Progress in research on the exploration and evaluation of deep geothermal resources in the Fujian-Guangdong-Hainan region,China

Deep geothermal resources in the Fujian-Guangdong-Hainan region,China,offer significant potential for sustainable energy.The diverse igneous rock formations along the southeast coast present intricate geological challenges that impede exploration and evaluation efforts.In this study,we address critical concerns related to the Fujian-Guangdong-Hainan region's deep geothermal resources,encompassing heat source composition,formation conditions,strategic favorable areas,and exploration directions.Our methods involve the analysis of regional geothermal reservoirs and cap rocks.Major findings include:the primary heat sources in the Fujian-Guangdong-Hainan region consist of the radioactive heat generation from granites in the crust,heat conduction in the mantle,and,in specific areas like Yangjiang and Shantou,melts within the middle and lower crust;the deep,high-temperature geothermal resources in the region predominantly reside in basins'depressed areas.These areas are characterized by the confluence of triple heat sources:heat from the Earth's crust,mantle,and other supplementary sources;our analysis led to the identification of three strategic areas favorable for deep geothermal resources in the Fujian-Guangdong-Hainan region.These are the Beibu Gulf Basin's continental area,the Yuezhong Depression,and the Fuzhou-Zhangzhou area.

Progress and prospect of mid-deep geothermal reinjection technology

Mid-deep geothermal reinjection technology is crucial for the sustainable development of geothermal resources,which has garnered significant attention and rapid growth in recent years.Currently,various geothermal reinjection technologies lag behind,lacking effective integration to address issues like low reinjection rates and thermal breakthrough.This paper reviews the basic principles and development history of mid-deep geothermal reinjection technology,focusing on various technical methods used in the process and analyzing their applicability,advantages,and disadvantages under different geological conditions.It highlights the unique challenges posed by deep geothermal resources,including high temperature,high pressure,high stress,chemical corrosion,and complex geological structures.Additionally,it addresses challenges in equipment selection and durability,system stability and operation safety,environmental impact,and sustainable development.Finally,the paper explores future directions for mid-deep geothermal reinjection technology,highlighting key areas for further research and potential pathways for technological innovation.This comprehensive analysis aims to accelerate the advancement of geothermal reinjection technology,offering essential guidance for the efficient reinjection and sustainable development of geothermal resources.

Deep geothermal resources in China:Potential,distribution,exploitation,and utilization

Deep geothermal resources mainly refer to the thermal energy stored in subsurface rocks and fluids therein at a depth of 3-10 km,which is a kind of renewable and sustainable clean energy unaffected by weather and seasonal changes.Large scale exploitation of the deep geothermal resources is of great significance to ensuring national energy security and achieving the“Carbon Peak and Carbon Neutrality”.Based on the latest terrestrial heat flow data,this paper estimated the potential of deep geothermal resources in the terrestrial areas of China,and the results show that the total amount of geothermal resources within 3e10 km under the Earth's surface in the terrestrial areas of China is 24.6×10^(15)GJ.In line with climate zones categorized,the geothermal resource proportion is 43.81%for severe cold regions,29.19%for cold regions,6.92%for mild regions,13.82%for hot summer and cold winter regions,and 6.26%for hot summer and warm winter regions.Statistics according to the burial depth range reveal that the resources within depth ranges of 3-5 km,5-7 km and 7-10 km under the Earth's surface are 4.3119×10^(15)GJ,6.37674×10^(15)GJ and 13.89594×10^(15)GJ respectively,showing an increasing trend of geothermal potential with increasing burial depth.The deep geothermal resources are mainly of medium-to-high temperature reserves,and the energy supply strategy can be optimized by combining the climate conditions and population distribution,as well as considering power generation.In regions of cold or severe cold climate,the geothermal resources may be applied to geothermal power generation and district heating in combination;in regions of hot summer and cold winter or mild climates,the resources can be used for geothermal power generation combined with cooling and heating;in regions of hot summer and warm winter climates,the resources may be applied to geothermal power generation combined with cooling and industrial and agricultural utilization.Exploitation of deep geothermal resources also can be combined with carbon dioxide sequestration,multi-mineral resources extraction and energy storage to realize comprehensive exploitation and utilization of various energy resources.It is suggested that theoretical technology research should be combined with pilot tests and field demonstrations,and large-scale economic exploitation of deep geothermal resources should be arranged in a coordinated manner,following the principles of overall planning and step-by-step implementation.

