EFFECTS OF LITHOLOGY ON TELEVIEWER-LOG QUALITY AND FRACTURE INTERPRETATION.

Representative televiewer logs illustrating natural fractures in such common rock types as granite, gabbro, basalt, schist, sandstone, limestone and shale are presented in addition to photographs of the same fractures in core samples. These examples demonstrate the many difficulties in recognizing fractures on televiewer logs compared to fractures in logs because of the vertical scale distortion on televiewer logs and from drilling damage to the fractures at the borehole wall. All of these results demonstrate that significant fracture widening usually occurs during drilling, explaining why fractures described by the core logger as closed can be consistently detected on televiewer logs.