Wellbore mechanical caliper tool

Abstract

A wellbore caliper tool is provided for measuring a wellbore diameter without an additional wireline trip. The caliper tool includes a collar, measurement bands coupled to the collar at one end and sliding blocks on the other. The measurement bands can extend radially from the collar, which causes the sliding blocks to move within the collar. Electromagnetic sensors in the collar measure an electromagnetic field created by magnets in the sliding blocks to determine the position of the sliding blocks. The position of the sliding blocks is used to calculate the distance that the measurement bands extend and to calculate the wellbore diameter. The caliper tool includes an actuating mechanism that holds the sliding blocks in place until a differential pressure is applied by pumping fluid into the caliper tool.

What is claimed is: 
     
         1 . A wellbore caliper tool, comprising:
 a collar;   measurement bands coupled to the collar, the measurement bands configured to extend radially away from the collar when activated;   sliding blocks, each of the sliding blocks being coupled to one of the measurement bands, the sliding blocks being configured to freely move axially within the collar when activated; and   an actuation mechanism,   wherein, when the wellbore caliper tool is deactivated, the actuating mechanism exerts a force on the sliding blocks that holds the measuring bands in a position that is flush or nearly flush to an outer surface of the collar.   
     
     
         2 . The wellbore caliper tool of  claim 1 , wherein, when the wellbore caliper tool is activated, the actuating mechanism releases the sliding blocks, which causes the measurement bands to extend radially away from the outer surface of the collar and the sliding blocks to move axially based on a distance that the corresponding measurement bands extend. 
     
     
         3 . The wellbore caliper tool of  claim 2 , wherein the sliding blocks include magnets, and the wellbore caliper tool includes electromagnetic sensors that measure positions of the magnets to determine the positions of the sliding blocks. 
     
     
         4 . The wellbore caliper tool of  claim 1 , wherein the actuation mechanism comprises:
 an actuation driver;   an actuation member; and   a constraining member.   
     
     
         5 . The wellbore caliper tool of  claim 4 , wherein
 the constraining member holds a dynamic member of the actuation driver in a first position when the wellbore caliper tool is deactivated, and   the dynamic member holds the actuation member in a second position when the wellbore caliper tool is deactivated.   
     
     
         6 . The wellbore caliper tool of  claim 5 , wherein the wellbore caliper tool is activated by:
 pumping fluid through the wellbore caliper tool at a pressure that causes the constraining member to fail and release the dynamic member, and   reducing the pressure of the pumped fluid so that a coil spring exerting a force on the actuation member causes the actuation member to move axially away from the sliding blocks.   
     
     
         7 . The wellbore caliper tool of  claim 5 , wherein the dynamic member includes a cam profile that causes the dynamic member to rotate during activation and deactivation of the wellbore caliper tool. 
     
     
         8 . A method for measure the width of a wellbore, comprising:
 installing a wellbore caliper tool on drilling string, the wellbore caliper tool comprising:
 a collar, 
 a measurement bands coupled to the collar, the measurement bands configured to extend radially away from the collar when activated, 
 a sliding blocks, each of the sliding blocks being coupled to one of the plurality of measurement bands, the sliding blocks being configured to freely move axially within the collar when activated, and 
 an actuation mechanism, 
   inserting the wellbore caliper tool into the wellbore;   pumping drilling fluid into the wellbore caliper tool at a first pressure above a first threshold pressure;   reducing the pumped drilling fluid to a second pressure below a second threshold pressure;   receiving measurements corresponding to positions of the sliding blocks; and   calculating the wellbore width based on the measurements.   
     
     
         9 . The method of  claim 8 , wherein the actuation mechanism comprises:
 a dynamic member;   an actuation member; and   a constraining member, wherein, when the wellbore caliper tool is deactivated, the constraining member holds dynamic member in place, and the dynamic member holds the sliding blocks in place.   
     
     
         10 . The method of  claim 9 , wherein
 pumping drilling fluid into the wellbore caliper tool at the first pressure causes a constraining member of the actuation mechanism to fail,   the constraining member failing causes the dynamic member to axially separate from the actuating member,   reducing the pumped drilling fluid to the second pressure causes the actuating member to move axially toward the dynamic member, and   the actuating member moving axially toward the dynamic member released the sliding blocks, which in turn causes the measurement bands to extend radially from the collar to an inner surface of the wellbore.   
     
     
         11 . The method of  claim 10 , wherein a coil spring exerts a force on the actuating member that causes the actuating member to move axially toward the dynamic member when the drilling fluid is reduced to the second pressure. 
     
     
         12 . The method of  claim 10 , wherein the wellbore width is calculated based on a known relationship between positions of each of the sliding blocks and a corresponding distance that the measurement bands extend from the collar. 
     
     
         13 . The method of  claim 8 , wherein the measurements corresponding to positions of the sliding blocks are received from electromagnetic sensors and include measurements of an electromagnetic field created by magnets in the sliding blocks. 
     
     
         14 . The wellbore caliper tool of  claim 12 , wherein the wellbore width is calculated using the measurements of the electromagnetic field created by the magnets in the sliding blocks. 
     
     
         15 . An offset module that can be deployed in a wireline drilling assembly, comprising:
 a piston that separates a high pressure region from a low pressure region;   a constraining member that controls unintended movement of the piston, the constraining member being designed to fail at a predetermined differential pressure;   blades coupled to the piston;   angled members coupled to each of the blades such that the angled members convert advancement of the piston to radial deployment of the blades; and   a ratchet ring wrapped around an outer surface of the piston that allows the piston to move axially in a single direction.   
     
     
         16 . The offset module of  claim 15 , wherein the high pressure region corresponds to a bore in the wireline drilling assembly. 
     
     
         17 . The offset module of  claim 15 , wherein the low pressure region corresponds to an annulus in the wireline drilling assembly. 
     
     
         18 . The offset module of  claim 15 , wherein
 the ratchet ring includes first thread features on an inner diameter of the ratchet ring,   the piston includes second thread features on an outer diameter of the piston, the second thread features being complementary to the first thread features, and   the first thread features and second thread features having flank angles that are biased in a single direction such that an axial force applied to the ratchet ring allows the ratchet ring to expand over the piston in the single direction.   
     
     
         19 . The offset module of  claim 15 , wherein the piston advances axially in response to fluid being pumped into the offset module above a threshold differential pressure that causes the constraining member to fail. 
     
     
         20 . The offset module of  claim 15 , wherein the ratchet ring fails when a load above a threshold load is applied to the blades.