12. plugback cementing

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Page 1: 12. Plugback Cementing

Slide 1 of 6712. Plugback Cementing PETE 661 Drilling Engineering

PETE 661Drilling Engineering

Lesson 12Plugback Cementing

Page 2: 12. Plugback Cementing

Slide 2 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Plugback Cementing

Case I: No Spacer Case II: Equal Height Spacers Case III: Spacer Ahead of Cmt. (only) Case IV: Two Unequal Spacers Mixtures and Solutions

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Slide 3 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Read:Applied Drilling Engineering, Ch. 3

HW #7. Cementingdue October 21,2002

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Slide 4 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Balanced Cement Plug

Fig. 3.11- Placement technique used for setting cement plug.

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Slide 5 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Cementing (Open-Hole Plugging)

1. Plug-back for abandonment2. Plug-back for fishing or hole deviation

Open-hole plugging is usually performed with “slick” drillpipe or tubing.

In some cases, reciprocating scratchers may be run to enchance cement bonding.

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Slide 6 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Types of Balanced Plugs

Case I: No water or other fluid of different density from that in hole is run ahead or behind the cement slurry.

Case II: Water or other fluid of different density from that hole is run ahead and behind cement slurry. The volume of fluid ahead and behind slurry is calculated so that height in casing is same as height inside the string.

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Slide 7 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Displacement

Case III: Water or other fluid of different density from that in hole is run ahead of cement slurry and hole fluid only is used as displacing fluid.

Case IV: Water or other fluid of different density from that in hole is run ahead and behind cement slurry. In this case, the heights of fluid in annulus and drill string are not equal.

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Slide 8 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Case I

ftft capacity, pipe drillT

ftft capacity,annular C

3

3

C

Height of plugafter pulling pipe

Height of plug with

pipe in place

T

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Slide 9 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Case I

T)H(C T*HC*HV

placein pipeh witplugcement of heightHft slurry, of volumeV

ftft capacity, pipe drillT

ftft capacity,annular C

3

3

3

TCVH

CT

H Final

Height

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Slide 10 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Example Balanced Plug - Case I

Set a balanced cmt. plug from 8,500-9,000 ft, with no fluid spacers.

1. Open hole diameter = 10 3/4”2. Assume no washout3. Use 5”, 19.50 #/ft DP, open ended4. Use class H cement, 15.6 #/gal

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Slide 11 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Example - Case I

(a) Calculate volume of cement slurry required:

requiredslurry of ft 315.15

ft) 500(ft12

75.104

LD4

V

3

22

2H

DH

L

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Slide 12 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Example - Case I

(b) Calculate actual height of plug when DP is in place at 9,000 ft.

If

then H)TC(V

ft/ftin capacity drillpipeT

ft/ftin capacity annularC3

3

TCVH

CT

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Slide 13 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Example - Case I

(b) cont’d

In this case,

ft/ft 0997.0T

ft/ft 0.49394

ft/ft 1*ft144

575.104

C

3

3

222

( Halliburton Book )

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Slide 14 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Example - Case I

(b) cont’d

placein pipe with plug, ofheight ft 530.9

/)0997.049394.0(ft 15.315

3

3

ftftTCVH

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Slide 15 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Example - Case I

(c) Determine the quantity of mud displacement inside the DP that will ensure a balanced plug.

Balance requires that the pressures be equal inside the DP and in the annulus, at 9,000’.

MAMAMDMD

MACAMDCD

AD

)h0.052(ρ)h0.052(ρPPPΔP

PP

PD PAhMD = hMA

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Slide 16 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Example - Case I

ft 8,469.1

530.9-9,000

drillpipe inside mud ofheight

annulusin mud ofheight drillpipe inside mud ofheight

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Slide 17 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Example - Case I

33

ft 61.5bbl*ft 4.844

VDispl = 150.4 bbl (of mud)

Volume of mud displacement(behing the cement slurry)

= 8,469 ft * 0.0997 ft3/ft

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Slide 18 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Example - Case I

Also required:Class H cement req’d

Mix water req’d

sk/ft 18.1ft 15.315

3

3

sks 1.267

gal/bbl 42gal/sk 5.2*sks 1.267

bbl 1.33

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Slide 19 of 6712. Plugback Cementing PETE 661 Drilling Engineering

mud

water

cement

water

mud

Case II

hW

Height of plugafter pulling pipe

hWD = hWA

CV

TV WAWD

CVV WAWD

T

Height of plug with

pipe in place

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Slide 20 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Example, Balanced Plug - Case II

Set a balanced plug, 500 ft high, with its bottom at 9,000 ft. Use water spacers of equal height inside DP and in annulus.

