4) Mud Removal

1

2

Objectives of Primary

Cementation

•

_{Provide complete isolation of zones}

(Hydraulic Bond)

•

_{To support the casing (Shear Bond)}

•

_{Protect casing string}

3

Mud Removal

•

_{Most important aspect of cement job}

•

_{A 3-step process before cementing}

•

Hole cleaning

•

Conditioning the drilling fluid

4

Mud Removal

• _{Hole Cleaning}

• Controlled & optimized mud properties • Wiper trips

• _{> 95% Total hole volume in circulation} • Caliper log

• _{Conditioning Mud}

• Break gel strength • _{Lower ty + pv} • Drill solids < 6%

• Determine MPG to find qmin for all-around flow

• _{Displace Mud from Annulus}

• Optimized slurry placement ---> CemCADE • _{Casing centralization optimized (STO > 75%)} • Casing movement

5

Criteria for Effective Mud

Removal

Cementing Operation:

•

_{Centralize casing}

•

_{Casing movement}

•

_Scratchers

•

_{Wiper plugs}

•

_{Washes and spacers}

•

_{Flow regime selection}

6

The Ideal Wellbore Casing

Thin, impermeable mud filter cake (not gelled or unconsolidated)

BHST at top of cement >BHCT at TD Annular gap Minimum: 3/4” Ideal: 1 1/2” Properly conditioned

hole and mud

Gauge diameter No sloughing Uniform as possible ( no washouts or restrictions) NO FLOW NO LOSSES

Casing centered in borehole

8

Influence of the Casing

Stand-Off

V

V_narnar VV_widewide D

D_ii

D

9

Newtonian Fluid - Effect of

STO

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

Pattern Q Q D D₁₁ DD22 V V₂₂ V V₁₁ Q Q L L PP LL

11

Newtonian Fluid of Viscosity µ

Density



In Laminar Flow :

• _{1. Velocity} _{P = 32µ V1 = 32µ V2}

12

Newtonian Fluid of Viscosity µ

Density



In Laminar Flow : • _{1. Velocity} _{P = 32µ V1 = 32µ V2} L D12 D22 V2 = (D2)2 V1 (D1)2

13

Newtonian Fluid of Viscosity µ

Density



In Laminar Flow : • _{1. Velocity} _{P = 32µ V1 = 32µ V2} L D12 D22 V2 = (D2)2 V1 (D1)2 If D2 = 2D1

14

Newtonian Fluid of Viscosity µ

Density



In Laminar Flow : • _{1. Velocity} _{P = 32µ V1 = 32µ V2} L D12 D22 V2 = (D2)2 V1 (D1)2 If D2 = 2D1 V2 = 4V1 (For 67%)

15

Newtonian Fluid of Viscosity µ

Density



In Laminar Flow : • _{1. Velocity} _{P = 32µ V1 = 32µ V2} L D12 D22 V2 = (D2)2 V1 (D1)2 If D2 = 2D1 V2 = 4V1 (For 67%) • _{2. Reynolds Number} Re2 = V2 D2 = 4V12D1 = VD µ µ µ

16

Newtonian Fluid of Viscosity µ

Density



In Laminar Flow : • _{1. Velocity} _{P = 32µ V1 = 32µ V2} L D12 D22 V2 = (D2)2 V1 (D1)2 If D2 = 2D1 V2 = 4V1 (For 67%) • _{2. Reynolds Number} Re2 = V2 D2 = 4V12D1 = VD µ µ µ Re2 = 8Re1 (For 67%)

17

Laminar Flow in Eccentric

Annulus

Non-parallel plate model Ri/Ro = 0.8 Non-parallel plate model Ri/Ro = 0.8

0 10 20 30 40 50 60 70 80 90 100 1000 500 100 50 10 5 1 V_wide / V_narrow Stand-off % Stand-off % n = 1.0 n = 0.5 n = 0.2

18

In Turbulent Flow

• _Velocity _{p =}  L = If D2 = 2D1 • _{Reynolds Number} Re2= V2 D2 = 1.64V12D1 = 3.28V1D1 µ µ µ V₂ = 1.64V₁ (For 67%) Re₂ = 3.28Re₁ (For 67%) 0.241 x  0.75 _{x µ}0.25 _{x V1} D ₁2 4 1.75 D₁ 4.75 ( ) 0.241 x  0.75 _{x µ}0.25 _{x V}2 D 2 2 4 1.75 D₂ 4.75 ) ( V2 V1 = D 2 D1 0.714 ( )

19

Turbulent Flow in Eccentric

Annulus

0 10 20 30 40 50 60 70 80 90 100 1000 500 100 50 10 5 1 V_wide / V_narrow

API Stand - Off (%)

n = 1.0 n = 0.5 n = 0.2

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Casing Centralization

• Relative Variation of flow rate ratio as a function of eccentricityRelative Variation of flow rate ratio as a function of eccentricity 18 16 14 12 10 8 6 4 2 0 0 20 40 60 80 100 W W % Stand-off = w R_H - R_C X 100 API % STAND-OFF API % STAND-OFF F L O W R A T E R A T IO F L O W R A T E R A T IO RC R_H

