This document summarizes the subsea flowmetering configuration for an offshore oil and gas development located 210km off the coast of Angola at a depth of 1500m. It includes details on the wellhead and subsea tree, two 8-inch production flowlines and one 2-inch service line bundled in foam insulation and housed in a 30-inch carrier pipe. A multiphase flow meter uses pressure differentials and dual energy gamma rays to continuously measure individual phase flow rates without separation. Produced fluids flow up an insulated riser tower to a floating production, storage and offloading vessel.

1. SUBSEA FLOWMETERING
Group A- Anup Krishnan (6153739), Tinja Mazam (6123031) ,Tolani Adeleke (6184113), Mohammed Salman(6003216)
Flow Metering
Well details
Wellhead
• Standard FMC UWD 15
• 30in conductor housing with
36in OD by 2in wall thickness
extension
• 18-3/4in wellhead housing
• 13-5/5in & 10-3/4in casing
hanger with seal assembly
Subsea Tree
• Provide valve arrangement to
control flow of
produced/injected fluids to
reservoir and chemical
injection
• 47 FMC Vertical 5’’ X 2’’
5,000Psi Subsea Xmas tree
with a design life of 20years
at 1,500m depth
• ROV facilities to operate
valve, retrieve/install choke
insert and subsea control
module
• Thermal insulation to prevent
hydrate formation
Flow Meter : PhaseWatcher Vx 88
Multiphase flow meter with Vx technology that combines an instrumented
venturi with a dual energy fraction meter.
• Two by 8in production flowlines
• One by 2in service line
• Line contained in semi cylindrical modules of
syntactic buoyancy foam to ensure thermal
insulation of pipes
• One by 30in carrier pipe housing insulation
foam, production and service lines
• Submerged weight in production condition
90kg/m
• Bundle equipped with sled at each end for
installation and for structural support to tie-in
of spools connection bundles to manifold.
FPSO Production Bundle Riser & Riser Tower
Wellhead and Subsea Tree Umbilical
Provide control and
command to wells and
manifolds and deliver
chemicals to the
wellhead.
Production Umbilical
• 4 hydraulic supply
lines (2 HP & 2 LP)
• 6 chemical injection
lines
• 4 electrical cables
Injection Umbilical
• 4 hydraulic supply
lines (2 HP & 2 LP
• 4 electrical cables
• One 1in service line
8in and 2in risers integrated in freestanding
riser tower. The Riser tower includes:
• 1350m high, diameter of 1.5m and
neutral buoyant
• One by 22in structural core pipe
• Four by 8in production risers
• Four by 3in gas lift lines
• Two by 2in service lines
• Two by 8in injection risers
• Production and injection lines connected
to FPSO by flexible jumpers and service
and gas lift lines linked by super duplex
steel tubes
Manifold
• Depth – 1500m, Reservoir depth 2000
• Located 210 km off the coast of Angola
• Initial bottom hole pressure 268 bar
• Initial bottom hole temperature 58 – 69oC
• Maximum operating temperature =70°C
• API approx. 32o
• GOR 110 – 130 Sm3/m3
• High productivity up to 40,000 b/d ( 5,000 –
40,000)
• Seabed temperature 4°C
• Wax point 39°C
• Hydrate formation 20°C
• Time for hydrate formation – 8 hours
• Pressure in piping – 0 to 300 bar
• Closed Caisson Foundation (CCF)
provide support for manifold
assembly
• Manifold Support Structure (MSS)
support the manifold and the
connector guiding systems
• Equipped with multiphase
flowmeter of retrievable insert type
• 300m long and 60m wide
• Catenary mooring system with 16
anchor lines- 4 per corner
• Oil storage of 2mmbbls
• Oil production rate of 200,000b/d
• Liquid treatment of 300,000b/d
• Water injection plant for
390,000bw/d & sulphate removal
facility
• Gas production up to 8mmcm/d
• Accommodate 140 people
• Arrival temperature T>40°C for
Working Pressure : 0 – 5000psi (0-345 bar)
Temperature Rating : - 40 to 1500 C
Typical liquid flow range : 1000 – 100,000 bpd
Water- liquid ration : 100%
Venturi throat diameter : 87.5mm
Liquid viscosity : 0. to 2000 cp at line condition
Specification
Benefits
• Production rates and pressures and cumulative volumes could be reported
in real time
• Continuously measures gas, oil and water flow without physical
separation.
• No dynamic calibration with a separator or other reference was required
• Measurements were highly responsive to dynamic conditions of flow
• Pressure drop across the flowmeter less than that for conventional
separators
• Minimal footprints at location
• Maintenance free because of no moving parts
Working
Main Components
• Pressure is measured just before fluids enter venturi and as the flow passes
through venturi throat
• Dual energy spectral gamma ray detector which is directly across a Ba
source which emits gamma rays at various energy levels
• Detector detects gamma rays that are not absorbed by mixture
• A photomultiplier converts light pulses into electric signals that are digitally
processed
• Attenuation of the gamma rays by fluid are measured at 2 energy level
• A cross plot of resultant count rates is the basis for oil, water and gas
fraction determination
• Mixture attenuation at 2 energy levels are compared to the attenuations of
pure oil, water and gas from which parameters such as fluid fraction, water-
liquid ratio (WLR) and mixture density can be extracted.
• Dual energy fraction meter provide oil, water and gas hold-ups which are
used to determine fractions of each phase.
• Once fractions are known, venturi meter is utilised to measure total mass
flow rate and the individual phase flow rates can be calculated.
• Detectors measures radioactive counts rates – it makes complete
calculations of gas, oil and water fraction every 22 millisec- appox 45
measurements of fluid- mixture density and 3 phase hold up per second
Reference
Tubing Hanger
• 5in x 2in, 7500 psi
on top of 10-3/4in
casing hanger &
locks on 18-3/4
housing
• Provides hydraulic
and electronical
communication to
downhole equipment
• Suspends production
tubing
• Control from FPSO through subsea control module (SCM)
• Distribute chemical injection lines, electrical and hydraulic
lines to the trees
• Coated externally with thermal insulation to prevent hydrate
formation
• Connected to associated tree by jumper with one 6in
production pipe, one 2in service line, 8 by 0.5in duplex
piping and 2 cables
Measurement Principle
Floating, Production, Storage
and offloading
Subsea Tree
and Wellhead
Overview of the Subsea Configuration
Umbilical Station
Subsea Manifold
• Venturi for robust mass flow measurement
• Absolute and differential pressure sensors
• Dual energy spectral gamma ray detector
• Radioactive chemical source
• Low power compact field mounted computer for flow computation
• Atkinson, i., berard, m. and conort, g. (2005) A
New Horizon In Multiphase Flow Measurement.
• Bai, Y. and Bai, Q. (2012) Subsea Engineering
Handbook. Burlington, MA: Gulf Professional Pub.
• Barnay, G. (2002) Girassol: The Subsea Production System Presentation And Challenges. (OTC 14170)
Total Mass
Flow Rate
Phase Hold
Ups
Gas Mass Flow
Rate
Water-liquid
Ratio