Mud Removal- NExT

Mud Removal

Objectives of Primary Cementation  Provide complete isolation of zones – (Hydraulic Bond)

 To support the casing – (Shear Bond)

 Protect casing string

2

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Mud Removal & Cement Isolation The Most and First important aspect of cement job A 3-step process before cementing 1. Hole cleaning + Conditioning the drilling fluid 2. Displace the drilling fluid from the annulus &

Replace the mud by cement slurry

3. Cement is setting, properties and Isolation should not be affected by contamination (mud..) Avoid mud channelling 3

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Efficient Cement Placement Check for efficient mud removal to prevent mud channeling and to ensure zonal isolation  Optimize  casing centralization  fluid properties :mud – spacer – slurry(ies)  pumping rate

 Select Displacement Regime  Turbulent Flow  Efficient Laminar Flow

 Select Preflushes & Spacers  Ensure  Flat interfaces between fluids  Avoid static mud  Wall cleaning 4

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Bulk mud removal

The Flow of Fluids V2

A

F

r A A

V1

Shear Stress

τ

Shear Rate

γ· =

Apparent Viscosity

Oilfield units

 dv  v 2  v1    dr  r

 

shearstress shearrate

 lbf sec   100ft2   

1 Poise = 100 centiPoise = 0.2089 lbf.sec/100ft2 - 1 Pa.s = 2.089 lbf.sec/100ft2 6

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Flow Curves - Fluids Classification NEWTONIAN

or

NON-NEWTONIAN Shear Stress

Shear Stress

LAMINAR FLOW

TT R R A A N N SS II TT II O O N N

ZZ O O N N E E

TURBULENT FLOW

Bingham Plastic TT R R A A N N SS II TT II O O N N

Power Law ZZ O O N N E E

Shear rate

Shear rate

Power law & Herschel Bulkley fluids : shear thinning fluids Drilling and Cementing fluids : HB behaviour (API 13D:2006 – SPE98743) 7

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Herschel Bulkley

Flow Models  For mathematical representation, following models are used: 1. Newtonian model

t =  g·

2. Bingham plastic model

· t = ty + p g

ty BinghamYield p plastic viscosity 3. Power Law Model

t =K

· gn

 = p + ty / =K

· g

g· n-1

(Pseudo plastic model)

K consitency index (lbf.s^n/100ft²) n flow behaviour index (dimensionless) 4. Herschel Bulkley model

·n t = ty + K g

(Pseudo plastic model with a Yield) 8

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=

ty

·n Kg

+

g·

Fluid Flow Property Measurements  PROPERTIES MEASURED:  Shear stress  Shear rate  Gel strength

 EQUIPMENT USED: “Fann” 35 (12 speed)  Ramp up then Ramp down  Readings @ 3, 6, 30, 60, 100, 200, 300 rpm.  3 and 6 rpm not used for Bingham model .

 Rotational speed is proportional to shear rate  With R1B1 combination 

100 rpm = 170 sec-1

Bob deflection is proportional to shear stress t   * SCF  With R1-B1 - Spring 1 , spring factor SCF =1.065

9

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Flow of Fluids In fluid mechanics two types of flow are defined:

1.

Laminar Flow

Turbulent Flow

2.

 Plug flow is sub-laminar flow V=0 V max

DIRECTION OF FLOW

V=0

•

Sliding motion

• Velocity at the wall = 0 •

Velocity is maximum at the centre

• •

Swirling motion Average particle velocity is uniform throughout the pipe

Vmax = 2 V V = Average particle velocity

Laminar and Turbulent Flow regimes are found anywhere (pipe, concentric or eccentric annuli) 10

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Flow in Eccentric Annuli

Always

Vw

11

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>

Vn

Wall Shear Stress Mud, cement slurry : fluids with a yield (Herchel Bulckley, Bingham) WSS

0

WSS =

D DP 4 DL

In Pipe If WSS >

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4

DL

In Concentric Annulus

ty of displaced fluid in narrow gap,

then flow occurs. 12

WSS =

(Dout - dint) DP

Effect of Casing Stand Off  The Effect of the Casing Stand-Off on the Annular Flow is Qualitatively Equivalent to the Following Flow Pattern Q

