Patent ID: 8079414
Filing Date: 2011-12-20
Classification: E21B

Abstract:
1. A method for determining the free point of a downhole pipe comprising: (a) providing a downhole electromagnetic free point tool comprising a housing, a transmitter coil disposed within the housing, a plurality of receiver coils disposed within the housing, each receiver coil spaced at a different distance from the transmitter coil, a power source electrically coupled to the transmitter coil configured to apply an oscillating voltage to the transmitter coil so as to induce a current in each of the receiver coils, and electronics configured to measure the induced current in each of the receiver coils; (b) displacing the downhole electromagnetic free point tool within the pipe longitudinally for a first distance; (c) energizing the transmitter coil over the first distance with an oscillating voltage; (d) measuring a current induced in each of the receiver coils during step (b); (e) generating a first log of amplitude measurements based on steps b-d; (f) applying a physical stress to the pipe at or near the surface; (g) displacing the downhole electromagnetic free point tool longitudinal within the pipe for a second distance wherein the second distance overlaps at least a portion of the first distance during step (f); (h) energizing the transmitter coil with an oscillating voltage from the power source during step (g); (i) measuring a current induced in each of the receiver coils during step (g); (j) generating a second log of amplitude measurements based on steps g-i; and (k) comparing the amplitude change between the first log and the second log to determine the free point of the pipe.