METHOD OF ELECTROMAGNETIC FLAW DETECTION - THICKNESS GAUGING OF MULTISTRING WELLS, AND DEVICE FOR ITS IMPLEMENTATION Russian patent published in 2012 - IPC E21B47/00 G01N27/20 

FIELD: oil and gas industry.

SUBSTANCE: method is implemented by means of the device including axial and transverse probes, which are divided into two groups. Excitation of electromagnetic field is performed in steel casing strings with current pulses in exciter coils (EC) of probes. Signals of secondary non-stationary electromagnetic field (SNEF) are measured and primarily processed in measuring coils (MC) of probes after current pulses are switched off in EC. Signals are converted to digital shape, transmitted to the surface and processed by means of the computer. At that, for the second group of probes the duration of current pulses excited in EC and measurement time of SNEF signal in MC is chosen so that it is at least three times shorter than duration of current pulses in EC and measurement time of SNEF signal in MC of probes of the first group. Besides, measurements of SNEF signals in MC of probes of the first group are performed when current is not available in EC of probes of both groups, and excitation of current pulses in EC and measurements of SNEF signal in MC of probes of the second group are performed when current pulses pass in EC of probes of the first group.

EFFECT: improving measurement accuracy of thickness and reliability of detection of flaws in internal and external strings.

3 cl, 3 dwg