New Solutions for Annulus Pressure Management to Avoid Premature Failure in ESP Wells Joe Allan PTC
Agenda The Challenge Impact or Annulus Pressure Management on ESP Run Life/power cable integrity Current Solutions Manual/Sub Optimal New Solutions Description / Performance Simulation / Actual Results Conclusions
ESP Completion Hanger BOV Annulus Cable Wellhead Pkr ESP ESP
Annulus Pressure Management: Challenges Following well start up Well temperature increases A Annulus pressure increases Annulus Pressure, if not managed carefully can: Collapse tubing or burst casing Explosively Decompress Power Cable insulation 50 psi/min maximum bleed off rate Reduce by 50% then hold for 30 min
Annulus Pressure Management: Existing Approach Subsea wells Utilises subsea tree x over valves Requires monitoring-human factor Difficult to control bleed off rate Platform / Land Wells Utilises annulus line gate valve Requires monitoring-human factor Difficult to control bleed off rate Remote location Might this be a factor in ESP power cable failures?
Annulus Pressure Management in Practice 0.06 bbl(2.5 gal)~50 psi
Annulus Pressure Management (Subsea Wells) An Automatic, Controlled Solution Bleed Off Valve(BOV) Reconfiguration of existing field proven technology Automatic pressure relief valve with bleed off rate control Bleeds from A Annulus > Tubing Preferably installed just below tubing hanger Set to open/close at pre-set annulus pressure (P*ann) Bleed off rate controlled to protect ESP cable Also incorporates Well barrier accredited check valve Prohibits tubing > annulus flow Closes once Pann<= P*ann Metal / metal seal IPO stem/seat provides backup check valve Annulus debris protection BOV set shallow with inlet lowermost(gravity separation) Shearable filter allowing by-pass in event of blockage Shear module to facilitate annulus PT tested to +/- 5 %
Annulus Pressure Management (Subsea Wells) An Automatic, Controllable Solution Technology heritage Shear open device with reference chamber Labyrinth restrictors IPO gas lift valve Well barrier check valve assures well integrity IPO stem provides secondary barrier Bellows controls opening and closing pressures Shearable filter Dimensions 9.3 OD (10.75 csg, but can reduce for smaller csg sizes) 2 power cable slots 2 CL slots 5.5 VAM connections
Well Completion and Production Phases Two distinct modes of operation: Completion phase(constant temperature): Annulus PT required to confirm completion integrity Tool initially pinned closed Tool sheared immediately after annulus test Production phase(increasing temperature): When well is put on production, Pann will increase as consequence of T increase The BOV will control rate of pressure bleed-off during both phases
BOV Simulator Used during product development Integrate mechanical design with fluid mechanics Type and location of restrictors IPO specs Used during completion design phase Determine specification To ensure bleed off rate is < 50 psi/ min Unsteady state in time/location Models production phase from startup to stabilised production Temperature Increase Associated Annulus Pressure increase Flow processes through the BOV Models initial shear during completion phase dv dt = V T dt dt + V P dp dt dv = CT dt V dv = CP dp V
Simulator-Product Development Mechanical Design BOV Simulator Manufacture Determine BOV specification
Simulator Verification Test well used to check BOV operation Temperature effect mimicked by injecting fluid into annulus Simulator used to design test/bov setup Initial problems re location of shear sub resolved Tool sheared at correct pressure Bleedoff rate as expected Held pressure as expected The tool successfully catered for both the initial shear and post shear periods Actual and simulated performance demonstrated good correspondence
Pann(bar), Tann( C), Q(m3/d) dp/dt(psi/min) Simulation Example 300 Example Well - Annulus Pressure Bleed-off 300 250 Initial shear pressure 200 200 100 Pann dp/dt 150 0 dp/dt=50 psi/min 100 Annulus temperature increase due to ESP start-up Tann -100 50 Annulus pressure increase due to ESP start-up Auto bleed-off at 38 bar -200 Q ESP start-up 0-300 0 5000 10000 15000 20000 Time (sec) Vann=100 m3(630 bbl) dp/dt< 50 psi/min Total fluid bled off~1.2 m3(7.3 bbl) 5 off 225 LOHM resistors required Pdome~38 bar Shear setting 250 bar Completion Phase Production Phase
Annulus Pressure Management (Dry Tree Wells) An Automatic and More Controllable Solution Existing Scenario: Bleeding off through manual gate valve Enhanced Scenario: Surface Annulus Safety Valve (M SAS) Check valve buried in VR profile Hydraulic Actuated to open Local hand pump or Remote control hydraulics In response to P Ann> MAASP Choke in actuator flow tube Sized to control bleed off rate Can install actuator in modified gatevalve(msas G) Eliminates surface pipework mods
Conclusions ESP Lifted Well Annulus Pressure Management Guidelines Max Bleed off rate < 50 psi/ min Very difficult to achieve with existing technology Sub Sea Xmas tree x-over valves Dry tree annulus line valves May be a factor in premature ESP failures Explosive decompression of power cable insulation? Solutions to automate and control the process been developed Reconfiguration of existing field proven technology Simulator developed to model the tool performance Good history match achieved with test data
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P(psig) Test Results (Test2-I/R/S) 29/11/12-Test2(I/R/S) 4000 3500 3000 Ptbg_corr AKER-PSI 2500 2000 Pann_corr AKER- PSI 1500 1000 500 0 29/11/2012 12:00 29/11/2012 14:00 29/11/2012 16:00 29/11/2012 18:00 29/11/2012 20:00 Time Put shear sub at bottom to protect IPO Sheared OK Pann decreased to ~1300 psi and held (pumping small pmp throughout) Test successful
P(psig) P(psig) Test Results (Test4-R/S) 30/11/12-Test4(R/S) 4000 3500 3000 Ptbg_corr AKER-PSI 2500 2000 Pann_corr AKER- PSI 1500 1000 500 0 30/11/2012 12:00 30/11/2012 14:00 30/11/2012 16:00 30/11/2012 18:00 Time Test Redressed shear sub and rerun(r/s) Sheared OK Pumping at max rate of Ptbg_corr 12 l/min(109 AKER-PSI b/d) to test restrictor Pann_corr AKER- Good correspondence theory vs actual PSI 4000 3500 3000 2500 2000
PRESS(psig) Krest,DP Matching Restrictor Performance 30/11/12-Test4(R/S) 1000 900 800 700 Ptbg_corr AKER-PSIG Pann_corr AKER-PSIG DP(psi) Krest 40 35 30 600 25 500 20 400 300 200 100 15 10 5 0 30/11/2012 16:48 30/11/2012 17:06 30/11/2012 17:24 Time 0 Setup : R/S Krest=20.8 via matching(cf catalogue value of 20)
Vary Ptbg