1. No category

Compact, inline separation
technology – what and why?
Olav Kristiansen
Statoil RDI, Subsea Separation Technologies
NTNU, Flerfaseteknikk guest lecture, March 31 2014
Classification: Open
2014-03-31
Outline
• Separators, working principle, basic theory
• Existing inline separation applications in Statoil, examples
• Statoil’s subsea factory - subsea separator application
• Required technology development – inline separators
• Summary
2
Classification: Open
2014-03-31
What is separation?
Gas
Oil
Water and
sand
Multiphase wellstream: Oil, Water, Gas, Sand
3
Classification: Open
2014-03-31
Gas/oil/water separation
Gravity based, conventional separator
Inlet
Gas outlet
Oil/water droplets
18
Length
Gas bubbles
Velocity
Oil droplets
Gas bubbles
Water outlet
Settling
• Droplets fall/rise freely
Sedimentation
• Droplets go through interface between the phases
Retention time
• How long time have the droplets for settling and sedimentation
• Determines vessel size
4
Classification: Open
2014-03-31
Oil outlet
Conventional vs. compact separators size
5
Classification: Open
2014-03-31
Gas/oil/water separation
Cyclonic separator
• Gravity based settling: Stoke’s Law, constant settling velocity
when buoyancy and gravity are balanced:
• Cyclonic separation in «amplifies gravity» (radial velocity, Vr, instead of settling
velocity u) by addition of tangential velocity, Vt
− Cyclonic force:
− Drag force:
− Buoyancy force:
• Cyclonic force balance:
• Assuming terminal velocity has been reached:
• Cyclonic «settling velocity», i.e. radial velocity Vr:
• Tangential velocity (experimentally determined, very difficult):
6
Classification: Open
2014-03-31
18
Working principle
Separation chamber
(high Vr due to Vt)
Separated gas
Gas/liquid stream
Gas free liquid
Swirl element
(create high Vt)
Gas extraction
Increasing separation by inducing swirling flow – increasing g-forces
Enable separation of two phases with different densities
7
Classification: Open
2014-03-31
Videos – working principle
• Axial cyclone
− Fine separation, removing droplets down to a ~30 to 50 microns
− Induce flow spin and apply tangential force
• (A) Phase splitter (gas/liquid) separator
• (B) Phase splitter liquid film and carry over into
gas extraction pipe
(B)
− Bulk separation
− Induce two-phase flow spin ~100g
(A)
(B) Inline lens in the gas
The videos are courtesy of FMC Separation Technology
8
Classification: Open
2014-03-31
(A)
extraction pipe looking
against flow into the
separation chamber
Existing use of inline separators in Statoil
9
Classification: Open
2014-03-31
Statfjord B - Produced water slugging
Challenge solution
Major problem with slugs and strong vibrations in the
Statoil Statfjord B platform produced water system.
• Capacity limitation of the system
• Safety concern due to the vibrations.
• Solution: 18” De-gasser. Since 2003, gas has been
exported instead of flared. Slugging stopped.
10
Classification: Open
2014-03-31
Statfjord B
Veslefrikk slugging problem
11
•
•
•
Production through 150m flexible hoses between Veslefrikk A and B
Two-phase (3phase) flow
Slugging, pressure fluctuations and production instabilities
•
Solution?
Classification: Open
2014-03-31
Veslefrikk slugging problem
Phase splitter
Solution: Split gas and liquid using a Phase Splitter, produce outside slug flow
region. 2-4000 BOPD production increase (1-2 MNOK/day)
12
Classification: Open
2014-03-31
Sleipner T – Scrubber Overload
• Scrubber overloaded with liquid due to a
very high gas velocity through the vessel (Kfactor >0.2 m/s).
• Massive carry-over of condensate with the
outlet gas that is used to superheat the gas
to the amine absorbers.
• Solution: De-liquidiser to
remove the bulk of the
liquid condensate in the
feed stream prior to
entering the scrubber.
• This improves the
operating conditions for
the suction scrubber and
thereby the separation
efficiency.
13
Classification: Open
2014-03-31
Kvitebjørn – huge production increase
• Objective: Increase production capacity
• Solution: Installation of a 20” Phase Splitter
upstream the inlet separator and route some of the
gas (30 to 35%) directly to the scrubber.
• New application for Statoil – high pressure, gas
dominated flow (less than 5% liquid by volume in the
incoming flow).
• Qualification tests at K-LAB 2007 (8” unit)
• Gas capacity increase by 35% from 18.5 to
25MMSm3/d
14
Classification: Open
2014-03-31
Potential new users
being considered
• Peregrino II, offshore Brazil
− Phase splitter to split flows for
processing on different FPSOs
• Åsgard B, Norway (weight reduction, existing semi)
− Replace existing inlet separator(s)
• Krafla, Norway (low weight inlet separator, new field installation)
− Deliquidiser to lower liquid load on scrubber
15
Classification: Open
2014-03-31
Subsea Factory - separation
Oil export
Oil storage
Sea water injection
template with pumping
Oil pump
Gas export
Power distribution
and control
Produced water
injection template
Gas compression
Gas, oil, produced
water separation
Manifold
Production
template
Produced water
injection pump
Production
template
ROV
intervention
16
Classification: Open
2014-03-31
Deepwater separation for boosting
Goal: Lowered wellhead pressure
How: Reduce WHP by boosting the weelstream with a subsea pump
Problem: MMP/hybrid pumps have too low dP
Soluton: High dP boosting with conventional pump
What does it take: Gas-liquid separation upstream pump
Oil riser
Gas riser
3000m WD
CompactSep High-dP booster pump
Umbilical riser
Wellhead
Separator
P
Wellstream
Reservoir
17
Classification: Open
2014-03-31
Pazflor
subsea separation and boosting station already in operation
18
Classification: Open
2014-03-31
How large separator can we put subsea?
