| 摘要 |
<p>A resistivity tool for use in an LWD system includes an asymmetric transmitter design with multiple transmitters capable of generating EM signals at multiple frequencies. A pair of receivers (R1, R2) are positioned at one end of the transmitter array to detect the EM signals after they have traversed the region in the vicinity of the borehole. A calibrating transmitter (Tc) is positioned between the receivers (R1, R2), which can be used in two different modes of operation. In a first mode, the calibrating transmitter (Tc) is used to calibrate the receivers (R1, R2) for thermal drift. In this calibration mode, an attenuation correction and phase shift correction can be calculated to correct for thermal drift of the receivers while the resistivity tool is in the borehole. Thus, the thermal drift of the receivers can be re-calibrated as often as desired while the tool is in the well. In a second mode of operation, the calibrating receiver may be used to measure the resistivity of the drilling mud in the borehole.</p> |
