Apparatus for weight on bit measurements, and methods of using same

A weight-on-bit measurement tool, comprising:

• a body;
• at least two strain gauge cavities in said body, each of said strain gauge cavities having a strain gauge mounting surface that is located at a position such that a region of approximately zero axial strain due to downhole pressures during drilling operations exists on said mounting surface when said tool is subjected to said downhole pressures during drilling operations;
• and
• a weight-on-bit strain gauge operatively coupled to said mounting face above said region of approximately zero axial strain.

A method, comprising:

• providing a weight-on-bit measurement tool comprised of:
• a body;
• at least one strain gauge cavity in said body, said strain gauge cavity having a strain gauge mounting surface that is located at a position such that a region of approximately zero axial strain due to downhole pressures during drilling operations exists on said mounting surface when said tool is subjected to said downhole pressures during drilling operations;
• and
• a weight-on-bit strain gauge operatively coupled to said mounting face above said region of approximately zero axial strain;
• positioning said tool in a drill string comprised of a drill bit;
• drilling a well bore with said drill string;
• and
• obtaining weight-on-bit measurement data using said weight-on-bit strain gauge in said tool.

A method, comprising:

• identifying a region of approximately zero axial strain due to downhole pressures for a body to be positioned in a drill string when said body is subjected to downhole pressures during drilling operations;
• providing a strain gauge cavity in said body such that a strain gauge mounting face within said cavity is located at a position wherein said region of approximately zero axial strain exists on said mounting face when said body is subjected to said downhole pressures during said drilling operations;
• and
• coupling a weight-on-bit strain gauge to said mounting face above said region of approximately zero axial strain.