1. fundamentals of cementing technology-new

7/22/2019 1. Fundamentals of Cementing Technology-New

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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

Primary Cement Job


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Causes of improper zonal isolation are

micro-channeling and gas migration.

Both causes large effective permeability

behind the casing and through the cement

sheath.

Primary Cement Job


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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.

Primary Cement Job


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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.

Primary Cement Job


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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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Nov

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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Primary Cement Job

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 Cement Job

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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Top-up cementing.Used when lost

circulation occurs

during large casing

slurry displacement


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Typical one-stageprimary

cementing job on

a surface casing

string


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Two-stagecementing of an

intermediate

casing string


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ES Stage Cementer Job Sequence


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Liner cementing

Liner setting tool and

hanger assembly

C


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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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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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Surface Pressure+

Displacement Fluid Hydrostatic

+

Cement Slurry Hydrostatic

=

Total Bottom Hole Pressure

Greater Than

Formation Fracture Pressure



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Surface Pressure

+

Displacement Fluid

Hydrostatic

+Cement Slurry Hydrostatic

=

Total Bottom Hole PressureLess Than

Formation Fracture Pressure



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Squeeze Techniques


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Squeeze Techniques

Pressure to Squeeze



Pumping Techniques

Hesitation Squeeze



Squeeze Packer


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



Pumping Techniques

Hesitation Squeeze



Squeeze Packer


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

1. fundamentals of cementing technology-new

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