Identification Of Open Natural Fractures Using Conventional Wireline Logs, Borehole Imaging And Stoneley Waves

The identification of open natural fractures is an important and challenging task for oil and gas industry specialists, because such fractures have an important impact on fluids flow, within a reservoir or from reservoir to the borehole.

Due to high costs, it is not always possible to perform coring. In these situations, borehole geophysical imaging may partially compensate the lack of direct information. Given the ambiguity of open fractures detection using only borehole images, it is necessary to integrate different types of geophysical data and methods, as well as drilling events, for accurate fracture characterization.

Stoneley waves recorded by acoustic logging tools can be used to detect open fractures due to their attenuation and reflection in fractured intervals. The analysis of the differences between direct and reflected Stoneley modes, in combination with caliper and formation density data allows the discrimination of permeable fractures from cavings and bed boundary reflections.

The drilling mud weighting by barite addition strongly influences the density and photoelectric factor readings, but can help in the case of open natural fracture detection. Barite may invade open fractures and result in very high values of the photoelectric absorption factor at particular depths.