Patent ID: 6547016
Filing Date: 2003-04-15
Classification: E21B

Abstract:
An apparatus for sensing a force applied to a drill bit operating down hole in a well, comprising:a) a drill bit; b) a drill string operatively coupled to said drill bit, said drill string having a section disposed proximate said drill bit; c) at least first, second and third pockets formed in said section of said drill string, said pockets circumferentially spaced approximately equidistantly around said section of said drill bit, each of said pockets forming at least one wall; d) a set of strain sensors for each of said pockets, each of said sets of strain sensors affixed to said wall of its respective pocket, each of said sets of strain sensors comprising first, second, third and fourth strain sensors circumferentially spaced approximately equidistantly around said wall of its respective pocket, each of said first strain sensors in each of said sets of strain sensors disposed opposite said third strain sensor in its respective set, each of said second strain sensors in each of said sets of strain sensors disposed opposite said fourth strain sensor in its respective set; e) circuitry connecting each of said strain sensors in said sets of strain sensors, said circuitry forming a bridge, said bridge comprising (i) first, second, third and fourth legs, (ii) a first junction formed between said first and second legs, (iii) a second junction formed between said third and fourth legs, whereby said first and second junctions form a first pair of terminals, (iv) a third junction formed between said first and fourth legs, (v) a fourth junction formed between said second and third legs, whereby said third and fourth junctions form a second pair of terminals, (vi) each of said first strain sensors in each of said sets of strain sensors connected in series along said first leg of said bridge, (vii) each of said second strain sensors in each of said sets of strain sensors connected in series along said second leg of said bridge, (viii) each of said third strain sensors in each of said sets of strain sensors connected in series along said third leg of said bridge, and (ix) each of said fourth strain sensors in each of said sets of strain sensors connected in series along said fourth leg of said bridge; f) means for applying a voltage across one of said pairs of terminals; g) means for sensing a voltage across the other of said pair of terminals; h) means for determining at least one component of said force on said drill bit from said sensed voltage.