Fracture characterization using downhole camera in deep boreholes at Southern Johor Bahru, Malaysia

Abstract

Downhole camera is an effective tool to locate fractures and other geological features in boreholes although it does not quantify the characteristics of fracture directly. This study attempts to qualitatively characterize fractures in three deep boreholes, namely W1-W3 using downhole camera of R-CAM 1000 XLT as well as to investigate the geological features present at Southern Johor Bahru. The study area is underlain by Jurong Formation and Older Alluvium. Jurong Formation comprises of well cemented and consolidated volcanic-sedimentary rocks while Older Alluvium comprises of coarse, angular clayey sand with pebbles such as quartz, rhyolite, chert and argillite pebbles. The geological features encountered during the study are brecciated zone and veins such as quartz, calcite and pyrite. In addition, the fracture density in W2 (175/150 m) is found to be higher than W1 (79/165 m). Gently dipped (<20°), single set of joints with tight to open aperture (<0.1–4 cm) are dominant in both wells. Major orientation of discontinuities is north-east (0–90°) to south-west (180–270°) which is subparallel to bedding plane and lineament orientations. Meanwhile, no major structure is observed in W3. Thus, the study shows the importance of downhole camera survey in locating and characterizing fractures in rock mass qualitatively.