D2

D1 L

DP DL V2

V1

Q 13

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Newtonian Fluid of Viscosity µ Density ρ In LAMINAR FLOW :

 Velocity 

If



V V

D

2

2

D D



2

2 2

1

1



2D

Reynolds Number 2

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 V 2 D2   



Re

14

Pipe stand off : 67%

1

Re

2



8 Re  for 1

4V 2D 1



67% 

1



 8V 1 D1 

Laminar Flow in Eccentric Annulus Non-parallel plate model Ri/Ro = 0.8 1000 500

R H

Vwide /Vnarrow

RC 100

50

W % Stand-off =

w RH - RC

X 100

10 5

n = 1.0 n = 0.5 n = 0.2

1 0

10

20

30

40

50

Stand-off % 15

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60

70

80

90

100

Newtonian Fluid of Viscosity µ Density ρ In TURBULENT FLOW 

Velocity

If





2

2D

1

V2 =1 .64 V1



V V

2 1

for 67% stand off

Reynolds Number Re

2

 16

D



0,714

 D2      D1 

 1,64V 1 2D1  3,28V 1 D1  V 2 D2      

Re 2 = 3.28 Re 1 for 67% Stand off

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Turbulent Flow in Eccentric Annulus 1000

R

500

H

Vwide / Vnarrow

RC

100 W

50 % Stand-off =

RH - RC n = 1.0 n = 0.5 n = 0.2

10 5

1 0

10

20

30

40

50

60

API Stand - Off (%) 17

w

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70

80

90

100

X 100

Eccentric annulus : Flow rates & regimes 

Laminar Flow

NO

Velocity Profile (Sliding motion) 

YES

Turbulent Flow Velocity Profile

(Swirling motion)

HB Fluid 18

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NO

YES

Flow Regime Comparison Laminar

Turbulent

Centered Annulus

19

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Turbulent

Eccentered Annulus

Turbulent Flow Reynold’s number correction Correction factor to apply to centered annulus NRe to provide turbulence in the narrow side

RH

RC W % STO =

20

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W X 100 RH - RC

Turbulent Flow Guidelines The best flow regime for displacement : Cementing fluids in turbulent flow all around eccentered pipe  Function of standoff, annular flow rate, hole size  Contact time 10 min across zones of interest – Minimum contact time of 6 minutes – Must take u-tubing into account – Maximize by increased volume or decreased rate

 For chemical wash Allows for contamination – consider a viscosity of 5 cp

 BUT ! Due to differential density, interfaces are not stable in annulus : Preflushes (Spacer/wash) density should be close and higher than mud density

turbulent flow 21

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ρ(2) displacing  ρ(1) mud

Turbulent Flow Applications Turbulent flow is generally achievable with difficulties :  To get a flow turbulent in the narrow size need to take in account

– Annular size – Casing eccentration (stand off) – Rheology of cementing fluids : preflushes (spacer, washes), slurries

Turbulence in the narrow side could results in :  High rate, not compatible with pumping equipment  Well control : High friction pressure and risk of losses  Volume of preflushes/spacer : equipment, cost,…

Only for small casing diameters (< 7’’) in gauge hole with good centralization (> 80%) in a small annular gap. 22

 If Turbulent flow not possible,to achieve a flat interface between fluids : Use Effective Laminar Flow Conditions Copyright © 2001 – 2013, Schlumberger. All rights reserved

Efficient Laminar Flow  Alternative flow to provide a flat displacement front  Four (+ 1) rules must be satisfied: – Density differential – Friction pressure hierarchy – Minimum pressure gradient • Mud in motion • No Mud on the Wall

– Differential velocity criterion – Turbulence to be avoided 23

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Density Hierarchy Density of the displacing fluid is greater than the density of the fluid being displaced.

D ρ + 10% spacer > 1.1 (mud) cement > 1.1 (spacer)

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Friction Pressure Hierarchy  Promotes a flat stable interface with less possibility of viscous fingering

 Friction pressure of displacing fluid must be greater than friction pressure of fluid being displaced.

