Shear behavior and acoustic emission characteristics of propped rough fractures

Abstract

Shearing stimulation with proppant is widely used in geothermal and hydrocarbon reservoirs. However, the shear behavior associated with proppant-proppant and proppant-fracture interactions has not been clearly elaborated. This paper investigates surface damage and the interactions between proppant and surface roughness through direct shear tests with acoustic emission (AE) monitoring. The AE events show distinct spatial and temporal distribution patterns under the influence of proppant. The small magnitude AE events, representing proppant slipping and crushing, start to occur in large areas from the beginning of the shear deformation, and the large magnitude AE events occur mostly at the peak and during the residual phase and are concentrated on asperities. Crushed proppant grains and asperities form a gouge layer that prevents further damage to the fracture surface, reduces shear dilation and promotes aseismic creep. Fine proppant grains tend to remain intact, while the coarse proppant grains tend to be crushed. Our results suggest that acoustic emission characteristics can be used to infer different stages of shear behavior of propped fractures. These findings enhance our understanding of the shear behavior of propped fractures and provide evidence for monitoring their conditions using seismic signals.