Abstract: Hydraulic fracturing is the key technology for shale gas development. Brittleness is one of the most important parameters to evaluate the fracability of shales. One of the most commonly used methods in laboratory is the measurement of wave velocity of pillar core to obtain Young’s modulus and Poisson’s ratio, so as to evaluate the rock brittleness coefficient. However, it is difficult to obtain regular shale core samples. Therefore, in this study, we develop a new device and a novel method with high precision to measure the velocity of shale debris based on pulse echo. Major factors that influence the measurement precision of shale debris wave velocity are analyzed. This study also proposes a new pin-type high frequency sound wave probe and a digital signal processing data analysis method. The measurement precision is improved by increasing sampling frequency and signal-to-noise ratio as well as using the autocorrelation method and pulse echo method. The comparison between results from regular core and debris confirms the reliability of the proposed procedure.

Key words: fracturing, shale debris, wave velocity, brittleness