Characterization of a Fractured Ordovician Pipe Rock based on Image Logs and Core

We present a case history, in which the latest generation of borehole imaging technology was used in combination with high resolution full circumferential core photos to build a conceptual model of the fracture system in a fractured sandstone reservoir. The object of the study is the Hamra Quartzite Formation, which is currently the target of active exploration in North Africa. The study demonstrates the amount of detail, which can be obtained from dual acoustic/resistivity images, logged under optimal conditions, but also shows the limitation of the imaging technology. Core photographs allow picking of bedding and fractures in a manner similar to image logs but have much higher resolution. In addition, these show features that are not resolved on the image logs due to lack of contrast (such as quartz-cemented fractures) or can be misinterpreted on the image. In particular, it was noticed that fractures often develop parallel to linear burrows, which are a dominant feature of the formation. This means that fractures may be mistaken for burrows (or vice versa) on image logs, but also has important implications for fracture modelling and geomechanical applications (e.g. frac design).