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| Cable
Lowering in Open Hole Survey Trains |
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General
Cable lowering is restricted to holes
with inclinations steeper than 45 degrees. Since the magnetic effects of
the steel cable swivel and the cable itself are smaller than the
drilling rods, the Tropari instrument only needs to be separated from
the steel elements by several metres of non-magnetic elements.
Additional elements below the container (instrument is inside) are for
connections and weight for faster lowering in water filled holes. Other
arrangements of the train elements are possible to reduce weight for
example if hand manipulated rope lowering is used in short holes. |
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Notes: Cable
lowering techniques are used where the drill is no longer on the site of
as a fast surveying method in conventional drilling is desired. In the
latter case, some attention should be paid to the integrity of the rocks
penetrated by the bore-hole. Rock fragments may wedge the survey train
at a depth making the retrieval difficult. If a wedged situation occurs,
do not break the cable by using excessive pulling force. Once the cable
is broken, the best retrieval techniques can no longer be used. Contact
Pajari Instruments Ltd. for details. |
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(not to scale) |
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