Research On Reservoir Property And Permeability Under Hydraulic Fracturing In Hot Dry Rock

The development of clean and renewable energy is highly valued with rapid economic development and social progress in our country.Geothermal resources are abundant in China and the development and utilization of geothermal resources is of great significance.In the process of exploting geothermal resources,it is key and difficult to construct artificial heat storage with low cost and high efficiency in low porosity and low permeability dry hot rock reservoirs.So,it is very vital to study reservoir property and permeability under hydraulic fracturing of dry thermal rock,which is significant to promote the development and utilization of geothermal resources.In order to study reservoir property and permeability under hydraulic fracturing in hot dry rock.This paper takes granite as the research object,temperature gradient of granite after thermal shock with time as well as the variation of surface morphological characteristics of granite were analyzed by infrared thermometer scanning and graphic microscope.The microcomputer controlled hydraulic servo universal testing machine and acoustic emission instrument is used as the experimental platform to carry out various mechanical parameters and acoustic emission characteristics of granite under thermal shock.and the finite element software of CM was utilized to set up the numerical model of THM coupling,the deterioration mechanism and permeability of fractured rock mass after thermal shock was analyzed.Getting The following main conclusions:?1?Granite specimen within 600?are respectively subjected to thermal shock under 10?and 60?shock,and the cooling rates of specimen in 10?water significantly decline compared with 60?water cooling rate and temperature gradient is bigger.Therefore,heat shock of granite specimen in10?water is more significant than 60?water.?2?The color of granite gradually shallow with the increase of temperature gradient.On the surface of the granite,the distribution of biotite composition is reduced,and the granite is gradually showing a yellowish color.The more obvious the increase of micropores and fractures,and the weaker the bond strength between the mineral particles.?3?The uniaxial compressive strength and elastic modulus of granite specimen within 600?decreases with the increase of temperature gradient under60?water effect,and overally the peak strain is upward trend.The mechanical parameters of specimen also significantly decreased with the increase of temperature gradient under 10?effect.On the whole,the mechanical parameters better decrease than 60?effect.?4?During loading process,there are few acoustic emission signals in the compaction and line elastic phase.As the load time increases,ringing count rate and energy rate are peaking when transition from the online elastic stage to the plastic failure stage.The ring count rate and energy rate of acoustic emission under 10?effect overtops 60?effect.The degree of thermal damage and internal stability of specimens are better,emitted acoustic emission signal is less.?5?Through numerical calculation method by CM,under different depth and permeability,stress distribution is the stress distribution when water pressure is small,distribution of stress is tensile stress when water pressure is large in buried death,and the permeability of 10^-16m² fractured rock mass is better than 10^-17m² in fracturing effect.?6?The process of fracturing artificial heat reservoir,the decrease of injection temperature can effectively increase the permeability of reservoir,thus,it is easier to transform the reservoir.The injection temperature decreased by 50degrees,the permeability ratio increased by 0.04%.