The Response Characteristics of Dielectric Logging in Anisotropic Formation

Abstract

Formation resistivity and dielectric constant are the key parameters for evaluating reservoir characteristics. Among the discovered reservoirs, the proportion of electrically anisotropic reservoirs accounts for 30% of the total reservoirs. Conventional logging methods can only measure the resistivity in the horizontal direction. It cannot obtain the dielectric constant information and ignore the vertical resistivity and anisotropy index information, and the calculation substituting horizontal resistivity into the Alchi formula to calculate the oil saturation brings errors. Dielectric logging tools can measure the horizontal resistivity, vertical resistivity, horizontal relative permittivity, and vertical relative permittivity of the formation through two different polarized antennas (horizontal polarization, vertical polarization). With CRIM model, water saturation information obtained by the dielectric constant provides a new water saturation calculation method for logging analysis. In the dielectric measurement, the side wave and the guided wave are the most important modes of electromagnetic wave propagation in the formation. In this paper, an iterative method is used to give an accurate calculation formula of a wave mode solution in a layered medium. The finite element method is used to calculate the dielectric logging response characteristics under different well inclination conditions in anisotropic formations that are compared with analytical solutions in homogeneous medium conditions. The conversion characteristics of the dielectric logging instrument, the depth of detection, the resolution and the response characteristics of the horizontally polarized and vertically polarized antennas under different well inclination conditions are analyzed theoretically. The results show that the receiving phase of the whole antenna can be restricted between 0–360° in the stratum; the detection depth of the dielectric logging instrument is 0.15 m–0.25 m, and the detection depth of the vertical polarization mode is greater than the horizontal polarization mode. The resolution of the dielectric can reach 4 cm. In the case of vertical wells, the relative dielectric constant and resistivity measured by the horizontally polarized antenna only reflect the horizontal resistivity and horizontal relative dielectric constant of the formation. In the case of a flat well, the relative permittivity and resistivity measured by vertical polarization reflect only the vertical resistivity and the vertical relative dielectric constant of the formation. The response measured by the horizontal and vertical polarized antennas in the inclined well is both anisotropic and has a certain relationship with inclination angle.