Monitoring microseismic activity in core samples encased in core flooding apparatus subjected to confining and pore pressures

Geological sequestration of CO2 is considered as one of the most promising technologies to mitigate global warming. The process of CO2 injection and storage in the porous sandstones, however, may be accompanied with an increase in microseismic activity. In order to better understand the causes of microseismic events detected during and after CO2 injection, a sensitive, reliable and consistent data acquisition system was developed in the present study for monitoring microseismic (acoustic emission or AE) events emanating from rock samples tested in the core flooding apparatus at the Illinois State Geological Survey (ISGS) laboratory. Several types of sandstone and PVC core samples with various treatments were prepared and evaluated. These samples were subjected to loading/unloading patterns of confining and pore pressures, so as to simulate the environment of underground sandstone formations for carbon storage. The detected AE events were synchronized with the applied pressure profiles to show the temporal clustering of events. A simple one-dimensional localization model was built to determine the spatial variations of event source locations along the axis of the core sample. Criteria for noise elimination and for event characterization were proposed. Results were generally satisfactory and repeatable. Very few AE events were detected from solid PVC and sandstone samples. Many more AE events were detected from the fractured samples with visible damage, and the localized event source locations determined by the model were consistent with the induced cracking positions. When the sample was subjected to a combination of confining and pore pressures, AE event clustering was observed when the net pressure, defined as the differential pressure between confining and pore pressures, increased