| The thermal reservoir of Minghuazhen Formation is the main interval for the development and utilization of geothermal resources in the Yancheng uplift.The buried depth of the water level dropped from the initial 30 m to 110 m,and the disorderly mining caused great damage to the geothermal resources.In order to establish a balance between the utilization and protection of geothermal resources,the geothermal genetic mechanism and multi-field evolution driven by heat extraction were studied for the first time in semi-diagenetic thermal reservoirs.The thermal convergence model of the Yancheng uplift was established by using the data of rock thermophysical property test,X-diffraction,scanning electron microscope,CSAMT,well logging,gravity,and aeromagnetics.The recharge,runoff and discharge conditions of thermal reservoirs in Minghuazhen Formation were systematically studied by means of isotope testing and water quality testing;A series of experiments such as depressurization test and recharge test were carried out,supplemented by numerical simulation,to reveal multi-field evolution driven by heat extraction;The recharge capacity of the Minghuazhen Formation thermal storage was quantitatively evaluated;and the sustainable development plan was determined.The following are the main results of the thesis:（1）The"semi-diagenetic thermal reservoir"is defined,and the area of the semi-diagenetic thermal reservoir in the Minghuazhen Formation and the geological background and tectonic evolution of the geothermal field are systematically studied;Through microscopic analysis and testing,basic parameters such as thermal storage structure,mineral composition,pore structure,and thermophysical properties were obtained;By analyzing the results of the well temperature survey,the temperature field characteristics of the geothermal field in the study area and the terrestrial heat flow conduction were revealed.The semi-diagenetic thermal reservoirs of Minghuazhen Formation are mainly finegrained sandstones.It is mainly composed of quartz and feldspar,with poor cementation and loose structure;It has the characteristics of uneven vertical components and poor connectivity on the plane;The porosity is between 13.02%and 36.50%,and the permeability is between 19.35 and21.49μm2;The thermal conductivity of rock is positively correlated with the particle size of the rock,and the medium-grained sandstone,fine-grained sandstone,siltstone to mudstone are 3.44W/（m·℃）,2.69W/（m·℃）,2.46W/（m·℃）,1.51W/（m·℃）in turn;The specific heat is negatively correlated with the particle size of the rock,and the specific heat from medium-grained sandstone to mudstone is 1.12W/m°C,1.75W/m°C,2.04W/m°C,and 2.86W/m°C.The depth of the constant temperature zone was determined to be 22m,the temperature was 16.6°C,the average geothermal gradient was 3.60°C/100m,and the average geothermal flow value was 69m W/m2,the geothermal gradient and geothermal flow are high in the northwest and low in the southeast;According to the strata,structure,cap/reservoir lithology,etc.of the Yancheng uplift,a visual 3D geological model is established.（2）The genetic model of Yicheng uplift is studied by means of structural analysis,hydrochemistry and isotope,hydrochemistry,and isotopes.Through heat source judgment and structural analysis,the geothermal origin of the study area is summarized as the mode of"integration of storage and cap,ternary heat accumulation"which is the accumulation of heat source caused by the superposition of tectonic evolution,the accumulation of heat flow caused by the difference in thermal conductivity of rocks,and the formation of self-storage and self-cover.The hydrochemical types of semi-diagenetic thermal reservoirs in Minghuazhen Formation are mainly Cl-Na type and Cl·SO4-Na type,followed by Cl·HCO3-Na type and Cl-Na·Ca type;Geothermal water undergoes intense evaporation before infiltration to recharge,with primary salinity exceeding 50%.The macrocomponent and microcomponent characteristics show that the geothermal water undergoes long-distance runoff,water-rock reaction and isotopic fractionation.Geothermal water is terrestrial dissolved water with weak hydrodynamic conditions,and the runoff is slowly revealed by the coefficient of variation,salinization coefficient,desulfurization coefficient,chlorine-bromine ratio,chlorine-calcium ratio and Gibbs diagram.The isotopic information shows that the 13CDICcorrected age of geothermal water is23000-29000 years,which is derived from ancient atmospheric precipitation,and the recharge elevation is between 196m and 450m.The recharge area is located in the Funiu Mountains in the west and northwest;The genetic mechanism model of"fluid horizontal replenishment and heat vertical conduction"in the semi-diagenetic thermal reservoir geothermal system is established.