Jian-qun Wu and Macmillan M. Wisler
Teleco Qilfield Services Inc., Meriden, CT
Abstract
The effects of tool eccentering in boreholes on the MWD electromagnetic resistivity measurements are studied in a layered geometry model and in laboratory tests. The model assumes that, within each cylindrical layer, the medium is homogeneous and isotropic. The electromagnetic wave in each layer is the superposition of the cylindrically symmetric wave and various asymmetric waves. The amplitude of each wave is determined by electromagnetic boundary conditions at each boundary and at the source. The experiments are performed in a salt water tank. The borehole is simulated by a plastic tube full of salt water. The formation and borehole resistivities are controlled by varying the salinities in the tank and in the plastic tube, respectively. We find that the model results agree well with the tank tests. Corrections for tool eccentering effects must be applied in some cases to correctly deduce the true formation resistivity.