2007 Gas-Lift Workshop

Transcription

1 2007 Gas-Lift Workshop Field Application of Automation and Control Equipment by Cleon Dunham Oilfield Automation Consulting 2/11/ Gas-Lift Workshop 1

2 Gas-Lift Automation & Control Equipment Outline Gas-lift automation objectives, justification Essential & optional measurements Essential & optional controls Measurement & control specifications Alternative locations for measurement & control Alternative types of measurement & control Automation support systems Required staffing 2/11/ Gas-Lift Workshop 2

3 Gas-Lift Automation & Control Equipment Objectives 2/11/ Gas-Lift Workshop 3

4 Gas-Lift Automation & Control Equipment Most Important Objectives Continuous Gas-Lift Inject gas as deep as possible Maintain stable injection rate and pressure Maintain optimum gas-lift injection Dual Gas-Lift Keep both sides on production Achieve objectives for continuous gas-lift wells Intermittent Gas-Lift Optimize injection cycles frequency and volume 2/11/ Gas-Lift Workshop 4

5 Gas-Lift Automation Objectives Well Surveillance Detect gas-lift problems as soon as they occur Diagnose causes of problems Determine best courses of action Evaluate changes in operation or performance Goals Detect problems as soon as they occur Automatically link to diagnostic system Allow corrections to be made quickly Evaluate changes to continuously improve response 2/11/ Gas-Lift Workshop 5

6 Gas-Lift Well Surveillance 2/11/ Gas-Lift Workshop 6

7 Gas-Lift Automation Objectives Calibration Assist in calibrating gas-lift gradient curves Run flowing and static pressure surveys Use automation system to measure wellhead parameters, well test data Goals Calibrate the gas-lift gradient curve Use it for gas-lift design and downhole surveillance If there is time, review Calibration presentation 2/11/ Gas-Lift Workshop 7

8 Gas-Lift Automation Objectives Well Control Keep wells operating from deepest points For single gas-lift, keep injection deep and stable For dual gas-lift, keep both sides operational For intermittent gas-lift, optimize injection cycles Maintain stable injection rates Maintain stable injection pressures, if possible Inject at (close to) optimum rates at all times Must be balanced with available net supply 2/11/ Gas-Lift Workshop 8

9 Gas-Lift Well Control 2/11/ Gas-Lift Workshop 9

10 Gas-Lift Automation Objectives Distribution System Surveillance Detect problems Diagnose causes of problems Evaluate changes in operation or performance 2/11/ Gas-Lift Workshop 10

11 Gas-Lift System Surveillance 2/11/ Gas-Lift Workshop 11

12 Gas-Lift Automation Objectives Distribution System Performance Keep system in balance Keep outflow = inflow Keep system pressure (nearly) constant Keep pressure at agreed value Most gas-lift valves are designed based on pressure Optimize use of available lift gas Keep best wells at optimum injection at all times Cut back or turn off poorer wells, if supply is low Provide for special cases - e.g. difficult to re-start 2/11/ Gas-Lift Workshop 12

13 Gas-Lift System Performance 2/11/ Gas-Lift Workshop 13

14 Gas-Lift System Performance 2/11/ Gas-Lift Workshop 14

15 Gas-Lift Automation Objectives Compressor Surveillance Detect problems Diagnose causes of problems Evaluate changes in operation or performance 2/11/ Gas-Lift Workshop 15

16 Gas-Lift Automation Objectives Compressor Control Deliver required amount of gas Minimize inefficiency Minimize loss of gas Provide desired gas quality (dryness) Note: This may be part of production facility automation, instead of gas-lift automation. 2/11/ Gas-Lift Workshop 16

17 Gas-Lift Automation Justification With Effective Gas-Lift Automation You can Increase oil production by 10% or more Decrease gas usage by 10% or more Reduce OPEX Reduce CAPEX Improve gas-lift understanding Make better use of staff - field and office Increase ultimate recovery in some cases Extend reach of gas-lift (ESP s s are coming) 2/11/ Gas-Lift Workshop 17

