Downhole force and torque sensing system and method

Abstract

A system and method for sensing at least one force on a downhole tool connected in a workstring, according to which a mandrel is connected in the workstring and is subjected to the force. Two or more sensors sense axial or torsional force on the mandrel and are connected in an electrical circuit to convert the sensed force to an output signal.

What is claimed is:  
     
         1 . A system for sensing force on a downhole tool connected in a workstring, the system comprising: 
 a load-bearing member of the downhole tool;    a plurality of sensors mounted on the load-bearing member and oriented in a manner to sense a force acting on the load-bearing member; and    an electrical circuit connected to the sensors to convert the sensed force to an output signal corresponding to the force.    
     
     
         2 . The system of  claim 1  wherein the load-bearing member is a mandrel.  
     
     
         3 . The system of  claim 2  wherein the sensors are oriented and connected in the circuit in a manner so that sensed bending and torsional forces acting on the mandrel are cancelled.  
     
     
         4 . The system of  claim 2  wherein the sensors are oriented and connected in the circuit in a manner so that the circuit is insensitive to temperature changes.  
     
     
         5 . The system of  claim 2  wherein the sensors comprise: 
 a first pair of sensors mounted on a first portion of the mandrel; and  
 a second pair of sensors mounted on a second portion of the mandrel diametrically opposite the first pair of sensors.  
 
     
     
         6 . The system of  claim 5  wherein the first and second pairs of sensors are oriented in a manner to sense axial force acting on the mandrel.  
     
     
         7 . The system of  claim 6  further comprising: 
 a third pair of sensors mounted on a third portion of the mandrel; and  
 a fourth pair of sensors mounted on a fourth portion of the mandrel diametrically opposite the third pair of sensors, wherein the third and fourth pairs of sensors are oriented in a manner to sense torsional force acting on the mandrel.  
 
     
     
         8 . The system of  claim 7  wherein the third and fourth pairs of sensors are angularly spaced from the first and second pairs of sensors.  
     
     
         9 . The system of  claim 8  wherein the third and fourth pairs of sensors are angularly spaced approximately ninety degrees from the first and second pairs of sensors.  
     
     
         10 . The system of  claim 7  wherein the third and fourth pairs of sensors are oriented and connected in a manner so that sensed bending and axial forces on the mandrel are cancelled.  
     
     
         11 . The system of  claim 7  further comprising an additional circuit connected to the third and fourth pairs of sensors to convert the sensed torsional forces to an additional output signal.  
     
     
         12 . The system of  claim 11  further comprising a transmission system for transmitting the additional output signal to the surface.  
     
     
         13 . The system of  claim 11  further comprising a recording system for recording the additional output signal.  
     
     
         14 . The system of  claim 11  wherein the additional circuit is connected in a Wheatstone bridge configuration.  
     
     
         15 . The system of  claim 1  wherein the force is a torsional force.  
     
     
         16 . The system of  claim 1  wherein the force is an axial force.  
     
     
         17 . The system of  claim 16  wherein the axial force is tension and/or compression.  
     
     
         18 . The system of  claim 1  wherein the circuit is connected in a Wheatstone bridge configuration.  
     
     
         19 . The system of  claim 1  further comprising a transmission system for transmitting the output signal to the surface.  
     
     
         20 . The system of  claim 1  further comprising a recording system for recording the output signal.  
     
     
         21 . A method for sensing force on a downhole tool connected in a workstring, the method comprising the steps of: 
 mounting a plurality of sensors on a load-bearing member of the downhole tool;    orienting the sensors in a manner to sense a force acting on the load-bearing member; and    connecting an electrical circuit to the sensors to convert the sensed force to an output signal corresponding to the force.    
     
     
         22 . The method of  claim 21  wherein the load-bearing member is a mandrel.  
     
     
         23 . The method of  claim 22  wherein the sensors are oriented and connected in a manner so that sensed bending and torsional forces acting on the mandrel are cancelled.  
     
     
         24 . The method of  claim 22  wherein the sensors are oriented and connected in a manner so that the circuit is insensitive to temperature changes.  
     
     
         25 . The method of  claim 22  wherein the circuit is connected in a Wheatstone bridge configuration.  
     
     
         26 . The method of  claim 22  wherein the step of orienting the sensors comprises the steps of: 
 mounting a first pair of sensors on a first portion of the mandrel; and  
 mounting a second pair of sensors on a second portion of the mandrel diametrically opposite the first pair of sensors.  
 
     
     
         27 . The method of  claim 26  wherein the first and second pairs of sensors are oriented in a manner to sense axial force acting on the mandrel.  
     
     
         28 . The method of  claim 27  further comprising the steps of: 
 mounting a third pair of sensors on a third portion of the mandrel; and  
 mounting a fourth pair of sensors on a fourth portion of the mandrel, wherein the third and fourth pairs of sensors are oriented in a manner to sense torsional force acting on the mandrel.  
 
     
     
         29 . The method of  claim 28  wherein the third and fourth pairs of sensors are angularly spaced from the first and second pairs of sensors.  
     
     
         30 . The method of  claim 29  wherein the third and fourth pairs of sensors are angularly spaced approximately ninety degrees from the first and second pairs of sensors.  
     
     
         31 . The method of  claim 28  wherein the third and fourth pairs of sensors are oriented and connected in a manner so that sensed axial and bending forces on the mandrel are cancelled.  
     
     
         32 . The method of  claim 28  further comprising the step of transmitting the output signal to the surface.  
     
     
         33 . The method of  claim 32  further comprising the step of utilizing the transmitted output signal to control the operation of the downhole tool.  
     
     
         34 . The method of  claim 28  further comprising the step of recording the output signal.  
     
     
         35 . The method of  claim 28  further comprising the step of providing an additional circuit connected to the third and fourth pairs of sensors to convert the sensed torsional force to an additional output signal.  
     
     
         36 . The method of  claim 35  further comprising the step of transmitting the additional output signal to the surface.  
     
     
         37 . The method of  claim 36  further comprising the step of utilizing the transmitted additional output signal to control the operation of the downhole tool.  
     
     
         38 . The method of  claim 35  further comprising the step of recording the additional output signal.  
     
     
         39 . The method of  claim 35  wherein the additional circuit is connected in a Wheatstone bridge configuration.  
     
     
         40 . The method of  claim 21  wherein the force is tension and/or compression.