Cable length measurement correction system

A method for determining cable length in a well bore for an armored electrical cable coupled between a well tool in a well bore and a spooling winch at a surface above the well bore in which the cable has detectable valid measurement marks disposed along its length at predetermined intervals where the spacing between the valid measurement marks define a premeasured length of cable between the detectable valid measurement marks at a predetermined tension on the cable, the method including the steps of:

• positioning a well tool on the armored electrical cable in a well bore traversing earth formations,
• moving the well tool along the earth formations transversed by the well bore by operating the spooling winch,
• while said cable is moving, detecting only valid measurement marks on the cable which occur within a predefined span of cable length at each successive valid measurement mark on a premeasured length of cable and preventing detection of any measurement marks outside of such predefined span of cable length,
• continuously measuring with a wheel the length of cable between valid measurement marks for each premeasured length of cable at the earth's surface while moving the well tool through a well bore for deriving first wheel measurements of the length of cable between valid measurement marks for each premeasured length of cable,
• continuously comparing each first wheel measurement of the length of cable between valid measurement marks to a first predefined measurement for a length of cable between valid measurement marks for deriving first difference-in-length measurements for each first wheel measurement;
• continuously adjusting the magnitude of the next wheel measurement following each first wheel measurement relative to the magnitude of the preceding first difference-in-length measurement for continuously deriving corrected wheel measurements;
• measuring the tension of the cable in the borehole for deriving first tension measurements,
• determining the elastic stretch values for the cable for each premeasured length of cable as a function of said first tension measurements,
• continuously combining said elastic stretch values for each premeasured length of cable with said corrected wheel measurements for each premeasured length of cable for obtaining length measurements corrected for wheel error and tension;
• continuously determining the magnitude of permanent stretch values for each premeasured length of cable of the cable as a function of said first tension measurements and the number of tension cycles of the cable incurred by a table in well bores for obtaining length measurements corrected for permanent stretch, and
• continuously combining said permanent stretch values for each premeasured length of cable with said corrected wheel measurements for obtaining measurements corrected for permanent stretch.

A method for determining cable length in a well bore for an armored electrical cable coupled between a well tool in a well bore and a spooling winch at a surface above the well bore in which the cable has detectable valid measurement marks disposed along its length at predetermined intervals where the spacing between the valid measurement marks define a premeasured length of cable between the detectable valid measurement marks at a predetermined tension on the cable, the method including the steps of:

• positioning a well tool on the armored electrical cable in a well bore traversing earth formations,
• moving the well tool along the earth formations transversed by the well bore by operating the spooling winch,
• while said cable is moving, detecting only valid measurement marks on the cable which occur within a predefined span of cable length at each successive valid measurement mark on a premeasured length of cable and preventing detection of any measurement marks outside of such predefined span of cable length,
• continuously measuring with a wheel the length of cable between valid measurement marks for each premeasured length of cable at the earth's surface while moving the well tool through a well bore for deriving first wheel measurements of the length of cable between valid measurement marks for each premeasured length of cable,
• continuously comparing each first wheel measurement of the length of cable between valid measurement marks to a first predefined measurement for a length of cable between valid measurement marks for deriving first difference-in-length measurements for each first wheel measurement;
• continuously adjusting the magnitude of the next wheel measurement following each first wheel measurement relative to the magnitude of the preceding first difference-in-length measurement for continuously deriving corrected wheel measurements;
• measuring the tension of the cable in the borehole for deriving first tension measurements,
• determining the cable stretch .DELTA.L value for each predetermined interval of cable from the relationship of:
• .DELTA.L=(KLm2) (2T-CW+Cb-2T.sub.M)
• Where:
• K=elastic stretch coefficient
• T=indicated cable tension
• T.sub.m =tension at which line was marked
• L.sub.m =indicated first continuously corrected wheel measurements
• C.sub.w =Cable Weight
• C.sub.b =Cable Buoyancy
• continuously combining said cable stretch .DELTA.L value for each premeasured length of cable with said corrected wheel measurements for each premeasured length of cable for obtaining length measurements corrected for wheel error and cable stretch .DELTA.L.

