Geometry of layer-bound fractures based on fracture density and aperture-depth plots from resistivity image logs of deviated wells

Abstract

High resolution borehole resistivity image logs provide valuable bedding and fracture data from subsurface rocks including fracture type, orientation and aperture. The present study shows that common average shape and aperture geometry of uniformly located layer-bound fractures can be inferred from scan-line density and aperture-depth plots using image log data from a deviated well.The proposed method extends the use of borehole image logs and allows 3-dimensional (3D) modeling of fractures and fractured layers from subsurface data. So far, such 3D fracture studies could only be conducted using outcrop data. The approach is quite robust because correspondence between fracture geometry and image log plots is independent of fracture length and orientation, and applies to any fracture shape and aperture geometry.Joint interpretation of fracture scan-line density and aperture-depth plots, and bedding picks from borehole images also helps differentiate isolated/dispersed, unbound and multilayer fractures. Abundance of fractures that breach bed boundaries gives an idea about the cohesive bonding strength of bedding contacts and pave the way to construct fracture stratigraphy with several fractured layers that are separated by interfaces of varying bonding strength or by ductile beds. 3D fracture geometry may also provide some information on the type and mode of fractures and geo-mechanical conditions under which the fractures were generated.