Study On The Influence Of Tool Material And Structure On AC Logging Responses

The AC logging method measures the electromagnetic field generated by the transmitting coil in the formation to obtain the electrical information of the formation.It is necessary to clarify the influence of the electromagnetic characteristics and structure of the instrument on the logging responses.The influence of tool material and structure on Induction logging responses and Electromagnetic Wave Propagation Resistivity logging responses has been calculated and analyzed by using finite element numerical simulation software COMSOL in this paper.Firstly,the logging responses of High Definition Induction Logging tool are calculated.It is concluded that the conductivity of the metal mandrel has constant effect on the real part of the induced electromotive force.Comparing the response characteristics of different T-R spacing,responses of shorter T-R spacing is greatly affected by the metal mandrel conductivity.The magnetic properties of the mandrel can be neglected in the practical application because the mandrel of the tool can be seen as the ideal conductor.Secondly,the influence of tool conductivity,relative magnetic permeability on the Electromagnetic Wave Propagation Resistivity LWD instrument WPR logging responses are studied.The results show that the conductivity of the drill collar reduces the voltage amplitude,but doesn't affect the amplitude ratio and phase difference.The thicker the drill collar and the shorter the T-R spacing,the greater the impact,but the overall difference is small and can be ignored.Finally,this paper studies the Azimuthal Electromagnetic Resistivity LWD logging responses affected by the electromagnetic characteristics of the drill collar.It turns out that the metal drill collar has no effect on the amplitude ratio and phase difference no matter the receiving coil is tilted or not.Therefor the instrument model can be simplified and the simulation efficiency can be improved.Research results in this paper can provide theoretical basis for instrument design and log interpretation.