Method for pre-stressing armored well logging cable

Claim 2

In the method of manufacturing a well logging cable comprising a central cable core, a covering layer of flexible tape material wound about said central core, an inner armor layer of closely spaced helically wound metallic strands disposed about said central core and said covering layer, and an outer armor layer of closely spaced helically wound metallic strands disposed about said inner armor and inclined opposite to said inner strands, said central cable core containing a plurality of outer conductors disposed around a central conductor, each said conductor being insulated with a coating of viscoelastic thermoplastic insulation material, the improvement whereby said central cable core is permanently compacted, substantially eliminating the interstices between adjacent insulated conductors thereof, and the well logging cable is thereby made to exhibit essentially no irreversible permanent stretch when subjected to the tensions and temperature cycles encountered in logging a well, which improvement comprises the steps of: Taking the cable, after the armor layers have been wrapped around said central core, and passing said cable between a payout means and a takeup means under a substantially constant tension less than about two-thirds the breaking strength of said cable but sufficient to cause said armor layers to elongate and thereby supply inward radial compressive forces on said central cable core; as said cable passes between said payout and said takeup means, heating a portion of the thus-tensioned cable to a degree sufficient to cause said thermoplastic insulation material in such heated portion to deform under said inward radial compressive forces and substanTially to fill the previously existing interstices between the insulated conductors of said central cable core; and before the heated portion of the cable reaches the takeup means and while maintaining said tension, cooling said portion to ambient conditions.

Claim 3

The method of claim 1 wherein the step of heating the tensioned cable is performed by passing an electric current through the outer armor layers comprising a portion of the structure of the cable.

Claim 4

The method of claim 1 wherein the step of cooling the tensioned cable is performed by continuously passing the tensioned cable through a trough containing a coolant material.

Claim 5

In the method of manufacturing a well logging cable comprising a central cable core, a covering layer of flexible tape material wound about said central core, an inner armor layer of closely spaced helically wound metallic strands disposed about said central core and said covering layer, and an outer armor layer of closely spaced helically wound metallic strands disposed about said inner armor and inclined opposite to said inner strands, said central cable core containing a plurality of substantially cylindrical conductors, each said conductor being insulated with a substantially uniform thickness of thermoplastic ethylene-propylene polymer insulation material, the improvement whereby said central cable core is permanently compacted, substantially eliminating the interstices between adjacent insulated conductors thereof, and the well logging cable is thereby made to exhibit essentially no irreversible permanent stretch when subjected to the tensions and temperature cycles encountered in logging a well, which improvement comprises the steps of: passing the cable between a payout means and a takeup means under a substantially constant tension less than about two-thirds the breaking strength of said cable but sufficient to cause said armor layers to elongate and thereby supply inward radial compressive forces on said central cable core; heating a portion of the thus-tensioned cable, as it passes bween said payout and said takeup means, to a temperature below the melting point of said ethylene-propylene polymer but sufficient to cause said ethylene-propylene polymer to deform under said inward radial compressive forces and to fill substantially the previously existing interstices between the insulated conductors of said central cable core; and thereafter, while maintaining said tension and before said heated portion reaches said takeup means, passing said heated cable portion through a cooling trough long enough to reduce the cable temperature to ambient conditions.

Claim 6

In the method of manufacturing a well logging cable comprising a central cable core, a covering layer of flexible tape material wound about said central core, an inner armor layer of closely spaced helically wound metallic strands disposed about said central core and said covering layer, and an outer armor layer of closely spaced helically wound metallic strands disposed about said inner armor and inclined opposite to said inner strands, said central cable core containing a plurality of substantially cylindrical conductors, each said conductor being insulated with a substantially uniform thickness of thermoplastic ethylene-propylene polymer insulation material, the improvement whereby said central cable core is permanently compacted, substantially eliminating the interstices between adjacent insulated conductors thereof, and the well logging cable is thereby made to exhibit essentially no irreversible permanent stretch when subjected to the tensions and temperature cycles encountered in logging a well, which improvement comprises the steps of: passing the cable between a payout means and a takeup means under a substantially constant tension less than about two-thirds the breaking strength of said cable but sufficient to cause said armor layers to elongate and thereby supply inward radial compressive forces on said central cable core; heating a portion of the thus-tensioned cable, as it passes bween said payout and said takeup means, to a temperature below the melting point of said ethylene-propylene polymer but sufficient to cause said ethylene-propylene polymer to deform under said inward radial compressive forces and to fill substantially the previously existing interstices between the insulated conductors of said central cable core; and thereafter, while maintaining said tension and before said heated portion reaches said takeup means, passing said heated cable portion through a cooling trough long enough to reduce the cable temperature to ambient conditions.

Claim 7

The method of claim 4 wherein the tension between the payout means and the takeup means is maintained at approximately 6,000 pounds.

Claim 8

The method of claim 4 wherein the tensioned cable is heated by passing an electric current through the outer armor layers of said cable as the cable passes from said payout means to a point C intermediate between said payout means and said takeup means.

Claim 9

The method of claim 6 wherein the cable is heated sufficiently to raise the temperature of the conductor insulation to approximately 250*F.

Claim 10

The method of claim 7 wherein the cable is cooled by passing said cable through a trough of coolant material located between intermediate point C and said takeup means and long enough to lower the temperature of the conductor insulation of said cable to approximately 70*F while said cable moves through said trough.

Claim 11

A well logging cable manufactured by the method of claim 8.