Anisotropy evaluation and interface detection based on 3D holographic azimuthal electromagnetic resistivity logging instrument

Abstract

Abstract 3D holographic azimuthal electromagnetic resistivity logging-while-drilling (LWD) is a convenient and efficient technology to obtain information about formation. It has the advantages of being instant and accurate. It can be applied to fields of engineering such as evaluating anisotropy and detecting nearby geological interfaces. A 3D electromagnetic resistivity azimuthal LWD instrument consists of coaxial, coplanar, tilted and orthogonal antenna systems, being able to solve for all nine components. The explicit generic formulation is derived from presenting the response for a basic unit of one arbitrarily oriented transmitter and one arbitrarily oriented receiver. Combining the responses of basic units with different transmitter-receiver spacing and different components, an ‘anisotropy signal’ is defined with the phase difference ${M}_{px}$ and amplitude ratio ${M}_{ax}$. A ‘boundary signal’ is also defined with the phase difference ${M}_{pz}$ and amplitude ratio ${M}_{az}$. Forward simulation results show that the 2MHz ${M}_{px}$ can accurately identify geological anisotropy in highly deviated and horizontal wells. The ${M}_{az}$ can detect geological interfaces in highly deviated and horizontal wells. the 100 kHz${\rm{\ }}{M}_{az}\ $can detect geological boundaries in the range of 8–9 m.