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PETE 661 Drilling Engineering

Slide 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. . Slide 3 of 67. Read: Applied Drilling Engineering, Ch. 3 . . HW

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PETE 661 Drilling Engineering

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    1. Slide 1 of 67 PETE 661 Drilling Engineering

    2. Slide 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

    3. Slide 3 of 67 Read: Applied Drilling Engineering, Ch. 3

    4. Slide 4 of 67 Balanced Cement Plug Fig. 3.11- Placement technique used for setting cement plug.

    5. Slide 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 may be run to enchance cement bonding.

    6. Slide 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.

    7. Slide 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.

    8. Slide 8 of 67 Case I

    9. Slide 9 of 67 Case I

    10. Slide 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

    11. Slide 11 of 67 Example - Case I (a) Calculate volume of cement slurry required:

    12. Slide 12 of 67 Example - Case I (b) Calculate actual height of plug when DP is in place at 9,000 ft. If then

    13. Slide 13 of 67 Example - Case I (b) contd In this case,

    14. Slide 14 of 67 Example - Case I (b) contd

    15. Slide 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 equal inside the DP and in the annulus, at 9,000.

    16. Slide 16 of 67 Example - Case I

    17. Slide 17 of 67 Example - Case I

    18. Slide 18 of 67 Example - Case I Also required: Class H cement reqd Mix water reqd

    19. Slide 19 of 67

    20. Slide 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

    21. Slide 21 of 67 Example - Case II (a) & (b) From previous example:

    22. Slide 22 of 67 Example - Case II (c) Calculate height (length) of water spacer in DP: In annulus,

    23. Slide 23 of 67 Example - Case II (d) Volume of water spacer inside DP

    24. Slide 24 of 67 Example - Case II (e) A balanced plug requires that

    25. Slide 25 of 67 Example - Case II (e) contd

    26. Slide 26 of 67 Example - Case II Volume of mud required to displace cement and spacers = 833.0 ft3 VDispl = 148.5 bbls

    27. Slide 27 of 67 Check

    28. Slide 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

    29. Slide 29 of 67 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)

    30. Slide 30 of 67 Case III

    31. Slide 31 of 67 Case IV - General Case

    32. Slide 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 complete circulation to make sure system is balanced. 3. Pump spacers and cement per calculations and displace w/proper amount of fluid

    33. Slide 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 calculations has been made. Stab inside BOP, or have a heavy slug (small volume slug) ready to pump.

    34. Slide 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 completely balanced mud system. 6. If pulling wet, slug pipe and pull out of hole.

    35. Slide 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 with DP just above top of first plug.

    36. Slide 36 of 67 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)

    37. Slide 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

    38. Slide 38 of 67 Calculations for balanced plug 3. Find height (h, ft) cement will occupy when drillpipe is at bottom of plug during pumping:

    39. Slide 39 of 67 Calculations for balanced plug - contd 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

    40. Slide 40 of 67 7. 8. Convert this to feet inside DP. Calculations for balanced plug - contd

    41. Slide 41 of 67 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 reqd, Calculations for balanced plug - contd

    42. Slide 42 of 67 11. If yield not shown, calculate from formula for mixtures. Solve for in this formula. Add the Vs for yield. 12. Total mix water will be times number of sacks. VW total = (VW / sk) * N Calculations for balanced plug - contd

    43. Slide 43 of 67 Cementing - Salt Solutions Use of salt in Cement Slurries Unsaturated Salt Solutions Saturated Salt Solutions Types Cements Cement Additives Examples

    44. Slide 44 of 67 Salt in Cement Slurries Salt 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

    45. Slide 45 of 67 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.

    46. Slide 46 of 67 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.

    47. Slide 47 of 67 Salt in Cement Slurries

    48. Slide 48 of 67 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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    56. Slide 56 of 67 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.

    57. Slide 57 of 67 Problem : Salt Solutions (i) Assuming that

    58. Slide 58 of 67 Problem : Salt Solutions (ii) From the chart, { 9.51 lb/gal vs. 9.8 lb/gal !! } { what if we had 60% salt? }

    59. Slide 59 of 67

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    63. Slide 63 of 67 Problem Calculate the density and yield of a cement slurry consisting of: 65% Class A cement 35% Pozmix cement, 6% bentonite BWOC and 10.9 gal/sk of water.

    64. Slide 64 of 67 Problem (i) Initial tabulations and calculations: Weight Specific Density Component lbs/sk Gravity lbs/gal Class A 94 3.14 8.33*3.14 = 26.16 Pozmix 74 2.46 8.33*2.46 = 20.49 Bentonite 2.65 8.33*2.65 = 22.07 Water 1.00 8.33*1.00 = 8.33

    65. Slide 65 of 67 Problem (ii) Determine the properties of one sack of dry cement mixture; 65% Class A and 35% Pozmix:

    66. Slide 66 of 67 Problem (iii) Determine density and yield of final slurry:

    67. Slide 67 of 67 Problem

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