21

Types of Centralizers

• _{Bow Spring (Spiral or Straight):}

• Flexible bow springs

• _{Centralizer OD slightly larger than OH size}

• _{Rigid Bow (or Positive) type:}

• Non-flexible O.D. (Slightly less than previous casing ID) • Use inside cased-hole sections

• _{Effective in in-gauge OH intervals only}

• _{Rigid Solid slip-on type:}

• Solid body - no bows • _{Use: as per rigid type}

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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 to be effective}

• _{Casing may become stuck during movement}

• _{Excessive swab and surge pressures may be created} • _{Excessive pull and buckling}

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Rotation

• _{Circular movement of pipe}

• _{Must be done from the start of circulation to end}

displacement

• _{10 to 40 rpm}

• _{Scratchers help efficiency}

• _{Needs special rotary cement heads and power}

swivels

• _{Torque must be very closely monitored}

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Fluids Incompatibility

• _{Results In:}

• Detrimental Interface Reactions • High Rheological Properties

• _{Very high viscosities} • _{Very 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}

• _{Chemical Washes} • _Spacers

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Cement Wiper Plugs

• _{Keep Fluids Separate in Casing and Reduce}

Contamination

• _{Bottom Plugs}

• Remove mud ahead of cement

• _{Prevent cement falling through lighter fluid ahead}

• Wipe inner casing walls clean

• Use 2 or more if possible

• _{Top Plugs}

• Separate cement from displacing fluid

26

Why Run a Bottom Plug ?

• _{Bottom plug wipes accumulated mud cake,}

scale, etc. from inner casing walls out through float equipment into annulus.

• _{Volume of debris can be significant and fill-up}

shoetrack if not removed ahead of the top plug.

• EXAMPLE: 9 5/8” 47 lb/ft 10000 feet, collar at 9820

feet

• Volume of 1/16” film?

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Turbulent Flow

Displacement

• _{Preferred and best flow regime}

• _{Critical rate depends on:}

• _{Fluid rheologies}

• _{Casing stand-off}

• Annular gap, casing OD and bit size

• _{Formation fracture gradient}

• _{Use Chemical Wash and/or Mudpush XT/S spacers:}

• _{10 Min. Contact time or 750 ft (use greater volume))}

• _{Spacer density to be close to that of mud}

• _{Optimize cement slurry properties:}

• _{Minimum PV and TY without settling}

• Fluid loss and free water controlled

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Effective Laminar Flow

• _{Alternative flow regime when Turbulent flow is not}

possible

• _{Four criteria must be satisfied:}

• DENSITY DIFFERENTIAL (10%)

• MINIMUM PRESSURE GRADIENT (MPG)

• FRICTION PRESSURE HIERARCHY (20%)

• DIFFERENTIAL VELOCITY CRITERION

• _{Viscous spacer: Mudpush XL/XLO}

• _{Viscosity adjustable (Change D149 concentration)}

• Volume to use: 500 ft or 60 bbls

• _{Use 20 - 40 bbls chemical wash}

• Condition and clean mud

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Chemical Washes

• _{Water based fluids, low viscosity, density of water} • _{Easy to pump in turbulent flow}

• _{CW7 for intermediate casings, water based muds}

• _{41.5 gals water, 0.5 gals D122A}

• _{CW100 for production casings, water based muds}

• _{41.25 gals water, 0.5 gals D122A, 0.25 gals J237}

• _{CW8 for intermediate casings, oil based muds}

• 41.25 gals water, 0.5 gals D122A, 0.25 gals F40 last

• _{CW101 for production casings, oil based muds}

• 41 gals water, 0.5 gals D122A, 0.25 gals J237, 0.25 gals

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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}

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Events to be Recorded

• _{Was the mud conditioned - rate and time?}

• _{How many centralizers were run and where?}

• _{Was the casing rotated and/or reciprocated?}

• _{Where the plugs correctly dropped?}

• _{What was the density and rheology of the spacers?}

• _{Was the correct volume of preflushes used?}

• _{The following data must be recorded on the PRISM:}

• All densities, if possible of displacement fluid as well • All flow rates, if possible of displacement as well

• _{All pressures}

• _{Note any changes in flow rate, density, stoppages,}

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Conclusions

• _{Condition mud prior to cementing}

• Centralize to give optimum casing stand-off

• _{Rotate and/or Reciprocate casing}

• _{Use cable-type scratchers when reciprocating}

• _{Always use the bottom plugs: 2 preferred}

• Optimize slurry placement using CemCADE:

• Turbulent flow preferred, or

• Effective laminar flow technique

• _{Use chemical wash pre-flushes}

• _{Control Mudpush spacer/cement slurry properties:}

batch mix