【作者】 袁建飞；

【导师】 王焰新；

【作者基本信息】 中国地质大学 ， 地下水科学与工程， 2013， 博士

【摘要】 中国是世界上地热资源十分丰富的国家,高、中低温地热均有分布。相对于高温地热资源来说,中低温地热资源具有分布广,面积大,开发和利用条件较好的特点。近年来,随着我国传统能源的日益短缺和对清洁能源需求量的增加,中低温地热资源的开发和利用受到越来越多的重视。而开展中-低温地下热水组分含量和分布特点,演化特征和热水-围岩相互作用等基础研究,对该类型地热系统的成因和地热资源的开发利用具有重要的指导意义。自1958年以来,广东省地热勘查经历了热矿泉普查、重点地热区勘察、隐伏地热田勘查、商业地热勘查四个阶段。广东省地质局曾于1981年编写和出版了《广东地下热水水文地质特征及勘查方法》一书,系统地总结了广东省热矿水的形成条件、分布规律、热储特征及其勘查技术方法。在1983年,广东省地质矿产部水文工程地质二大队编制了《广东省1：100万热矿水图及说明书》。然而,前期的工作主要集中在广东省地热地质、地热资源量评估和勘查方法等方面,而末对区内地下热水的形成机理进行过系统的研究。到目前为止,对广东省地下热水,尤其是沿海地区地下热水的组分含量和分布特征,组分演化过程和咸热水成因的研究程度较低,部分内容处于空白阶段。本研究对广东沿海地区地下热水进行了全面的调查,系统性地采集和测试了区内地下冷水、地下热水、河流和海水样品,并深入分析了区内地下热水的水文地球化学特征。论文通过对广东沿海区域地质、构造、水文地质和地热地质资料的分析,总结了研究区地下热水的出露和分布规律；根据地下热水的水化学组分和同位素分析测试结果,分别阐述了粤东和粤西地区地下热水的水文地球化学特征和同位素地球化学特征,评估了地热系统热储温度,并对咸热水水化学过程及其形成原因做了探讨和分析；论文最后选定新洲地热系统为典型区,从“点”的角度深入分析了地下热水补给特征、水-岩作用、海-淡水混合作用,并给出了相应的概念性模型。1.广东沿海地区地下热水的水文地球化学特征对广东沿海地区不同热泉和地热钻孔出露点,分4次共采集了地下冷水、地下热水、河水、大气降水和海水在内的水样147组和岩石样品8组,进行了样品中常规元素、微量元素(包括稀土元素)、溶解性气体组分等指标的测定。通过对测试结果的分析,得到：(1)广东沿海地下热水水化学分组明显,粤东和粤西沿海地下水均分为四个组：其一是Na-HCO3型水；其二是Na-Cl和Na-Ca-Cl型水;其三是Ca-SO4型水；第四组为上述混合形成的水化学类型。从平面分布上讲,广东沿海地区地下热水水化学类型具有有这样的演化趋势：靠近沿海地区地下热水水化学类型以氯化物型热水为主,向内陆地区逐渐过渡为重碳酸盐型热水,阳春地带发育有硫酸盐型热水,水化学类型在整体上分带明显。(2)广东沿海地区Ca2+、Mg2+、Na+、K+、HCO3-、SO42-、Cl-和EC组分的含量从内陆到沿海地区呈变大的趋势,说明海水对地下热水主要离子组分具有重要的影响。而微量组分如锂和锶含量也表现出相似的变化趋势,但内陆地区热水中氟含量普遍高于沿海地区,且分别在粤西和粤东内陆地区有高氟含量的区域。(3)广东沿海地区地下热水中溶解性气体以氮(N2)和氧(O2)为主,其中氮气古绝对的优势,其百分含量值在地下冷水中介于78%-93%,在热水中介于85%-94%之间,这说明区域地下水来源于大气降水。一般来说,地下热水中H2百分含量的高低能作为分析地热系统属于高温地热系统还是中-低温地热系统的的标志,广东沿海地下热水中H2百分含量几乎为零,这也说明该区域可能不存在高温地热系统。2.热水-围岩相互作用结合地下水(冷水和热水)各组分含量与温度关系、组分之间离子比值关系图对地下热水中离子组分的形成过程进行了分析,获得下列认识：(1)在Na-K-Mg三角图中,粤西沿海地区地下冷水尚处于水岩作用的初级阶段,而地下热水绝大多数位于“半平衡区”;粤东沿海地区地下热水样点均位于“平衡线”以下,部分水样位于“平衡线”和“半平衡线”之间的局部平衡区。对比粤西和粤东沿海地区地下热水样在Na-K-Mg三线图中位置,推断粤西沿海地区地下热水与围岩介质的水岩作用强度要高于粤东地区,或与“成熟度”更高的水溶液发生了混合作用。(2)从TDS与Cl-/(Cl-+HCO3-)的关系图,(Ca2++Mg2+)与(SO42-+HCO3-)关系图,(Mg2+/Ca2+)与(Na+/Ca2+)关系图和(Na++K+)与Cl-的关系图分析了研究区内地下热水主要组分的来源。区内硅酸岩、碳酸盐和硫酸盐矿物可能均发生了溶解,共同影响了地下热水组分的形成。此外,海水对地下热水的混合导致地下热水中部分组分的海水来源。(3)广东沿海地下热水中F组分受到地下水类型和pH的影响。重碳酸钠型的地下热水中F毫克当最百分含量值最大,而当地下热水中S042-和Cl-的当量百分值增加时,F毫克当量百分含量值较重碳酸钠型的地下热水有显著的降低。碱性环境有利于F-的富集。3.同位素地球化学特征(1)氢氧同位素①广东沿海地区地下冷水、地下热水和地表水均落在全球大气降水线附近,说明大气降水是这些水体的主要补给来源。②粤西地区部分水体在818O-δD关系图中较分散,有明显的“分层”现象,即地下冷水、地表河水、岩溶型热水和孔隙型热水具有不同的氢氧同位素组成特征,这说明这些水体接受补给的时期,水体的流动系统不同。③在δ18O和cl、EC关系图中,粤西部分地下冷水、孔隙型热水和裂隙型热水与海水之间成一线,说明海水和地下冷水可能是热水的两个影响端元,存在了海水和地下冷水的混合,这与水化学分析结果一致。(2)碳同位素①粤西沿海地区地下水中14C校正年龄介于933-11721年,平均为6528年；而粤东地区地下热水年龄处于4937-8239的范围内,平均为6635年。从14C等值线图可以看出,粤西内陆向沿海一带地下热水中14C含量值逐渐减小,地下水年龄增大。阳江和阳春地区存在低值封闭区,反映了这些区域地下热水属局部径流和排泄系统,这与前面水化学和氢氧同位素数据分析结果相一致。②广东沿海地区地下热水中δ13C值介于-17.8‰～-1.7‰之间,平均值为-8.9‰,说明其碳的多种来源性。粤东地区地下热水δ13C值介于-2.2‰～-3.8‰,接近于碳酸盐变质作用形成的δ13C值,说明该区域地下热水中碳来源于碳酸盐变质作用。粤西地区不同类型的地下热水其δ13C值含量不同,孔隙型热水中δ13C值介于-10‰～-15‰之间,其碳的来源可能是生物成因或有机物成因的碳；裂隙型热水中δ13C值范围较宽,介于-1‰～-18‰之间,说明其碳来源的多重性。(3)锶同位素广东沿海地区地下水中87Sr/86Sr平均值接近砂、页岩的87Sr/86Sr平均值,而低于花岗岩类岩石87Sr/86Sr平均值,这说明两类岩石对地下水中锶含量的影响。