Flux of4He from Carnmenellis granite: modelling of an HDR geothermal reservoir

The diffusion coefficient (D) of He in the Carnmenellis granite, recovered from the Rosemanowes hot dry rock (HDR) geothermal reservoir, is experimentally determined in the laboratory in a temperature range of 100–300°C. Temperature variation of D fits an Arrhenius plot, but yields an activation energy for He release from rock significantly lower than the value for feldspar or quartz, suggesting that most of the He in the reservoir granite resides within grain boundaries and jointing cement and may be easily released.The reservoir surface area (S) is estimated based on the laboratory determined value of D from granite and the measured⁴He contents of circulation fluids from RH 15 well. In the first year of reservoir circulation,⁴He-based reservoir surface area was about twice that based on²²²Rn. It increased and stabilized at about 6 times after 2 a. The excess He release from newly opened up fracture surfaces within the reservoir during its expansion is shown to be responsible for the temporal increase in the He-based reservoir surface area over that of Rn.     

Rn solution by the circulating fluids in a “hot dry rock” geothermal reservoir

The mechanism of²²²Rn release into fracture fluids by direct alpha-recoil, lattice and grain boundary/micro-crack diffusion is discussed. Experimental measurements of²²²Rn release into surrounding air and water phases have been made for crystalline rock specimens with well defined surface areas. The²²²Rn flux from an infinite plane surface and hence the effective diffusion length of²²²Rn in the rock matrix has been estimated.The²²²Rn flux from plane crystalline rock surfaces has been used in conjunction with a simple hydrological model of the reservoir to calculate the²²²Rn content of the return fluids of a geothermal doublet circulation system. For given production rate and piezometric difference between the injection and production wells, the²²²Rn content of the return fluid is dependent upon the distribution of flow path lengths and fracture apertures in the reservoir. Matching of the calculated and experimental²²²Rn contents of the return fluids has been used to select appropriate parameters for the reservoir model and hence to estimate the extent of the heat-transfer surface. The model estimates the fracture width of the flow paths, total swept surface area and fracture volume within the reservoir.     

222Rn solution by the circulating fluids in a “hot dry rock” geothermal reservoir

The mechanism of²²²Rn release into fracture fluids by direct alpha-recoil, lattice and grain boundary/micro-crack diffusion is discussed. Experimental measurements of²²²Rn release into surrounding air and water phases have been made for crystalline rock specimens with well defined surface areas. The²²²Rn flux from an infinite plane surface and hence the effective diffusion length of²²²Rn in the rock matrix has been estimated.The²²²Rn flux from plane crystalline rock surfaces has been used in conjunction with a simple hydrological model of the reservoir to calculate the²²²Rn content of the return fluids of a geothermal doublet circulation system. For given production rate and piezometric difference between the injection and production wells, the²²²Rn content of the return fluid is dependent upon the distribution of flow path lengths and fracture apertures in the reservoir. Matching of the calculated and experimental²²²Rn contents of the return fluids has been used to select appropriate parameters for the reservoir model and hence to estimate the extent of the heat-transfer surface. The model estimates the fracture width of the flow paths, total swept surface area and fracture volume within the reservoir.     

黄土高原地表能量闭合特征及土壤通量参数化

利用兰州大学半干旱气候与环境观测站(简称SACOL站)2008年夏季晴天的湍流、 辐射、 土壤温度和通量梯度观测资料, 确定了晴天土壤热参数, 并结合土壤热流量板测量的温度积分法把实际测量通量推算到地表; 讨论了典型黄土高原沟壑区土壤热量储存对地表能量闭合率的影响; 建立了计算地表土壤热通量的模型. 结果表明: 黄土高原典型沟壑区夏季晴天平均土壤热容量为1.23×10⁶ J5m^-35K^-1; 能量平衡方程中, 以5 cm 埋深处HFP01SC热流量板观测值 (G₅) 表示土壤热通量时, SACOL站地表能量闭合率为75.7%. 采用温度积分法, 将HFP01SC的直接测量结果校正到地表(G_s)后, 地表能量闭合率可以达到81.8%; 0~5 cm土壤层的热量储存对能量平衡的贡献为6.1%. 模型计算得土壤热通量(G_m)与G_s之间的线性回归斜率为0.973(显著性水平为0.1‰). (H+LE)与(R_n-G_m)进行线性回归, 得到地表能量闭合率为81.7%. 表明模型与温度积分法计算计算土壤热通量非常接近, 但通过参数化方法计算时仅需要知道R_n即可.     

