Transcript Slide 1

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Total System Optimisation
in Gas-Lifted Fields
ASME/API/ISO Fall 2003 Gas-Lift
Workshop , Kuala Lumpur,
October 21-22, 2003
ZR Lemanczyk & CJN McKie
Edinburgh Petroleum Services
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Optimisation in Gas-Lifted Fields
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• Optimisation: maximisation of ‘benefit’ subject to
constraints imposed by external conditions and the
performance of the producing system
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Reservoir
Wells
Pressure drops in pipes
Performance of surface equipment
Delivery pressures
Single Well Optimisation
Lift Gas
Export Gas +$
Oil +$
Q
P
Lift
Gas
Water -$
Oil Production or $/day
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Increasing THP
-$
Gas Injection Rate
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Single Well Optimisation
• Assumptions
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– Fixed tubing head pressure for all gas lift rates
– Lift gas is available to the well at the rate and pressure
required
• Considered in the optimisation
– Combined reservoir inflow and tubing outflow
performance
• Not considered in the optimisation
– Effect of other equipment on the well and vice-versa
– How lift gas is supplied to the well
– Whether lift gas injected into this well would
give more benefit in another well
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Multi-well Optimisation
Prod
Manifold
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Flowline
Prod
Manifold
Prod
Manifold
Water Oil
-$ +$
Flowlines
Flowlines
Flowlines
Lift
Gas
-$
5
Lift
Gas
-$
Lift
Gas
-$
Export
Gas
+$
Lift
Gas
Multi-well Optimisation
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• Assumptions
– Fixed separator pressure
– Fixed total lift gas availability
• Considered in the optimisation
– Interactions between wells in production gathering
network
– Optimal allocation of limited supply of gas between wells
• Not considered in the optimisation
– How lift gas is supplied to the well
– How changing operating conditions affect
total amount of lift gas available
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Total System Optimisation
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Prod
Manifold
P
Prod
Manifold
Prod
Manifold
Water Oil
-$ +$
Lift Gas
Manifold
Export Gas
+$
Lift Gas
P
P
P
Q
P
P
P
P
Fuel Gas
Q
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External Q
Fuel Supply
-$
Compressor Performance
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Gas Turbine
Discharge Pressure
Compression Stage
Power
100%
Decreasing
Efficiency
Speed
100%
Fuel Gas
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Increasing
Speed
Suction Flowrate
Relationship between CHP and Qgi
CHP
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Ptub at operating valve
Increasing
CHP
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Gas Injection Rate
Tubing
Valve
Gas Injection Rate
Well E Performance
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WPS for GL Optimisation
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Well Completion Details
• Tubing
• Gas-lift Valves
• Open interval(s)
• Reservoir completion
Reservoir Pressures
kh, Skin, PI
Production Tests
FBHP, FBHT Observations
Flowing Gradient Surveys
Well Performance
Surfaces
Production System Geometry/Dimensions
Well Active/Inactive Statuses
Production Choke Sizes
Current Flow Routing (Block Valve Statuses)
Surface Eqpt Active/Inactive Statuses
Current Pressures and Flowrates
Economic Parameters
Optimiser
Recommendations
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Solution Technique
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• A model is constructed containing all of the wells,
the gathering & distribution networks and the
surface equipment
• The optimal solution to the model is found using
Sequential Linear Programming (SLP)
– Generic optimisation capability which can be applied to
many different types of problems
– Simultaneous simulation and optimisation
– Proven ability to handle large, non hierarchical
networks with loops and branches and
hundreds of wells
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Automation & Optimisation
• Off-line
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– Data input manually into system model
– Results from system model implemented manually
• Open loop
– Data input automatically into model from SCADA
– Results from model implemented manually
• Closed loop
– Data input automatically into model from SCADA
– Results from model implemented automatically via set
point controllers
– Operator review may be required to ensure that
implemented results are “sensible”
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Open Loop
Closed
LoopOptimisation
Optimisation
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Automatic Data Input
Data Output
Optimiser
OPERATOR
•Advice
•Approval
•Implementation
Field
OPERATOR
Setpoint
• Advice
Controllers
• Approval
• Implementation
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Offline Optimization Workflow
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Production
Report
Current production
equipment and
network status
• Process takes
weeks
Corporate
economic
parameters
• Highly skilled
resource required
performance
curves
Enter and validate
production test data,
re-tune well models
Import updated well
models into network
models
Update network model
Implement in field
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Archive well and
network models used
for optimization
Update corporate
information
systems
Run optimization
Review and output
optimiser results
Why Online?
