Deep Fracture Imaging Using Dipole Acoustic Data

Characterizing acoustic fractures in reservoir rocks is important because these fractures provide critical conduits for hydrocarbon production from the reservoir into the wellbore. The standard method uses shallow borehole imaging services, both acoustic and resistivity, which image the intersection of the fractures at the borehole wall. Cross-dipole technology has extended the depth of evaluation some 2 to 4 ft around the borehole by measuring the fracture-induced azimuthal shear-wave anisotropy. A recently developed shear-wave reflection imaging technique provides a method for fracture characterization in a much larger volume around the borehole with a radial extent of approximately 70 ft. This technique uses a dipole acoustic tool to generate shear waves that radiate away from the borehole and strike a fracture surface. The tool also records the shear reflection from the fracture. The shear-wave reflection, particularly the SH waves polarizing parallel to the fracture surface, is especially sensitive to open fractures, enabling the fractures to be imaged using this dipole-shear reflection data. We use field examples to demonstrate the effectiveness of this shear-wave imaging technology that maps fractures up to 70 ft away and even detects fractures that do not intercept the borehole.