考虑土体非均质传热的河岸带水热耦合模型

为弥补当前河岸带水热交换模拟对土体非均质传热考虑不足的缺陷,在饱和-非饱和渗流及多孔介质传热理论基础上,引入土体有效导热系数模型,构建考虑土体非均质传热的河岸带水热耦合模型。结合COMSOL软件的特点,给出河岸带水热耦合模型的实现方法及求解流程,并通过河岸带温度和水位原型观测资料验证和对比分析不同有效导热系数模型下河岸带水热耦合模型的模拟效果。结果表明：与传统不考虑土体非均质传热方法相比,该模型能够较好地反映河岸带水热交换过程。此外,基于Johansen有效导热系数模型的河岸带水热耦合模型模拟效果表现最佳,模拟结果与前人试验结果一致。研究成果可为河岸带水热交换及污染物迁移过程的深入研究提供技术支撑。     

热屏障井对地下水源热泵换热影响模拟

对于场地受限的地下水源热泵项目,随着系统运行时间的增加易引发热贯通现象进而降低机组运行效率。地下水源热泵设计中,在抽灌水井连线间布设热屏障井可改变地下水流场,降低热量在抽灌井间的运移速度,有利于延长热贯通发生时间并缓解热贯通程度。通过构建地下水换热模型,模拟计算夏季制冷工况条件下36组热泵运行场景,分析了热屏障井的位置,过滤管长度及回灌量对热贯通和含水层温度场的影响规律。结果表明:热屏障井回灌量的增加有利于提升热屏障效果,但提升幅度随回灌量的增加逐渐减弱;最大水位降深值随着热屏障井回灌量的增加呈线性增长;增加热屏障井滤管长度可提升热屏障效果,提升效果随屏障井回灌量的增加逐渐增强。通过模型多周期、长时间模拟计算发现,热屏障井的运行可促使回灌的冷热量集中在回灌井一侧,对于采用冬夏季抽灌井交换运行模式的热泵系统,可充分利用含水层储能,提升机组运行效率。     

模糊数学在岩溶储层地热资源勘探风险评价中的应用——以重庆山地型岩溶热储为例

重庆市岩溶储层地热资源丰富,开发利用历史悠久,但地热资源勘探风险较大。本文利用模糊综合评价法建立了风险评价模型,该模型中包含了热储构造开启程度、热储构造部位、沟谷切割程度、物探效果、热储埋深、热储厚度、热储岩层倾角、热异常情况、热储层位9个风险因子,每个因子划分为风险小、风险中等、风险大3级,并对其进行量化处理。最后对全市23个高隆起背斜两翼46个相对独立的山地型高隆起岩溶地热田共79个地热单元进行了地热资源勘探风险模糊数学综合评判。结果表明,有18个单元为风险小,42个单元为风险中等,19个单元为风险大。风险小的地热田一般热储汇水面积较大、补给径流循环条件好、热储顶板埋深1000-1800 m、热储厚度≥300 m、热储岩层倾角25-40°、深部裂隙较发育;风险大的地热田热储汇水面积较小、补给径流循环条件差、热储顶板埋深≥2500 m、热储厚度〈200 m、热储岩倾角〈20°176;或≥40°176;、深部裂隙不发育;风险中等地热田的地质特征则介于二者之间。评价结果较好地反映出了重庆市岩溶热储地热资源勘探风险状况。     

山东临沂地区古生代复合热储成矿模式研究

山东临沂地区地热资源丰富,前人对于临沂地区沂沭断裂带成热模式存在诸多争议。通过对研究区地热地质条件、地球物理特征和地热井数据进行综合研究,从地热产生的源、通、储、盖四要素进行分析,研究结果表明研究区地热成矿模式为古生代层状和带状复合热储地热成矿模式,断裂带为带状热储,断裂带周边稳定区域为层状热储。研究区热储为古生代砂岩,同时张性、张扭性断裂发育,导致热储为层状和带状的复合热储,较单一成因热储要复杂。对地热井数据归一化处理分析表明,盖层岩性及厚度对深部地热水温度存在较大影响,并且热储厚度对水温也存在影响,表现为表层有第四系覆盖的地热水温度,较无第四系覆盖的要高;盖层厚度越大,水温越高,热储厚度越大,水温也越高。这为进一步地热勘查与开采提供了理论指导。     

