Experimental Study Of The Influence Of Cyclic Heating-Cooling On Hot Dry Rock

Fossil fuels give rise to serious environmental problems and face the pressure from limited reserves.Recyclable clean energy is gaining more and more focus.Geothermal energy has long been considered a kind of promising future energy.Hot dry rock(HDR),as an important part of geothermal energy,fascinates researchers with its huge reserves.A series of key problems should be solved before HDR can be efficiently developed,including a cost-effective way to create well-connected fracture systems between wells.Liquid nitrogen fracturing has shown its advantages over conventional hydraulic fracturing in its applications in unconventional oil and gas reservoirs.If applied to HDR development,low temperature(-196℃)of liquid nitrogen will induce thermal shock within rock underground,giving rise to new cracks and promoting crack growth.To study damage caused by such thermal shock,alternative temperature experiments are taken on marble and granite.Damages of 25%,40%,39% are observed to be induced to marble heated to 200℃,400℃ and granite heated to 400℃ only by one shock.Damages go up to extremes as recycle time grows,40%,43% and 45% individually.After that,marble begins to recover slowly while granite stay the same damaged state.With heating temperature going up through 100℃ to 600℃,damage increases from 9% to 69%.Results reveal that thermal shock plays an important role in creating cracks during liquid nitrogen fracturing.This damage becomes heavier within HDR with higher temperatures.This study shows that liquid nitrogen fracturing is a promising fracturing technology and provides data reference and guidance to further study and field applications.