A method for determining cable length in a well bore for an armored electrical cable coupled between a well tool in a well bore and a spooling winch at a surface above the well bore in which the cable has detectable valid measurement marks disposed along its length at predetermined intervals where the spacing between the valid measurement marks define a premeasured length of cable between the detectable valid measurement marks at a predetermined tension on the cable, the method including the steps of:

• positioning a well tool on the armored electrical cable in a well bore traversing earth formations,
• moving the well tool along the earth formations transversed by the well bore by operating the spooling winch,
• while said cable is moving, detecting only valid measurement marks on the cable which occur within a predefined span of cable length at each successive valid measurement mark on a premeasured length of cable and preventing detection of any measurement marks outside of such predefined span of cable length,
• continuously measuring with a wheel the length of cable between valid measurement marks for each premeasured length of cable at the earth's surface while moving the well tool through a well bore for deriving first wheel measurements of the length of cable between valid measurement marks for each premeasured length of cable,
• continuously comparing each first wheel measurement of the length of cable between valid measurement marks to a first predefined measurement for a length of cable between valid measurement marks for deriving first difference-in-length measurements for each first wheel measurement;
• continuously adjusting the magnitude of the next wheel measurement following each first wheel measurement relative to the magnitude of the preceding first difference-in-length measurement for continuously deriving corrected wheel measurements;
• measuring the tension of the cable in the borehole for deriving first tension measurements,
• determining the cable stretch .DELTA.L value for each predetermined interval of cable from the relationship of:
• ##EQU4## Where:
• K=elastic stretch coefficient
• T=indicated line tension (in 1000 lbs )
• T.sub.m =tension at which line was magnetically marked
• L.sub.m =indicated length of corrected wheel measurement
• C.sub.w =Cable Weight
• C.sub.b =Cable Buoyancy
• D=Temperature Coefficient ft./1000 ft. 1000 lbs./.degree.F.
• F=Bottom Hole Temperature (.degree.F.)
• continuously combining said cable stretch .DELTA.L value for each premeasured length of cable with said corrected wheel measurements for each premeasured length of cable for obtaining length measurements corrected for wheel error and cable stretch .DELTA.L.

Apparatus for determining cable length in a well bore where there is a change in length of a cable due to stretch of the cable in a well bore wherein the cable is an armored electrical cable coupled between a well tool in a well bore and a spooling winch at a surface above the well bore and in which the cable has valid detectable marks disposed along its length at predetermined intervals and at a predetermined tension to define premeasured lengths, said apparatus including:

• detecting means for detecting valid detectable marks on a cable as the cable transports a well tool through a well bore,
• window means coupled to said detecting means and resposive to a valid detectable mark for initiating a detection span interval in said detecting means for detecting detectable marks as a fucntion of such predetermined intervals where said detection span interval occurs for a defined length of cable which straddles a location on a cable at which a next occuring valid detectable mark should occur,
• measuring means for continuously measuring the length of cable between valid detectable marks at the earth's surface while moving a well tool through a well bore for deriving continuous first measurements of cable length between said valid detectable marks,
• error means responsive to said detecting means for receiving and comparing said first measurements of cable length for each predetermined interval of cable measured between valid detectable marks relative to such premeasured length of cable between valid detectable marks for deriving difference-in-length measurements for each of said first measurements from detected mark to detected mark,
• adjusting means for adjusting each of said continuous first measurements relative to each of the difference-in-length measurements in response to said error means for obtaining first continuously corrected measurements where each of the difference-in-length measurement is applied to each of said first measurements next following a derived difference-in-length measurement so that said continuous first measurements are continuously corrected by said adjusting means.