而热水绝大多数出露于花岗岩和沉积岩的接触带上,热水径流过程中与上述围岩的相互作用导致地下热水呈现出与围岩相似的87Sr/86Sr比值。(4)硼同位素①粤西地区地下冷水和地下热水中B含量和δ11B值分为四个区：Ⅰ区中B>0.1mg/L, δ11B>10‰,这部分热水有一个共同的特征就是热水中总溶解性固体含量值‘(TDS)大于4000mg/L；Ⅱ区为3>0.1mg/L,δ11B<‰,这部分热水属于裂隙型热水,其同位素介于-10-10‰之间,与美国黄石公园热水具有相似的δ11B值；m区为3<0.1mg/L,δ11B>10‰的地下冷水；Ⅳ区为3<0.1mg/L,δ11B<‰的岩溶热水、部分裂隙热水和孔隙热水。②在δ11B与Cl/B,Li/B和Sr/B的二变量关系图中,粤西地下热水和地下冷水分别位于不同位置,说明所采集的地下热水与地下冷水之间不存在水力联系,这可能是地下热水与地下冷水采集区域不同,不属于同一流动系统。但TDS含量值大于4g/L的地下热水其δ11B与Cl/B趋势线的箭头指向海水端元(δ1’B为39.5‰),这说明海水对热水的混合作用。4.咸热水形成的原因对广东沿海地区TDS值介于1g/L至13g/L的地下热水形成的原因进行分析,通过对该类型热水中离子组分比值、H、O、B同位素分析,得出如下认识：①对比分析广东沿海地下热水与海水中Ca/Cl.Mg/Cl、Na/Cl.K/Cl.HC03/Cl、S04/Cl和Cl/Br比值,Ca-Cl.Na-Cl.Br-Cl的相关关系图,说明存在海水对咸热水组分的影响。②通过咸热水和海水的δD、δ18O与Cl-含量分析,经拟合计算获得混合体系中淡水端元δD和δ180初始值：δD=-50.73‰和δ18O=-7.25‰。③从咸热水和海水δ18O-δD拟合线与大气降水线的交点,准确地求出端元组成数据：δD=-51.86‰和δ180=-7.73‰。5.地热系统温标估算和相对地热梯度采用常用的二氧化硅和阳离子地球化学温标对研究区地下热水系统热储层温度进行了估算和误差分析,认识到：①玉髓温标和Na-K-Ca温标所计算的热储温度与实际测试的温度误差较小,且玉髓温标计算值更接近实际测试的温度；石英温标(无蒸汽损失和最大蒸汽损失)计算值误差次之,其值介于Na-K温标和玉髓温标计算值之间；Na-K温标计算获取的热储温度与实际测试温度之间的误差最大,说明该温标不适合于研究区热储温度的计算。②广东沿海地下热水相对地热梯度在近海一带较高,如阳西儒洞温泉和阳东县新洲沸泉地区,其相对地热梯度值介于70-86之间。总体来说,广东沿海地区相对地热梯度值均低于100,说明研究区热流背景值不高,形成高温地热的可能性不大。③广东沿海地区地下热水的最大循环深度介于1013-5679m之间,最小循环深度介于566-3148m之间。不难推断,在同一地质构造和地热地质背景下,当地温梯度越高时,地下水加热增温至一定温度所需要的循环深度就越小。6.典型地热异常区的水文地球化学演化以广东阳东县新洲地热系统为典型地热系统开展了水文地球化学演化特征的详细研究,主要认识有：①通过对离子组分和氢氧同位素的分析,得出新洲地热系统及其外围热水为当地地下冷水与海水混合的结果,初步推断新洲热田热水中海水的混入比例介于9.8-11.4%,而神灶热泉中海水的混入比例为38%。②从δ11B与Cl/B的关系图中可以看出,新洲地热系统混入的海水可能不是现代海水,而是由海水演化来的一种类似海水的端元(贫硼组分,而富δ11B),这可能是全新世海侵过程中残存于岩石裂隙或断裂带中的海水。从新洲地热系统几个钻孔热水碳同位素的校正年龄可以看出,地热系统内热水年龄介于3947-6528年之间,与全新世早期第二次海侵的事件相吻合,推测新洲热田内混入的海水端元就为该时期残存海水。③新洲地热系统地下热水的形成模式为：在偏异常的区域大地热流值背景下,大气降水沿深、大断裂带入渗,深循环加热后与全新世海侵残存的古海水混合,形成Na-Cl型水；混合后的地下热水沿断裂带继续上升,随后分两个途径到达浅部地表和出露,第一类途径未经第二次混合直接出露地表,如编号为YX-1的钻孔热水(实际钻孔编号ZK-03),第二类途径为经历第二次浅部混合的地下热水,其TDS、 T和C1等组分有所降低,如编号为YX-41的钻孔热水(实际钻孔编号ZK-05)。更多还原

【Abstract】 There is huge geothermal resource in China, including high and low to medium temperature geothermal resource. Compared to high temperature geothermal resource, the low to medium geothermal resource is rich in reserve, wide in distribution and cost-effective for exploration. In recent years, more and more attentions have been paid on low to medium geothermal resource as the demand for cleaner energy keeps increasing. To study on the water-rock interaction, the chemical components and its evolution of thermal water, is significance for analyzing the genesis and utilization of geothermal system.Since1958, there are four stages for the development of geothermal exploration in Guangdong, including the investigation of hot spring, the exploration of remarkable thermal fields, the underlying geothermal fields and commercial geothermal exploration. Books of "The hydrogeological characteristics and exploration methods of thermal water in Guangdong" and "The map of hot mineral water and its instruction in Guangdong" are published in1981and1983, which