Insights on Injection-induced Seismicity Gained from Laboratory AE Study—Fracture Behavior of Sedimentary Rocks

Injection-induced seismicity associated with applications, in which fluids are intensively pressed into the deep formations of the Earth's crust such as Enhanced Geothermal System (EGS), fracking shale gas, geological sequence of CO2, have attracted growing attentions. Motivated by the desire to better understand the mechanism of damaging events so that they can be avoided or mitigated, we have started an integrated study on rock fracturing and fault reactivation in multiscales. In this paper, we present some preliminary results of an ongoing experimental study utilizing acoustic emission technique in laboratory scale. We systematically carried out rock fracture tests using samples of typical sedimentary rocks collected from the Sichuan Basin, China, where a number of injection-induced seismic swarms with sizable earthquakes ranging up to M4~5 have been observed in some gas/oil reservoirs. Since most injection-induced earthquakes are located in sedimentary strata of a wide range of lithology and depth, the fracturing behaviors of such rocks are thus important. Our results indicate that the Pre-Triassic rocks in the Sichuan Basin, including dolomite or dolomitic limestone and shale are strong and demonstrate brittle fracturing behaviors. Such properties are necessary conditions for maintaining high level reservoir stress and resulting seismic fracturing.