D DP DL

25

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DP DL

> 1.2 displacing

+ 20% DP DL displaced

Minimum Pressure Gradient To get a flow of the fluid (mud) all around the eccentric annulus Wall Shear Stress must exceed the yield stress of the fluid on the narrow side:  Function of standoff  Applies only to fluids with a yield point

 Translates into a lower limit for flow rate Laminar Flow

Approximated from: DP DL

No Flow

4ty

>

STO (DOH-Dc)

Q mini = Mud circulation rate above MPG 26

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WSS

> ty

MPG and Mud On the Wall 

Minimum Pressure Gradient for the mud  Mud in motion (eccentered annulus size E) if DP WSS mud = (1/4) (E) > Gel mud DL

x

E

t

tMax (WSS) v

0

L



To displace Mud by Spacer and Spacer by Slurry: Avoid Stable layer of mud (or Spacer) left on casing and formation  Wall shear stress (WSS spacer)

if WSS Spacer>ty,mud => no mud film

if WSS spacer Mud On the Wall - Looks” like a channel – But thicker on the formation – Dehydration at the formation face 27

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Friction Pressure vs. Rate 15.0

Annulus ID : 9.625 in - OD : 15.000 in

0.0

Friction Pressure (psi/1000ft) 5.0 10.0

Mud Tail Slurry Spacer

0.0

2.0

4.0 Flow Rate (bbl/min)

29

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6.0

Calculating Annular Shear Rate In concentric annulus

.

g

(2471) Q (Do - Di)2 (Do + Di)

where: . g  Annular Shear Rate Q = Rate (BPM) Do = Outer Diameter (in.) Di = Inner Diameter (in.)

Fann 35 Speed (RPM) 300

Shear Rate -1 (sec ) 511

200

340

100

170

60

102

30

51

6

10

3

5

Annular shear rate should be compared to Fann measurements 30

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Differential Velocity Criterion In mud channel situation to prevent channel growth : Displacing fluid does not flow faster on the wide side than the narrow side of the annulus  Function of standoff and density differential  Imposes a maximum annular flow rate V2 narrow side > V1wide side

Q

dP/dz

D2

D1

V1

L

V2 < V1

DP V1

V2 > V1

V2

DL Q

V2

Velocity

DP (displacing narrow side) –DP (displaced wide side)+ D .g cos  > 0 31

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Channeling Fluids will naturally climb faster on the wide (upper) side  Density drives displacing fluid to the narrow side – Density hierarchy and differential velocity – For non-newtonian fluids additional viscosity effects s

c > s

 Horizontal wells – Axial vs. azimuthal – Dynamic vs. static channeling

 Differential velocity vs. MPG – Static channel depends on ty 32

MPG

Diff Vel.

Mud On the Wall

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Effective Laminar Flow Minimum Annular Rate

Maximum Annular Rate

 MPG Exceeded

 Turbulence of displacing

 Beginning of 20% Pfriction

 End of 20% Pfriction

 Arbitrary limit of 1 BPM

 Arbitrary limit of 40 BPM

 Beginning of stable front

 End of stable front

Assume deviation even in “vertical” wells 0.02 to 0.04°/100 ft vertical deviation 0.05°/100 ft azimuthal bearing change

33

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Casing Stand Off For Mud removal efficiency

Use casing Centralisers

 Objective SO > 80% ( minimum 75%) RH

Di Do

RC % Stand-off =

w RH - RC

Vnar

X 100 W

S.O % = 100 W/ (RH - RC) 34

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Vwide

Always,

Vnarrow < Vwide

Flow improvement in eccentric annulus Casing movement : Reciprocation & Rotation ?

35

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Reciprocation  Movement of casing up and down during the job  Must be done from the start of circulation to end displacement  20 to 40 feet stroke

 1 to 5 minutes per cycle

 Needs scratchers

Poor Stand Off

(cable type) to be effective

Slurry

 Casing may become stuck

Slurry

 Excessive pull and buckling

Static Mud

swab and surge pressures

Slurry

 Possible excessive

during movement

 Cannot be the only method of mud removal 36

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Improved Stand Off

Rotation  Circular movement of pipe  Must be done from the start of circulation to end displacement  10 to 30 rpm  Scratchers help efficiency  Needs special rotary

Flowing Cement

cement heads and power swivels

 Torque must be very closely monitored

Gelled Mud

 Cannot be the only method

of mud removal  More effective than reciprocation 37

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Casing Stationary Rotation Started Mud Almost Removed