systematically summarized the formation and distribution of thermal water, the characteristic of reservoir, and its exploration methods. However, little research is carried on the hydrogeochemical evolution of chemical components and the genesis of geothermal systems in Guangdong, especially in the coastal area.In this paper, water samples, including cold groundwater, hot spring, river water, rainy water and seawater, were collected to analyze the hydrogeochemical characteristics of the low to medium geothermal system. The occurrence of thermal water was studied based on regional geology, tectonics, hydrogeology and geothermal geology. The chemical and isotope characteristics, the calculated temperature of geothermal reservoir, the genesis of saline water, were analyzed and discussed by using the chemistry and isotope analysis results. A typical geothermal system, the Xinzhou geothermal field, was selected to discuss the recharge area, water-rock interaction, mixing processes of sea water and hot water. Finally, a conceptual model for the Xinzhou geothermal field was given. 1. Hydrogeochemistry of thermal water in the coastal areas of GuangdongOne hundred and forty-seven water samples and eight rock samples were collected to determine the major, minor and trace elements, and the types of dissolved gas in the study area. The results are as follows:(1) There are four hydrochemical types, named Na-HCO3, Na-Cl and Na-Ca-Cl, Ca-SO4, and the mixing type, in the coastal area of Guangdong. In addition, from the coastal area to the inland, the water changes from Cl to HCO3for hydrochemical type, and there is Ca-SO4type in the area of Yangchun sity.(2) The concentrations of Ca2+、Mg2+、Na+、K+、 HCO3-、SO42-、Cl-and EC increase from inland to coastal area, indicating that the impact of sea water on the chemical components of thermal water.(3) Nitrogen (N2) and oxygen (O2) are the major dissolved gas in water samples, and the percentage values of Nitrogen are78%to93%, and85%to94%for cold groundwater and thermal water, respectively. The results of dissolved gas indicate that the thermal water is meteoric origin. The contents of hydrogen (H2) in thermal water are used to determine the high and low temperature geothermal system of geothermal fields. However, the percentage of H2in thermal water is almost zero, which means that there are not high temperature geothermal systems in Guangdong.2. Thermal water-rock interactionThe hydrochemical processes of major ions in thermal water were analyzed by the relationship between the chemical constituents and temperature, and ion ratios, the results are shown as follows:(1) The cold groundwater in the west coastal area of Guangdong is so-called "immature water", while the thermal water was fell into the area between "mature water" and "immature water". It indicated that the ion exchange between water and rock is still under equilibrium. The groundwater collected in the east coastal area of Guangdong is also plotted into the area between "mature water" and "immature water", moreover, it near to the "immature water" area. Compare thermal water of the east coastal area with that of the west coastal area, there is more extensive water-rock interaction in the west coastal area, or other "mature water" mixed into thermal water.