Study On The Effect Of Chemical Stimulants On Enhanced Geothermal Reservoir In Matouying District,Hebei Province

As a clean and renewable energy,geothermal energy has attracted attention from many countries.Hot dry rock is a kind of geothermal energy.Enhanced Geothermal Systems(EGS)can economically extract deep geothermal energy from the geothermal reservoir.However,the permeability of the geothermal reservoir is very low.So,the reservoir needs to be reformed and meet the production demand.Chemical stimulation,as a commonly used technology for reservoir reconstruction,improve permeability of geothermal reservoirs by using chemical stimulants dissolving fracture channel minerals and expanding primary fissures even generating new fissures.It is gradually widely used due to strong penetrability and good controllability.In this paper,Matouying geothermal reservoir,Hebei province,is taken as the research object.Based on mineral characteristics of this reservoir,static experiments of 7 acid chemical agents and 5 alkaline chemical agents have been carried out,and 5kinds of chemical agents have been selected.The dynamic experiments were carried out using the selected chemical agents to reveal the chemical agents and mineral mechanism.Combined with the experiment data,a reactive solute transport model was established and the parameters in the model are determined.Then,a one-dimensional radial flow model was constructed,and the simulations of chemical agents-rock under different durations and different injection rates were developed.At last,propose 4 chemical stimulation modification plans for enhanced geothermal reservoirs in this area.The main conclusions from this study are as follows:(1)At the reaction time of acid chemical agents 2.5mol/LHCl+0.5mol/LHF,2.5mol/LHCl+0.5mol/LHF+1%LAN-826 and rock was 12 hours,the dissolution rate of rock per unit surface area reached 1.5%.At the same time,alkaline chemical agent2.5mol/LNaOH+1mol/LDTPA reached 0.51%.(2)Chemical agents have a certain positive effect on the rock core permeability under laboratory conditions.2.5mol/LHCl+0.5mol/LHF increases the rock core permeability by 1.62 times;2.5mol/LHCl+0.5mol/LHF+1%LAN-826 makes the rock core permeability increase by 1.5 times;2.5mol/L NaOH can increase the rock core permeability by 2.4 times;2.5mol/LNaOH+1mol/LDTPA increases the rock core permeability by 2.45 times;but 2.5mol/LNaOH+1mol/LNTA makes the permeability of rock core decreased by 66%.Acid chemical agents will produce secondary precipitation such as chlorite,spherical silica,and montmorillonite.Alkaline chemical agents will produce secondary precipitation plagioclase,and chelating agents can inhibit the production of plagioclase.(3)The results of the one-dimensional radial flow model show that the acid chemical agent 2.5mol/L HCl+0.5mol/L HF reacts strongly with the geothermal reservoir rock,which can effectively dissolve quartz,plagioclase,and K-feldspar,but generates secondary precipitation such as chlorite and montmorillonite.Alkaline chemical agent 2.5mol/L NaOH can dissolve quartz,K-feldspar,chlorite,and montmorillonite,but produced plagioclase as secondary sedimentary due to the a lot of Na~+in the chemical agent.DTPA can reduce the formation of secondary sedimentary plagioclase.(4)The radial distance of the acid chemical agent to the reservoir dissolution is larger than alkaline chemical agentt,and the greater the injection flow rate,the longer the reaction durations,the permeability of the reservoir near the injection well will increase more and the longer the radial distance of the chemical agent to reform the reservoir.Alkaline chemical agent dissolves the minerals strongly in the reservoir,and the permeability increases obviously,and the permeability increases with durations and flow rate,but the radial distance for reservoir reconstruction is small.(5)For the enhanced geothermal reservoir in Matouying,Hebei province,four chemical stimulation plans are proposed,which are acid chemical agents:2.5mol/L HCl+0.5mol/LHF,2.5mol/LHCl+0.5mol/LHF+1%LAN-826 and alkaline chemical agent 2.5mol/LNaOH+1mol/LDTPA,and a combination of alkaline chemical agents and acid chemical agents.