（3）The evolution process of the temperature field and the pressure field was revealed.According to the results of the different/same layer recharge test,the temperature of the recharge fluid is corrected to the same condition（at 25°C）,and the water injection permeability coefficients are obtained as 0.0783 m/d and 0.1072 m/d respectively,and the water conductivity coefficients are 9.2840m2/d,10.8750m2/d.The maximum natural recharge rates of different/same layers are 26.76 m3/h and33.06 m3/h.In the case of only mining but not irrigation,the heating season is calculated based on the mining volume of 50m3/h,the thermal storage pressure drop value is about 0.04 MPa/a,and the mining life is 22 years;When the mineable life is100 years,the maximum extraction volume of a single well should be limited to less than 30m3/h.The recharge amount has a linear relationship with the attenuation of the recharge pressure.For every 5m3/h increase in the recharge amount,the reservoir pressure recovers to 3268.10Pa.At 100%recharge rate,the thermal storage pressure is 509Pa higher than that before mining.After intermittent reinjection,The temperature dropped the fastest in the first five years,and after 25 years,it has basically dropped to the recharge water temperature.In the first 50 years,the expansion rate of cold halo was fast.With the increase of time,the range of cold halo was basically fixed,and the influence range of cold halo in the direction of cold water runoff was larger than that in other directions.In the case of a certain mining age and recharge amount,a reduction of 2°C is the thermal breakthrough limit,and the thermal breakthrough distance is 376.75m when recharged at 25°C,and the recommended recharge well spacing is 400m.The thermal breakthrough distance is 352.8m when recharged at 35°C,and the recommended recharge well spacing is 375m.（4）Based on PHREEQC,the chemical field evolution laws and water quality changes of different water sources were simulated.In the early stage of recharge,the content of each component in the geothermal water changes slightly,and the minerals containing calcium and magnesium precipitate in small amounts.In the later stage of recharge,the same-layer recharge and different-layer recharge are easy to precipitate different substances.Under the two conditions,the SI of carbonate minerals（aragonite,calcite and dolomite）,chrysotile and talc all show an increasing trend,which is easy to generate Precipitation and scaling are enhanced;The SI of carbonate minerals in the mixed fluid of the same layer recharge increases more and is more likely to be precipitated.However,the SI of chalcedony and iron-bearing minerals gradually decreased after recharge in the same layer,while the SI of chalcedony and iron-bearing minerals further increased after shallow well recharge,and they were more likely to be precipitated.With the recharge,the water quality of the geothermal water gradually improved,and the water quality of the different-layer recharge was better,and the water quality after the recharge was better than that of the same-layer recharge;After recharging,the content of most ions showed a significant downward trend,the total hardness and TDS of geothermal water gradually decreased,and only HCO3+and p H showed an upward trend;The recharge of geothermal water is not sufficient to change the chemistry of the groundwater.（5）Based on the corrosivity,scaling,suspended solids content,median diameter of suspended solids particles,bacterial content（iron bacteria,saprophytic bacteria,sulfate reducing bacteria）,sulfide,p H value and total iron of the recharge water index,the rechargeability of geothermal water in the study area was evaluated,The result is that the geothermal tail water in the study area can be used as the recharge water source after desulfurization and iron removal.Taking porosity,permeability,shale content,structure and thickness as evaluation factors,the rechargeability of semi-diagenetic thermal reservoirs was evaluated.The results showed that the porosity and permeability were average,the rechargeability was poor,and the recharge amount was slightly smaller.The dynamic evaluation formula of the recoverable amount of a single well based on numerical simulation under the driving of heat production was established;The geothermal resources in the study area are evaluated according to different development schemes;The mining mode of one mining and two tanks is recommended.The recharge rate in the early stage has an exponential relationship with the recoverable amount,and it tends to be constant in the later stage due to the influence of the single well production amount.The pollution saving and emission reduction and carbon trading value of different mining modes were evaluated.The pollution saving and emission reduction and carbon trading value of different mining modes are evaluated.Under the one mining and two irrigation mode,the geothermal mining of a single well group creates carbon trading of 136,600 yuan/a.In this dissertation,there are 131 figures,36 tables and 213 references. |
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