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30 Cards in this Set
- Front
- Back
What is Gas Migration?
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Gas Migration is the invasion of formation fluids into the annulus, due to a pressure imbalance at the formation face ( loss of Hydrostatic pressure)
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What are the Consequences of gas migration?
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Poor zone isolation, Blow out, Repair required, Environmental damage
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3 Paths for gas migration.
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Channel, Invasion during setting cement, Set cement failure
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Cause of a channel
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Inadequate mud removal, excessive free fluid in deviated well
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Cause of invasion
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Fluid-loss during and after placement
Chemical shrinkage Gel strength development Free Fluid Highly Permeable Slurry |
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4 Phases of setting cement
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liquid, early gelation, hydration, set
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CHP
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Critical Hydration Period
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PDA
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Pressure Decline Limit
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Dynamic Fluid Loss
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Increased rheology
Change in other slurry properties |
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Static Fluid Loss
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Loss of overbalance
Promote early gelation Bridging Accelerated hydration kinetics Recommended fluid loss: < 50 mL/30 min |
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Cause of set cement failure
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Down hole stresses
Change in Temperature Change in Pressure Poor Interfacial Bonding (Microannulus) High Shrinkage |
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Essential for Successful Cementing of Gas Wells
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mud removal, cement slurry design, set cement mechanical properties, cement hydration, fluid density control
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Essential for good mud removal
and schlumberger's slurry solution. |
Centralization
Conditioning of mud to follow the Density and viscosity hierarchy Pipe movement during placement Displacement regime and rate Spacers/Pre-flushes: WELLCLEAN II |
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Ideal Slurry Properties that minimize the gas migration during cement setting and schlumberger's solution
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During Placement:
Appropriate Rheology for good mud/spacer removal Zero Free Fluid (Inclined Section) Fluid Loss less than 50 ml/30min After Placement: Short transition time from 100 to 500 lb/100ft2 Low Fluid Loss to avoid early Gelation Pore throat plugging materials GASBLOK |
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Cement that can withstand cyclical stress variations avoiding set mechanical failure.
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Flexstone
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Physical means of preventing gas migration
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Annular Pressure
Multistage Cementing Reduced cement column length ECP / CFP Casing seal ring Increase mud density |
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Cement solutions to gas flow
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Compressible Cements
Thixotropic cements Right angle set cements Surfactant cements Expansive cements Microsilica Cements Impermeable cements |
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Slurry property optimization to prevent gas migration
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Free water
Fluid loss control Gelation control Thickening time Hydration kinetics Slurry density (overbalance) Special properties |
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API testing for testing and handling
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10
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Recomended lab tests for gas migration
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Thickening Time
Compressive Strength Fluid Loss Rheology Slurry Stability Free Fluid & Sedimentation or Settling Static Gel Strength Development Gas Flow Test |
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What is the lab equipment used to evaluate gas migration? What does it test for?
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Vane Rheometer, Measures true static gel strength
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Gas flow analyzer
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?
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Slurry properties of GASBLOK
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Well dispersed, thin, non gelling slurry
Excellent Fluid loss control Film is Impermeable to gas during the liquid to solid transition period |
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GasBlok density range
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8-24 ppg
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Temperature range for gasblok
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<375F
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Gasblok D codes low med high temp
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D500, 600, 700
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GASBLOK* Slurries Design Considerations
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<50mL/30 min fluid loss
Dispersed to minimize gel strength development (<35 lb/100 ft2 ) Rheology for displacement (ELF) Slurry stability Short transition times (Bc) Ty <10-15 lb/100 ft2 |
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GASBLOK* Concentration depends upon two factors
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BHST & SVF (Soild Volume Fraction)
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Stabalizer for gasblok 700,600
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D701,D135
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D600G > 2 gal/sk =
D600G < 2 gal/sk = |
gasblok system , fluidloss system
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