reliability & optimisation of artificaial lift system 21 st october 2005 by dr sib akhtar mse...

RELIABILITY & OPTIMISATION OF ARTIFICAIAL LIFT RELIABILITY & OPTIMISATION OF ARTIFICAIAL LIFT

SYSTEMSYSTEM

2121stst October 2005 October 2005

By Dr Sib AkhtarBy Dr Sib AkhtarMSE (Consultants) LtdMSE (Consultants) Ltd

Carshalton, Surrey SM5 2HWCarshalton, Surrey SM5 [email protected]@mse.co.uk

www.mse.co.uk Tel: 020 8773 4500www.mse.co.uk Tel: 020 8773 4500

Effects of Extended Recycle on Effects of Extended Recycle on Gas Lift Compressors in Mature Gas Lift Compressors in Mature

AssetsAssets

© MSE 2005

MSE Consultants LtdMSE Consultants LtdMSE Consultants LtdMSE Consultants Ltd

Established UK Engineering Consultancy - 1988

Specialises in Oil & Gas production facilities

Process-Machinery-Controls

De-bottlenecking

Testing

Equipment design & redesign and compressor re-wheel

Modelling of oil and gas production

Maintains a large database of Heavy machinery Gas Compression, gas turbines and control systems

A single source of design and application information on all makes and types of heavy machinery used in Oil and Gas

© MSE 2005

Current Projects - 1Current Projects - 1Current Projects - 1Current Projects - 1

2nd Largest Gas (Condensate) Field in UK

Expansion with New Satellite Fields

New Bridge-Linked Platform Developed by AMEC

AMEC Want to Optimise Compression Facilities

MSE Developing New MP Compression System

GASMAN Model Built to Verify Design & Performance

Performance Testing and re-design options study

Britannia FieldBritannia FieldBritannia FieldBritannia Field

AMEC/ConocoPhillipsAMEC/ConocoPhillipsAMEC/ConocoPhillipsAMEC/ConocoPhillips

© MSE 2005


UK’s Largest Gas Field

Re-design of compressors for post-plateau production

Update of existing GASMAN model

Expansion to include new satellites (Bains)

Optimise offshore and onshore compression

Compressor vendor design audits

South Morecambe FieldSouth Morecambe FieldSouth Morecambe FieldSouth Morecambe Field

British Gas Hydrocarbon Resources British Gas Hydrocarbon Resources LtdLtdBritish Gas Hydrocarbon Resources British Gas Hydrocarbon Resources LtdLtd

© MSE 2005


Largest new oil field in Oman’s southern province

100,000 bpd capacity using miscible gas injection for enhanced oil recovery

Feasibility of world’s highest pressure gas injection compressors at 710 bar

Design of very high pressure compressors

Vendor design audit

Harweel Gas Injection Compressor StudyHarweel Gas Injection Compressor StudyHarweel Gas Injection Compressor StudyHarweel Gas Injection Compressor Study

Petroleum Development of Oman/ShellPetroleum Development of Oman/ShellPetroleum Development of Oman/ShellPetroleum Development of Oman/Shell

© MSE 2005


Visit Lekhwair and evaluate gas lift system for enhanced oil recovery

Oil production limited by gas lift compression

Identify options for improved gas lift capacity

Submitted proposal for further study and remedial work

Lekhwair Oil Field DebottleneckingLekhwair Oil Field DebottleneckingLekhwair Oil Field DebottleneckingLekhwair Oil Field Debottlenecking

Petroleum Development of Oman/ShellPetroleum Development of Oman/ShellPetroleum Development of Oman/ShellPetroleum Development of Oman/Shell

© MSE 2005


ConocoPhillips

BP Exploration

BG Group

ENI Lasmo

Centrica (British Gas HRL)

Identify causes of compressor performance loss

Compile compressor design/selection guide

Seek trends, commonalities and best practices

Compressor Users Forum

Joint Industry Project (JIP) – Phase IIIJoint Industry Project (JIP) – Phase IIIJoint Industry Project (JIP) – Phase IIIJoint Industry Project (JIP) – Phase III

Five Operating CompaniesFive Operating CompaniesFive Operating CompaniesFive Operating Companies

© MSE 2005

Recent Projects - 2Recent Projects - 2Recent Projects - 2Recent Projects - 2

Independent audit of gas lift compressors

Design

Operation

Machinery reliability problems

High seal failure rate

Proposals for further work highlighted by audit

Thistle Field Compression StudyThistle Field Compression StudyThistle Field Compression StudyThistle Field Compression Study

