METHOD OF ELECTROMAGNETIC FLAW DETECTION IN WELL STEEL PIPES Russian patent published in 2001 - IPC

FIELD: geophysical investigations in wells; applicable in electromagnet flaw detection in steel pipes found in well, such as drilling, casing and tubing ones. SUBSTANCE: method includes radiation of sounding bidirectional electromagnetic pulses with the help of transmitter coil and measurement of electromotive force induced in receiver coil by process of electromagnetic field decay caused by sounding pulses. Then, carried out is subtraction of values of electromotive force obtained after positive and negative transmitting pulses. Measured additionally is intensity of natural magnetic field along pipe. For this purpose, measurements of electromotive force across receiver coil in two half-cycles of transmitter coil are summed up. In this case signals induced by pulses of sounding current having opposite polarities are subtracted, and signals induced by natural magnetic field are added. Break of pipe string is detected by value of resulting signal corresponding to value of rate of natural magnetic field variation. EFFECT: additional information on places of breaks of pipe string and disconnection in casing couplings through tubing pipes by measuring natural constant magnetic field with determination of thickness of casing pipe walls. 4 dwg