A critical review of the experimental and theoretical research on cyclic hydraulic fracturing for geothermal reservoir stimulation

Hydraulic fracturing is necessary to stimulate deep geothermal reservoirs. Compared with traditional hydraulic (THF), cyclic (CHF) decreases the breakdown pressure (BP), generates a more complex crack network and reduces induced seismicity; thus, it has attracted increasing attention. In this work, state-of-the-art studies on CHF are comprehensively reviewed for first time. Six loading schemes clarified, their stimulation results discussed. It difficult assess which most advantageous because reservoir boundary conditions properties of rock specimens vary. The effects critical influential factors in detail. A higher confining generally produces longer cracks, lower-viscosity fluid easily connects micropores widens cracks. existing theoretical numerical models CHF, based mainly fracture mechanics damage mechanics, summarized Based comprehensive review, some aspects through failure mechanism can be further understood suggested. This work benefit application exploit resources.