Sunday, January 1, 2012

FRACTURE IDENTIFICATION FROM FMI LOGS


The electrical images are made by applying a gray scale to the resistivity wiggle-traces produced from the electrodes on the tool. In this way, low resistivity zones appear dark and high resistivity, low porosity intervals appear white. Since the array on each pad is two and a half inches wide, irregular features, such as vugs and fractures, show up as dark spots and lines on the images. Colour tones may be used instead of grey.
The image depth scale is usually 1:20 or 1:40, and the X axis is scaled from -180 to +180 degrees around the borehole, putting North in the middle of the track. Examples are provide  in the image. A dramatic near vertical fracture can be seen. Two vertical scales are used: one for reconnaissance and one for detail evaluation. Fracture orientation is roughly NNW - SSE dipping at more than 80 degrees. Other images on these two figures illustrate induced fractures, borehole breakout, inter-bedding laminations, slump brecchia, vugs with fractures, and stylolites.


image