Spacers & Washes Cementing Plugs

38

Contamination : Fluids Incompatibility Results In:  Detrimental Interface Reactions  High Rheological Properties – Very high viscosities and high gel strengths

 Change in Cement Slurry Properties – Thickening time altered – Increase in fluid loss – Reduction in compressive strength

 Reduction in Hydraulic Bond

Prevented By  Wiper Plugs in Casing

 Compatible Preflushes in Annulus – Spacers and Chemical Washes 39

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Cement placement: Down the casing Down : Inside the casing :  Fluid interfaces are unstable (mud < spacer < cement)  Mechanical plugs should be used to separate the fluids

 Top plug also designed to give indication of end of job (plugs bump on landing collar)  Lack of bottom plug(s) will lead possibly to – Fluid contamination (intermixing) or even fluid swapping – Improper displacement in the annulus – Poor cement at shoe (top plug scrapping mud film at casing wall)

40

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Cement Wiper Plugs Keep Fluids Separated in Casing and Reduce Contamination  Bottom Plug(s) – – – –

Remove mud ahead of cement Prevent cement falling through lighter fluid ahead Wipe inner casing walls clean Use at least 1 ..or more if possible • Long cemented interval • Critical operation

 Top Plug

41

–

Separate cement from displacing fluid

–

Positive indication of end of displacement

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Why Run a Bottom Plug ? Bottom plug wipes accumulated mud cake, scale, etc. from inner casing walls out through float equipment into annulus. SPACER

MUD

MUD

SPACER

MUD

MUD

Volume of debris can be significant and fill-up shoe track if not removed ahead of the top plug.     42

Example : 9 5/8” 47 lb/ft (ID 8.681” 0.41cuft/ft) at 10000 ft (collar at 9820ft) Volume of 1/32” film? Height corresponding to this volume ? Conclusions ?

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Why Run a Bottom Plug ? Volume of residual mud scrapped by the top plug : Π x ID x L x e 3.14 x (8.681 /12) x 9820 x (1/32 x 1/12) = 58.1 cuft Length of 9 5/8 casing filled by scrapped mud 58.1 / 0.41 = 141.7 ft Shoe track length : 180 ft If an overdisplacement is occuring potential displacement of mud around the 9 5/8 shoe

43

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Cement placement: Up the annulus Up : inside annulus  Fluid interfaces can be stable (mud < spacer < cement) but casing has to be properly centralized.  Fluids density, rheology and pumping rate to be designed properly depending on the flow regime (laminar vs. turbulent).  Improper displacement (design or execution) in the annulus will lead to : – Mud/spacer channels in the annulus – Mud/spacer films at the casing/formation walls

– Fluid contamination (intermixing)

44

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Up the annulus to separate mud from cement : USE SPACERS in order to prevent contact and incompatibilities between drilling mud and cement slurries  Some mud additives are retarders for cement – e.g. lignosulfonate (dispersants)

 Others act as accelerators – CaCl2

 Drilling mud/cement mixtures can be very viscous (NABM): – Absolutely avoided – Higher friction pressures than expected •

possibly overcoming frac pressure

– Mixtures possibly very difficult to displace from the annulus (gelation)

 Improve cement bonding by water wetting casing and borehole (NABM) 45

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Spacers & Washes - Definitions Compatible:  Capable of forming a mixture which does not undergo any undesirable chemical or physical reactions

Wettability:  The preferential adhesion of polar fluids, such as water, versus non-polar fluids, such as oils, to solid surfaces

46

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Washes & Spacers Spacers    

Densified polymer fluids with insoluble weighting agent (generally barite) Designed rheology for efficient laminar or turbulent flow displacement Fluid loss control should be required Contains always a surfactant when used with NABM – compatibility,water wet surface.