DNODNODNODNO

© MSE 2005

Recent Projects - 3Recent Projects - 3Recent Projects - 3Recent Projects - 3

Re-configuration of onshore compression facilities

Account for current and future compression demands

Demand increases with well depletion

Two-stage project to accommodate seasonal issues

Measured performance degradation taken into account

North Morecambe FieldNorth Morecambe FieldNorth Morecambe FieldNorth Morecambe Field

British Gas Hydrocarbon Resources British Gas Hydrocarbon Resources LtdLtdBritish Gas Hydrocarbon Resources British Gas Hydrocarbon Resources LtdLtd

© MSE 2005

Current ProjectsCurrent ProjectsCurrent ProjectsCurrent Projects

ONGC – Heera Gas Lift Compression System

Chevron – Benchamas Gas Lift Compression

Lundin – Thistle

PDO – Zalzala Gas Injection

PDO - Saih Rawl ; Upstream LNG feed

Britannia – Production Optimisation

LNG - Project

© MSE 2005

Gas Lift System in Mature AssetsGas Lift System in Mature AssetsGas Lift System in Mature AssetsGas Lift System in Mature Assets

Differ from newly installed systems

Changes in reservoir fluids being handled( e.g. more water and less oil and formation gas)

Differences in flow capacities

Changes in Process conditions ( lean out due to continuous recycling of gases over several years)

Older machinery ( compressors and gas turbines)

Old control systems

Import Gas for start-up

© MSE 2005

Visual Representation of Visual Representation of Gas Lift SystemGas Lift SystemVisual Representation of Visual Representation of Gas Lift SystemGas Lift System

© MSE 2005

Typical Gas Lift Compressor Typical Gas Lift Compressor for Mature Assetsfor Mature AssetsTypical Gas Lift Compressor Typical Gas Lift Compressor for Mature Assetsfor Mature Assets

© MSE 2005

John Crane have recommended that the seals, especially on the NDE are upgraded to the improved version of the 28AT, the 28XP. Advantages of the 28XP over the current 28AT:

Polymer rings incorporated, increase operating temperature up to 600OF, polymer rings also have a higher resistance to chemical attack

Sliding Carriers, eliminates extrusion gaps through differential thermal expansion

Carbide seats have shrouding to protect seal and shaft in the event of a catastrophic failure

The cost of an upgraded cartridge is approximately £50,000

Gas Seals – Replacement SealGas Seals – Replacement SealGas Seals – Replacement SealGas Seals – Replacement Seal

© MSE 2005

Project Conclusions Very high compressor discharge temperatures High Molecular weight changes cause drastic swings

in compressor operation HP compressor operation stable within the central

region of the head map Gas seals operating above their specification for the

o-rings

Reasons Poor Cooler Performance Shallow LP Compressor curve towards lower flow

region of the compressor HP compressor operation stable within the central

region of the head map

© MSE 2005

Where is the current LP Control Line?

How effective is current setting able to protect the LP compressor for a sudden decrease in molecular weight

Optimise control lines, and set points on both machines to give adequate protection for the swing in molecular weight observed with LP machine

Increase control line further into the map for LP, and reduce HPIncrease the head capacity to aid gas lift

Recommendations – Control SystemRecommendations – Control SystemRecommendations – Control SystemRecommendations – Control System

© MSE 2005

Contamination by process gas

Contamination by seal gas

Lube Oil Contamination

Operation outside design specification

Due to the high number of seal containing oil, all the areas of possible contamination have been investigated

Gas Seal - ContaminationGas Seal - ContaminationGas Seal - ContaminationGas Seal - Contamination

© MSE 2005

13000

18000

23000

28000

33000

9000 10000 11000 12000 13000 14000 15000 16000 17000 18000

Suction Volumetric Flow (Am3/hr)

Hea

d (m

)

100% Speed Line

Operating Pts

Gurantee Pt

Light Gas 23.0g/mol

Protect LP Compressor from Low Molecular weight swing by increasing surge control line

Small loss in head and discharge pressure due to shallow curve

Recommendations - Control System – Recommendations - Control System – LP Surge LineLP Surge LineRecommendations - Control System – Recommendations - Control System – LP Surge LineLP Surge Line

© MSE 2005

Increase the Head of the HP Compressor, and the overall pressure of the GLC, by decreasing surge line.

