Downhole wireline tension measurement

Abstract

A downhole string and method of operating where tension in the downhole string is monitored real time so that the tension in the downhole string does not exceed its yield strength. Included with the string is a tension sub for monitoring the tension that includes a sensor in the housing of the tension sub. The sensor can be a strain gauge and can be placed proximate an upper end of the downhole string so that tension in a wireline attached to the string can also be monitored. The portion of the housing having the sensor is narrowed for enhancing sensitivity of monitoring.

What is claimed is: 
     
         1 . A tension sub for use in a downhole string comprising:
 a housing;   a box end on an end of the housing that is coupled to a wireline;   a pin end on an end of the housing that is distal from the box end and that is coupled to a downhole tool; and   a sensor coupled with the housing that is responsive to tension in the housing, so that when the downhole string is deployed downhole and the wireline is put into tension, the tension is transmitted to the housing and sensed by the sensor.   
     
     
         2 . The tension sub of  claim 1 , wherein the sensor comprises a strain gage. 
     
     
         3 . The tension sub of  claim 1 , wherein the sensor is disposed on a reduced diameter portion of the housing. 
     
     
         4 . The tension sub of  claim 1 , further comprising electronics in the housing for communicating what is sensed by the sensor to surface so that tension in the wireline can be monitored real time. 
     
     
         5 . The tension sub of  claim 1 , further comprising a switch for selectively providing communication between the sensor and surface and the downhole tool and surface. 
     
     
         6 . The tension sub of  claim 5 , further comprising electronics in a communication path between the sensor and the switch. 
     
     
         7 . The tension sub of  claim 1 , wherein communication with surface and the downhole tool is through the housing. 
     
     
         8 . The tension sub of  claim 1 , wherein an upper end of the housing connects to a cable head, wherein the cable head attaches to the wireline. 
     
     
         9 . A tension sub for use in a downhole string comprising:
 a housing having a box end that couples with a conveyance means for conveying the downhole string in a wellbore and a pin end that couples with a downhole tool; and   a sensor engaged with the housing and that selectively communicates a signal to the surface that corresponds to a tension in the housing that is sensed by the sensor.   
     
     
         10 . The tension sub of  claim 9 , further comprising electronics in the housing for communicating the signal to the surface. 
     
     
         11 . The tension sub of  claim 9 , wherein the tension in the housing is dependent on a tension in the conveyance means. 
     
     
         12 . The tension sub of  claim 9 , wherein the conveyance means comprises an element selected from the group consisting of a wireline, coiled tubing, a slickline, and combinations thereof. 
     
     
         13 . The tension sub of  claim 9 , wherein the sensor comprises a strain gauge and wherein the strain gauge is placed on a portion of the housing having a reduced outer periphery. 
     
     
         14 . A method of downhole operations comprising:
 providing a tension sub having a housing, a box end, a pin end opposite the box end, and a sensor coupled with the housing;   coupling the box end with a wireline and coupling the pin end to a downhole tool to define a downhole string;   deploying the downhole string in a wellbore; and   monitoring tension in the housing with the sensor and estimating tension in the wireline based on the tension monitored in the housing.   
     
     
         15 . The method of  claim 14 , further comprising adjusting an amount of tension exerted onto the wireline based on the step of monitoring tension in the housing. 
     
     
         16 . The method of  claim 15 , wherein the step of adjusting an amount of tension exerted onto the wireline comprises controlling pressure in the wellbore by pressurizing fluid and pumping the fluid into the wellbore. 
     
     
         17 . The method of  claim 15 , wherein the step of adjusting an amount of tension exerted onto the wireline comprises controlling a pulling force exerted onto the wireline at surface.