# 12. Plugback Cementing

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12. Plugback CementingPETE 661 Drilling EngineeringSlide 1 of 67 PETE 661 Drilling Engineering Lesson 12 Plugback Cementing 12. Plugback CementingPETE 661 Drilling EngineeringSlide 2 of 67 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 12. Plugback CementingPETE 661 Drilling EngineeringSlide 3 of 67 Read: Applied Drilling Engineering, Ch. 3HW #7. Cementing due October 21,200212. Plugback CementingPETE 661 Drilling EngineeringSlide 4 of 67 Balanced Cement PlugFig. 3.11- Placement technique used for setting cement plug. 12. Plugback CementingPETE 661 Drilling EngineeringSlide 5 of 67 Cementing (Open-Hole Plugging) 1. Plug-back for abandonment 2. Plug-back for fishing or hole deviation Open-hole plugging is usually performed with slick drillpipe or tubing. In some cases, reciprocating scratchers maybe run to enchance cementbonding. 12. Plugback CementingPETE 661 Drilling EngineeringSlide 6 of 67 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. 12. Plugback CementingPETE 661 Drilling EngineeringSlide 7 of 67 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. 12. Plugback CementingPETE 661 Drilling EngineeringSlide 8 of 67 Case I ftftcapacity, pipe drill Tftftcapacity, annularC33==C Height of plug after pulling pipe Height ofplug withpipe in place T 12. Plugback CementingPETE 661 Drilling EngineeringSlide 9 of 67 Case I

+ =+ =====T) H(CT * H C * H Vplace inpipe hwitplug cementof height Hft slurry, of volume Vftftcapacity, pipe drill Tftftcapacity, annularC333T CVH+=CT HFinal Height 12. Plugback CementingPETE 661 Drilling EngineeringSlide 10 of 67 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 washout 3. Use 5, 19.50 #/ft DP, open ended 4. Use class H cement, 15.6 #/gal 12. Plugback CementingPETE 661 Drilling EngineeringSlide 11 of 67 Example - Case I (a)Calculate volume of cement slurry required: required slurryofft 315.15ft) 500 ( ft1275 . 104L D4V3222H=|.|

\|= =t tDH L 12. Plugback CementingPETE 661 Drilling EngineeringSlide 12 of 67 Example - Case I (b)Calculate actual height of plugwhen DP is in place at 9,000 ft. If then H ) T C ( Vft / ft incapacitydrillpipe Tft / ft incapacityannular C33+ ===T CVH+= CT 12. Plugback CementingPETE 661 Drilling EngineeringSlide 13 of 67 Example - Case I (b)contd In this case, ft / ft 0997 . 0 Tft / ft 0.49394

ft/ft 1 * ft1445 75 . 104C3322 2==||.|

\|= t( Halliburton Book ) 12. Plugback CementingPETE 661 Drilling EngineeringSlide 14 of 67 Example - Case I (b)contd place inpipe withplug, of height ft 530.9/ ) 0997 . 0 49394 . 0 (ft 15 . 31533==+=+= ft ft T CVH12. Plugback CementingPETE 661 Drilling EngineeringSlide 15 of 67 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 equalinside the DP and in the annulus, at 9,000. MA MA MD MDMA CA MD CDA D)h 0.052( )h 0.052(P P P PP P=A + A = A +=PDPA hMD = hMA 12. Plugback CementingPETE 661 Drilling EngineeringSlide 16 of 67 Example-Case I ft 8,469.1

530.9 - 9,000 drillpipe inside mud of height annulus inmud of height drillpipe inside mud of height ==

=

12. Plugback CementingPETE 661 Drilling EngineeringSlide 17 of 67 Example-Case I 33ft 61 . 5bbl* ft 4 . 844 =VDispl=150.4bbl(of mud) Volume of mud displacement (behing the cement slurry) = 8,469ft*0.0997ft3/ft 12. Plugback CementingPETE 661 Drilling EngineeringSlide 18 of 67 Example -Case I Also required: Class H cement reqd Mix water reqd sk / ft 18 . 1ft 15 . 31533=sks 1 . 267 =gal/bbl 42gal/sk 5.2 * sks 1 . 267=bbl 1 . 33 =12. Plugback CementingPETE 661 Drilling EngineeringSlide 19 of 67 mud water cement water mud Case II hW Height of plug after pulling pipe hWD = hWA CVTVWA WD=|.|