Mapping and resource evaluation of deep high-temperature geothermal resources in the Jiyang Depression,China

In China,geothermal resource utilization has mainly focused on resources at shallow and medium depths.Yet,the exploration of deep,high-temperature geothermal resources holds significant importance for achieving the“dual carbon”goals and the transition of energy structure.The Jiyang Depression in the Bohai Bay Basin has vast potential for deep,high-temperature geothermal resources.By analyzing data from 2187 wells with temperature logs and 270 locations for temperature measurement in deep strata,we mapped the geothermal field of shallow to medium-deep layers in the Jiyang Depression using ArcGIS and predicted the temperatures of deep layers with a burial depth of 4000 m.Through stochastic modeling and numerical simulation,a reservoir attribute parameter database for favorable deep,high-temperature geothermal areas was developed,systematically characterizing the spatial distribution of geothermal resources within a play fairway of 139.5 km2 and estimating the exploitable deep geothermal resource potential by using the heat storage method and Monte Carlo data analysis.The study reveals that the Fan 54 well block in the Boxing-Jijia region is of prime significance to develop deep,high-temperature geothermal resources in the Jiyang Depression.Strata from the Cenozoic to the Upper Paleozoic are identified as effective cap layers for these deep geothermal resources.The Lower Paleozoic capable of effectively storing thermal energy and possessing an exploitable resource volume up to 127 million tons of standard coal,is identified as a target system for the development of deep high-temperature geothermal resources,providing significant insights for the efficient development of geothermal resources in the Jiyang Depression.

Wellhead anti-frost technology using deep mine geothermal energy

The auxiliary shaft is an important location for coal mine heating in the winter, where the main purpose of heating is to prevent icing of the shaft. Wellhead heating requires characteristics of openness, no-noise and big heat loads. The original coal-fired boiler heating mode causes significant waste of energy and environmental pollution due to the low efficiency of the heat exchange. Therefore, to solve these prob- lems, we will use deep mine geothermal energy to heat the wellhead by making full use of its negative pressure field and design a low-temperature water and fan-free heating system. Through numerical cal- culations we will simulate temperature fields, pressure fields and velocity fields under different air sup- ply temperatures, as well as different air supply outlet locations and varying number of radiators in the wellhead room of a new auxiliary shaft to find the proper layout and number of radiators that meet well- head anti-frost requirements from our simulation results, in order to provide guidelines for a practical engineering design. Tests on the Zhangshuanglou auxiliary shaft wellhead shows good, look promising and appear to resolve successfully the problem of high energy consumption and high pollution of well- head heating by a coal-fired boiler.

Characterization of deep ground geothermal field in Jiahe Coal Mine

Research into the characteristics of geothermal fields is important for the control of heat damage in mines. Based on measured geothermal data of boreholes from 200 m to 1200 m in a Jiahe Coal Mine, we demonstrate non-linear but increasing relations of both geo-temperatures and geothermal gradients with increases depth. Numerically, we fitted the relationship between geo-temperatures and depth, a first-order exponential decay curve, formulated as: T(h) = 4.975 + 23.08 exp(h/1736.1).

Clogging mechanism in the process of reinjection of used geothermal water: A simulation research on Xianyang No.2 reinjection well in a super-deep and porous geothermal reservoir

In the process of geothermal exploitation and utilization, the reinjection amount of used geothermal water in super-deep and porous reservoir is small and significantly decreases over time. This has been a worldwide problem, which greatly restricts the exploitation and utilization of geothermal resources. Based on a large amount of experiments and researches, the reinjection research on the tail water of Xianyang No.2 well, which is carried out by combining the application of hydrogeochemical simulation, clogging mechanism research and the reinjection experiment, has achieved breakthrough results. The clogging mechanism and indoor simulation experiment results show: Factors affecting the tail water reinjection of Xianyang No.2 well mainly include chemical clogging, suspended solids clogging, gas clogging, microbial clogging and composite clogging, yet the effect of particle migration on clogging has not been found; in the process of reinjection, chemical clogging was mainly caused by carbonates(mainly calcite), silicates(mainly chalcedony), and a small amount of iron minerals, and the clogging aggravated when the temperature rose; suspended solids clogging also aggravated when the temperature rose, which showed that particles formed by chemical reaction had a certain proportion in suspended solids.

