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Advanced Cementing toIncrease Well Productivity
November 12 14, 2008
The University of OklahomaNorman, Oklahoma
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Fundamentals ofCementing Technology
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Primary Cement Job
Oil/gas well cementing operation is theprocess of mixing and displacing a cement
slurry down the casing and up the annular
space behind the casing where it is allowed
to set, thus bonding the casing to theformation.
No other operation in the drilling and
completion process plays as important a rolein the producing life of a well as does a
successful primary cementing job.
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Implications of Cementing on WellPerformance
Zonal isolation is surely the most important
function of the cement sheath.
It is critical that no shortchanging in the
quality of the cement and the cement/casing
or cement/formation bonds can ever bejustified
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Implications of Cementing on WellPerformance
Causes of improper zonal isolation are
micro-channeling and gas migration.
Both causes large effective permeability
behind the casing and through the cement
sheath.
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Implications of Cementing on WellPerformance
Gas migration can open additional flow
paths, in the form of interconnected porositythrough the setting cement.
The resulting set cement suffers from an
unnaturally high permeability, because ofthis earlier disruption, and may not provide
a competent seal.
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Implications of Cementing on WellPerformance
Flow paths may also take the form of
microannulus at the pie/cement orcement/formation interfaces.
These paths, and their effective width, then
corresponds to a certain permeability that ishigher than the permeability of the
undisturbed set cement.
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Zonal Isolation This figure shows a
typical completion. In the
middle is a perforated
interval with two otherpotentially producing
intervals.
The simple equation of
flow for oil is given as
Primary Cement Job
sr
rB
PPkhQ
w
e
wfe
ln2.141
)(
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Zonal Isolation Crossflow from the
adjoining formations into the
producing layer may occur
at the cement sheath. UsingDarcy equation, the flow
rate through the cement
sheath is as follows
Primary Cement Job
1
22*
2.141 LB
PPrrkQ
wfecasw
cem
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2008 Zonal Isolation
This equation provides the oilflow rate that can be either
through the cement sheath
matrix permeability, through a
microannulus formed within the
sheath, or through amicroannulus formed between
the cement/casing or
cement/formation
Primary Cement Job
1
22*
2.141 LB
PPrrkQ
wfecasw
cem
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Index of Zonal Isolation (IZI) Index of Zonal Isolation is the ratio of the
flow rate into the well from the intended
formation to the flow rate through thecement. It is given by the following equation
Primary Cement Job
s
r
rrrk
Lkh
q
qIZI
w
e
casw
cemln22*
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2008 Permeability for Flow Through a Slot
Primary Cement Job
Since permeability has the dimension of [L2], the K for
the flow through a slot is given by the following
equation
K = w2/12 where w is in inches
K = 5.4 x 1010w2 (md)
The above equation implies that while a large matrix
perm within the cement sheath is unlikely, a largeequivalent perm can result from a relatively small
microannulus width. Note: a microannulus width would
probably not be detectable by bond logging.
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An oil-well set cement becomes very ductile
under low effective confining pressures.
However, under high pressure required forfracturing (a tensile failure mechanism), a cement
sheath is potentially subjected to two phenomena:
Fracture propagation within the cement sheath
Dislodging of the cement sheath from the pipe by
overcoming the cement/pipe bond.
Cement/Pipe Bond and Fracturing
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Primary Cement Job
The ability of a well to achieve its production
potential is influenced most by the degree of
zonal isolation achieved during completion bycementing
The quality of the cement sheath is in turn the
most important factor influencing zonal isolation.
Hence, the cementation of a well should be of
critical importance to every operator.
