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 eases of variable formation water resistivity. 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 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 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 presence of hydrocarbons in zones of variable connate water resistivities where traditional resistivity measurements are not easily applied. Introduction The purpose of this paper will be to present an overview of the The Deep Propagation (DPT*) Tool and summarize the results achieved to date. The DPT Tool radiates electromagnetic energy into the formation surrounding the borehole. Measurements of the attenuation and velocity (wavelength) of this electro-magnetic 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. Previous devices used to measure the dielectric constant of the formation have had relatively shallow depths of investigation. The DPT Tool uses a unique antenna array in order to return formation electrical parameters characteristic of the uninvaded formation. parameters characteristic of the uninvaded formation. The theoretical basis for the DPT Tool is similar to that for induction devices. This theory will be presented in Section 2 in conjunction with the design of the tool (Section 3). Measurements have been made in wells in both Europe and South America. Results of these tests 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. This will be discussed in Section 4. However, it should be pointed out that the interpretation of the measurements of the DPT Tool is in its infancy. Work is continuing at Schlumberger centers in order to better understand the electrical properties of complex mixtures such as make-up, hydrocarbon, and water properties of complex mixtures such as make-up, hydrocarbon, and water bearing sedimentary rocks. Section 5 will summarize this paper.