Enhanced-Clarity Imaging of High-Resistivity Formation Despite Hypersaline Mud System, Oman | Schlumberger
Case Study
Oman, Asia

Challenge: Acquire microresistivity images of a high-resistivity formation in a highly conductive mud environment, where conventional imaging logs cannot provide detailed data.

Solution: Deploy the new FMI-HD high-definition formation microimager with improved operating range and image quality to provide clear, high-fidelity images even in extreme resistivity conditions.

Results: Visualized the borehole with excellent-quality static and dynamic images from the FMI-HD microimager to support structural and sedimentological interpretation.

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Enhanced-Clarity Imaging of High-Resistivity Formation Despite Hypersaline Mud System, Oman

FMI-HD high-definition formation microimager provides high-quality images where extreme resistivity contrast prevented conventional image logging

High-resistivity formation, high-conductivity mud

Drilling high-resistivity tight sandstone formations with hypersaline (240,000-ppm) mud systems was causing an extreme contrast between the true formation resistivity and the mud resistivity (Rt/Rm). The downhole mud resistivity of 0.02 ohm.m in comparison with the formation resistivity of 80 to 100 ohm.m resulted in an Rt/Rm ratio exceeding 4,000:1. This high contrast posed a challenging logging environment for Petroleum Development Oman (PDO) to use conventional microimaging. Diligent real-time analysis of image quality and repeated log passes with carefully optimized parameters would be required.

High-definition microimaging

The new FMI-HD high-definition formation microimager greatly improves operating range, reliability, and image quality through the addition of all-new electronics to the field-proven FMI microimager sonde. The enhanced analog-to-digital circuitry and parallel signal processing increase the measurement signal-to-noise ratio and image clarity fourfold. The tool's tolerance of Rt/Rm in excess of 2,000:1 results in excellent image quality in challenging logging environments, with images successfully acquired at Rt/Rm contrasts up to 200,000:1. Sixteen-bit data acquisition further enhances the image contrast, even with very low signals.

High-detail, high-clarity images

The FMI-HD microimager delivered excellent-quality images in the challenging pairing of high-conductivity mud and high-resistivity formation. Fracture trends and thin laminations with subtle variation in dip and texture are well detailed on the images. Image-based interpretation of the present-day stress regime and natural fractures was used to plan an optimized completion design.

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The images at 0.2-in vertical resolution from the FMI-HD microimager can be displayed on a virtual 3D core by the Techlog* wellbore software platform at any scale down to 1:1.
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Comparison of images from a conventional imager (left) and the FMI-HD high-definition microimager (right) shows the step-change improvement in image quality despite extreme resistivity conditions.
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