Conventional Geothermal Systems and Unconventional Geothermal Developments: An Overview

This paper provides an overview of conventional geothermal systems and unconventional geothermal developments as a common reference is needed for discussions between energy professionals. Conventional geothermal systems have the heat, permeability and fluid, requiring only drilling down to °C, normal heat flow or decaying radiogenic granite as heat sources, and used in district heating. Medium-temperature (MT) 100°C - 190°C, and high-temperature (HT) 190°C - 374°C resources are mostly at plate boundaries, with volcanic intrusive heat source, used mostly for electricity generation. Single well capacities are °C - 500°C) and a range of depths (1 m to 20 Km), but lack permeability or fluid, thus requiring stimulations for heat extraction by conduction. HVAC is 1 - 2 m deep and shallow geothermal down to 500 m in wells, both capturing °C, with °C are either advanced by geothermal developers at <7 Km depth (Enhanced Geothermal Systems (EGS), drilling below brittle-ductile transition zones and under geothermal fields), or by the Oil & Gas industry (Advanced Geothermal Systems, heat recovery from hydrocarbon wells or reservoirs, Superhot Rock Geothermal, and millimeter-wave drilling down to 20 Km). Their primary aim is electricity generation, relying on closed-loops, but EGS uses fractures for heat exchange with earthquake risks during fracking. Unconventional approaches could be everywhere, with shallow geothermal already functional. The deeper and hotter unconventional alternatives are still experimental, overcoming costs and technological challenges to become fully commercial. Meanwhile, the conventional geothermal resources remain the most proven opportunities for investments and development.

Geochemical genesis of geothermal waters from the Longling hydrothermal area, Yunnan, Southwestern China

Longling is characterized by a wide distribution of hydrothermal areas, among which the Banglazhang hydrothermal system is the most geothermally active. Banglazhang is marked by intensive hydrothermal activities including hot springs, geysers, fumaroles and hydrothermal explosions. The geothermal waters from the Longling region are mainly HCO3-Na type with low but comparable SO4 and Cl concentrations. Calculations based on a variety of chemical geothermometers and a K-Ca geobarometer indicate that the Banglazhang hydrothermal system has much higher subsurface temperature and CO2 pressure compared to the other systems such as Daheba, Dazhulin and Huangcaoba. However, geothermal water samples collected from all these alternative hydrothermal areas are either partially equilibrated with reservoir minerals or are immature. The silica-enthalpy relationships of Banglazhang geothermal waters indicate the presence of a deep geothermal fluid with an enthalpy value and silica concentration of 945 J/g（up to around 220 °C） and 339 mg/L. Our work indicates the Banglazhang area is a promising source in terms of long-term utilization of hydrothermal resources.

深层地热井考虑水泥环损伤的套管预热应力设计

深层地热资源相较于传统地热资源具有更大的开发潜力,但由于深层地热井井底温度更高,在开发开采中高温流体使套管受热膨胀,易引起套管屈服变形损坏。而目前对于深层地热井套管安全问题在理论研究和技术实践上均面临着诸多挑战。为此,根据厚壁圆筒理论和热弹性力学基本理论,利用对套管预先施加热应力降低套管的轴向热应力,考虑高温水泥石损伤后地层-水泥环-套管的接触问题,并以套管有效应力控制在相应温度下的最小屈服极限内为原则,根据套管柱强度设计安全系数,评价套管安全性能,建立深层地热井套管预热应力设计方法,缓解高温对套管热损伤的问题。结果表明,水泥浆的密度对损伤因子影响不大,水泥环的弹性模量对损伤因子起主导作用。在预热情况下,注水条件下(注水温度为65℃)在预热250℃以下能够满足设计条件,在地热生产条件下(地热温度为346℃),需要超过200℃才能够满足安全设计要求。

Geothermal Investigations in Permafrost Regions—The Duration of Temperature Monitoring after Wellbores Shut-In

The most important data on the thermal regime of the Earth’s interior come from temperature measurements in deep boreholes. The drilling process greatly alters the temperature field of formations surrounding the wellbore. In permafrost regions, due to thawing of the formation surrounding the wellbore during drilling, representative data can be obtained only by repeated observations over a long period of time (up to 10 years). Usually a number of temperature logs (3 - 10) are taken after the well’s shut-in. Significant expenses (manpower, transportation) are required to monitor the temperature regime of deep wells. In this paper we show that in most of the cases (when the time of refreezing formations is less than the shut-in time) two temperature logs are sufficient to predict formations temperatures during shut-in, to determine the geothermal gradients, and to evaluate the thickness of the permafrost zone. Thus the cost of monitoring the temperature regime of deep wells after shut-in can be drastically reduced. A simple method to process field data (for the well sections below and above the permafrost base) is presented. Temperature logs conducted in two wells were used to demonstrate utilization of this method.

