Comparison of Formation Microscanner Images to Cores in Sandstone Reservoirs, Saudi Arabia

Abstract

ABSTRACT The Formation MicroScanner (FMS) tool was first run in Saudi Arabia in 1986. Since then, both the tool and software used for viewing and manipulating the FMS images have been improved. Recent developments in interactive software by Schlumberger have greatly increased the usefulness and ease of interpreting the FMS images. The FMS log is better than the dipmeter because it allows calculation of dips in the presence of fractures and in zones of poor lateral continuity. The FMS uses arrays of microresistivity sensors to make high resolution images of the borehole. The images are displayed on a variable intensity color scale with sufficient resolution to enable comparison to core photographs. Detailed FMS analysis requires the use of an interactive computer-graphics workstation for image enhancement and dip calculations. The FMS images were found to be effective in the interpretation of sedimentary structures, paleocurrent direction, thin bed analysis, depositional environment, and fracture identification. Because of the photo-like quality of the images, features such as concretions, rip-up clasts, bioturbation, flaser bedding, and grain size changes can often be identified. Also faint crossbedding in core may be more obvious on the images as the microresistivity contrast is often greater than the visual contrast. Once the FMS images have been calibrated with core data, the FMS log can be an effective way to reduce the need for core in offset wells. At times a FMS image is better than conventional core since true dip azimuth and magnitude can be calculated.