONTROL SYSTEMS TYPES Types of Control Systems There are four basic types of production control systems: y Direct Hydraulic Control System y Piloted Hydraulic Control System (Discrete and Sequential) y Electro-Hydraulic Piloted Control System y Electro-Hydraulic Multiplexed Control System Only 1 and 4 considered further here
Characteristics of Different Types of Control Systems Response Rate Features Systems Direct
Umbilical(s) Discrete Control
Complexity
Signal
Actuation
Subsea Functions
Data Readback
Type
Size
Length
Low
Slow
Slow
Yes
Separated if desired
Hydraulic
Large
Short
Discrete piloted hydraulic
Moderately low
Slow
Fast
Yes
Separated if desired
Hydraulic
Moderately Large
Moderate
Sequential piloted hydraulic
Moderate
Slow
Fast
No
Separated if desired
Hydraulic
Small
Moderate
Direct electro- Moderate hydraulic
Very fast
Fast
Yes
Separated if desired
Hydraulic and electric or composite
Moderate
Long
Moderate
Very fast
Fast
Yes
Integral
Hydraulic and Small electric or composite
hydraulic
Multiplexed
Long
Direct Hydraulic System
Electro-Hydraulic Multiplex System
Electro-Hydraulic Multiplex System HYDRAULIC POWER UNT
ELECTRONIC COOLING / DECODING CONTROL INPUTS
MODEM
TOPSIDE
DISPLAY
UMBILICALS
SEA LEVEL
SUBSEA
ELECTRONIC LOGIC SOLENOID CONTROL VALVE TO REMOTE SENSOR
POWER SIGNAL
TO ACTUATOR DISCHARGE TOSEA OR RETURN TO SUFACE (OPTIONAL)
SCMs are usually mounted on the each Tree, but Developments will require some Control Functions on the Manifold (for valves there).
CHEMICAL INJECTION REQUIREMENTS CORROSION INHIBITOR If the reservoir fluids contain Hydrogen Sulphide or Carbon Dioxide, then these could cause corrision in normal steel lines. Inhibitors can be continuously injected to avoid the consequence of a corroded flowline. HYDRATES INHIBITOR To avoid hydrate formation in Pipelines / Flowlines, Xmas trees, Risers and export headers liquids like methanol, ethanol, LDHI or MEG are injected. The quantities will be relatively large. WAX & ASPHALTENES INHIBITOR Wax deposition in pipelines and risers can have a significant effect on oil production efficiency. Build-up in pipelines can cause increased pressure drops, resulting in reduced throughput and thus reduced revenue. In more extreme cases, pipelines/processing facilities can plug, halting production and leading to potentially huge losses in earnings. Chemical Injection is one of the possible solutions SCALE INHIBITOR The precipitation of Scale and Salt is a serious problem and can block the flow path of hydrocarbons. Scale may be Barium Salts. Salt scaling is particularly severe in wells with high saline (>200 g/l) formation brines which may be near saturation with respect to sodium chloride. The phenomena occurs more frequently in gas wells than in oil wells, and can be caused by low pressures, decreasing temperatures reservoir water constituents. EMULSION INHIBITOR The reservoir fluids often contain soap like chemicals naturally. These can form emulsions between the oil and water molecules. These give rise to flow and separation problems.