(2) From the plot of TDS and Cl-/(Cl-+HCO3-),(Ca2++Mg2+) and (SO42-+HCO3-),(Mg2+/Ca2+) and (Na+/Ca2+),(Na++K+) and Cl-, it can be suggested that the dissolved of silicate, carbonate and sulfate minerals influence the chemical component of thermal water. In addition, there is a mixture between sea water and thermal water.(3) The contents of F-in thermal water are controlled by hydrochemical types and pH values. The concentrations of F in HCO3-type are relatively higher than that of in SO42-and Cl-types. In addition, the contents of F-in alkaline water are high.3. Isotope geochemistry in thermal water (1) Hydrogen and oxygen isotope①The cold groundwater, thermal water, and surface water samples are all plot along the global meteoric water line, indicating those water samples are recharged by precipitation.②The values of8I8O and δD in cold groundwater, thermal water, river water are different, and scatted in the plot of δ18O and δD. It indicates that those water samples belong to different water system③There are linear relationship between δ18O vs Cl and EC, which suggest that cold groundwater and sea water are possible two end-members for thermal water. These results are consistent with that of the chemical analysis.(2) Carbon isotope①The corrected14C data of thermal water samples in the west and east coastal area of Guangdong range from933-11721a, and4937-8239a, respectively. According to the counter map, the values of14C increase from inland to coastal area, while the corrected14C data decrease. In addition, the counter map of14C enclosed in Yangjiang and Yangchun sity, indicating a local groundwater recharge and drainage system. It is consistent with the results; of chemical analysis.②The value of δ13C ranges from-17.8‰to1.7‰, with an average of-8.9‰, indicating a variety of source.(3) Strontium isotopeThe value of87Sr/86Sr ratio in thermal water is close to that of sand and shale, but lower to that of granitic rock, indicating water-rock interaction is the main processes for87Sr/86Sr ratio in thermal water. In fact, most of thermal water samples display on the boundary of granitic rock and sedimentary rock, then the components of wall rock can be dissolved into thermal water during water up flow forward to surface.