Conclusions
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Plug
ContainerProduction
Casing
Bottom
Plug
Reciprocating
Cleaner
Centralizer
Top
Plug
Float
Collar
Float
Shoe
Displacement
Fluid
Casing Accessories
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2008 High Wiping Efficiency Plugs
Deep cup design
Greater wiper contact
area
Greater wear
resistance
750 psi shear disk in
bottom plug
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Primary Cementing Techniques
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Nov
2008 There are two systems: bulk and manual handling
systems
Bulk system
Facilitates storage and dry mixing of cement
Cement is transported in trucks (onshore) or
boats (swamp or offshore)
Decreases mixing time and better cementing job
Manual system
Good for small cementing jobs such as plug-back
and squeeze
Field Handling of Cement
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Cementing Best Practices
Typical through-
drillpipe stab-in
cementing
technique
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Cementing Best Practices
Top-up cementing.Used when lost
circulation occurs
during large casing
slurry displacement
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Cementing Best Practices
Typical one-stageprimary
cementing job on
a surface casing
string
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Cementing Best Practices
Two-stagecementing of an
intermediate
casing string
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ES Stage Cementer Job Sequence
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Cementing Best Practices
Liner cementing
Liner setting tool and
hanger assembly
C
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Cementing Best Practices
Flow rate
target turbulent flow Pipe Centralization (70% Stand-off)
Optimum Hole Size
Circulation to Condition Mud
Address Gas Flow Issues
Good Mud Properties (PV
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Cementing Best Practices
Good Mud Fluid Loss Properties (API=7)
Top & Bottom Cementing Plugs are used
Pipe movement (Reciprocation & Rotation) Use Spacer Volume for 10 min Contact Time
Place Weighted Viscous Pill in Rat Hole
Minimum Shoe Joint Length of 1 Casing Joint
C ti P bl
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Unsuccessful cement jobs lead to water orgas contamination or migration during the
well life
Remedial work is time consuming and
expensive and hence must be avoided.
Cementing Problems
C ti P bl d C
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Problems and causes: Communication between zones and micro-
channeling due to poor mud, inadequate
(laminar) displacement, poor centralization
Flash cement setting due to dehydration,
high temperature
Mechanical failures due to porous cement,
poor cement design
Cementing Problems and Causes
C t E l ti
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Nov
2008 1. Evaluating the cement job is important sothat (a) problems can be identified quicklyand (b) to avoid if possible a futurerecurrence of the problem.
2. One important way that the cement job isevaluated is by following the correct qualitycontrol and data recording procedures.
3. These can be divided up into three: before,during and after the job.
Cement Evaluation
C t E l ti P i t J b
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Cement Evaluation Prior to Job
1. Samples taken of cement & additives.
2. Samples tested in the lab to meet
specifications (pilot testing)
3. Program discussed and agreed by all
concerned.
C t E l ti D i J b
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1. Samples taken of mixed slurry andspacers during the job.
2. All the main job parameters recorded
(pressures, flow rates, densities, event
log).
Cement Evaluation During Job
C t E l ti Aft J b
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1. Compare planned vs. actual job,analyze differences.
2. Ensure all valid comments are captured
in the end of job report.
3. Simulate job to analyze the root causes
of problems.
Cement Evaluation After Job
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Nov
2008 Techniques used are:cement top, temperature log,
cement bond log (CBL) and variable density log(VDL)
Temperature log must be run within 12 hrs of job
CBL and VDL most common methods
Both are acoustic (sound) logs
Compare to VDL, CBL cannot easily identifysmall channels and may be used with
segmented bond log (SBL)
Cement Evaluation Techniques
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Leak-Off Test
Leak-off test also called formationstrength or integrity test serves as a
pressure test on the primary
cementing behind the casing shoe.
The general procedures for
pressure testing below the casing
seat follows:
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Drill 10 - 20-ft of hole belowthe casing seat.
Pump mud slowly at a rate
of 1/4 -1/2-barrel per min
using the cementing
pumping unit (do not use
the rig pump).
Record pressure and rateand cumulative volume of
mud pumped.
Procedure for Leak-Off Test
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Leak-Off Test
The max. pressure depends on theoperators objectives.
For example if the operator needs to
assure a subsequent mud weight will notcause failure at the casing shoe or needs
to know the maximum leak-off and rupture
pressure.
