Patent ID: 6816435
Filing Date: 2004-11-09
Classification: E21B,G01V

Abstract:
A method for determining the position of a drill bit during drilling, comprising the steps of:determining the starting position, {overscore (r)}start, of the drill bit and the positions of m geophones, r_igeogh,â€ƒwhere 1&lE;i&lE;m, and recording the received transient seismic waves generated by the drill on impact, using the geophones, and estimating, from said transient seismic waves, the estimated difference in arrival time, tdobs&it;(i,â€ƒ&it;k1,â€ƒ&it;k2),â€ƒfor geophone i, for events k1 and k2, calculating an initially assumed theoretical arrival time T(i,k), for event k, and calculating arrival time difference residuals, ed&af;(i,â€ƒ&it;k1,â€ƒ&it;k2)=tdobs&af;(i,â€ƒ&it;k1,k2)-T&af;(i,â€ƒ&it;k2)&it;â€ƒ+T&af;(i,â€ƒ&it;k1)&it;â€ƒ,â€ƒwhere k1 and k2 are different, and calculating a function of the residuals, Q(ed(i,k1,k2)), which is an increasing function of positive valued terms and a decreasing function of negative valued terms, and calculating the relative distances, {overscore (r)}d(k1,k2)={overscore (r)}(k2)âˆ’{overscore (r)}(k1), between the positions of the drill bit at events k1 and k2, giving theoretical arrival times T(i,k), which minimises Q and calculating the present position, {overscore (r)}present, of the drill bit by calculating the sum of the starting position, {overscore (r)}start, of the drill bit and a sum comprising the relative distances, r_present=r_start+&Sum;k=1n-1&it;â€ƒ&it;r_d&af;(k,â€ƒ&it;k+1)&it;â€ƒ.