(4) Boron isotopeFour distinct area can be distinguished for groundwater based on the value of B and δ11B: the first one is B>0.1mg/L and δ11B>10‰, most thermal water with TDS value higher than4g/L belongs to this type; the second one is B>0.1mg/L and δ11B<10‰, and most fissure water are of this type, and the value of δ11B ranges from-10to10‰, which is similar to the hot spring of Yellowstone Park; the third one is B<0.1mg/L and δ11B>10‰, and cold water is this type; the last is B<0.1mg/L and δ11B<10‰, some of fissure water, pore water samples belong to this type.②Groundwater samples of west coastal area scatted in the plot of δ11B vs Cl/B, and Li/B, and Sr/B, indicating the different groundwater systems. However, the thermal water samples, with TDS value higher than4g/L, are plotted into a sea water mixing line, indicating the mixing processes of sea water.4. The genesis of saline thermal water Water samples with TDS value between1g/L and13g/L are classified into saline thermal water, and the genesis of this type is discussed by using H、O and B isotopes, the results are as follows:①It is shown from the ratios of Ca/Cl、Mg/Cl、Na/Cl、K/Cl、HCO3/Cl、SO4/Cl and Cl/Br, and the plots of Ca vs Cl、Na vs Cl、Br vs Cl, that there is a mixing process between sea water and groundwater.②The initial values of δD and δ18O for one end-member are of-50.73‰and-7.25‰, respectively, based on the plot of δD and δ18O vs Cl-.③Another result of this end-member can be calculated from the intersection between the meteoric water line and the fitting line of δ18O and δD values, the value of δD and δ18O is-51.86‰and7.73‰, respectively.5. The calculated temperature of geothermal reservoir and the relative geothermal gradientThe geothermometer of silica and cation is used to calculate the geothermal reservoirs, the results are:①Compare to the water temperatures tested in situ, the calculated values of silica are more reasonable than that of K-Na-Ca geothermometer, and the estimated values of Na-K geothermometer is the highest among other results.②The value of relative geothermal gradient in coastal area is relatively higher than that of inland, with a range of70to85. All in all, there may not exist high temperature geothermal system in Guangdong according to the relative geothermal gradient.③The largest and lowest circulation depth of thermal water in the study area ranges from1013to5679m and566to3148m, respectively.6. Hydrogeochemistry of typical geothermal fieldThe Xinzhou geothermal field is selected as a typical area to analyze the evolution of hydrogeochemistry, the results are shown as follows:①From the ion ratios and hydrogen and oxygen isotope results, it can be seen that the thermal water collected in and around Xinzhou geothermal field are mixture of sea water and cold groundwater, and the mixing ratio of sea water are of9.8to11.4%for thermal water of Xinzhou geothermal field, and38%for Shenzao geothermal field.②One end-member of Xinzhou geothermal field is paleo-seawater, with low B contents and high δ11B values.③The conceptual model of Xinzhou geothermal field was given.更多还原