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• Large Number of Wells
• Complex optimisation problem
• Reduce cycle time
– Optimisation-to-implementation
– Engineer’s time concentrated on value adding tasks
• Goals
– Automate Process
– Automate Repetitive Tasks
– Optimise
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Sustainable Production Optimisation
Increased Value Over ‘Do Nothing’
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Sustained Gains
Optimisation gains revert to norm
as system changes: automation of
process is key to sustain the gains
Gains
Time
Simple Manual Optimisation
Complex Manual Optimisation (Offline)
Complex Automated Optimisation (i-DO)
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Online Optimisation
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• Process takes
minutes
• Fully automated
Data
SCADA
Historian
Expired
Data
Historical
Data
Server
Real-time
Data
Targets
Conditions,
Status
Data
SCADA
Server
Process Data
Production Data
Management
Optimized
Set-points
Network Model
and Optimizer
Production
Tests
Well Perf
Curves
Well
Models
Economic
Parameters
Review,
Approval
Results
LAN/WAN/Internet/Intranet
Data
Corporate
Database
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Web Client
Engineer
PCs
Conclusions
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• Optimisation considering the total system can
deliver additional production gains and costs
savings over and above considering the production
gathering network alone
• The capability to perform total system optimisation
in gas-lifted fields exists today.
• A number of online gas lift optimisation systems
have been installed and are operational today.
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Case Study: PDVSA - Venezuela
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• Lake Maracaibo, Venezuela
• Large-scale implementation of gas lift
• Pilot Area (Centro Lago)
– Over 200 wells
– 4 separation plants
– 5 compressor trains
MARACAIBO
CABIMAS
– 10 lift gas manifolds
3.5 million BOPD 1.5 million BOPD
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Case 1: PdVSA On-Line
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– SCADA data automatically loaded to give current block valve and
compressor status and to constrain the optimisation to stay close to
existing operating conditions
– Price/cost and equipment constraint data loaded from Corporate
databases
– Gas injection well set-points sent directly to SCADA controllers (after
production operator review as a block)
– Recommended pressure control valve set-points and compressor
operating conditions sent to production operators in open-loop
advisory messages
– Results stored in central database for access by other applications.
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Optimal Separator Pressure
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From Wells
Water
To Wells
Export Gas
Lift Gas
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Oil
Significant
Pressure
Drop
• Separator pressure has to
be high enough to transfer
gas to compression plant
• Total System Optimisation
showed that it was possible
to simultaneously reduce
Psep and Qgi
• 3% increase in oil
production, 14% decrease
in lift gas requirement
Field Implementation Results
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Producing Well
Oil
Oil Prod
Area
Count Production Increase
STB/D
STB/D
Revenue Gas Injection
Increase Reduction
($/day)
MMSCF/D
Centro
Lago
203
39,300
2,594
(6.6%)
$61,000
5.9
(2.9%)
Other
Areas
606
74,700
2,510
(3.4%)
Production History of Flow
$59,000
9.1
(6.0%)
Station
(Group of Gas Lifted Wells)
Total
Oil
Rate
Lake
Maracaibo
Average Rate 23.9 Mbbl/d
Average Rate 23.1 Mbbl/d
(bbl/day)
Start of New
GL Set Points
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20000
11/06/00
24 hr pumped volume of oil
TIME
11/07/00
KOC POIS
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In 2000 KOC awarded a contract for Production Optimization
and Information Systems to a consortium including EPS
Objective - Deliver an integrated optimization and advisory
system interfacing to the automation and SCADA systems
covering four fields in North Kuwait
Scope
– Four fields in North Kuwait including 411 well strings
– Of these 33 are water injectors, 91 gas-lifted producers,
and 30 wells producing with ESP’s.
– Complex network configuration allows wells to be
switched between high, medium and low pressure
separators as well as between wet and dry trains.
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KOC POIS
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Production Operation Information System (POIS)
EPS in partnership with Aspentech
On-Line Optimisation (inc. GL) implemented 2000-2002.
253 NF + 91 GL + 34 ESP + 33 Injectors = ~400 wells
5 Fields; 8 Producing Layers; 13 Fluid Models
600,000 bopd
217 SCADA – RTU Systems
Engineering support contract awarded 2003 despite intense
competitive pressure
KOC POIS
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Abdali:
16 Wells
to 2 GC
378 producers
connected to 3
GCs through of
21 headers
via 13 6in lines
Abdal i -[AD]
Ratqa:
20 Wells
to 2 GC
via 36in & 10in lines
Sabriyah:
Ratqa-[RQ]
142 Wells
to 1 GC thru’ 7 MF
Sabri yah-[SA]-GC23
Raudhatai n-[RA]-GC15&GC25
Raudhatain:
195 Wells
Bahra:
to 3 GC
C-GC15
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thru’ 7 MF each
C-GC25
C-GC23
5 Wells
to 1 GC thru’ 7 MF
Bahra-[BH]
KOC POIS
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Inside Raudhatain
5x7 Possible inputs from RQ & AD fields
Lift-Gas System
Lift gas to SA field
9 Sub-sheets holding 20-25 wells each
7x3 MF interconnecting all 194 wells
across the field
7x3 MF outlets to production terminals
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KOC POIS
Inside Raudhatain Subsheet RA-1
Multi-header choice for lift-gas
at present & for future
Multi-MF choice for production
at present and for future
NP & GLwells (FG)
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