A apparatus for determining cable length in a well bore where there is a change in length of a cable due to stretch of the cable in a well bore and wherein the cable is an armored electrical cable coupled between a well tool in a well bore and a spooling winch at a surface above the well bore and in which the cable has valid detectable marks disposed along its length at predetermined intervals and at a predetermined tension to define premeasured lengths including:

• detecting means for detecting valid detectable marks on a cable as the cable transports a well tool through a well bore;
• window means coupled to said detecting means for responding to a valid detectable mark for initiating a detection span interval in said detecting means for detecting detectable marks as a fucntion of cable length where said detection span interval occurs for a defined length of cable which straddles a location on a cable at which a next occuring valid detectable mark should occur;
• wheel means for continuously measuring the length of cable between valid measurement marks with a measuring wheel at the earth's surface while moving the well tool for deriving continuous first wheel measurements of cable length between said valid measurement marks,
• error means responsive to said detector means for receiving and comparing said first wheel measurements of cable length for each predetermined interval of cable measured between valid detectable marks relative to such premeasured length of cable between marks for deriving difference-in-length measurements for each of said first measurements from detected mark to detected mark,
• tension means for measuring the tension of the cable in the borehole for deriving first tension measurements,
• elastic stretch means for determining the elastic stretch values for each predetermined interval of cable as a function of said first tension measurements and for supplying said elastic stretch values to said error means for correcting said difference-in-length measurements,
• adjusting means responsive to said error means and said elastic stretch means for providing a length measurement of cable adjusted for changes-in-length due to tension and due to wheel measurements.

Apparatus for determining cable length in a well bore where there is a change in length due to stretch of the cable in a well bore and wherein the cable is an armored electrical cable coupled between a well tool in a well bore and a spooling winch at a surface above the well bore and in which the cable has valid detectable marks disposed along its length at predetermined intervals and at a predetermined tension to define a premeasured lengths, said apparatus including:

• detector means for detecting valid detectable marks on the cable as the cable transports a well tool through a well bore,
• window means responsive to a valid detectable mark for initiating a detection span interval in said detector means as a function of such predetermined intervals where said detection span interval occurs for a defined length of cable which straddles a location on a cable at which a next occuring valid detectable mark should occur;
• measuring means for continuously measuring the length of cable between valid detectable marks at the earth's surface while moving the well tool for deriving continuous first measurements of cable length between said valid detectable marks,
• error means comparing said first measurements for an interval of cable measured between a first valid detectable mark until the next detection of a valid detectable mark within a detection span interval for deriving first difference-in-length measurements of said first measurements from detected mark to detected mark relative to the premeasured lengths of cable between valid detectable marks,
• tension means for measuring the tension of the cable in the borehole for deriving first tension measurements,
• means for determining the cable stretch .DELTA.L from the relationship of:
• .DELTA.L=(KLm2) (2T-CW+Cb-2T.sub.M)
• Where:
• K=elastic stretch coefficient.
• T=indicated cable tension
• T.sub.m =tension at which line was marked.
• L.sub.m =cable length between detectable marks in proper dimensional units.
• C.sub.w =Cable Weight
• C.sub.b =Cable Buoyancy
• and means for adjusting eac of said continuous first measurements with respect to a preceeding continuous first measurement according to the above relationship for correcting cable length measurements.

Apparatus for determining cable length in a well bore where there is a change in length due to stretch of the cable in a well bore and wherein the cable is an armored electrical cable coupled between a well tool in a well bore and a spooling winch at a surface above the well bore and in which the cable has valid detectable marks disposed along its length at predetermined intervals and at a predetermined tension to define premeasured lengths, said apparatus including:

• detector means for detecting valid detectable marks on the cable as the cable transports a well tool through a well bore,
• window means responsive to a valid detectable mark for initiating said detection span interval in said detector means as a function of cable length where said detection span interval has a defined span interval which occurs for a defined length of cable which straddles a location on a cable at which a next occuring valid detectable mark should occur;
• measuring means for continuously measuring the length of cable between valid detectable marks at the earth's surface while moving the well tool for deriving continuous first measurements of cable length between said valid detectable marks,
• error means comparing responsive to said detector means for receiving and comparing said first measurements for an interval of cable measured between a first valid detectable mark until the next detection of a valid detectable mark for deriving first difference-in-length measurements of said first measurements from detected mark to detected mark relative to a premeasured length of cable between marks,
• tension means for measuring the tension of the cable in the borehole for deriving first tension measurements,
• means for determining the cable stretch .DELTA.L from the relationship of:
• ##EQU5## Where:
• K=elastic stretch coefficient.
• T=indicated line tension (in 1000 lbs.)
• T.sub.m =tension at which line was magnetically marked.
• L.sub.m =indicated length (1,000 ft.) as measured by counting detectable marks.
• C.sub.w =Cable Weight
• C.sub.b =Cable Buoyancy
• D=Temperature Coefficient ft./1000 ft. 1000 lbs./.degree.F.
• F=Bottom Hole Temperature (.degree.F.)
• and means for adjusting each of said continuous first measurements with respect to a preceeding continuous first measurement according to the above relationship for correcting cable length measurements.

