Transient response of some borehole mandrel tools

Abstract

The response of transient mandrel tools in realistic well‐logging environments is simulated by first solving the problem analytically in the frequency domain using an efficient high‐speed computer model. Gaussian pulses of reasonable bandwidths are assumed. The geometry modeled includes a borehole, invasion layers, and bed boundaries. Both TE and TM type sources are considered. The resulting receiver voltages, displayed in variable‐density log (VDL) format, yield visually interpretable information regarding signal amplitude and attenuation. The speed and generality of the analytical model makes this approach practical for analyzing tool response in a wide variety of logging geometries. Preliminary results generated by this model demonstrate that transient electromagnetic logging tools have the potential to yield useful information for characterizing the conductivity and dielectric constant of beds penetrated by a wellbore. In the future, the model could be helpful in validating signal processing and data inversion algorithms.