Modeling of triaxial induction logging responses in multilayered anisotropic formations

Triaxial induction logging tools have been widely applied to formation characterization due to its sensitivity to electric anisotropy. To model triaxial induction logs in multilayered general anisotropic formations, where the anisotropy can be arbitrary, an analytical method is applied to compute the tool responses. For the analytical method, Maxwell's equations in the spectral domain are written into a compact first-order differential equation. The equation is solved to obtain the spectral-domain fields, which are transformed to the spatial domain through the inverse Fourier transform. The singular issue for the tool located in highly deviated wells, is handled by subtracting the singular term in the spectral domain. The singularity treatment makes the integrands in the inverse Fourier transform decay faster, thus making the infinite integration computation faster. Formations with isotropic, transversely isotropic, biaxially anisotropic and general anisotropic conductivity are modeled and compared to investigate the effects of anisotropy on the tool responses. For a tool in a general anisotropic formation, all the H components are nonzero. For a tool in a vertical well in transversely isotropic and biaxially anisotropic formations, only the diagonal components of H are nonzero. For a tool located in a deviated well, the effects of tool deviation and electric anisotropy are coupled. The diagonal components are more sensitive to the electric anisotropy than the off-diagonal components, and the off-diagonal ones can clearly indicate bed boundaries.

REVISITING SOME OLD UNEXPLAINED EFFECTS IN INDUCTION LOGS WITHIN LAMINATED FORMATIONS WITH THE TRIAXIAL INDUCTION TOOL

ABSTRACT. Modern induction triaxial or multicomponent well logging tools provide resistivity anisotropy logs, and estimates of the electrical resistivity of sand laminae in thinly laminated formations. In this paper, coaxial and coplanar vertical logs were modeled in one-dimensional (1D) laminated packages and in their equivalent anisotropic beds, neglecting the presence of the borehole and the invasion...Keywords: well logging, multicomponent induction tool, laminated reservoirs, electrical anisotropy. RESUMO. As atuais ferramentas de perfilagem em poço por indução eletromagnética, denominadas triaxias ou multicomponentes, fornecem perfis de anisotropia elétrica e permitem estimar a resistividade de lâminas de areia em ambientes finamente laminados. Neste artigo, os perfis dos arranjos coaxial e coplanar de bobinas foram simulados em modelos...Palavras-chave: perfilagem de poço, ferramentas multicomponetes, reservatórios laminados, anisotropia elétrica.

Numerical Simulation of Array Induction Logs Time-Lapse Responses and Formation Resistivity Profile Reconstruction with 5-Parameter Inversion

In order to improve reservoir fluid recognition, sensitivities of array induction response to different invasion properties in both oil-bearing layer and water layer are analyzed. A numerical algorithm is adopted to simulate time-lapse response of array induction logs during mud invasion and signal processing of the array induction log is developed. Features of array induction responses during mud invasion were researched. A “five-parameter model” (r1, r2, Rxo, R1/2, Rt) which can match a variety of invasion conditions is approached and carried out suing a fast invasion method. Therefore, the identification of fluid type can be realized effectively by inversion of array induction log combined with time-lapse responses of array induction log. It is demonstrated that the inverted resistivity presents a typical non-monotonic variation in oil-bearing layer and a monotonic variation in water layer, which agrees well with the actual invasion property. It provides quantitative information for the discrimination of oil/gas or water zone.