A method for determining cable length of a cable under tension for determining the change in length of cable due to stretch of the cable coupled between weight means applying tension to a cable and a spooling winch and in which the cable has valid detectable marks disposed along its length at predetermined intervals and at a predetermined tension to define premeasured lengths of cable, including the steps of:

• applying tension on the cable by a weight means,
• moving the cable to change the length of cable between a spooling winch and the weight means,
• detecting a valid detectable mark on the cable for initiating a detection span interval as a function of cable length where said detection span interval occurs for a defined length of cable which straddles a location on a cable at which a next occuring valid detectable mark should occur;
• measuring the length of cable at a spooling winch while spooling or unspooling cable from a spooling winch for deriving continuous first measurement of cable length between valid detectable marks,
• comparing said first measurements for the interval of cable measured between a first valid detectable mark until the next detection of a valid detectable mark within a detection span interval for deriving a first difference measurement of said first measurements from detected mark to detected mark relative to said premeasured length of cable between valid detectable marks,
• adjusting each of said continuous first measurements relative to each of the first difference measurements for obtaining first continuously corrected measurements for each of the next predetermined intervals of cable so that said continuous first measurements are continuously corrected relative to the first difference measurements.

Apparatus for determining cable length between a weight means and a spooling winch for determining the change in length of cable due to stretch of the cable under tension applied by the weight means and in which the cable has detectable marks disposed along its length at predetermined intervals and at a predetermined tension to define premeasured lengths, said apparatus including:

• detecting means for detecting valid detectable marks on a cable as the cable supports the weight means and the weight means is spooled or unspooled from a winch,
• window means responsive to a valid detectable mark for initiating a detection span interval as a function of cable length where said detection span interval occurs for a defined length of cable which straddles a location on a cable at which a next occuring valid detectable mark should occur;
• measuring means for measuring the length of cable at a spooling winch while moving a weight means relative to a spooling winch for deriving continuous first measurements of cable length between valid detectable marks,
• error means responsive to said detector means for receiving and comparing said first measurements for the interval of cable measured between a first valid detectable mark until the next detection of a valid detectable mark within a detection span interval and for deriving a first difference-in-length measurements of said first measurements from detected mark to detected mark relative to a premeasured length of cable between detectable marks,
• adjusting means for adjusting each of said continuous first measurements relative to each of the difference-in-length measurements in response to said error means for obtaining first continuously corrected measurements for each of the next predetermined intervals of cable so that said continuous first measurements are continuously corrected.

Apparatus for determining cable length for determining the change in length of cable due to stretch of the cable between a spooling winch and a weight means and in which the cable has detectable marks disposed along its length at predetermined intervals and at a predetermined tension to define premeasured lengths, said apparatus including:

• detecting means for detecting valid detectable marks on the cable as the cable moves a weight means under tension relative to a spooling winch,
• window means responsive to a valid detectable marks for initiating a detection span interval as a function of cable length where said detection span interval has defined length of cable which straddles a location on a cable at which a next occuring valid detectable mark should occur;
• measuring means for measuring the length of cable at spooling winch while moving the well tool for deriving continuous first measurements of cable length,
• error means responsive to said detecting means for receiving and comparing said first measurements for the interval of cable measured between a first valid detectable mark until the next detection of a valid detectable mark within a detection span interval and for deriving a first difference-in-length measurement of said first measurements from detected mark to detected mark relative to said premeasured length of cable between marks,
• means for measuring the tension of the cable for deriving first tension measurements,
• means for determining elastic stretch correction values for correcting the change of cable length for elastic stretch and,
• means for combining said elastic stretch correction values and said difference-in-length measurements for correcting each of said first measurements.