增强型地热系统垂直裂隙热储热开采过程数值模拟

增强型地热系统(Enhanced Geothermal System,EGS)作为开采深层地热资源最为有效的方法已经成为国际研究热点。充分探究EGS运行时热储内热量的开采过程对评估EGS性能及今后EGS商业开采过程中工程优化控制有着重要意义。文章建立了平行相间的垂直裂隙系统EGS开采模型,运用FLUENT软件对多平行垂直裂隙情形下增强型地热系统热储热开采过程进行了数值模拟。同时,通过改变对热储热开采过程有影响的裂隙宽度和水流速度两个参数,对比研究了其对热储热开采过程的影响。研究结果显示,裂隙宽度和水流速度对热储热开采过程影响较大,且影响效应几乎一致。当裂隙宽度为1 mm、裂隙水流速度为1 cm/s时,开采20 a时间内无论是裂隙宽度扩大1倍还是水流速度提高1倍,对热储内经济可用热能的开采率提升均超过25%,对热储内热能开采速率提升达到252%。     

增强型地热系统井筒-储层耦合数值模拟分析

干热岩是指地下3~10 km处低渗透性的高温岩体。增强型地热系统(EGS)是利用水力压裂等作业措施形成人工热储层,通过注入载热流体以经济地开采出干热岩中热能的人工地热开采系统。目前,关于干热岩储层开采潜力是否满足商业开采目标,以及如何提高EGS开采潜力是EGS研究的重点。文章首先对EGS的发展及技术可行性进行了概述,然后以松辽盆地为研究场地,以水为载热工质,采用井筒-储层耦合数值模拟程序T2WELL对储层开采潜力进行了定量研究,并通过不确定因素和参数分析探讨了优化EGS开采潜力的可行方案。不确定因素和参数分析表明,储层初始温度、裂隙间隔、布井方式是影响储层开采潜力的关键因素,渗透率对储层开采潜力影响较小。     

增强型地热系统水平井平行多裂隙换热过程数值模拟

干热岩(HDR)是一种清洁的可再生能源,主要通过增强型地热系统(EGS)进行开发。由于将水平井多裂隙开发技术应用于EGS中,能够提高EGS的经济效益,因此文章建立三维EGS水平井平行多裂隙模型,并采用CFX软件模拟分析了不同注水流量条件下EGS的运行性能,揭示了裂隙内流体的流动特征与EGS釆热机理之间的关系。研究结果表明:裂隙中的流体会形成流动短路和流动死角,导致EGS的开采率降低;裂隙中流体的温度场会受到流体的流动特征以及热储层温度场的影响;注水流量是影响EGS运行寿命和开采率的关键因素,较大的注水流量会产生流动短路,进而缩短EGS的运行寿命,但会提高EGS的开采率。     

增强型地热系统热开采性能的数值模拟分析

增强型地热系统(EGS)作为一种极富发展潜力的可再生清洁能源利用技术,正逐渐成为世界各国新能源发展的重点关注方向之一。EGS地下采热过程直接影响EGS的产能和寿命。文章使用一套自主开发的三维动态数值模型对不同地质条件下双井EGS的长期热开采运行进行了模拟,额外引入平均产热速率和地热开采率作为采热性能评价指标,结合EGS运行寿命和产热速率综合分析了热储渗透率、循环流体流量和周围热储岩石的热补偿对采热的影响及其作用机理。     

地热开采系统的工艺形式

本文通过总结现行的地热开采方式，对地热系统工艺形式进行分类，为建立合理的地热开采系统及理论研究打下基础。     

增强型地热系统数值模拟研究进展

作为地热领域最有潜力的发展方向之一,增强型(或工程型)地热系统(EGS)的研究受到发达国家的高度重视,但在我国还处于萌芽状态。通过介绍EGS含义及发展,结合EGS数值模拟软件应具备的特点,对目前已经用于和可以用于EGS数值模拟的HDR和水热型地热系统中的典型求解器进行综述,总结其优缺点,讨论目前EGS数值模拟面临的挑战。     

