TON MILE CALCULATION

• Heavy wear would occur in a few localized sections where the rope makes contactwith the traveling block sheaves, and where the rope makes contact with the crown block sheaves when the slips are pulled going in or coming out of the hole, and on the drum where each wrap of rope crosses over the rope on the layer below. Broken wires at these points of critical wear would result in the retirement of the entire string up, even though the remainder of the rope is in good condition.

• Do not cut too much wire rope frequently, there will be an obvious waste of usable drilling line, which will result in higher than necessary rig operating costs. However, if the rope is moved through the reeving system too slowly, sooner or later some section of the drilling line will become worn and damaged to such an extent that there will be a danger of failure, injury to personnel, damage to equipment and expensive downtime. At the very least, it will be necessary to make a “long cut” to eliminate some broken wires.

• For these reasons, it is important that the drilling line be cut at the proper rate. The purpose of this simplified cut-off practice is to give the drilling crew a method for keeping track of the amount of work done by the drilling line, and a systematic procedure for making cuts of the appropriate length at the appropriate time. The objective is to obtain maximum rope service without jeopardizing the safety of the rig operation.

• In conjunction with the record keeping required for the cut-off procedure, daily visual inspection of the drilling line should be made for broken wires and any other rope damage. It must be remembered that in all cases, visual inspection of the wire rope by the drilling crew must take precedence over any pre-determined calculations.

• The only complicated part of a cut-off procedure is the determination of how much work has been done by the wire rope. Methods such as counting the number of wells drilled or keeping track of days between cuts are not accurate because the load changes with depth and with different drilling conditions. The various operations performed (drilling, coring, fishing, setting casing, etc.) subject the rope to different amounts of wear.

• For an accurate record of the amount of work done by a drilling line, it is necessary to calculate the weight being lifted and the distance it is raised and lowered. In engineering terms, work is measured in foot-pounds. On a drilling rig the loads and distances are so great that we use “ton-miles.” One ton-mile equals 10,560,000 foot-pounds, and is equivalent to lifting 2,000 pounds a distance of 5,280 feet.

• Use the Ton-mile indicator.

FORMULA FOR WORK DONE: Total work done by line during trip is equal to;

T = 2000 x 5280 M 4D Wm D) D(Ls C₂⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + + + where;

D = Depth of the hole in meter ft, Ls = Length of drill pipe stand, meter ft N = Number of stands of drill pipe, Wm = Effective weight of drill pipe lb/ft.

M = Total weight of traveling block assembly lb

C = Effective weight of drill collar minus the effective weight of same length of drill pipe lb T = Ton miles

Note : For round trip work done will be twice of the calculated above. 9.13 CUT-OFF PROGRAM

So long as the maximum ton-mile accumulation shown on the program is not exceeded, a cut may be made whenever it is convenient. It is only necessary to total the ton-miles accumulated since the last cut and divide by 19.0 to determine what length to cut. This way the ton-miles per foot cut will always be exactly 19.0, and the wear on the drilling line will be uniformly spread along its length.

1. Work done can be calculated by the following method. During slip and cut operations the travelling equipment (block and hook) will be properly secured with hanging off pendants so that inadvertent movement is not possible. Slip & cut programs should be continually evaluated to maximize efficiency and minimize waste.

2. Whatever program is used, it should be followed throughout the life of one entire drilling line. If no long cuts are required, and it is believed that more service can be obtained from a line, the goal can be raised one ton-mile per foot cut. This procedure should be followed until the optimum goal is found.

3. Daily visual inspection of the drilling line should be made for broken wires and any other rope damage.

4. Avoid accumulating more ton-miles between cuts than the maximum shown on the program for your rig even on the first cut of a new line.

5. It is best not to run up to the maximum permitted ton-miles each time between making a cut, as some problem on your rig could prevent a cut being made at the proper time and lead to a ton-mile over run. A better approach is to bounce around on your program, cutting with a new ton-mile accumulation sometimes and alternating with a medium or higher ton-mile accumulations. This practice does not waste wire rope because you are always cutting off lengths in proportion to the work accumulated.

6. Accurate measurement of the length to cut is very important. A steel tape should be used when making this measurement.

7. When stringing back from 12 to 10 lines, or from 10 to 8 lines, make a cut of the appropriate length based upon the ton-mile accumulation at that time. This procedure will shift the critical wear points on the rope during heavy operations such as casing lowering.

8. Keep your wire rope history sheets accurate and complete.

9. Calculate ton-miles during drilling after each round trip. Failure to record Ton-miles during drilling is probably the most common mistake made in cut-off practice.

10. The best cut-off program is the one with the most consistent ton-mile per foot cut values. By staying as close as possible to the Ton-mile goal you will avoid long cuts and maintain the safest and most economical use of drilling line.

11. No. of slips between cut offs can vary considerably depending upon drilling conditions and on the length and frequency of cut offs.

9.14 CUT-OFF PRACTICE FOR DRILLING LINE Cumulative work before first Cut- off

Work done by a wire line in Ton -miles with respect to height of mast & diameter of wire line for the first cut can be obtained as:

Derrick Formation Total work of drilling line before the first cut off

or Mast Hardness _{1” 1 1/8” 1 1/4” 1 3/8” 1 1/2”} Height (ft)

Ton miles Ton miles Ton miles Ton miles Ton miles

80-87 Very hard 500 Hard 500 Medium 500 Soft 600 94-100 Very hard 500 600 Hard 500 700 Medium 500 800 Soft 600 900 126-131 Very hard 600 1000 Hard 700 1100 Medium 800 1200 Soft 900 1300 133-138 Very hard 600 1000 Hard 700 1100 Medium 800 1200 Soft 900 1300 142-147 Very hard 1000 1600 Hard 1100 1800 Medium 1200 2000 Soft 1300 2100 187-189 Very hard 1600 2000 Hard 1800 2200 Medium 2000 2400 Soft 2100 2600

Note: All the ton-miles in the table have been calculated using a safety factor of 5.Every body is

aware of that this safety factor often falls consistently below 5