抄録
In the field of oil well drilling, EM-MWD (Electromagnetic Measurement While Drilling) is taken note of. It can transmit measured data from the well bottom to the surface with high speed using electromagnetic waves. To develop the EM-MWD technology, it is necessary to analyze an electric field around a drillstring. In most of conventional works, the drillstring was usually assumed to be a perfect conductor and/or the earth was assumed to be a uniform medium. In this paper, we consider the drilistring as a rod with finite conductivity, and assume that the earth is composed of several formations. We take three steps for the electric field analysis. First, a quasistatic electric field near the drillstring is analyzed using Finite Element Method combined with Boundary Element Method. Secondly, results of the quasistatic electric field analysis are compensated to consider attenuation of electromagnetic waves propagated in the earth. Finally, the drillstring is divided into many small segments, and an electric field near the surface is calculated as a synthesized vector of electric fields generated by the segments. The verification of the method is shown by a field experimental system using a well of 500m depth.
