Impacts of Accuracy of Azimuthal Electromagnetic Logging-while-Drilling on Resistivity and Interface Prediction

During the course of logging while drilling with an azimuthal electromagnetic wave instrument,the amplitude ratio and phase difference conversion can be used to obtain the formation resistivity data,and, combined with the signal inversion of directional electromotive force to predict and identify the interface. So,it is necessary to clarify the relationships among the measuring signal accuracy,resistivity and distance to the interface. According to the inversion principle of resistivity conversion and interface distance,the effect of measurement accuracy of receiving antenna on resistivity and interface distance can be simulated,calculated and analyzed under different conditions of formation. Simulation results showed that measurement accuracy of receiving antenna may have great impacts on amplitude resistivity and phase resistivity in high resistivity formation,with an approximately log-linear relationship between directional electromotive force amplitude and interface distance. The farther the distance away from the directional electromotive force amplitude and interface instrument,the smaller the conductivity at two sides of interface of directional electromotive force amplitude,and the lower the working frequency of the instrument,so,the bigger the impact of measuring accuracy on the inversion result of interface distance inversion. The research results can provide the theoretical basis for evaluating measurement accuracy,and lowering the risks of formation evaluation and geosteering applications.