Improved Borehole Imaging by Ultrasonics

Abstract

A new ultrasonic tool for borehole and casing imaging has been developed based on recent cementation imaging technology. A rotating ultrasonic transducer scans the borehole at a high sampling rate to provide detailed images of echo amplitude and radius. A 250 or 500 kHz focused transducer gives high resolution, penetration in heavy mud and low sensitivity to tool eccentering. The echoes are analyzed by a downhole digital signal processor to optimize the accuracy and reliability of the radius measurement. The measurements are corrected for eccentering, and the image color scales are dynamically adjusted for optimum sensitivity in real time by the surface computer. Comparisons with electrical imaging tools show the ultrasonic amplitude measurement tends to respond to lithology indirectly via changes in borehole radius or rugosity. Ultrasonic imaging is unique in making quantitative high-resolution measurements of borehole geometry that are useful for borehole stability analysis. Examples of automatic hole shape analysis are shown. The tool can also evaluate internal casing corrosion and detect holes. 1. Introduction Detailed images of the borehole can be produced by three common techniques: video cameras, microelectrical imagers and ultrasonic scanners. Video cameras operate only in clear liquids or gases. Electrical imagers cannot be used in oil-base mud. The ultrasonic method works in water-base and oilbase muds and is the only technique that provides a high-resolution caliper (borehole geometry) survey. The first- ultrasonic instrument, the borehole televiewer, was introduced over 25 years ago [1]. In the 1980s Shell and Amoco updated the design and in the last few years the technique has enjoyed a revival of interest with the introduction of new tools by service companies [2,3].

Seismic and Aseismic Slips Induced by Large-scale Fluid Injections

“…For this reason, a method has been developed (HAYMAN et al, 1994) for determining an accurate cross-section geometry without knowledge of the exact cross-sectional position of the tool. It is based on the determination of the radius of curvature of the well within a chosen sector.…”

Drilling-induced and logging-related features illustrated from IODP–ICDP Expedition 364 downhole logs and borehole imaging tools

“…Borehole-imaging logging tools are commonly used by both the IODP and ICDP (e.g., Lovell et al, 1998). They involve measuring either the electrical conductivity of the borehole wall (Formation MicroScanner tool, Pezard and Lovell et al, 1990;Gaillot et al, 2007;Pezard et al, 1992a, b;Ekstrom et al, 1987) or the sonic travel time and amplitude of a reflected ultrasonic pulse (acoustic borehole imager -ABIin this study; Table 1; Zemanek et al, 1969Zemanek et al, , 1970Zoback and Anderson, 1982;Anderson and Zoback, 1983;Hayman et al, 1998). A third category allows for the recording of an optical image of the borehole wall (optical borehole imager -OBI -in this study; Table 1; e.g., Paillet et al, 1990;Inwood et al, 2008).…”

Field Demonstrations of Logging Technologies for Reservoir Characterization

“…Modern tools, however, generate the high acoustic frequenaes (in the hundreds of kilohertz to megahertz range) required for high resolution and adequate penetration of energy through most drilling muds (Hayman et al, 1994). Modern tools also have flexibility to vary sampling rate and frequency to optimize tool response for each borehole's geometry, rugosity, and fluid conditions.…”

“…Image data are then collected as the tool is withdrawn and vertical variations in fluid acoustic properties are re-introduced during computer processing to produce the most accurate borehole images possible (Hayman et al, 1994).…”