18 Gas-Lift Automation & Control Equipment Measurements 2/11/ Gas-Lift Workshop 18

19 Essential Gas-Lift Well Measurements Essential Well Measurements Injection pressure Well stability Depth of lift Problems (e.g. heading, frozen, blowing around) Injection rate Must measure rate to control rate Production pressure Well stability Depth of lift 2/11/ Gas-Lift Workshop 19

20 Optional Gas-Lift Well Measurements Optional Well Measurements Injection temperature To compensate injection rate measurement Production temperature Potential value as indicator of flow / no-flow Production differential pressure Useful to estimate production rate and to detect high / low / off production Downhole measurements Potential for enhanced gas-lift performance analysis 2/11/ Gas-Lift Workshop 20

21 Production Estimate with Differential Pressure Olom-30S Gross Production Calculated from dp and Test Separator SEPARATOR VALUES dp VALUES Well closed-in to change bean Flow restricted with block valve Liftgas shut-off /11/ Gas-Lift Workshop 21

22 Essential Gas-Lift System Measurements Essential System Measurements Gas-lift system inflow rate(s) Gas-lift system outflow rate(s) Inflow and outflow rate(s) are used to determine net amount of gas available for lift Gas-lift system pressure System pressure must be measured so gas-lift system control can be tuned to maintain (nearly) constant, stable pressure 2/11/ Gas-Lift Workshop 22

23 Optional Gas-Lift System Measurements Optional System Measurements System temperature To compensate rate measurements Other inflow and outflow rates To fine tune gas-lift system measurements 2/11/ Gas-Lift Workshop 23

24 Gas-Lift Automation & Control Equipment Controls 2/11/ Gas-Lift Workshop 24

25 Essential & Optional Gas-Lift Controls Wells Essential controls Gas-lift injection rate Optional controls Well-head back pressure, for stability control (1) Gas-lift injection pressure (2) (1) This control technique has been tested. Stability can be achieved with minimal additional dynamic back-pressure control. The method needs more testing and confirmation. (2) I have not tried this control technique. 2/11/ Gas-Lift Workshop 25

26 Essential & Optional Gas-Lift Controls System Essential controls System outflow to gas-lift wells Optional controls Other system inflows and/or outflows Compressor output 2/11/ Gas-Lift Workshop 26

27 Gas-Lift Automation & Control Equipment Specifications 2/11/ Gas-Lift Workshop 27

28 Measurement & Control Specifications Measurement Accuracy Pressure +/- 1% full scale (e.g. +/- 10 psi on 1000 psi system) Rate +/- 5% full scale (e.g. +/- 50 Mcf/Day on 1000 Mcf/Day) 2/11/ Gas-Lift Workshop 28

29 Measurement & Control Specifications Measurement Repeatability Target 0.1% - 1.0% of full scale repeatability E.g. +/- 1 Psi on 1000 Psi E.g. +/- 10 Mcf/Day on 1000 Mcf/Day Measurement Frequency Obtain readings once per minute Use average value (of pressure, rate, etc.) over one- minute period 2/11/ Gas-Lift Workshop 29

30 Measurement & Control Specifications Well Control Keep injection rate stable Avoid set point seeking Use deadband of +/- 25 Mcf/Day Use ramping to avoid rapid set point changes Limit rate of set point change to 100 Mcf/Day/Minute Ignore ramping if need to stop injection altogether 2/11/ Gas-Lift Workshop 30

31 Measurement & Control Specifications Distribution System Control Respond to system upsets within 1-2 minutes Compressor trip Compressor start-up Production station trip or start-up Change in big well(s) System control approach Control based on rate (e.g. keep outflow = inflow) Use pressure tuning to keep system pressure stable Do not use system pressure for primary control - it is too slow 2/11/ Gas-Lift Workshop 31

32 Gas-Lift Automation & Control Equipment Locations 2/11/ Gas-Lift Workshop 32

33 Alternative Measurement & Control Locations Measurement and Control at Well-Head Measure & control injection rate Measure injection & production pressures Other measurements P P DP Q P I 2/11/ Gas-Lift Workshop 33