C
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2008 Objective - to repair faulty primary job or abandon non-
productive or depleted zones, or shut-off troublesomezones
Above objectives achieved by cement squeeze job and
there are many depending on the pressure Poor boy squeeze or squeeze without a packer
Squeeze with packer and various types: hesitation
squeeze and circulation squeeze In general the squeeze pressure is greater than the
formation pressure but less than fracture pressure
Remedial Cementing Techniques
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SQUEEZE TECHNIQUES
S T h i
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Squeeze Techniques
Pressure to Squeeze
High Pressure Squeeze
Low Pressure Squeeze
Pumping Techniques
Hesitation Squeeze
Running or Walking Squeeze
Placement Techniques
Squeeze Packer
Bradenhead (Including Coiled Tubing)
Hi h P S
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High Pressure Squeeze
Surface Pressure+
Displacement Fluid Hydrostatic
+
Cement Slurry Hydrostatic
=
Total Bottom Hole Pressure
Greater Than
Formation Fracture Pressure
High Pressure Squeeze
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High Pressure Squeeze
Low Pressure Squeeze
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Low Pressure Squeeze
Surface Pressure
+
Displacement Fluid
Hydrostatic
+Cement Slurry Hydrostatic
=
Total Bottom Hole PressureLess Than
Formation Fracture Pressure
Low Pressure Squeeze
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Low Pressure Squeeze
Squeeze Techniques
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Squeeze Techniques
Pressure to Squeeze
High Pressure Squeeze
Low Pressure Squeeze
Pumping Techniques
Hesitation Squeeze
Running or Walking Squeeze
Placement Techniques
Squeeze Packer
Bradenhead (Including Coiled Tubing)
Hesitation Squeeze
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Hesitation Squeeze
Running/Walking Squeeze
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Running/Walking Squeeze
Squeeze Techniques
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Squeeze Techniques
Pressure to Squeeze
High Pressure Squeeze
Low Pressure Squeeze
Pumping Techniques
Hesitation Squeeze
Running or Walking Squeeze
Placement Techniques
Squeeze Packer
Bradenhead (Including Coiled Tubing)
Squeeze Packer Method
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Squeeze Packer Method
Retrievable or
drillable squeeze
packer set above
injection point
Isolates casing abovepacker from squeeze
pressure
Higher squeeze
pressure possible
Annular pressure can
be applied
Bradenhead Method
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Bradenhead Method Spot cement across squeeze
interval
Pull workstring above cementtop
Close BOP/Bradenhead &reverse tubing clean
Apply squeeze pressureDisadvantages
Casing exposed to squeezepressure
Limited squeeze pressureAdvantages
Cost reduction
Wash cement out of casing
Coiled Tubing Method
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CHOKE
+PSI
CEMENT
Coiled Tubing Method
It is a form ofBradenhead
Inside ProductionTubing
Higher PressurePossible
Improved controlof slurry placement
Primary Cement Job
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Primary Cement Job
Bannister, C. E. et al, SPE 11982, 1983
Cheung, P.R. and Beiruite, R. M., JPT (June
1985)
Garcia, J. A. and Clark, C. R. SPE 5701, 1976
Stewart, R.B. and Schouten, F. C., (SPEDEMarch 1988)
References
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Appendix
M j P ti f C t Sl
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Nov
2008 1. Density - ranges between 14.8 and 16.4 ppg
2. Thickening time pumpability time - affected
by pressure and temperature; can be
controlled with accelerators or retarders
3. Water loss (wL) - high wL causes flash set
4. Compressive strength - 500-psi is all that is
needed to continue drilling operation
5. Permeability - almost impermeable
6. Stability - use cement with 3% C3A
Major Properties of Cement Slurry
Special Cements & Cement Additives
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Special purposes cements are Pozmix, resin, latex,
expanding, diesel-bentonite
Pozmix - mixture of regular cement & pozzoloan material
(50:50 or 70:30) and used as fill-up or preflush
Low cost, light weight, long thickening time
Cement additives
Major additives are accelerators (CaCl2), retarders Minor additives are agents to control density,
thickening time, water-loss, and friction reducer
Special Cements & Cement Additives