12. plugback cementing
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Slide 1 of 6712. Plugback Cementing PETE 661 Drilling Engineering
PETE 661Drilling Engineering
Lesson 12Plugback 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
Slide 3 of 6712. Plugback Cementing PETE 661 Drilling Engineering
Read:Applied Drilling Engineering, Ch. 3
HW #7. Cementingdue October 21,2002
Slide 4 of 6712. Plugback Cementing PETE 661 Drilling Engineering
Balanced Cement Plug
Fig. 3.11- Placement technique used for setting cement plug.
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.
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.
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.
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
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
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
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
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
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 )
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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)
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
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.
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
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.
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.
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.
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
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.
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
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
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
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
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
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
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
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.
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.
Slide 47 of 6712. Plugback Cementing PETE 661 Drilling Engineering
Salt in Cement Slurries
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.
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
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)
Slide 51 of 6712. Plugback Cementing PETE 661 Drilling Engineering
Density of Sodium Chloride Solution
Slide 52 of 6712. Plugback Cementing PETE 661 Drilling Engineering
Slide 53 of 6712. Plugback Cementing PETE 661 Drilling Engineering
Slide 54 of 6712. Plugback Cementing PETE 661 Drilling Engineering
Slide 55 of 6712. Plugback Cementing PETE 661 Drilling Engineering
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.
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
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
Slide 59 of 6712. Plugback Cementing PETE 661 Drilling Engineering
Slide 60 of 6712. Plugback Cementing PETE 661 Drilling Engineering
Slide 61 of 6712. Plugback Cementing PETE 661 Drilling Engineering
Slide 62 of 6712. Plugback Cementing PETE 661 Drilling Engineering
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.
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
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
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
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
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