干热岩增强型地热系统平行三裂隙传热影响因素分析北大核心CSCD

干热岩作为可再生能源,其有效开采途径是形成干热岩增强型地热系统,而建立干热岩增强型地热系统首先要通过水力压裂,在岩石间形成裂隙,其中压裂尺寸和工况参数均对传热产生影响。文章建立二维平行三裂隙模型,采用商业软件进行数值模拟计算,分析压裂尺寸和工况参数对传热的影响。结果表明:当工况参数一定时,不同压裂尺寸对传热的影响程度由高到低依次为裂隙宽度,裂隙长度,岩石开采宽度;当裂隙尺寸一定时,不同工况参数对传热的影响程度由高到低依次为进口水温,进口水流量,岩石初始温度。因此,根据生产生活需要,恰当改变压裂尺寸或工况参数,可以延长干热岩增强型地热系统使用寿命,节约施工成本。     

增强型地热系统热开采过程的数值模拟研究

增强型地热系统（EGS）是指采用人工方法在地下3 ~ 10 km内的干热岩体中形成储层、通过灌输采热流体以开采出干热岩中热能用于地面发电的地热利用系统,是一种极富潜力的可再生清洁能源利用技术。循环流体在地下热储中的流动与换热对EGS的采热性能有重要影响。本文首先对EGS数值模型进行了综合评述,然后基于一套自主开发的三维瞬态数值模型模拟了不同渗流条件下EGS地下热储内的热流过程。通过对模拟结果的分析,揭示了均匀压裂的人工热储中流体短路的形成机理,并通过对比双井和三井系统中流场和局部地热开采率分布,结合当前钻井工艺和裂隙激发技术水平,探讨了抑制流体短路、优化EGS采热性能的可能方案。     

低渗透煤层气井产能数值模拟研究

在煤层气开采过程中,设计合理的开采流程可减少开采过程造成的煤层损伤,这是提高煤层气井产量的关键。叙述了煤层气储层特征及运移产出机理,利用Comet3软件进行了低渗透煤层气井产能数值模拟。     

A borehole temperature during drilling in a fractured rock formation

Drilling in brittle crystalline rocks is often accompanied by a fluid loss through the finite number of the major fractures intercepting the borehole. These fractures affect the flow regime and temperature distributions in the borehole and rock formation. In this study, the problem of borehole temperature variation during drilling of the fractured rock is analyzed analytically by applying the approximate generalized integral-balance method. The model accounts for different flow regimes in the borehole, for different drilling velocities, for different locations of the major fractures intersecting the borehole, and for the thermal history of the borehole exploitation, which may include a finite number of circulation and shut-in periods. Normally the temperature fields in the well and surrounding rocks are calculated numerically by the finite difference and finite element methods or analytically, utilizing the Laplace-transform method. The formulae obtained by the Laplace-transform method are usually complex and require tedious numerical evaluations. Moreover, in the previous research the heat interactions of circulating fluid with the rock formation were treated assuming constant bore-face temperatures. In the present study the temperature field in the formation disturbed by the heat flow from the borehole is modeled by the heat conduction equation. The thermal interaction of the circulating fluid with the formation is approximated by utilizing the Newton law of cooling at the bore-face. The discrete sinks of fluid on the bore-face model the fluid loss in the borehole through the fractures. The heat conduction problem in the rock is solved analytically by the heat balance integral method. It can be proved theoretically that the approximate solution found by this method is accurate enough to model thermal interactions between the borehole fluid and the surrounding rocks. Due to its simplicity and accuracy, the derived solution is convenient for the geophysical practitioners and can be readily used, for instance, for predicting the equilibrium formation temperatures.     

Renewable hot dry rock geothermal energy source and its potential in Pakistan

Geothermal energy source, one of the viable renewable energy sources, has encouraging potential to generate full base-load electricity, which has not been explored so far in Pakistan. Though the country can be benefited by harnessing the hydro-geothermal options of energy generation in areas where sources exist, but most of these sources lie in extreme remote and inaccessible rugged mountainous ranges away from the urban-industrial centers. On the other hand, the present study shows that the HDR geothermal option is one of the most viable renewable sources considering the tectonic setup of Pakistan. Results of the study highlight the HDR geothermal energy prospects at relatively deeper depths than hydro-geothermal resources in water-free condition. The basement tectonic analyses reveal that the HDR prospects could be found even just below the urban-industrial centers of Pakistan where there are no hot springs and/or geysers like southern Indus basin in Sindh province or the Kharan trough in the western Balochistan province. Presence of high earth-skin temperature gradient trends derived from satellite temperature data and the high geothermal gradient anomalous zone derived from scanty data of bottom-hole temperatures of some of the oil and gas exploratory wells, indicates encouraging prospects for HDR energy sources in southern Indus and Thar Desert regions inclusive of Karachi synclinorium area. These high geothermal gradients have been inferred to be the result of the deep-seated southern Indus and the Thar fossil-rift structures. Moreover, the prospects of the HDR geothermal energy sources have also been inferred in the Chagai Arc region and the Kharan–Panjgur tectonic depression in the western part of Pakistan based on the analysis of integrated geophysical data. If HDR prospects are developed, they can offer the sustainable, CO₂-free and independent of time, of day, of weather or season, and the base-load energy-generation resource.     