Chemical Washes or Preflushes  Generally not densified (Brine) : water, diesel, or thin fresh mud  CW contains additives to thin the mud, to control leak off as water wetting surfactant (NABM)  CW pumped in turbulent flow but are not really effective in annulus – casing eccentration, Taylor instabilities 47

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NABM - Spacer Surfactants Efficiency

48

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Required Properties of Spacers  Compatible with all other well fluids  Stability (good suspending capacity)  Controllable density and rheology  Good fluid loss control  Environmentally safe and easy to handle in the field

 Water Wet surface with NABM

50

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Composition & Field Mixing Order  Water: Fresh or Brackish  Antifoam  Spacer Blend (viscosifier, leak off control)  Shearing and hydration  Salt (NaCl or KCl) : If required  Weighting Agent :

CaCO3 < 1.35 sg (11.5 ppg)

Barite 1.35 –1.92 sg (11.5-16 ppg) Hematite > 1.92 sg (16ppg)

 Surfactant(s) for NABM : type and concentration depends on base oil / spacer / mud used.

51

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Cement placement : Turbulent or Laminar Flow In all cases Prevent Cement contamination by using/pumping  Along casing down to shoe : – Separation plugs : Bottom & Top Plugs • 2 Bottom plugs if possible

– Chemical wash ahead plug : • Mud dilution

and/or turbulence

 Up along the annulus :  Spacer ( laminar or turbulent)  Chemical wash (brine?) only with

• Compatible mud ( WBM) with slurry • Low density mud (< 1.20 sg)

Weatherford plugs

 A must do for compatibility with Non Aqueous Base Muds : Chemical wash & spacer + surfactant 52

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Conclusions & Resume Mud displacement and removal

Criteria for Effective Mud Removal Cementing Operation :  Centralize casing  Casing movement  Wiper plugs

 Spacer and Washes  Flow regime selection With

 Conditioned mud in hole

55

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Mud Removal  Hole Cleaning – Controlled & optimized mud properties – Low gravity drill solids < 6% – Break gel strength • Wiper trip and intermediate circulation RIH casing – > 95% Total hole volume in circulation (calliper fluid) • Calliper log

 Conditioning Mud – – – – 56

Lower TY and PV, flat gel Clean hole, LGS < 6% Maximum flow rate compatible with minimum frac pressure Rate above minimum rate to flow all-around pipe (MPG)

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Conclusions: Mud displacement  Centralize to give optimum casing stand-off (80% minimum 75%)  Rotate and/or Reciprocate casing – Rotation is preferred – Use cable-type scratchers when reciprocating

 

Always use a bottom plug: 2 preferred….when possible! Optimise slurry placement using a simulator: – Turbulent flow preferred, or in combination with – Effective laminar flow technique

  

Use Chemical wash pre-flushes ahead bottom plug Use Spacer to avoid contact mud/cement slurry Control spacer/cement slurry properties: batch mix when possible  Compatibility test mud/spacer/cement slurry : lab/field test

58

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Effective Laminar Flow displacement (1) General Flow regime when Turbulent flow is not possible Four criteria must be satisfied (for spacer and slurries)  Density differential (10%)  Minimum pressure gradient (MPG)  Friction pressure hierarchy (20%)  Differential velocity criterion Wash : To clean inside casing ( turbulent flow)  Use 3 – 7 m3 (20 - 40 bbls) chemical wash  Turbulent flow inside casing  Ahead of bottom plug

59

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Effective Laminar Flow displacement (2) Viscous spacer  Conditioned and clean mud  Viscosity adjustable – Higher than mud – WSS > ty,mud

 Volume to use: > 150 m - 10 m3 ( 500 ft or 60 bbls)  Surfactant with NABM for water wetability and compatibility Slurry (ies)  Viscosity adjusted and higher than the spacer

Casing Centralization : Stand off > 75%

60

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Turbulent Flow Displacement (1) Preferred and best flow regime …..When possible  Applicable at least to Spacer when possible ( laminar slurry)

Critical rate depends on:  Fluid rheologies  Casing stand-off : 85% recommended, minimum 80%

 Annular gap, casing OD and Open hole size (bit size)  Formation fracture gradient

61

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Turbulent Flow Displacement (2) Use Turbulent Spacer and/or Chemical Wash 10 min. Contact time (> 6 min) or 300m (use greater volume)) Spacer density to be close to that of mud Wash applicable only with low density mud (< 1.20 sg -10 ppg) Turbulent spacer + Wash to clean inside casing ( preserve the spacer for annulus)  Water wet casing and formation with NABM (surfactant)    

Optimise cement slurry properties:  Turbulence at the lowest rate : Minimum PV and TY without settling  Fluid loss and Free Fluid controlled 62

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