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 (R_t/R_m). The downhole mud resistivity of 0.02 ohm.m in comparison with the formation resistivity of 80 to 100 ohm.m resulted in an R_t/R_m 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 R_t/R_m in excess of 2,000:1 results in excellent image quality in challenging logging environments, with images successfully acquired at R_t/R_m 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.