Volume of annular water spacer = 10 bbl Open hole diameter = 10 3/4”. No washouts

5” DP, 19.50 #/ft, open ended.Use class H cement, 15.6 #/gal

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Slide 21 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Example - Case II

(a) & (b) From previous example:

placein drillpipe with plug ofheight ft, 9.530

TCVH

capacity drillpipe ,ft/ft 0.0997T

capacityannular ,ft/ft 0.49394C

slurrycement of vol.,ft 15.315V

3

3

3

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Slide 22 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Example - Case II

(c) Calculate height (length) of water spacer in DP:

In annulus,

ft 6.113h

ft 113.6

ft/ft 49394.0bblft5.61*bbl 10

CVh

WD

3

3

WAWA

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Slide 23 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Example - Case II

(d) Volume of water spacer inside DP

bbls 02.2

ft/ft 49394.0ft/ft 0.0997*bbls 10

CT*annulus in spacer of .Vol

3

3

V W,DP

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Slide 24 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Example - Case II

(e) A balanced plug requires that

surface. the toextendmust drillpipein mud

MAWACAMDWDCD

AD

PPPPPP

PP

PD PA

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Slide 25 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Example - Case II

(e) cont’d

ft 5.355,8

6.1139.530000,9

h-9,000

drillpipein mud ofHeight

CD

WDh

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Slide 26 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Example - Case II

ftft0.0997*ft 8,355.5

3

Volume of mud required to displace cement and spacers

= 833.0 ft3

VDispl = 148.5 bbls

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Slide 27 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Check

OK. I Case - problem previous answer to

bbls 150.5

bbls 2.02bbls 5.148

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Slide 28 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Pumping Sequence:

1. Water spacer for annulus:

10 bbls

2. Cement Slurry for Plug:

3. Water spacer behind cement:

2.0 bbls

bbls 2.56ft 15.315 3

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Slide 29 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Pumping Sequence

4. Mud displacement behind second water spacer:

148.5 bbls

Total fluid pumped = 10 + 56.2 + 2 + 148.5 = 216.7 bbls

(at 10 bbl/min this would require ~22 min)

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Slide 30 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Case III

Hole fluid density > density of water

Hydrostatic heads in DS and annulus must balance at top of cement slurry with DS in hole.

hW

Height of plugafter pulling pipe

Height of plug with

pipe in place

MDWDCDMAWACA

DA

PPPPPPPP

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Slide 31 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Case IV - General Case

MDWDCDMAWACA

DA

PPPPPP

PP

Hole fluid density is greater than water density.

Hydrostatic heads in DS and annulus must balance at top of cement slurry with DS in hole.

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Slide 32 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Procedure in setting balanced plug

1. Run drillpipe in to depth where plug is to be set; in this case 9,000 ft. (open ended).

2. Circulate and condition mud one complete circulation to make sure system is balanced.

3. Pump spacers and cement per calculations and displace w/proper amount of fluid

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Slide 33 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Procedure in setting balanced plug

4. Stop pumps; break connection at surface.

A. If standing full, plug is balanced.

B. If flowing back, a mistake in calculations has been made. Stab inside BOP,

or have a heavy slug (small volume slug) ready to pump.

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Slide 34 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Procedure in setting balanced plug

5. Once the end of the drillpipe clears the plug, there is a good chance the pipe will pull wet. This is because pressures have gone back into a completely balanced mud system.

6. If pulling wet, slug pipe and pull out of hole.

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Slide 35 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Procedure in setting balanced plug

7. Even if plug is severely out-of-balance, never try to reverse cement out of hole.

8. Tag plug with DP at end of 8 hours. If too high, plug may have to be drilled out and another plug spotted. If too low, spot another plug to required height with DP just above top of first plug.

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Slide 36 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Calculations to Design a Balanced Open Hole Cement Plug

1. Calculate cu. ft. of slurry required for plug in open hole.

2. Multiply this volume by excess factor (50% excess factor = 1.50)

n tables.Halliburto use or, ft Ld4πV 32

1

3 12 ft , * factorVV

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Slide 37 of 6712. Plugback Cementing PETE 661 Drilling Engineering

When dealing with a washed-out hole, where an excess factor is required, it is usually easier to calculate a new, effective hole size, and use that instead of the excess factor.

Calculations for balanced plug - HINT

5112 .*VV If 50% excess is required

51.*d4πd

4π 2

12

2

112 225.15.1dd d Use d2 for calculationsThis is the effective dia.

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Slide 38 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Calculations for balanced plug

3. Find height (h, ft) cement will occupy when drillpipe is at bottom of plug during pumping:

ftft

ftft

)(VolVolft ,Vh

33

2annulusDP inside

32

donbased

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Slide 39 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Calculations for balanced plug - cont’d

4. Find height (ft) water spacer ahead of cement will occupy in annulus. Use

d2 to calculate this (to account for the excess factor).

5. Find height (ft) water spacer behind cement will occupy in DP. Do

not use excess factor.

6. Pressures must balance at bottom of plug

annDP PP

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Slide 40 of 6712. Plugback Cementing PETE 661 Drilling Engineering

7.

