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Wireline Heave Compensator (WHC)
 The wireline heave compensator (WHC) is an extremely important component in the wireline logging program, due to its role in preventing degraded data as a result of ship's heave. The WHC is a large hydraulic ram with a wireline sheave on one end and is designed to reduce the effect of ship's heave on the downhole tool. As the ship heaves with the billowing sea, an accelerometer located near the ship's center of gravity measures the movement and feeds the data in real time to the WHC. The WHC responds to the ship's heave by adding or removing cable slack to decouple the movement of the ship from the desired movement of the toolstring.
The WHC can adequately compensate in seas of 10 meters or less. Aborting the logging effort should be considered if the seas are greater than 10 meters, as the WHC could reach the end of its operating limits and automatically shut down. This could place the toolstring at risk. Should you be caught in a situation where the ship's heave is greater than 10m and a tool is downhole, you should increase logging speed to 1500 ft/hr to prevent the tool from traveling too far downward as the ship reaches the wave trough.
The WHC is LDEO property and therefore its status should be known and monitored by the logger. However, during logging events the assistant driller or Coretech will operate the WHC, so the logger will not always be directly involved. Also, ODP Logging Services employs a SEDCO mechanic to perform routine maintenance on the unit.
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Hole Finder
 The hole finder is a solid rubber extension that may be run at the end each tool string, excluding the GHMT, to assist the tool past ledges. Experience has shown that it only provides a real benefit in deviated holes, as it closely follows the curves of the borehole and guides the tool down. The Schlumberger engineer is responsible for maintaining and deploying this device. It is important to note that the TAP and TLT cannot be run when the hole finder is deployed.
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Cableheads
Cableheads are used by all wireline logging tools to make a physical connection between the wireline and the tool string. Several different cablehead models exist, including ones with a cablehead tension measurement. The LEH-QT is the most widely used cablehead with tension measuring capability. Tension data are only available when the cablehead is connected to digital tools; therefore, tension data is not available for the WST.
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Wireline
In ODP wireline logging operations, three types of logging cable are typically used. All are 15/32" in diameter and all contain 7 copper conductors. Differences in the cable insulation determine temperature rating.
The standard 7 conductor cable used in ODP is the Vector 7-46P. For moderately high temperature boreholes a short length of Vector 7-46NA is spliced to the main wireline.
For detailed specs, click on the relevant cable type:
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Cable
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Insulation
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Capacitance
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Breaking
Strength
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Temp Rating
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7-46P
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Propylene
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40 pf/ft
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16,700 Lbf
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300° F
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7-46NT
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Teflon
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55 pf/ft
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16,700 Lbf
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450° F
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7-46NA
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Fluoropolymer
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55 pf/ft
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16,700 Lbf
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450° F; 500° F up to 2 hrs
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Sheaves
Sheaves (or pulleys) are used during the logging operation to route the wireline around bends and curves on the rig floor. Sheaves are located at the WHC, at the crown block and adjacent to the pipe racker. It is extremely important that these be given plenty of clearance when rigged to avoid personal injury!
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Another view of a sheave. (This is a night photo.)
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Logging tool string with rigged-up sheave.
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Sources
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Name
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Type
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Uses
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| Cesium 137 |
Chemical
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LithoDensity tool and LWD-CDN |
| Americium-beryllium |
Chemical
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Compensated Neutron Porosity tool and LWD-CDN |
| Californium 252 |
Chemical
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Geochemical tool |
| Minitron |
Electrical
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Accelerator Porosity tool and Geochemical tool |
Sources are handled only by the Schlumberger engineer, including all permitting and paperwork. Should a tool containing a radio-source become stranded or lost downhole, appropriate actions such as tool fishing and well abandonment would occur. Please see the stuck/lost tool section.
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