Weakpoint
Overview • We Weak akpo poin intt ca calc lcul ulat atio ion n pr proc oces ess s • Cable weigh ghtt in in fl fluid • Maximum Safe Pull • Min an and Ma Max Pu Pullout
Why do we need a W eakpoint?
A weak point is needed to enable us to free the cable from the Tool in the event of Tool getting stuck Whether we actually free the cable at the weakpoint or not depends on other factors, but at all times a Wireline service company is expected to be able to free the wireline from the tool. The weakpoint should never be broken unless both the Service company and the Customer are in agreement. Breaking the weak point inadvertently can bring heavy penalties to the Service company Not being able to break the weak point, when needed, can also bring heavy penalties to the service company
Properties of Cables Summary Cable
O.D”
B.S
Max Load lbs
Inner / Strength
Outer / Strength
Temp degF
Min Sheave Inch
Cond Resist. Ω /kft
Wt in air Lbs/kft
Stretch Ft/kft/kl bs
Sp. Gravity
1K22PP
7/32
5200
2600
15/125
15/272
300
14
4
94
2.2
6.48
1K22PZ
7/32
5200
2600
15/125
15/272
500
14
4
97
2.2
6.67
1N22PZ
7/32
5200
2600
12/204
18/204
500
14
4
97
2.5
6.67
1N32PTZ
5/16
11000
5500
12/420
18/420
500
18
2.1
195
1.2
6.56
7J46RTZ
15/32
18000
9000
24/323
24/520
500
24
9.8
341
0.77
5.08
7H47RTZ
0.474
22000
11000
18/469
18/910
500
30
9.8
392
0.61
5.91
Cable identification used above is f or Camesa cables
Tension measured here
Vertical air well with 15/32” cable
Weakpoint
5,000’ Tension on surface = 341 x 5 (kft) = 1705 lbs 10,000’ Tension on sur face = 3410 lbs
Straight Hole No Sources of Friction No MUD Tool wt? Cable stopped
Tension measured here
Vertical well with mud and 15/32 cable
Weakpoint
5,000’ Tension on Surface 341 x 5 (kft) x 0.733 = 1250 lbs
10,000’ Tension on surface = 3410 x 0.733 = 2500 lbs
Straight Hole No Sources of Friction MUD of 11.32 ppg Cable stopped Specific gravity of cable =5.08 or 42.4 ppg Buoyancy Factor = (42.4 – 11.32)/ 42.4 = 0.733
1 gm/cc = 8.3454 ppg
(SG * 8.3454) − Mudwt SG * 8 . 3454
So far we have seen
When the Tool is stuck, the Tool weight is supported by whatever is holding the Tool and therefore Tool weight does NOT act on the Weakpoint In order to put tension on the weakpoint we MUST pull over and above the Cable weight in Mud At the same time we can never exceed 50% of the Minimum Breaking strength of cable OR Tension on Weak Point + Cable Weight in Mud < Half Breaking Strength of Cable
Therefore a simply formula for weakpoint can be:
Weak Point < Half Breakin g Strength of Cable – Cable Weight in Mud
Process… 1.
Determine the weight of the wireline in air and in water and min. breaking strength
2.
Calculate the weight of wireline in BH fluid
3.
Calculate the weight of wireline at TD
4.
Calculate the ideal weak point
5.
Select a weak point (WP) with max breaking strength less
How to select a correct WeakPoint The weakpoint has to be selected before our tools enter the well To select Weakpoint we need: 1. Breaking Strength of the Logging Cable
Example 1: Cable is 15/32” T.D = 16,000 ft
2. Target Depth (T.D) of Well
Mud = 9 ppg
3. Mud Density in well
1 gm/cc = 8.3454 ppg
Steps 15/32 cable means Breaking strength = 18000 lbs, sp.gravity = 5.08, Wt.in air = 341 Convert T.D into Kft. Apply formula
CableCard
15/32 Camesa
WeakPoint < Half Breaking Strength of Cable – Cable Weight in Mud Weak point < 9000 – (16 x 341 x BF) or 9000 – (5456 x BF) Weak point < 9000 – 4298 = 4702 lbs
BF = (42.4 – 9)/42.4 = .7877
How to select a correct WeakPoint The weakpoint has to be selected before our tools enter the well
Example 1 Cable is 15/32”
To select Weakpoint we need
T.D = 16,000 ft
1. Breaking Strength of the Logging Cable
Mud = 9 ppg
2. Target Depth (T.D) of Well 3. Mud Density in well
Steps: 15/32 cable means Breaking strength = 18000 lbs, Wt.in air = 341, Wt in water = 274 Convert T.D into Kft. Apply formula
cable_cards.xls
15/32 Camesa
WeakPoint < Half Breaking Strength of Cable – Cable Weight in Mud Weak point < 9000 – 16 x {341 – [(341-274) x 9/8.33]} Weak point < 9000 – 4298 = 4702 lbs
It’s not over yet
Depending on the type of Cable Head being used, weak points can be selected from a set of fixed values. We MUST select the highest value available that is lesser than our calculated weakpoint In the last example we calculated 4702 lbs Available weak points for DITS Cable Head are 1. 4000 lbs 2. 5000 lbs 3. 6000 lbs
(A Weak Point cannot be selected with a maximum breaking strength in excess of the ideal weak point value)
4. 7000 lbs
Write down the weak point finally selected and installed on the Cable Head Record and inside the Logging Truck. In this example we have selected 4000 lbs.