新疆塔什库尔干谷地地热资源研究进展

归纳了新疆塔什库尔干谷地地热地质条件,分析了区内地质构造、地温分布、地热流体化学及同位素特征,研究了地热形成机理,计算了曲曼地热田的地热资源量和可开采量。结果表明: 研究区地热资源受断裂构造控制; 地温变化与盖层、完整基岩、断裂带(热储)表现出明显的一致性,目前实测最高热储温度为161 ℃,深部热储计算温度可达222~268 ℃,地温梯度最高为149.20 ℃/100 m; 地热流体具有深循环特征,与浅表冷水的水化学和同位素特征具有明显的差异; 地热流体来源于大气降水,在断裂及裂隙内储存、运移、富集,在侵入岩体放射性生热和结晶余热的热量供应下,地下流体不断与围岩进行热量及物质交换,在热储围岩和盖层中,热量以传导方式为主,在热储内,热量以对流方式为主; 曲曼地热田储存的热量为55.919×10¹¹ MJ,地热流体可开采量约为12 593 m³/d,产能(热能)约为77.9 MW。因此认为,塔什库尔干谷地热储埋藏深度浅,易开采,具有可观的直接和间接经济价值。     

含水层热量输运中自然热对流和水-岩热交换作用的研究

本文对含水层热量输运过程中存在的自然热对流和水-岩热交换作用进行了深入研究, 目的是为了弄清两种作用对热量输运的影响。首先针对普通水流方程和热量输运方程的局限性, 给出了能够描述这两种作用的新的数学方程, 并通过建立一个非线性三维含水层热量输运模型加以实现。然后利用上海第二承压含水层的群井储能试验资料, 根据不同的条件进行计算。计算结果与实测数据的对比分析表明, 自然热对流通常对含水层的热量输运有明显作用, 定量研究时不应忽略；水-岩热交换作用持续时间短, 对整个热量输运过程影响较小。     

A study of the thermal behaviour of exposed karst water systems in a mountainous area of Zigui County,Hubei Province,Central China

Temperature, discharge, and stable isotope ratios of five karst springs in a mountainous area of Zigui County, Hubei Province, Central China, were analyzed. The purpose was to illustrate the heat exchanges linked to circulation depth in the exposed karst water systems through the development of a method for estimating heat input and heat flux during a rainstorm. Meteorological water in the study area conformed to a local meteoric water line (δD?=?8.37 δ¹⁸O?+?12.99) with a mean δ¹⁸O elevation gradient of ?4.0‰ km^?1, which was used to estimate mean circulation depths of 209–686 m. The mean spring temperatures defined a vertical gradient of ?5.4 °C km^?1, which resembled that of the stable atmosphere of the Earth, indicating that the thermal response patterns are mainly controlled by surface air temperature. Thermal convection after rainfall events dominated heat exchange between baseflow and recharge water, leading to a warmer and colder recharge during summer and winter, respectively, whereas thermal conduction dominated the heat exchange only between groundwater, surrounding geology, and the interface air under a condition of no rainfall, resulting in only small temperature variations of the baseflow. Successful application of the method for estimating heat exchange showed that the characteristics of shallow circulation, strong karstification, and well-developed epikarst readily allowed disruption of the thermal balance of the Yuquandong system, resulting in a poor heat regulation capacity, a larger variation of heat input, a lower mean heat flux, and lower baseflow temperatures compared to those of the Dayuquan system.

     

西宁盆地热储构造概念模型的建立

基于西宁盆地地热地质条件的研究,在Donaldson管状模型的基础上,提出的西宁盆地热储构造概念模型是大地热流为热源一低热导率岩层聚热-深循环逐渐加热受迫对流为机制-构造控水控热。进而揭示出,尽管西宁盆地地热异常分布范围较广,但也并非“遍地有热”。在生产实践中,关键是要较为准确地确定地热井的最佳构造部位和找到高渗透率的热储。     

Analysis of the exchange of groundwater and river water by using Radon-222 in the middle Heihe Basin of northwestern China