34 Alternative Measurement & Control Locations Control at Flow Station Measure & control rate at flow station manifold Measure IP, TP, others at well-head Q P I P P P L 2/11/ Gas-Lift Workshop 34

35 Alternative Measurement & Control Locations All Measurement & Control at Flow Station Measure & control rate at flow station Measure IP at flow station, downstream of meter and control valve Reasonably accurate if maintain stable system Measure TP upstream of production manifold Measure DP upstream of production manifold These are only recommended if there is no good alternative 2/11/ Gas-Lift Workshop 35

36 Alternative Measurement & Control Locations Distribution System Measure inflow rates at sources E.g. compressor discharge, pipeline connection Measure pressure at representative location(s) Recommend having a back-up measurement location Measure rate(s) to individual manifolds If applicable, this can provide an injection system balance 2/11/ Gas-Lift Workshop 36

37 Gas-Lift Automation & Control Equipment Equipment Types 2/11/ Gas-Lift Workshop 37

38 Alternative Measurement & Control Types Pressure, Temperature Measurement Conventional analog transducers Widely used Digital systems (e.g. Fieldbus) Coming on the scene Several potential advantages Multi-variable transmitters E.g. combined P, DP or P, T, DP Requires DCS or special RTU 2/11/ Gas-Lift Workshop 38

39 Typical Field Measurement Devices Standard Pressure Transducer Digital Pressure Transducer with Foundation FieldBus Multi-Variable Transducer Note: Pictures compliments of Fisher-Rosemount 2/11/ Gas-Lift Workshop 39

40 Alternative Measurement & Control Types Gas Flow Measurement Orifice meters Turbine meters Vortex meters Hybrid Devices Measurement & control in one device Measurement based on variable flow coefficient My experience has not been positive Problem with measurement accuracy 2/11/ Gas-Lift Workshop 40

41 Measurement & Control Devices Vortex Gas Meter Standard Control Device Hybrid Combined Measurement & Control Device 2/11/ Gas-Lift Workshop 41

42 Gas-Lift Automation & Control Equipment Automation Support Systems 2/11/ Gas-Lift Workshop 42

43 Automation Support Systems Well-Head Support Well-head remote terminal units (RTUs) Data acquisition & communication Averaging, processing, and buffering of data, if needed Well-head control, if pertinent Well-head connected to flow station DCS or RTU Via hardwire, fiber optic, or other communication means Pertinent for offshore platforms 2/11/ Gas-Lift Workshop 43

44 Automation Support Systems Flow Station (or Manifold) Support Facility RTU Facility Program Logic Controller (PLC) Facility Distributed Control System (DCS) Data acquisition and communications Flow measurement, multiple wells Flow control, multiple wells Note: In some cases, a DCS may be able to stand alone without the need for a host system 2/11/ Gas-Lift Workshop 44

45 Automation Support Systems Field Control Host computer system UNIX NT Communicate with field devices Hardwire Microwave Radio Other 2/11/ Gas-Lift Workshop 45

46 Automation Support Systems Field Control Primary host system functions Data gathering Routine surveillance - alarms, reports, plots Gas-lift system & well control Interface with gas-lift diagnostic system Interface with gas-lift optimization system Interface with other field systems, e.g. well testing Interface with web-based based systems 2/11/ Gas-Lift Workshop 46

47 Gas-Lift Automation & Control Equipment Staffing 2/11/ Gas-Lift Workshop 47

48 System Support Required Staffing Hardware support Instrumentation Automation support systems Note: Modern technology permits plug and play IT support System Database Applications Web interface Note: Have choice of using own or contractor staff 2/11/ Gas-Lift Workshop 48

49 Required Staffing Gas-Lift System Operations Well analysis Well servicing Production engineering Use of own staff is recommended For most of us, gas-lift is core business Key is training, training, training 2/11/ Gas-Lift Workshop 49

50 Field Application of Automation and Control Equipment To quote an un-named, named, somewhat pesky but ardent, gas-lift hand, I I can t t conceive of operating an important gas-lift field without an appropriate level of field automation and control. Can you? 2/11/ Gas-Lift Workshop 50