Some more examples Example 2 Cable is Slammer
Weak point < 11000 – (16 x 392 x BF) or 11000 – (6272 x BF) < 11000 – (6272 x 0.81752)
BF = (49.32 – 9)/49.32
T.D = 16,000 ft Mud = 9 ppg Example 3
< 5872 lbs
Weak point < 9000 – (10 x 341 x BF) or 9000 – (3410 x BF)
Cable is 15/32” T.D = 10,000 ft Mud = 9 ppg
Example 4 Cable is 15/32” T.D = 16,000 ft Mud = 12 ppg
Weak point < 9000 – (16 x 341 x BF) or 9000 – (5456 x BF) Alternate formula for finding weight of Cable in Fluid WCBF = WCair – [(WCair – WCwater ) X Mud wt in ppg / 8.33]
Weak points
Open Hole Cablehead
Weakpoint Hardware
Counting Conductors – see next slide! •
“ 10/08 Manual_D00000402_1.pdf Confidential & Proprietary Cable Strength and Safety Consideratio ns 3-7
•
The rope sock et strength f or a new monoconductor line is:
•
85% x Total number of outer armors x outer armor breaking strength
•
The rope socket strength for a new Multi-conductor li ne is:
•
For 7/16 and 15/32 cables: 85% x Number of outer armors x outer armor breaking strength
•
For sl ammer cables (larger th an .468) : 80% x Number of outer armors x outer armor breaking strength
•
ONLY use Outer Armors in your calcu lation as per OEB 2010-042 -Cased Hole Cable Head,
Mono-cable Head Rehead Standardization (Supersedes OEB 2006/065 and OEB 2008/104) . –
*make comparison to chart
Mono-head Weak points
Mono-head weak points_REV3.xls
MSP Max Safe Pull At Halliburton, Maximum Safe Pull (MSP) at any depth = Weight of Cable in Mud at that d epth + 66% of Weak Point Rating installed in t he Cable Head (when a weak point has a min and max rating, we use the MIN for MSP calculation as extra safety)
Maximum Safe Pull is NOT one value but a value that depends on the depth where the Tool is STUCK
Maximum Safe Pull can be calculated quickly for a vertical well.
For deviated wells it can only be estimated. Use Halliburton Weakpoint and Pull Calculator. WPCalc or Cerebus.
Note: Some other service companies use 75% of weak point as overpull. Please note we use 66%
Back to Example1 Example 1
What is the MSP at 16000ft? Cable weight at 16000 ft + 66% of 4000 (16 x 341 x BF) + 2667 4298 + 2667 = 6965 lbs
BF = 42.4 – 9 = .7877 42.4
Surface Tension should NOT exceed 6965 lbs
Cable is 15/32” T.D = 16,000 ft Mud = 9 ppg 1 gm/cc = 8.3454 ppg Calculated WP = 4702
What is the MSP at 12000ft?
Installed WP = 4000
Cable weight at 12000 ft + 66% of 4000 (12 x 341 x BF) + 2667 3223 + 2667 = 5890 lbs
BF = 42.4 – 9 = .7877 42.4
Surface Tension should NOT exceed 5890 lbs
Some more examples Example 2
Weak point < 11000 – (16 x 392 x BF) or 11000 – (6272 x BF)
Cable is Slammer
< 11000 – (6272 x 0.81752)
BF = 49.32 – 9
T.D = 16,000 ft Mud = 9 ppg
< 5872 lbs
Engineer decided to install 6000 lbs WP Calculate the MSP at 9000 ft MSP at 9000 ft = Weight of Cable at 9000 ft + 66% of 6000 MSP = (9 x 392 x BF) + (4000) MSP = 3528 x 0.81752 + 4000 MSP = 2884.2 + 4000 MSP = 6884 lbs
49.32
Cased Hole Example Example 3 Cable is 7/32” 1K22
Cable
O.D”
B.S
Max Load lbs
Inner / Strength
Outer / Strength
1K22PP
7/32
5200
2600
15/125
15/272
1K22PZ
7/32
5200
2600
15/125
15/272
T.D = 10,000 ft Mud = 11 ppg
Wt in air /water Lbs/kft
Stretch Ft/kft/kl bs
Sp. Gravity gm/cc
94 / 74.9
2.2
6.48
97 / 77.8
2.2
6.67
Calculate Weak Point Select Weak Point Find MSP at 5000 ft 1 gm/cc = 8.3454 ppg
Min and Max Pull out Tension
This is the tension that needs to be applied on the Weakpoint to break it free from the Cablehead.
Example The # 6 weakpoint has a min of 5900 lbs and a max of 6600 lbs Therefore in order to break a #6 weakpoint
Min tension on surface = Cable weight in mud at stuck depth + Min rating of WP Max tension on surface = Cable weight in mud at stuck depth + Max rating of WP
Conclusion • Weakpoint calculation process • Cable weight in fluid • Maximum Safe Pull • Min and Max Pull out tension “The will to win means nothing without the will to prepare” Juma Ikangaa , Marathon Runner and Trainer
RWCH – Releasable Wireline Cable Head • What is the benefit? – Consider the following… •
2000lb toolstring
•
Cable 24k# MBS
•
260lb/kft cable weight in mud
•
TD 18000ft, CSG 10000ft
•
What is the ideal weak point? Assuming the ideal weak point is available – what max safe pull can you exert when the tool is stuck at TD? How about if you had an RWCH?
– Now consider the tool is stuck at 10000 ft what’s the max safe pull? How about if you had an RWCH?