\|=CV VWA WDTHeight ofplug withpipe in place 12. Plugback CementingPETE 661 Drilling EngineeringSlide 20 of 67 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 12. Plugback CementingPETE 661 Drilling EngineeringSlide 21 of 67 Example -Case II(a) & (b)From previous example: place indrillpipewithplug of heightft, 9 . 530T CVHcapacity drillpipe , ft / ft 0.0997 Tcapacity annular, ft / ft 0.49394 Cslurry cementof vol. , ft 15 . 315 V333= =+====12. Plugback CementingPETE 661 Drilling EngineeringSlide 22 of 67 Example-Case II (c)Calculate height (length) of water spacer in DP: In annulus, ft 6 . 113 hft 113.6ft / ft 49394 . 0bblft5.61 * bbl 10CVhWD33WAWA= == =12. Plugback CementingPETE 661 Drilling EngineeringSlide 23 of 67 Example-Case II (d)Volume of water spacer inside DP bbls 02 . 2ft / ft 49394 . 0ft / ft 0.0997* bbls 10CT* annulus in spacer of . Vol33==|.|

\|=V W,DP 12. Plugback CementingPETE 661 Drilling EngineeringSlide 24 of 67 Example-Case II (e)A balanced plug requires that surface. the to extend mustdrillpipe inmud

A + A + A = A + A + A=MA WA CA MD WD CDA DP P P P P PP PPDPA 12. Plugback CementingPETE 661 Drilling EngineeringSlide 25 of 67 Example-Case II (e)contd ft 5 . 355 , 8 6 . 113 9 . 530 000 , 9 h - 9,000 drillpipe inmud of Height CD= = =

WDh12. Plugback CementingPETE 661 Drilling EngineeringSlide 26 of 67 Example-Case II ftft0.0997 * ft 8,355.53=Volume of mud required to displace cement and spacers =833.0ft3

VDispl=148.5bbls 12. Plugback CementingPETE 661 Drilling EngineeringSlide 27 of 67 Check OK. I Case - problem previous answer tobbls 150.5bbls 2.02 bbls 5 . 148

~~+12. Plugback CementingPETE 661 Drilling EngineeringSlide 28 of 67 Pumping Sequence: 1. Water spacer for annulus: 10 bbls 2. Cement Slurry for Plug: 3. Water spacer behind cement: 2.0 bbls bbls 2 . 56 ft 15 . 3153~12. Plugback CementingPETE 661 Drilling EngineeringSlide 29 of 67 Pumping Sequence 4. Mud displacement behind secondwater 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) 12. Plugback CementingPETE 661 Drilling EngineeringSlide 30 of 67 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 plug after pulling pipe Height ofplug withpipe in place MD WD CD MA WA CAD AP P P P P PP PA + A + A = A + A + A= 12. Plugback CementingPETE 661 Drilling EngineeringSlide 31 of 67 Case IV - General Case MD WD CD MA WA CAD AP P P P P PP PA + A + A = A + A + A= 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. 12. Plugback CementingPETE 661 Drilling EngineeringSlide 32 of 67 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 completecirculation to make sure system is balanced. 3. Pump spacers and cement per calculationsand displace w/proper amount of fluid 12. Plugback CementingPETE 661 Drilling EngineeringSlide 33 of 67 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 calculationshas been made.Stab inside BOP, or have a heavy slug (small volume slug) ready to pump. 12. Plugback CementingPETE 661 Drilling EngineeringSlide 34 of 67 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 completelybalanced mud system. 6.If pulling wet, slug pipe and pull out of hole. 12. Plugback CementingPETE 661 Drilling EngineeringSlide 35 of 67 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 withDP just above top of first plug. 12. Plugback CementingPETE 661 Drilling EngineeringSlide 36 of 67 Calculations to Design a Balanced Open Hole Cement Plug 1. Calculate cu. ft. of slurry required forplugin open hole. 2. Multiply this volume by excess factor (50%excessfactor=1.50) ( ) n tables. Halliburto use or, ft L d4V3 21 =31 2ft, * factor V V =12. Plugback CementingPETE 661 Drilling EngineeringSlide 37 of 67 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 5 11 2. * V V =If 50% excess is required 5 1. * d4d42122 =1 1 2225 . 1 5 . 1 d d d = =Use d2 for calculations This is the effective dia. 12. Plugback CementingPETE 661 Drilling EngineeringSlide 38 of 67 Calculations for balanced plug 3. Find height (h, ft) cement will occupy when drillpipe is at bottom of plug during pumping: ftft

ftft ) ( Vol Volft , Vh3 32 annulus DP inside32d on based +=12. Plugback CementingPETE 661 Drilling EngineeringSli

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