Borehole AE monitoring during in-situ hydraulic fracturing stress measurements

AE (Acoustic emissions) were monitored during in-situ hydraulic fracturing stress measurements using a borehole sonde. At a monitoring point, the time interval between the peak pressure and th,start of AE occurrence became longer with repetition of the reopening procedure. This phenomenon was most likely due to the crack extension growing deeper from the borehole wall. At another point, during a reopen procedure, two AE bursts were recorded. The pressure at the end of the first burst corresponds to the reopening pressure, while that at the start of the second burst corresponds to the shut-in pressure. Both pressure magnitudes were consistent with those determined using a conventional method employing pressure-time records. These results indicate that AE monitoring could be used to observe behavior of a hydraulically induced crack and could help to improve reliability and accuracy of hydraulic fracturing stress measurements.