In arid regions of western China, water resources come from mountain watersheds and disappear in the desert plain. The exchange of surface water and groundwater takes place two or three times in a basin. It is essential to analyze the interaction of groundwater with surface water to use water resources effectively and predict the change in the water environment. The conventional method of analysis, however, measures only the flow of a stream and cannot determine groundwater seepage accurately. As the concentration of Radon-222 (²²²Rn) in groundwater is much higher than in surface water, the use of ²²²Rn was examined as an indicator for the analysis of the interaction between surface water and groundwater. Measurement of the ²²²Rn concentration in surface water was conducted to detect groundwater seepage into a stream in the middle Heihe Basin of northwestern China. Furthermore, the simultaneous groundwater flow into and out of a stream from the aquifers was quantified by solving the ²²²Rn mass balance equation, in which the losses of gas exchange and radioactive decay of ²²²Rn are considered. Meanwhile, river runoff was gauged to determine the exchange rates between surface water and groundwater. The result shows that ²²²Rn isotope can be used as a good environmental tracer with high sensitivity for the interaction between surface water and groundwater, especially in the fractured aquifer system, karst aquifer system and discharge basins.     

花岗岩粗糙单裂隙对流换热特性的数值模拟

在干热岩储层中开采地热能,往往需要对储层进行人工水力压裂以形成贯穿的换热通道。然而,热储中的对流换热对干热岩的采热率有重要影响,经过人工刺激的储层会形成几何形态各异的裂隙面,而裂隙粗糙程度的不同则会引起换热性能的显著差异。因此,选取4条Barton的经典岩石裂隙粗糙度曲线,在试验室条件下建立一个单裂隙对流换热模型。详细分析了花岗岩粗糙裂隙中热工质的换热特性。结果表明：局部对流换热系数沿着裂隙长度方向逐渐降低;节理粗糙系数JRC值越大,平均对流换热系数就越大,表明换热性能越好;局部对流换热系数的分布与JRC曲线的几何轮廓形态有很好的相关性,波峰波谷的变化趋势相一致;相对于温度而言,高流速对局部对流换热系数具有放大效应,流速越大,局部对流换热系数波动越大。     

盆地潜凸起岩溶热储地热田成因机理：以菏泽潜凸起为例

盆地潜凸起岩溶热储地热田是我国主要供暖用热储之一,具有分布面积广、水温高、水量大等特点,是北方清洁供暖的重要可再生热源。本文以菏泽潜凸起岩溶热储地热田为例,通过地质构造、岩溶发育特征、同位素和水文地球化学特征、地温场空间分布规律、地热水动力场的系统分析,揭示地热田岩溶地热水补给源、运移途径和富集机理：地热水来源于东北部梁山、东部嘉祥一带基岩山区大气降水入渗补给,主要循环富集于层间岩溶与断裂破碎带复合处。根据地温场空间分布特征揭示的热源及其传递和聚集特征,提出了四元聚热机制,一元是大地热流毯状传导聚热、二元是凸起区高热导率分流聚热、三元是导热断裂或岩体接触带带状对流聚热、四元是地下水运移传导-对流聚热。在热储富集和聚热成因机理研究基础上,构建了基于水源、热源及深部岩溶发育特征的地热田成因机理模型,揭示了地热能富集规律。     

苏北盆地老子山地热田成因模式

老子山地热田是苏北盆地的典型地热田之一,阐明其成因模式对于该地热田的进一步开发和热水资源的可持续利用具有一定的指导意义。基于大地热流测试和水文地球化学方法对其进行了系统研究。结果表明:该区大地热流背景值为63.9 mW/m²,地热水与浅层地下水和地表水之间在水化学和同位素组成上存在明显差异。经分析,该地热系统属于中低温对流型。其补给区位于距地热田南部约60 km处的盱眙－张八岭一带的丘陵地区,热储温度为73~120 ℃,循环深度为2 350~4 200 m,循环周期约为7 800 a,热水在区内NNE－SSW向与NW－SE向断裂的交汇处上涌,形成地热田。     