Effected less by fluctuations in molecular weight, due to steeper curve

10000

12000

14000

16000

18000

20000

22000

24000

400 500 600 700 800 900 1000Suction Volumetric Flow (Am3/hr)

Hea

d (m

)

100% SpeedLine

Operating Pts

Gurantee Pt

Recommendations - Control System Recommendations - Control System – LP Surge Line– LP Surge LineRecommendations - Control System Recommendations - Control System – LP Surge Line– LP Surge Line

© MSE 2005

ONGC – Heera AssetONGC – Heera AssetONGC – Heera AssetONGC – Heera Asset

MSE invited by ONGC to InvestigateHeera Asset

Carried out a detailed investigation

© MSE 2005

Study Objectives Study Objectives Study Objectives Study Objectives

Quantify existing compression system capacity

Identify factors limiting existing capacity – Root Cause Analysis

Compare machinery availability to typical industry averages

Identify opportunities to increase production

Optimise existing compression system

Upgrade / replace machinery

Gas turbines

Compressors

© MSE 2005

Activities Activities Activities Activities

Design data collection

Offshore testing – compressors and turbines

Turbine performance analyses

Compressor performance analyses

System performance analyses using GASMAN™

Aerodynamic analyses using CENTRIF

Process analyses using Hysys

Tentative conclusions produced

© MSE 2005

Facilities OverviewFacilities OverviewFacilities OverviewFacilities Overview

© MSE 2005

Factors With The Potential To LimitFactors With The Potential To LimitMaximum Production ThroughputMaximum Production ThroughputFactors With The Potential To LimitFactors With The Potential To LimitMaximum Production ThroughputMaximum Production Throughput

Turbine performance

GG compressor, combustor, power turbine

Process gas compressor performance

Head, efficiency

Unwanted recompression of process gas (recycling)

Process and control instabilities

Offshore testing and subsequent analyses identifies capacity limits

© MSE 2005

Testing & AnalysisTesting & AnalysisTesting & AnalysisTesting & Analysis

© MSE 2005

Offshore TestingOffshore TestingOffshore TestingOffshore Testing

All five trains tested

PGC flows varied by adopting 5 out of 4 train operation and speed control

Good spread of flows and turbine loads achieved

Gas samples collected at various strategic points

Additional design data collected

Detailed analyses of test data completed at MSE

© MSE 2005

Turbines A, B, C: Summary of FindingsTurbines A, B, C: Summary of FindingsTurbines A, B, C: Summary of FindingsTurbines A, B, C: Summary of Findings

All gas turbines suffering in excess of 15% power loss (between 1000kW and 3000 kW loss in power)

Bleed valve malfunction suspected responsible for losses in Trains A and B

Train C suffering compressor efficiency loss primarily due to IGV malfunction

Lack of some instrumentation readings hindering understanding of machinery health

Recommend regular performance analysis to maintain high performance and sustain higher levels of reliability

© MSE 2005

PGC Performance AnalysesPGC Performance AnalysesTrains A, B & CTrains A, B & C

PGC Performance AnalysesPGC Performance AnalysesTrains A, B & CTrains A, B & C

© MSE 2005

Compression TrainCompression Train Compression TrainCompression Train

© MSE 2005

GASMAN™ Modelling of Compressor TrainsGASMAN™ Modelling of Compressor TrainsGASMAN™ Modelling of Compressor TrainsGASMAN™ Modelling of Compressor Trains

© MSE 2005

Performance Assessments – Key Performance Assessments – Key MethodologiesMethodologiesPerformance Assessments – Key Performance Assessments – Key MethodologiesMethodologies

Gas properties – from composition sampling taken during testing

Flow meter readings corrected for mol weight effects

Compressor head and efficiency maps from Factory Acceptance Test (F.A.T.) performance curves

GASMAN™ model allows whole-train analysis

Power Balancing

Total gas compression power to match turbine shaft power

Power balance based upon actual machinery performances

All sources of mass flow considered – recycle, leakage etc

© MSE 2005

Head & Efficiency CurvesHead & Efficiency CurvesHead & Efficiency CurvesHead & Efficiency Curves

Non-dimensional curves allow various speeds to be shown against same datum

Performance datum curves taken from Manufacturers F.A.T. results

© MSE 2005

Train B Stage 1 Head PerformanceTrain B Stage 1 Head PerformanceTrain B Stage 1 Head PerformanceTrain B Stage 1 Head Performance

Train B Stage 1 Head Performance

0.06

0.065

0.07

0.075

0.08

0.085

0.09

0.095

0.1

0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00

Q/N

H/N

2 *

10

00

© MSE 2005

Train B Stage 1 Efficiency PerformanceTrain B Stage 1 Efficiency PerformanceTrain B Stage 1 Efficiency PerformanceTrain B Stage 1 Efficiency Performance