8. Convert this to feet inside DP.

ΔPfor Solve

ΔPΔPΔPP

ΔPΔPΔPP

mud DP

mud DPspacercmtDP

mud annulusspacercmtann

mudDPΔP

Calculations for balanced plug - cont’d

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Slide 41 of 6712. Plugback Cementing PETE 661 Drilling Engineering

9. Convert this footage to bbls inside DP for proper displacement.

10. To find sx cmt required, divide volume, V2, by yield/sk. This yield, Ysk, may be

in the Halliburton tables.

Number of sx req’d, sk

2

YVN

Calculations for balanced plug - cont’d

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Slide 42 of 6712. Plugback Cementing PETE 661 Drilling Engineering

11. If yield not shown, calculate from formula for mixtures. Solve for in this formula. Add the V’s for yield.

12. Total mix water will be times number of sacks.

VW total = (VW / sk) * N

11vWV

sk/VW

Calculations for balanced plug - cont’d

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Slide 43 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Cementing - Salt Solutions

Use of salt in Cement Slurries Unsaturated Salt Solutions Saturated Salt Solutions Types Cements Cement Additives Examples

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Slide 44 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Salt in Cement SlurriesSalt Zones Salt-saturated cements were originally used for

cementing casing strings through salt zones.

Fresh or unsaturated salt cement slurries will not bond satisfactorily to salt formations because the slurry tends to dissolve or leach away the salt at the wall of the hole.

Salt-saturated cements will not dissolve any more salt so a good bond can be achieved

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Slide 45 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Salt in Cement Slurries

Shale Zones

Many shales are sensitive to fresh water.

Salt helps to protect these shales in that they tend to prevent excessive sloughing or heaving of the shales.

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Slide 46 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Salt in Cement Slurries

Accelerator In low concentrations salt tends to

accelerate the setting of cement.

Retarder In high concentrations ( >5% by wt. of water) the salt will tend to retard the setting of the cement.

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Slide 47 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Salt in Cement Slurries

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Slide 48 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Salt in Cement Slurries

Expansion Salt results in a more expansive cement.

Freezing Salt reduces the freezing

temperature of cement slurries.

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Slide 49 of 6712. Plugback Cementing PETE 661 Drilling Engineeringof solution

EXAMPLE:200,000 mg of NaCl800,000 mg of H2O1,000,000 mg of solution < 1 litre of solution

ppm

or

mg/

L

mg/L

ppm

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Slide 50 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Volume of Sodium Chloride Solution

EXAMPLE:Adding 30 lbs of NaClto 100 lbs of H2Oincreases the volume of solution by ~10.7%

30% by weight = 13.8% by volume(SG = 2.17)

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Slide 51 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Density of Sodium Chloride Solution

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Slide 56 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Example: Salt Solutions

30% NaCl (by weight of water) is added to one gallon of fresh water.

Calculate the density of the mixture:

(i) Before the salt goes into solution (ii) Using the solubility charts shown above.

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Slide 57 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Problem : Salt Solutions

(i) Assuming that

lb/gal 9.51

8.33) * (2.17 / 8.33) * (0.3011 x 8.33 * 0.301 * 8.33

VVρVρρ

VρVρVρ:Vρ...VρVρ

mix

SSwwmix

mixmixSSWWmixmix2211

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Slide 58 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Problem : Salt Solutions

(ii) From the chart,

{ 9.51 lb/gal vs. 9.8 lb/gal !! }

{ what if we had 60% salt? }

lb/gal 8.9mix

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Slide 63 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Problem

Calculate the density and yield of a cement slurry consisting of:

65% Class “A” cement35% Pozmix cement,6% bentonite BWOC and10.9 gal/sk of water.

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Slide 64 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Problem

(i) Initial tabulations and calculations:

Weight Specific Density Component lbs/sk Gravity lbs/galClass “A” 94 3.14 8.33*3.14 = 26.16Pozmix 74 2.46 8.33*2.46 = 20.49Bentonite 2.65 8.33*2.65 = 22.07Water 1.00 8.33*1.00 = 8.33

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Slide 65 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Problem(ii) Determine the properties of one sack of dry cement mixture; 65% Class “A” and 35% Pozmix:

3.600 87.0

264.120.4925.9 25.974*0.35sk 0.35 ,

336.226.1661.1 61.194*0.65sk 0.65 A, Class

(gal) Vol. (lbs)ht Weig

Pozmix

Cement

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Slide 66 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Problem

(iii) Determine density and yield of final slurry:

14.7365 183.02

10.9 90.808.33*10.9 gal 10.9 Water,

2365.022.075.22 5.2287*0.06 6% Bentonite,

3.600 87.0 sk 1 mix, Cmt.

(gal) Vol. (lbs) Weight Component

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Slide 67 of 6712. Plugback Cementing PETE 661 Drilling Engineering

Problem

sk/ft 97.1gal/ft 48.7

gal/sk 14.7365Yield

lb/gal 42.127365.14

02.183

33

mix