Method To Generate Full-Bore Images Using Borehole Images and Multipoint Statistics

Abstract

Summary Borehole-image logs, which are produced by tools being lowered into a well, provide oriented electrical and acoustic maps of the rocks and fluids encountered in the borehole. Electrical borehole images in water-based (conducting) and oil-based (nonconducting) muds are generated from electrodes arranged in fixed patterns on pads that are pressed against the borehole wall. Depending on the borehole diameter, gaps nearly always occur between pads. Because of these gaps, it is common to have nonimaged parts of the borehole wall. Full-bore images are complete, 360° views of the borehole wall. They are generated by "filling in the gaps" between the pads in borehole-image logs. This method uses the Filtersim algorithm of multipoint statistics (MPS) to generate models, or realizations. Measured (incomplete) borehole images themselves are used as "training images." Recorded data are perfectly honored (i.e., the models are conditioned to the real data). Gaps are filled with patterns similar to those seen elsewhere in the log. Patterns in the gaps match the edges of the pads. The frequency distribution of continuously variable pixel colors in the gaps matches the distribution of pixel colors in the measured images. Full-bore images facilitate visualization and interpretation of borehole-image logs in any lithology, although case studies shown in this paper are developed in vuggy and fractured rocks. These images can be used to draw closed contours around electrically resistive or nonresistive patches in the borehole wall. Full-bore images can be used to repair logs with bad electrodes, low pad pressure, or poor acoustic reflections. Therefore, they can be used to enhance any commercially available electrical or acoustic borehole images.