Study On Stimulation Technology Of Thermal Reservoir Of Wumishan Formation Of Jixian System In Xianxian Uplift,Hebei Province

The carbonate thermal reservoir of Wumishan stratum of Jixian system is one of the main geothermal horizons in Xianxian,Hebei Province.At the moment,it's still unclear how to develop the geothermal resources efficiently,especially through the artificial stimulation.A large number of engineering practices at home and abroad show that fracturing technology is an effective means to stimulate carbonate thermal reservoir,and hydraulic fracturing is one of the important means.In this paper,the geothermal reservoir of Wumishan formation is taken as the research object.Being based on determining the thermal physical characteristics and mechanical parameters of typical rock specimens of geothermal reservoir,the laboratory fracturing process simulation physical experiment and hydraulic fracturing numerical simulation are carried out,and the mechanism and effect of hydraulic fracturing stimulation are studied.The results are as follows:(1)The physical characteristics of the reservoir rocks in Wumishan stratum of Jixian system are tested,and the parameters such as confining pressure,permeability,and thermal characteristics(?,Cp,?)are determined.(2)The laboratory test shows that: when the rock fracture of geothermal reservoir is not developed,the break pressure of frequently-used hydraulic fracturing is obviously exceed that of acid fracturing;the fracture development degree of reservoir rock directly affects the fracturing effect;when the rock fracture of geothermal reservoir is developed,the initial rupture pressure and fracture shape of hydraulic fracturing are determined by the development degree of natural fracture,which has little relationship with temperature.The main permeability increasing effect of fracturing on thermal reservoir is to activate natural fractures.The development angle of original fractures has great effect to hydraulic fracturing conditions and fracture morphology.(3)The results of simulation state that the original fracture is vertical to the trend of the minor principal stress.The maximum stress is at the crack tips,and the stress decreases from the tips to the surrounding in a "Butterfly" shape.During the frequently-used hydraulic fracturing,the fluid pressure and crack entrance width can be summarized as 3 stages with time: pressure accumulation stage,starting fracture along perforation stage and fracture stable extension period.The pressure at stable extension is basically consistent with the crack initiation pressure measured in laboratory.The transformation of water viscosity and the velocity of pumping has little influence on fracture width.(4)On the basis of the small-scale fracturing test,the fracturing technology was adjusted to reduce the amount of sand and liquid,change the sand adding method and pumping program,and the main fracturing test was carried out.The unit water inflow increased by more than 1 times,and the fracturing effect increased by 104.66%.(5)Geothermal cascade utilization shows that the operation effect of geothermal generating units in winter is better than that in spring.The utilization rate of geothermal energy is 24.3% ? 35.4%,with an average of 29.2%.