LWD response characteristics based on orthogonal sampling

Key words:  LWD  resistivity  orthogonal sampling  amplitude ratio  phase difference

Abstract:

Accurate measurement of layer-earth resistivity parameters is a key task in the measurement of electromagnetic wave resistivity logging instruments while drilling. The kernel point of this measurement lies in calculation of the amplitude ratio and phase difference of the induced electromagnetic wave signal. According to the accuracy calculation requirements for the amplitude ratio and phase difference, we adopt an orthogonal sampling method, which preprocesses and orthogonally samples the induction electromagnetic wave signal adjacent to the receiver coil. The amplitude ratio and phase difference of the induction electromagnetic wave signal adjacent to the receiver coil were calculated. In the light of the simulation experiment, the response curves on the amplitude ratio and phase difference of the induction electromagnetic wave signal at the neighborhood receiver coils are analyzed, when the coil system structure passes through the layer-earth model with different resistivity parameters. The advantages of the quadrature sampling method in accurately calculating the amplitude ratio and phase difference of the electromagnetic wave signal were verified. The results demonstrate that each signal is averaged after multi-period sampling in the digital sampling of the induced electromagnetic wave signal, which improves the calculation accuracy of the amplitude ratio and the phase difference of the induced electromagnetic wave signal. In addition, by using the orthogonal sampling method, the calculation speed is improved after sampling each signal at T/4 intervals. This method can meet the real-time requirements of the electromagnetic wave resistivity logging instruments while drilling.