深层地热花岗岩体地震波数值模拟及传播机制

深层地热资源是一种可再生的、蕴藏巨大能量的清洁能源,但其地球物理响应特征不明确,中深层地热探测成功率较低。为了研究地震波在深层地热岩体中的传播规律与波场特征,建立两种深层地热花岗岩模型,并使用等效交错网格有限差分法实现声波与弹性波的数值模拟。结果表明:地热花岗岩体速度在温度的影响下要高于围岩的,会产生高速屏蔽现象,使得透射波能量变弱,限制了地热岩体下部地震波传播能量;相比于声波,弹性波具有更丰富的波场信息,波型与能量转换使得弹性波地震记录也比声波地震记录复杂。

深层地热能丛式多分支U型井采热技术及传热算法

深层地热能是一种分布广、资源量大具有发展前景的可再生新能源,当前的主要开采方法有增强型地热系统(EGS)、环绕式井筒换热系统(AGS)、断层带流体循环开采和同轴套管开采法,但存在采热功率不稳定、地震风险高和采热效率低等难题。针对当前深层地热开采技术面临的瓶颈问题,本文以开采过程只有能量交换而没有物质交换为原则,以深层干热岩地热规模化可持续稳定开发为目标,提出了深层地热能丛式多分支U型井采热方法(UMW-DGS)及关键技术,在此基础上建立了井筒轴对称热传导模型,以青海共和盆地恰卜恰深部干热岩储层为背景,提出了高温高压岩石热导率测试新方法,计算了在定井径条件下井周温度场和采热功率的时空演化规律,分析了温度差、热导率和井径等3个敏感因素对采热功率的影响。此外,针对UMW-DGS定解问题,研发了基于有限体积法(FVM)的三维热流固耦合数值算法,研究了UMW-DGS单水平井段换热效率和在不同泵注量条件下温度场时空演化。通过分析不同流量的有效换热量、换热时长和功率发现:泵注流量的增加会导致有效换热能量和有效换热时长的降低,并且使有效换热功率先增加后减少。研究结果表明,深层地热能开发需要在平衡换热温度和功率的条件下设计注入排量,从而得到最优的换热效果。

中深层水平连通地热井取热特性研究

高效取热技术是实现地热效益化开发的关键,建立了水平连通地热井数值仿真模型,计算了连续开采和间歇开采工况下的出口流体温度和换热量,研究了注入温度、注入流量、水平段长度对系统换热性能和岩层温度恢复能力的影响。结果表明,随着注入流量增加,地热井出口水温下降,但整个系统换热量提高;当注入温度较高时,可有效提高出口水温,但系统换热量降低较大;随着水平段长度增加,出口水温和换热量逐渐上升,换热性能提高;岩层温度恢复能力随注入流量和注入温度的增加而提高。综合考虑钻井成本、水泵功耗等因素,适量增加注入流量、降低注入温度、增加水平段长度能有效提高水平连通换热井的换热性能;虽然高的注入温度可提升岩层温度恢复能力,但不利于提高系统换热性能。

同轴套管换热器井下换热性能实验研究

本文介绍了一种适用于中深层地热井的同轴套管式换热器技术,可以做到传热不传质,取热不取水,在最大限度利用深层地热的同时,不消耗深层地下水。通过实际测试单井取热量可达到118 W/m,具有取热量大、后期运行费用低等优点。实际工程应用显示,利用“地热+”模式可以有效解决因地热井关停带来的诸多问题。利用关停的中深层地热井,只取热而不抽取地下水,有效避免中深层地热井闲置造成的资金浪费,同时可为用户提供高效清洁的能源供给。

