1. Institute of Intelligent Control and Image Engineering, Xidian University, Xi'an, Shaanxi 710071, China; 2. School of Electronic Engineering, Xi'an Shiyou University, Xi'an, Shaanxi 710065, China
Abstract:Thin beds cannot be distinguished since the conventional tri-component coplanar coil system causes various responses in them.Therefore we propose a new coplanar coil system based on two-transmitters and one-receiver sub-array configuration.First a modelling is achieved with the analytic method.With tangential continuity in a bed boun-dary and the Bessel function,the horizontal component of magnetic field intensity is obtained.Then we calculate the response of 8 sub-arrays of two coplanar coil systems in bedded formations,and analyze logging response influence caused by coil spacing,bed thickness,and thin-bed conductivity.The following understandings are obtained:a.The boundary position is clearly shown by the new coplanar coil system when the thin bed thickness is greater than the distance between the primary transmitting and receiving coils,and the measurement accuracy is improved by 53.1% compared with the conventional coplanar coil system; b.Fluctuations occur at the bed boundary due to the influence of the coplanar coil system and surrounding rocks when the thin bed thickness is less than the distance between the primary transmitting and receiving coils,but these fluctuations are less than that of the conventional coplanar coil system.Based on the analysis of the eddy-current distribution of the transmitter coil,we have found the mechanism that the skin-effect and negative-response are reduced by the new coplanar coil system.Our research results have an important significance for the tri-component array meter design and logging response evaluation.
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