Train B Stage 1 Efficiency Performance

70.0

72.0

74.0

76.0

78.0

80.0

82.0

84.0

86.0

0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00

Q/N

Eff

icie

ncy

© MSE 2005



0.045

0.055

0.065

0.075

0.085

0.095

0.105

0.115

0.125

0.135

0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55

Q/N

H/N

2 *

1000

© MSE 2005



58.0

60.0

62.0

64.0

66.0

68.0

70.0

72.0

74.0

76.0

78.0

80.0

0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55

Q/N

Eff

icie

ncy

© MSE 2005



0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0.14 0.16 0.18 0.20 0.22 0.24 0.26

Q/N

H/N

2 *

1000

© MSE 2005



42

44

46

48

50

52

54

56

58

60

62

64

66

68

70

72

74

76

78

80

82

84

0.12 0.14 0.16 0.18 0.20 0.22 0.24 0.26

Q/N

Eff

icie

ncy

© MSE 2005

Average Compressor Performance Average Compressor Performance LossesLosses(ref F.A.T. Curves)(ref F.A.T. Curves)

Average Compressor Performance Average Compressor Performance LossesLosses(ref F.A.T. Curves)(ref F.A.T. Curves)

Stage 1 Stage 2 Stage 3

Average Head Loss % 5.5 5.3 13.3

Average Efficiency Loss % 2.4 2.3 16.2


Average Efficiency Loss % 10.4 2.5 13


Average Efficiency Loss % 11 4.8 20.4

Note: Losses calculated using performance curves from F.A.T as a datum,not vendor predicted performance curves from API datasheet.

Tra

in A

Tra

in B

Tra

in C

© MSE 2005

Average Compressor Performance Average Compressor Performance LossesLossesAverage Compressor Performance Average Compressor Performance LossesLosses

Performance losses should be viewed in light of more reasonable performance expectations

© MSE 2005

Realistic Compressor Performance Realistic Compressor Performance ExpectationsExpectationsRealistic Compressor Performance Realistic Compressor Performance ExpectationsExpectations


Head m 10205 13313 20922

Head Coefficient --- 0.513 0.496 0.595

Peak Efficiency % 85 79 81

Head m 9598 12947 19160

Efficiency* % 85.2 74.1 72.7

Head Loss From F.A.T % 6.0 2.8 8.4

Efficiency Loss From F.A.T % 0.4 6.1 10.6

Head Coefficient --- 0.482 0.483 0.545

Efficiency % 78.9 72.2 67.4

Efficiency Loss From F.A.T % 7.77 8.53 17.08

Note: Losses calculated using performance curves from F.A.T as a datum,not vendor predicted performance curves from API datasheet.

* From discharge temperature.

CE

NT

RIF

P

erfo

rman

ceV

endo

r P

redi

cted

P

erfo

rman

ceF.

A.T

. P

erfo

rman

ce

© MSE 2005

Compressor Performance LossesCompressor Performance LossesUsing More Realistic ExpectationsUsing More Realistic ExpectationsCompressor Performance LossesCompressor Performance LossesUsing More Realistic ExpectationsUsing More Realistic Expectations

When more realistic performance expectation are used as a datum;

Much of the efficiency “losses” in the three stages can be accounted for

Much of the head “losses” in the 3rd stage can be accounted for

If API datasheets provided are representative of the as-built machines, the head and efficiency profiles generated by the machine in the field are reasonable

© MSE 2005

Compressor Performances - ConclusionsCompressor Performances - ConclusionsCompressor Performances - ConclusionsCompressor Performances - Conclusions

Trains A and B are exhibiting reasonable in-service head and efficiency. It is unlikely a replacement machine for the same duty would yield significant increases in gas rates once in service

Train C appears to be exhibiting higher losses in Stage 1, and may benefit from an overhaul

© MSE 2005

Flow & Power ReconciliationFlow & Power ReconciliationFlow & Power ReconciliationFlow & Power Reconciliation

Flows are not consistent across the stages of compressor trains

Later stages show additional flow

Flows readings checked from flow meter DP’s

If additional flows are ignored, the calculated turbine shaft power cannot be achieved.

When additional stage flows are included, the PGC compression powers can be reconciled with the actual turbine shaft powers.

© MSE 2005

Additional PGC Stage FlowsAdditional PGC Stage FlowsAdditional PGC Stage FlowsAdditional PGC Stage Flows


0 4

Flows In Addition To Forward Flows

0 15

4 16

kSm3/hr

kSm3/hr

kSm3/hr 0

0

4T

rain

AT

rain

BT

rain

C

© MSE 2005

Potential Sources of Additional Stage FlowsPotential Sources of Additional Stage FlowsPotential Sources of Additional Stage FlowsPotential Sources of Additional Stage Flows

Anti-Surge Valves – Not likely as positions are at zero

Internal leakages in compressor casings – not always detected by flow meters. Flows would be too large to reconcile heads and efficiencies.

