The appearance of potential sealing faults on borehole images

Abstract

Abstract Electrical and acoustic borehole images provide data on the structure, width, spacing and orientation of potential sealing faults in the subsurface. These data bridge the ‘scale of observation gap’ between the resolution limits of more conventional data such as seismic data and core, and provide continuous records often up to several thousand feet long. Potential fault seals can be measured from vertical, deviated or horizontal wells and from either clastic or carbonate rocks. Five categories of potential fault seals can be described from images: juxtaposition fault seals place reservoir against seal lithologies and appear as sharp image contrasts; clay lined fault seals commonly appear as shale rich bands on electrical images, which may be either resistive or conductive depending on the resistivity of the host lithology, and low amplitude bands on acoustic images; grain size reduction fault seals appear as resistive or high amplitude features; cemented fault seals appear as highly resistive or very high amplitude features, and open/vuggy faults appear as conductive or very low amplitude features. An integrated approach to image interpretation incorporates not only borehole image data but also core, conventional wireline logs, pressure data and production information.