L08 - SUBSEA CONTROL SYSTEMS

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

Control functions include :Opening and closing subsea tree production, annulus and crossover valves.Opening and closing the SCSSV.Opening and closing subsea production manifold flowline valves and pigging valves.Opening and closing chemical injection valves.Adjusting subsea choke position. Monitoring pressure, temperature and other data from tree-mounted, manifold mounted or downhole instrumentation.

The control of the components of a production system is managed by the subsea production control system.

CONTROL SYSTEM / DESIGN ISSUES

Offset distance. Distance affects signal strength, hydraulic pressure loss, response time and cost.Valve control requirements: The number of valves, types of valves, types of actuators, size of valves, failure position of valves.Chemical injection requirements. Valve operation, umbilical sharing.Instrumentation requirements: Pressure or temperature monitoring, pig detection.Installation and workover requirements and interface with the IWOC system.Redundancy requirements / availabilityExpandability. Future wells, future flowline tie-ins

Key design issues that must be considered when specifying or designing the subsea control system:

CONTROL SYSTEMS TYPES

Direct Hydraulic Control System

Piloted Hydraulic Control System (Discrete and Sequential)

Electro-Hydraulic Piloted Control System

Electro-Hydraulic Multiplexed Control System

Only 1 and 4 considered further here

Types of Control Systems

There are four basic types of production control systems:

Characteristics of Different Types of Control SystemsResponse Rate Umbilical(s)

Features Discrete Control Data

Systems Complexity Signal Actuation Subsea Functions Readback Type Size Length

Direct

hydraulicLow Slow

Slow

Slow

Slow Yes

Yes

Yes

Yes

Separatedif desired

Separatedif desired

Separatedif desired

Separatedif desired

Hydraulic Large Short

Discretepilotedhydraulic

Moderatelylow

Fast Hydraulic

Hydraulic

Hydraulic andelectric orcomposite

ModeratelyLarge

Moderate

Sequentialpilotedhydraulic

Moderate

Moderate

Moderate

Direct electro-hydraulic

Multiplexed Very fast

Very fast Fast

Fast

Fast No

Integral Hydraulic andelectric orcomposite

Small

Moderate

Small

Moderate

Long

Long

Electro-Hydraulic Multiplex System

Direct Hydraulic System

MODEM

DISPLAYCONTROL INPUTS

ELECTRONICCOOLING / DECODING

HYDRAULIC POWERUNT

ELECTRONICLOGIC

UMBILICALS

TOPSIDE

SEA LEVEL

SUBSEA

SUBSEAUMBILICAL

TERMINATION

DISCHARGETOSEA

OR RETURNTO SUFACE(OPTIONAL)

POWER

SIGNAL

SOLENOID CONTROL VALVE

TO REMOTESENSOR

TO ACTUATOR

Electro-Hydraulic Multiplex System

LINEAR GATE VALVE

ROTARY CHOKE VALVE

VALVES TO BE ACTUATED

Topsides EquipmentTOPSIDES EQUIPMENT (Under Construction)

SURFACE CONTROL CABINET

PRODUCTION HYDRAULIC POWER UNIT

TOPSIDES UMBILICAL TERMINATION UNIT

SUBSEA CONTROL UMBILICAL

SUBSEA CONTROL UMBILICAL

Subsea Control Module (SCM)Control Module

Directional Control Valve

Subsea Electronics Module

Interface Cards Optical Modems

Hydraulic HP Intensifier

SUBSEA CONTROL MODULE (SCM)

SUBSEA EQUIPMENT

SUBSEA CONTROL MODULE (SCM)

SCM MOUNTING BASE

ASSEMBLY

SUBSEA CONTROL MODULE

DIVERLESS SCM CONNECTION SYSTEM –With Connection pins at the base

Alignment Pins

Fluids & Electrics Connecting Pins

Locking Pin

SUBSEA CONTROL MODULE (SCM)

Lifting and Lock Down Connection

Upper part “Computer Intelligence”Unit

Lower Part Pilot Control Valves

SCM Housing

Master ControlStation

PlatformJunction

Box

HydraulicPowerUnit

UmbilicalTerminationAssembly

(UTA)

SubseaControlModule

XmasTree

Typical Diver installed layout

Umbilical TerminationAssembly UTA Subsea

Control Pod

Pod Base

XmasTree

Typical ROV installed layout

Flexible jumper

Flexible jumperFlexible jumper

Hard piping

Temperaturetransducers

Pressuretransducers

Temperaturetransducers Pressure

transducers

Choke cables

Choke cables

SCMs are usually mounted on the each Tree, but Developments willrequire some Control Functions on the Manifold (for valves there).

SCM

CHEMICAL INJECTION REQUIREMENTSCORROSION INHIBITORIf 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 INHIBITORTo 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 INHIBITORWax 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 INHIBITORThe 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 INHIBITORThe 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.

CHEMICAL INJECTION REQUIREMENTS

DRILLING CONTROL SYSTEM