Oil Well cementing
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Transcript of Oil Well cementing
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WELL CEMENTING
Well CementingIntroduction to Drilling
Learning Objectives
Explain the main reasons for cementing wells Describe slurry properties that must be controlled Describe slurry thickening time Explain API classes of cement commonly used Explain various cement additives and their function Describe methods of evaluating a cement job
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Well CementingIntroduction to Drilling
Reasons for cementing
Achieve Zonal Isolation
Provide Casing Support
Protect Casing
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Well CementingIntroduction to Drilling
Casing
Casing Support
Casing bonded withformation rockssupports its ownweight andload of surfaceequipment that ismounted on it
Cement
Zonal Isolation
Properly cementedcasing preventscommunicationbetween zonesof differingcharacteristics toenable drillingdeeper
Low pressureloss zone
Higherpressurepermeablezone
Reasons for cementing
Casing ProtectionSome formations contain fluids that can attack casing
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Well CementingIntroduction to Drilling5
Slurry Design
Density Solids/water ratio
Thickening Time Fluid Loss Free Water Rheology Compressive Strength
Future? Tensile Strength Young’s Modulus Poisson’s Ratio
Well CementingIntroduction to Drilling
Slurry Density Hierarchy
Spacer at least one-half ppg heavier than mud
Lead slurry at least one-half ppg heavier than the spacer
Tail slurry always heavier than the lead slurry
Example
Mud to surface12.0 ppg
Spacer12.5 ppg
Lead Slurry13.0 ppg
Tail Slurry15.8 ppg
Casing Shoe
** When pumping “normal” circulation, not reverse circulation
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Well CementingIntroduction to Drilling
Pressurized Mud Balance
Eliminates the effect of air in the cement slurry
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Well CementingIntroduction to Drilling
Slurry Thickening Time
The time available to place a slurry before it becomes too thick to pump.
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Well CementingIntroduction to Drilling
Thickening Time Test
Consistometers are used to measure the thickening trendof a slurry under simulated conditions of temperature and pressure
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Well CementingIntroduction to Drilling
Consistometer Slurry Cup
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Well CementingIntroduction to Drilling
Thickening Time Requirements
The thickening time should equal job time (mix, pump, displace) plus a reasonable safety factor such as 1 to 2 hours.
A slurry exhibiting a “right-angle set” rather than a “gel set”, is generally preferred. In actual well, slurry is static when set occurs, not
continuously sheared until set as in consistometer.
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Well CementingIntroduction to Drilling
API Classification for Oil Well Cements
Class A: Ordinary cement intended for use from surface to 6,000 ft.Class B: Sulfate resistant, intended for use from surface to 6,000 ft.Class C: High early strength, intended for use from surface to 6,000 ft.Class D: Intended for use from 6,000 ft. to 10,000 ft.Class E: Intended for use from 10,000 ft. to 14,000 ft.Class F: Intended for use from 10,000 ft. to 16,000 ft
Class G & H: Intended for use as a basic cement from surface to8,000 ft. as manufactured, or can be used for a wide range of welldepths and temperatures with suitable additives. Class G iscommonly used in California and Rocky Mountains and overseas, and Class H in Oklahoma and Texas as well as the Gulf Coast.
Manufacture and testing conforms to API Specification 10 12
Well CementingIntroduction to Drilling
Cement Slurry Additives
ACCELERATORS: To shorten the thickening time
RETARDERS: To lengthen the thickening time
EXTENDERS: To lighten slurry density
DENSIFIERS: To increase slurry density
FLUID LOSS CONTROL: To reduce loss of filtrate into
formation
FRICTION REDUCERS: To improve flow properties
HIGH TEMPERATURE: To prevent the cement from losing
strength under high temperature conditions over time
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Well CementingIntroduction to Drilling
Conventional Primary Cementing
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Well CementingIntroduction to Drilling
Good Cementing Practices
Casing Movement Centralizers Scratchers and Wipers Casing Wiper Plugs Two Floats Adequate Shoe Joint
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Well CementingIntroduction to Drilling
Centralizers
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Well CementingIntroduction to Drilling
Centralizers
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Well CementingIntroduction to Drilling
Float failure means pressure must be held on the casing until the cement sets. Can cause micro-annuli
Use a float shoe and a float collar for redundancy.
FloatCollar
FloatShoe
Casing
Two Floats
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Well CementingIntroduction to Drilling
The length of casing between the float collar and float shoe. Also called the “shoe track”
The purpose of the shoe joint to to contain contaminated or lightweight cement
Use at least two joints - more in larger casing
ShoeTrack± 80’
Adequate shoe joint
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Well CementingIntroduction to Drilling
Evaluating the Job
Temperature Survey Leak-off Test Bond Logs
Sonic Tools: CBL, CBT, SBT etc.Ultrasonic Tools: CET, PET, USIT
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