Cascade system between Knock Out Drums

© MSE 2005

Potential Leakage Paths via KOD CascadesPotential Leakage Paths via KOD CascadesPotential Leakage Paths via KOD CascadesPotential Leakage Paths via KOD Cascades

© MSE 2005

Offshore Test Performed 27-6-05Offshore Test Performed 27-6-05Offshore Test Performed 27-6-05Offshore Test Performed 27-6-05

Possible to eliminate cascade recycle via manual block valve at entry to next KOD in cascade.

Measurements taken on Trains A and B with cascade system open

Cascade isolation valves shut stage by stage and traces of stage flows recorded.

Train A turbine power maintained at constant level (via EGT control)

Forward flows recorded

© MSE 2005

Cascade Test – Flow Traces Train ACascade Test – Flow Traces Train ACascade Test – Flow Traces Train ACascade Test – Flow Traces Train A

© MSE 2005

Cascade Test – Train A Flows At Same PowerCascade Test – Train A Flows At Same PowerCascade Test – Train A Flows At Same PowerCascade Test – Train A Flows At Same Power

With Cascade Without Cascade

Fin

al

Dis

char

ge

kSm3/hr 44.5 50.9

Sta

ge 3

kSm3/hr 53.2 50.5

51.5S

tage

2

kSm3/hr 37.5 50.7

EGT Approx. 695 oC

Sta

ge 1

kSm3/hr 43.5

© MSE 2005

Cascade Testing – Practical ConsiderationsCascade Testing – Practical ConsiderationsCascade Testing – Practical ConsiderationsCascade Testing – Practical Considerations

Build up of liquid in final KOD was observed to be rapid – caution during additional testing

Liquid level control valves may be over-sized – rapid draining of liquid after reinstating cascade was observed

Possible that liquid control valve set-points set to values that “stabilise” the system through permanent recycling (valve open)

© MSE 2005

Cascade – Liquid StabilityCascade – Liquid StabilityCascade – Liquid StabilityCascade – Liquid Stability

Simulations indicate that phase equilibrium is highly sensitive – small changes in temperature can produce quantities of liquid

“Crux” point is around 40 oC, all coolers operate above this area

Production of liquids may be related to JT affect across drain valves

© MSE 2005

Cascade – ConclusionsCascade – ConclusionsCascade – ConclusionsCascade – Conclusions

Current liquid level control of KOD is problematic

Liquid level control valve settings are allowing gas to re-circulate around compression stages – this wastes power and limits maximum rates

Recirculation reduces rates by 6 to 7 kSm3/hr

For the same power, rates could be increased by 16% if recirculation of gas was removed

© MSE 2005

Cascade – RecommendationsCascade – RecommendationsCascade – RecommendationsCascade – Recommendations

Recommend that valve sizes be investigated to more effectively regulate rate of liquid drain and prevent formation of gas leakage path

Two new trains appear to achieve liquid level control effectively – liquid levels maintained at around 15%, thus preventing gas recycle loop and unstable operation

A better understanding of liquid stability and its relation to temperature and pressure would be beneficial

© MSE 2005

ConclusionsConclusionsConclusionsConclusions

Gas Lift Compression System for mature assets were analysed by testing and careful analysis

Model analysis necessary to verify test performance of gas compressor and drivers

Compressor power and engine power balance achieved

Turbine ISO power of 9.2 MW reduced to 7.6 MW when corrected for high ambient temperature 30 C

Gas path analysis identified additional power losses from bleed valves and Inlet Guide Vanes settings. These losses are fully recovered by maintenance activities

© MSE 2005

ConclusionsConclusionsConclusionsConclusions

Gas Compressors performance was found reasonable when compared with industry norms

Flow discrepancies found between compressor were investigated and analysed

This lead to the discovery of gas recycling through the KOD liquid flow lines. This was later verified with a simple test procedure

This helped to with an immediate increase in gas delivered by the compressors

GASMAN software helped to identify problems with gas turbines and flow recycle in compressors.

This was verified by test carried out in the field where mass flow through compressor stages were carefully measured and problem rectified

reliability & optimisation of artificaial lift system 21 st october 2005 by dr sib akhtar mse...

Documents

gas slide

typical gas lift compressor

miscible gas injection

improved gas lift capacity

formation gas differences

compression facilities

head map gas seals

startup slide