The Reduction of Near Zone Effects on the Multi-component Induction Logging Tool

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe multi-component induction tool (3DEX) developed by Baker Atlas is comprised of three mutually orthogonal transmitter-receiver pairs measuring the secondary magnetic field at ten different frequencies. The measured data include the conventional coaxial component, Hzz, parallel to the borehole axis, and two coplanar components, Hxx and Hyy, perpendicular to the wellbore. In addition, two crosscomponents, Hxy and Hxz, are acquired to determine the formation dip and azimuth angles. The objective of this tool is to derive the horizontal and vertical resistivities of thinly laminated sand/shale sequences and anisotropic sands.The tool responses are influenced by near zone anomalies, such as drilling mud, elliptic invasion, drilling induced fracture, and tool eccentricity. Because the tool uses a relatively large transmitter-receiver separation, the near zone effects are fairly small on the coaxial component, Hzz, but they remain strong on the coplanar components, Hxx and Hyy.To reduce the near zone effects, a multi-frequency data processing technique was developed. We validated the technique with synthetic data produced by both 2-D and 3-D modeling algorithms. In an example of the borehole effect, the relative difference in responses with and without the borehole is 22% in the single frequency data but only 0.1% in the multifrequency processed data. In an example of the eccentricity effect, the relative difference in responses with and without tool centralization is 213% in the single frequency data but reduced to only 0.3% in the multi-frequency processed data. Therefore, after the multi-frequency data processing, a simple 1-D vertically layered model can be utilized for data interpretation because much of the near zone effects have been removed. The applicability of the MFF technique is limited in highly resistive formations due to a decreased signal-to-noise ratio as a result of the hardware noise .

Biaxial Anisotropy: Its Occurrence and Measurement With Multicomponent Induction Tools

“…We discuss the MFF processing algorithm in biaxially anisotropic formations in more detail in the next section. Elimination of the various environmental effects using MFF was extensively studied using numerical simulations by Yu et al (2003) and with field data by Hussain et al (2005). The MFF processing algorithm for TI formations is discussed in detail in Rabinovich et al (2006).…”