The Deep Propagation Tool (A New Electromagnetic Logging Tool)

Abstract

ABSTRACT This paper will discuss a new well logging tool, the Deep Propagation Tool (DPT*). The device radiates electromagnetic energy into the formation surrounding the well bore. Measurements of the attenuation and velocity (wavelength) of this electromagnetic wave will yield the resistivity and dielectric constant of the formation. The use of an accurate measurement of formation resistivity is well known. The measurement of formation dielectric constant has recently been shown to be of use in formation evaluation for cases of variable formation water resistivity.(1) Previous devices used to measure the dielectric constant of the formation have had relatively shallow depths of investigation. The Deep Propagation Tool uses a unique antenna array in order to return formation electrical parameters characteristic of the uninvaded formation. The device operates at a frequency in the tens of megahertz range and performs accurate measurements of signal level and relative phase at four receivers locations. These eight measurements can then be used to return a value for the formation resistivity and dielectric constant. The theoretical basis for the design of the tool will be presented. This will be applied to predict the environment effects on the response of the device. Attention will be paid to the effect of the borehole on the measurement, the depth of investigation of the device, and its vertical resolution. Measurements have been made in wells in both Europe and South America. Results of these measurements are quite interesting and show that the measurement of formation dielectric constant can be used to determine the presence of hydrocarbons in zones of variable connate water resistivities where traditional resistivity measurements are not easily applied.