f Ultrasonic monitoring of hydraulic fracturing experiments

This paper describes a state-of-the-art data acquisition system built at Delft University of Technology which allows rapid acquisition of reflection, pulse-echo and transmission records during hydraulic fracturing experiments on cement or rock samples. Recent experiments show that it is possible to observe clean acoustic signals from a hydraulic fracture that is very thin compared to the wavelength of the illuminating elastic waves. Imaging with reflected compressional signals produces a clean image of the fracture. The signals diffracted from the fracture tip carry important information about the position of the fracture.