Cyclic hydraulic fracturing of pocheon granite cores and its impact on breakdown pressure, acoustic emission amplitudes and injectivity

Cyclic hydraulic fracturing, which employs cyclic injection with alternating high and low injection rates or pressurization, is suggested to assist in reducing induced seismicity. Our laboratory work demonstrates the impact of cyclic hydraulic fracturing on tensile-dominated fracturing of intact Pocheon granite core specimens. Cyclic injection of water reduces the breakdown pressure by up to ∼20% and the maximum acoustic emission amplitude is reduced by ∼14 dB on average. We observe hydraulic fractures in granite specimens through using computed tomography. Cyclic hydraulic fracturing creates complex fractures with more branches and smaller apertures compared with those created by continuous injection. The average injectivity of the fractured specimens by cyclic injection is smaller than the injectivity measured on specimens fractured by continuous injection.