Analysis of environment influence in electromagnetic logging while drilling

On the basis of the principle of electromagnetic logging while drilling, the paper gave the calculation procedure of apparent resistivity for triple coil electro-magnetic log and adopted vector finite-element method based on weighted remainder method to carry out analysis, which resulted in influence on formation environment on measured results by electromagnetic logging apparatus while drilling, including the influence of mud resistivity, invaded zone, surrounding bed and dielectric constant of formation. The calculated results showed the influence of mud resistivity on attenuation resistivity is smaller than on phase-shift resistivity; when the invasion depth is shallower, the apparent resistivity mainly reflects the resistivity of original formation and the resistivity of invaded zone when the invasion depth is deeper; the influence of dielectric constant is relative to the frequency of measurement apparatus and resistivity of formation, when dielectric constant increases, the phase difference and ratio of amplitude between two receivers increase too; the influence of surrounding bed is mainly relative to contrast of resistivity between the formation and the surrounding bed.