• Tordis separator and boosting station
− Diameter 2.1m
− Skid dry weight 1 300 tons.
− Water depth 200m
− Possible and in operation
Max 1000m
w.d.
• A Tordis separator at 3000m w.d.
− 17cm wall thickness due to outer
pressure.
− Difficult to produce
− Difficult (if possible) to heave!
19
Classification: Open
2014-03-31
Max weight
300tons at
3000m w.d.
Technical challenge
performance of cyclonic compared to conventional separators
Compact
Conventional
• Turndown 50 to 120% of design
operational rate. Swirl breakdown at too
low rate.
• Turndown 0 to >100%
• Pressure drop 0.5-2 bar
• Two or three clean output streams
• Optimised for one outlet stream, e.g. low
liquid carry over
• Can handle transients
• Homogenous inflow is required (no stratified
or slug flow)
Systems will be needed to
overcome these limitations –
single-units are not sufficient
20
Classification: Open
2014-03-31
• Pressure drop very low
Slug flow performance – single Phase Splitter
Incoming slugs propagate through the separator
(little or no slug damping)
Hydrodynamic slugs upstream
1
1
0,9
0,9
0,8
0,8
0,7
0,7
GVF Hold-up
Hold-up
0,6
0,5
0,4
GVF liq
GVF gas
Hold-up
GVF liq avrage=0,34
GVF gas avrage=0,78
0,5
0,4
0,3
0,3
0,2
0,2
0,1
0,1
0
0
15
17
19
21
23
25
27
Time (s)
21
0,6
Classification: Open
2014-03-31
29
31
33
35
15
17
19
21
23
25
Time (s)
27
29
31
33
35
Compact separator systems
– to overcome the limitations of single inline separators
Positive:
• Can handle turndown 0-100%, full start-up
and shutdown
• Handles hydrodynamic slugs
• Can be optimised for both outlet streams
• Lower weight
Classified information
• Smaller footprint
Negative:
• Pressure drop (~2 bar)
• Fast controls
• Bulk separation
CompactSep JIP separation system
Development project with
Statoil, Petrobras and Chevron
Patent Application priority filing date 22-12-2012
PCT/EP2011/073881
22
Classification: Open
2014-03-31
Turndown problem solved
Production start-up
Shut-down
250
Inlet liquid flow rate
Inlet gas flow rate
Gas flow rate, Phase Splitter liquid outlet
Liquid flow rate, De-liquidiser gas outlet
200
3
Flow rate (Am /hr)
100% liquid
100% gas
100% liquid
100% gas
150
100
100% liquid
50% gas
100% liquid
50% gas
50
0% production0
0% production
1000 1060 1120 1180 1240 1300 1360 1420 1480 1540 1600 1660 1720 1780 1840 1900 1960 2020
Relative time (s)
Liquid carry over and gas entrainment within acceptance criteria during
startup and shutdown
23
Classification: Open
2014-03-31
Slug flow (rapid transient) problem solved
Variation in
gas quality
Incoming
slugs 5±4m
Variation in
liquid quality
24
Classification: Open
2014-03-31
Compact Sep vs Conventional subsea template
system
Classified information
25
Classification: Open
2014-03-31
Technology development takes time!
K-lab
K-lab
FAT Drammen
SINTEF
Rotvoll
Classified informationFull System v2
Degasser
Deliquidiser v2
GLCC v1
Phase splitter
Deliquidiser v1
Full System v1
GLCC
PS & DeLiq v1
Control system
2008-2009
26
Classification: Open
GLCC v2
Degasser
Deliquidiser v2
2010
2014-03-31
2013
2014
Full System v3
Control System v2
Summary
• Inline working principle: Cyclonic amplification of settling bubble/droplet velocity
• Examples of existing and potentially new topside inline separators in Statoil
− De-bottlenecking/capacity increase
− Flow conditioning (getting out of slug flow range)
− Weight reduction
• Subsea factory - subsea separation technology is required. Inline solution is
considered an enabling technology where gravity separators are too large/heavy to
manufacture and/or install and maintain.
• There is a large effort on technology development of compact separators and
separation systems – understanding the physics and solving limitations related to
inline separators. Ongoing JIP with one vendor and four oil companies.
27
Classification: Open
2014-03-31
Acknowledgements
Joint Industry Programme – CompactSep JIP
JIP operator
28
Classification: Open
2014-03-31
Compact, inline separation technology –
what and why?
Olav Kristiansen
Principle Researcher, Statoil RDI,
Subsea Separation Technologies
[email protected]
Tel: +4790213317
www.statoil.com
29
Classification: Open
2014-03-31