时频电磁法在金牛湖地区深部地热资源勘查中的应用

南京金牛湖地区地质构造复杂、低阻覆盖层厚、电磁干扰强,为了查明该地区深部地热资源,应用时频电磁法进行探测。本次布置了2条时频电磁法剖面,采用大功率发射信号能够有效地穿透低阻覆盖层,获得了信噪比较高的原始数据。通过对时频电磁数据的处理、分析、反演及综合解译,获得了勘查区4000 m以浅的二维电性结构模型。结合地热地质条件,优选了地热钻探井位,经钻探最终验证,推测地层与实际钻探基本吻合,在1600 m钻遇断裂,终孔深度2800 m,经后期抽水试验确定,日出水量大于500 m 3,钻井井口水温51℃,说明获得了优质的深部地热资源。综上所述,时频电磁法在金牛湖地区深部地热资源勘查中的应用效果较好,揭示了南京金牛湖地区较好的地热地质条件,为该地区地热旅游资源的开发利用奠定了坚实的基础。

Geothermic activity and seismotectonics in the altitude of the Tibetan plateau

In the present analysis on the relationships among the depth of lithosphere brittle fracture, seismotectonics and geothermal anomalous active in Tibetan plateau were investigated using the seismic dada from ISC and Chinese seismic net and geothermal data. The results suggest that the region of anomalously geothermal activity almost coincides with that of the normal faulting type earthquake. The geothermal anomaly activity region coincides spatially with that of the events deeper than 60 km as well as. The normal faulting earthquakes may be mainly tectonic activity regimes until 110 km deep in the thermal anomaly region. The strike directions of events are likely the N-S direction, coinciding with the strike of the thermal anomaly active belts. The earthquakes align along the normal faults and faulted-depression zone with the N-S direction. The thermal anomaly activity also distributes along the faulted-depression zone. Many events deeper than 60 km exist in the anomalously geothermal activity region in the plateau. Events extend to bottom of the lithosphere of 110 km from the surface, like columnar seismic crowd. The lithosphere extends along the E-W direction due to the E-W extensional stress in the central and southern Tibetan plateau, altitude of the plateau. The t6nsional stress in the E-W results in the lithosphere fractures and the normal faults striking N-S direction, grabens and faulted-depression zones. Thermal material from the asthenosphere wells upward to the surface along deep seismic fractures and faults through the thick crust. The anomalously thermal activities are attributable to the upwelling thermal material from the mantle in the altitude of Tibetan plateau.

中深层水热型地热资源集群式开发井位部署参数研究与应用——以HTC地热田为例

在中国“双碳”战略背景下,清洁能源的高效开发利用逐渐成为各行业关注的焦点,而中深层水热型地热资源是一种储量丰富、运行稳定、绿色环保的清洁能源。近年来,随着地热资源开发利用程度逐渐增加,开发模式逐渐向集群式发展,相比以往的分布式开发模式,集群式开发具有经济、稳定、抗风险能力高、改扩建能力强等优点。但开发模式、采灌井网、采灌井距等关键参数仍在探索阶段,这些参数对集群式开发影响明显,亟须对此开展机理研究、优化关键参数。以HTC地热田作为研究对象,利用数值模拟技术,耦合地下温度场、压力场、水流场建立数学模型,分析不同开发模式、采灌井网、采灌井距条件下地下温度场、压力场、水流场变化规律,确定最优参数,指导矿场生产。实践证实,该方法可有效保障地热开发项目稳定运行,实现地热开发项目经济效益最优化。

冀中坳陷区深部碳酸盐岩分布特征

前人研究表明冀中坳陷深部地热储层主要为蓟县系雾迷山组、长城系高于庄组碳酸盐岩地层,区内广泛分布的以黏土、砂岩、含砾砂岩为主的新生界地层为盖层,现今的地温梯度和大地热流具有从西向东先增大后降低的趋势,其平面展布与构造地形起伏具有一致性(常健等,2016)。因此研究由综合地球物理剖面解释推断(1)的碳酸盐岩分布特征,结合区内热储盖层、大地热流特征,有助于分析该区深部地热资源的赋存特征。

面向深部地热岩体的弹性波逆时偏移成像方法

地热能作为一种清洁能源正受到全世界的日益关注,因此对于深部地热岩体的高精度成像格外重要。传统的弹性波逆时偏移方法是利用耦合纵横波直接成像,从而得到耦合波场的成像结果;然而这种方法可能会出现串扰假象,导致成像结果不够清晰;为了解决这个问题,采用基于解耦的弹性波方程,实现纵横波场的分离;通过利用内积成像条件,对两个典型的干热岩模型进行数值测试。结果表明,相较于耦合波场成像结果,基于解耦方程分离得到的弹性波成像剖面具有更清晰的同相轴,深部能量更加均衡,该方法能够实现对深部地热岩体的高质量成像。