实验室尺度高地温梯度模拟地层的实现方法研究

地热井与周围热储层的传热过程对地热井产热性能研究有重要意义。由于实际工程中在地热井周边布置测点较难,无法获取地热井周围热储层的参数变化,进而为地热热储模拟结果提供验证,故以往大多地热热储模拟仅将地热井作为源项处理,未考虑地热流体和储层的耦合流动换热。实验室条件下的模拟试验方便布置测点,可为热储-井筒耦合流动传热模型提供试验验证,其中如何实现实验室尺度下有温度梯度的模拟地层是试验研究的关键,目前尚未有类似研究。基于传热学基本原理,研究了实验室条件下有较高温度梯度多孔地层的快速实现方法,通过确定模拟热储层和热储盖层几何尺寸、优选填充多孔介质和实现恒定温度的模拟热储层,设计了一套实验室尺度下有高温度梯度的模拟地层系统,通过分层加热与边界动态热补偿方法,较快实现了热储层温度分别为60 ,65,70 °C下模拟地层的线性温度分布,采用有限体积法得到的数值模拟与试验结果的相对误差在±2.5%范围内,二者吻合较好。文章设计搭建的模拟地层系统可为开展地热井筒-热储耦合模拟试验提供条件,进而为开发的地热热储-井筒耦合传热数值软件提供试验验证。     

A three-dimensional heat transfer and thermal cracking model considering the effect of cracks on heat transfer

A simple three-dimensional heat transfer model is developed to consider the hindering effect of cracks on heat transfer. The 3D heat transfer model can also be applied to numerical methods such as the combined finite-discrete element method (FDEM), discrete element method (DEM), discontinuous deformation analysis (DDA), the numerical manifold method (NMM), and the finite element method (FEM) to construct thermo-mechanical coupling models that allow these methods to solve thermal cracking problems and dynamically consider the hindering effect of cracks on heat transfer. In the 3D heat transfer model, the continuous-discontinuous medium is discretized into independent tetrahedral elements, and joint elements are inserted between adjacent tetrahedral elements. Heat transfer calculations for continuous-discontinuous media are converted to heat conduction in tetrahedral elements and the heat exchange between the adjacent tetrahedral elements through the joint element. If the joint element between adjacent tetrahedral elements breaks (ie, a crack generates), the heat exchange coefficient of the joint element is reduced to account for the hindering effect of cracks on heat conduction. Then the model and the FDEM are combined to build a thermo-mechanical coupling model to simulate thermal cracking. The thermally induced deformation, stress, and cracking are investigated by the thermo-mechanical coupling model, and the numerical results are compared with analytical solutions or experimental results. The 3D heat transfer model and thermo-mechanical model can provide a powerful tool for simulating heat transfer and thermal cracking in a continuous-discontinuous medium.     

四川宜宾金沙江河谷区地热资源成藏条件分析

[摘 要] 本文从地热地质背景、水文地质条件、构造条件、热储条件等几方面对金沙江宜宾段河谷区 的地热成藏条件及开发潜力进行了较为深入的论述。研究表明:该区的古地理环境有利于地表水向深部 补给、运移、往更纵深循环以及形成与深部热储充分进行热交换,有利于形成保持相对封闭的热水构造,使 深部地热水处于承压状态;热储层盖层对地下热水具有良好的保温防热扩散作用,且阻隔浅层地表水向下 运移;东西向断裂与南北向断裂或与NE、NW 向断裂的多方向构造的交切复合部位为深部地热水向上运 移排泄的极为有利构造部位;区内地下热水其热源主要是地热增温,大气降水经由深循环加热,与深部热 储层岩石进行充分的热交换,温泉水以补给地高、运移途径长、循环深、滞留时间长为特征。     

FDEM-TH3D: A three-dimensional coupled hydrothermal model for fractured rock

This paper proposes a three-dimensional coupled hydrothermal model for fractured rock based on the finite-discrete element method to simulate fluid flow and heat transport. The 3D coupled hydrothermal model is composed of three main parts: a heat conduction model for the rock matrix, a heat transfer model for the fluid in the fractures (including heat conduction and heat convection), and a heat exchange model between the rock matrix and the fluid in the fractures. Four examples with analytical solutions are provided to verify the model. A heat exchange experiment of circulating water in a cylindrical granite sample with one fracture is simulated. The simulation results agree well with the experimental results. The effects of the fracture aperture, fluid viscosity, and pressure difference on the heat exchange between the fluid and rock are studied. Finally, an application concerned with heat transport and fluid flow in fractured rock is presented. The simulation results indicate that the 3D fully coupled hydrothermal model can capture the fluid flow and temperature evolution of rocks and fluids.