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3.2 2 . 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. . 3.2 3 . Balanced Cement Plug . . Fig. 3.11- Placement technique used for setting cement plug.. 3.2 4 . Cementing (Open-Hole Plugging).

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3.2

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    1. 3.2 1 3.2

    2. 3.2 2 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 There There

    3. 3.2 3 Balanced Cement Plug Fig. 3.11- Placement technique used for setting cement plug. Setting balanced cement plugs requires that careful calculation and measurement of the volume of displacement fluid be made so that the height of the cement in the annulus will be the same as inside the drillpipe or workstring.Setting balanced cement plugs requires that careful calculation and measurement of the volume of displacement fluid be made so that the height of the cement in the annulus will be the same as inside the drillpipe or workstring.

    4. 3.2 4 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 may be run to enchance cement bonding. Reasons for plug-back are given above.Reasons for plug-back are given above.

    5. 3.2 5 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. There are four cases explained in the next few slides.There are four cases explained in the next few slides.

    6. 3.2 6 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.

    7. 3.2 7 Case I In planning a balanced plug, we must first calculate the desired height of the plug after the job is complete. We must then calculate the height of the plug just after placement of cement when the workstring is still in place. Case I is where there is no spacer between the cement and mud either in front or behind the cement.In planning a balanced plug, we must first calculate the desired height of the plug after the job is complete. We must then calculate the height of the plug just after placement of cement when the workstring is still in place. Case I is where there is no spacer between the cement and mud either in front or behind the cement.

    8. 3.2 8 Case II is planned with an equal height of spacer ahead of the cement and behind.Case II is planned with an equal height of spacer ahead of the cement and behind.

    9. 3.2 9 Pumping Sequence: 1. Water spacer for annulus: 10 bbls 2. Cement Slurry for Plug: 3. Water spacer behind cement: 2.0 bbls A hypothetical pumping sequence for a Case II balanced plug is shown here.A hypothetical pumping sequence for a Case II balanced plug is shown here.

    10. 3.2 10 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)

    11. 3.2 11 Case III Case III is a balanced plug with a spacer ahead of the cement but none behind.Case III is a balanced plug with a spacer ahead of the cement but none behind.

    12. 3.2 12 Case IV - General Case Case IV is a balanced plug with un-equal heights of spacer ahead and behind the cement, and is the general case.Case IV is a balanced plug with un-equal heights of spacer ahead and behind the cement, and is the general case.

    13. 3.2 13 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 The next few slides gives the general procedure for setting a balanced plug.The next few slides gives the general procedure for setting a balanced plug.

    14. 3.2 14 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.

    15. 3.2 15 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.

    16. 3.2 16 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.

    17. 3.2 17 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) Here are the calculations to design an open hole balanced plug.Here are the calculations to design an open hole balanced plug.

    18. 3.2 18 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

    19. 3.2 19 Calculations for balanced plug 3. Find height (h, ft) cement will occupy when drillpipe is at bottom of plug during pumping:

    20. 3.2 20 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). Find height (ft) water spacer behind cement will occupy in DP. Do not use excess factor. 6. Pressures must balance at bottom of plug

    21. 3.2 21 7. 8. Convert this to feet inside DP. Calculations for balanced plug - cont’d

    22. 3.2 22 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, Calculations for balanced plug - cont’d

    23. 3.2 23 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 Calculations for balanced plug - cont’d

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