Cementing in oil_From book.docx
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Cementing in oil & gas wells 1. Functions of cement 2. Cement slurry chemistry & use of addict ive 3. Displacement mechanics & rheology consideration 4. Primary cementing 5. Liner cementing; techniques, problem, how to evaluate 6. Special cementing 7. Job evaluation Function of cement Supporting the formation and protecting the casing from various kind of damages; fault shear, perforating deformation & joint loss while drilling Primary cementing used: o To support the axial load. Factor affecting axial load are ↑ cement strength ↓cement strength Casing collar Low water/cement ratio Radial loads imposed on cement and casing by formation increased friction between pipe-cement Roughness of exterioe casing surface ( rust or special resin-sand coatings) Oil based mud wetting Mill varnish on the exterior of the casing Cement contamination by mud Raw cement characteristics: fineness of grind) Displacemnet mechanics & efficiency Pressure/temperature o Zonal isolation to support borehole o Seal intended production/injection intervals from overlaying & underlying permeable sections o Protect the casing from damage or failure o Support borehole Basic cement properties Soundness = measure of the expensive properties of a cement, fineness is the particle size to which a clinker is ground. Will affect: o setting time o early strength o water addition API cement classification o 9 classes Depth rating based on o Thickening time = time required to r each the approximate upper limit of pumpable consistency
Transcript of Cementing in oil_From book.docx
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Cementing in oil & gas wells
1. Functions of cement
2. Cement slurry chemistry & use of addictive
3. Displacement mechanics & rheology consideration
4. Primary cementing
5. Liner cementing; techniques, problem, how to evaluate
6. Special cementing
7. Job evaluation
Function of cement
Supporting the formation and protecting the casing from various kind of damages; fault
shear, perforating deformation & joint loss while drilling
Primary cementing used:
o To support the axial load. Factor affecting axial load are↑ cement strength ↓cement strength
Casing collar
Low water/cement ratio
Radial loads imposed on cement and
casing by formation increased
friction between pipe-cement
Roughness of exterioe casing surface
( rust or special resin-sand coatings)
Oil based mud wetting
Mill varnish on the exterior of the
casing
Cement contamination by mud
Raw cement characteristics: fineness of grind)
Displacemnet mechanics & efficiency
Pressure/temperature
o Zonal isolation to support borehole
o Seal intended production/injection intervals from overlaying & underlying
permeable sections
o Protect the casing from damage or failure
o Support borehole
Basic cement properties
Soundness = measure of the expensive properties of a cement,
fineness is the particle size to which a clinker is ground. Will affect:
o setting time
o early strength
o water addition
API cement classification
o 9 classes
Depth rating based on
o Thickening time = time required to reach the approximate upper limit of pumpable
consistency
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o Minimum compressive strength development
Specified after 8 hrs or 24 hours curing times for samples
o Depth rating extended if temp gradient is low and vice versa (gradient high, depth
rating lower)
o Water content differs upon
o Finess of grind
o Cement class
o Free water content is usually higher at increased temperature due to thinning. Free
water can minimized by:
Limiting the amount of mix water
Add bentonite in small quantities
Selecting & control quantity of other slurry
o Yield cost calculation
Cement additives
Thickening time- Accelerator: Calcium chloride, sodium silicate, sodium chloride, seawater,
gypsum ammonium chloride
Thickening time - Retarder: calcium lignosulfonate, organic blends, carboxy methyl hydroxyl
ethyl cellulose, borax, sdium chloride, fluid loss agents
Slurry density reducer: Bentonite, sodium meta-silicate, pozzolan etc.
o Low density frequently desired to decrease likelihood of breaking down the
formation & lost circulation
o Less cost/ cuft – as yield /sack increase
o Density decrease
o Strength decrease
Bentonite
o “filler” type cement
o Reduces API fluid loss
o Permeable and les sulphate resistance
Friction reduction: alkyl aryl sulfonate,salt & organic acid
o Tend to cause settling & excessive free water
Fluid loss (filtrate)
o Preventing gas leakage
o In squeeze cement
o Maintain pumpability in primary casing & liner casing
Lost circulation
o Drilling fluids & cement usually lost to either natural or induced formation fractures
o Treatment is during drilling by add bridging material in higher concentration
o Blocky granular material: walnuts, shell, gilstone
o Fibrous material: nylon fibers
Cement plug
o Quick gelling
o Low density (high yield)
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o Rapid set
o Fluid loss (filtrate)
o Cement plug drillout rate
Properties of set cement
Function of P & T
Strength retrogression (loss strength)
o Affecting: Temp, pressure composition & time
o Strength at downhole condition
Strength increase & more or less comparable to rock at that condition
o Expansion – suggestion for mitigation is by eliminating microannulus at the
cement/casing surface
Special cement
Salt cement
High temperature cement- calcium aluminate cement
Permafrost cement: Gypsum-Portland cement
Flow, displacement principles
2 forces in fluid displacement & these determine the flow regime & pressure drop:
o Differential pressure
o Cement on mud (fluid on fluid) drag forces
resisting drag forces influences by:
o gel strength
o viscosity
o borehole-casing distance
Newtonian (water) & non-newtonian (cement)
How to improve mud displacement
o Centering pipe in the borehole
o Rotating vs. reciprocal casing movement & the effects
o Pressure velocity surges
o Pipe moving technique
o Standoff ringso Scratcher
o Mud condition
