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30 Cards in this Set

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