Electrode system design and response simulation of azimuth lateral resistivity logging while drilling tool

A novel azimuth laterolog resistivity sonde based on non～contact coupling measurement principle is proposed, which has radial, longitudinal and circumferential detection abilities. The electrode system structure was designed using the 3D finite～element method(FEM) and the investigation characteristics under the influence of wellbore size, flushing zone resistivity, formation inclination, layer thickness and surrounding rock resistivity were simulated. The simulation results show that the investigation depths of the toroidal coil excitation LWD laterolog tool is generally smaller than that of the cable lateral instrument, which is about 0.3 m in relatively low resistivity formation and 0.11 m in high resistivity formation (10 000 Ω·m). This investigation depths can satisfy the needs of LWD for the little mud invasion impact. The layer of 0.5 m thickness can be well distinguished under high-resistivity formation. Moreover, the low and high resistivity anomalies can be well detected and the formation tendency can be estimated by means of quadrangular measurement. This study is meaningful for the structural design of azimuth lateral LWD tool and the evaluation of high～resistivity reservoirs.