The exploitation of hydrogen sulfide for hydrogen production in geothermal areas

Hydrogen is a valuable energy resource and it is widespread in nature. As a matter of fact, researches on hydrogen production are currently experiencing an increasing interest from scientists around the world since this resource is clean and renewable. Several methods of producing hydrogen have been developed in industrialized countries such as the United States of America and Germany.This paper is interested in the process by which hydrogen sulfide of geothermal areas is exploited for hydrogen production. In fact, research advances in this field have concluded that hydrogen sulfide of geothermal resources can contribute significantly and economically in the process of hydrogen generation.The present paper was principally conducted from a literature study and a synthesis of works achieved in recent years in order to highlight the various aspects of hydrogen production from hydrogen sulfide and particularly to study the possibility of the exploitation of Algeria’s thermal resources in this field.     

Gas-water interface rise during early exploitation tests in alfina geothermal field (Northern Latium, Italy)

Alfina geothermal field is made up of a gas-cap (CO₂) overlying an almost closed aquifer. The wells drilled in the highest part of the reservoir produce gas while the others either produce hot water or are sterile.During the first production tests the analysis of pressure and water-levels showed that the gas-water interface had risen. This was later confirmed when a gas-producing well began carrying water.This paper attempts to explain field behaviour by means of simple calculations and assuming an idealized geological structure.This study gives an estimation of the average porosity and initial gas in place.     

我国中深层地热开发技术专利综述与分析

近年来地热能开发的传统抽灌模式因回灌问题受到诸多限制,一些地方甚至出台了一刀切的“封井”管理模式。中深层地热井下换热是一种取热不取水、取热效率较高,同时可突破传统地热利用中地热资源条件限制的利用模式。该技术的关键在于如何进行系统优化设计,在有效避免冷、热流体换热损失的同时获取最大取热功率,目前国内已有多项相关的授权专利。检索了国内中深层地热开发利用技术的相关专利,从申请地域、年份、申请人等方面进行了归纳分类和统计分析,并重点从技术原理的新颖性、实用性及技术经济可行性方面分析了有代表性的中深层地热开发技术专利,结果可为推进我国中深层地热开发利用技术提供理论参考,并为中深层井下换热系统的实际应用及其市场的健康发展提供帮助。     

The numerical simulation of coupled unsteady ablation and heat transfer in the porthole region during reentry

The complicated phenomena in the porthole region of a vehicle, which consists of coupled thermolysis/ablation with heat transfer in different thermal protection materials, are numerically simulated in this paper. The different characteristics of temperature increment at some important positions in the porthole region are, respectively, given under both constant heating and variable heating on the upper surface of the porthole. Also, the mechanism of the heat transfer in the porthole region is given, which is significant for the design of local thermal protection structure. © 1999 Scripta Technica, Heat Trans Asian Res, 28(7): 597–605, 1999     

Enel activity in the research, exploration and exploitation of geothermal energy in Italy

In Italy the utilization of geothermal resources for industrial purposes began about 150 years ago. Prior to 1913, geothermal fluids were utilized both as a source of heat and chemical products; from 1913 to 1965, combined chemical and electric production was achieved; from 1965 on, power generation prevailed over chemical production, which was abandoned immediately thereafter; between 1975 and 1984, geothermal energy was mostly used for generating electricity, but a number of thermal projects were also started.An overview is given of Italian geothermal development after 1975, including electric production and direct applications of geothermal heat.More in particular, the research and development activity in the period 1975–1985 is first presented, and the criteria, programmes and development objectives through 1995 are then illustrated.     

Forecast and evaluation of hot dry rock geothermal resource in China

Utilizing information from plate tectonics characteristics, volcanic activities, and geothermal anomaly, this paper identifies areas where hot dry rock (HDR) may exist as potential geothermal resource in China. Further investigations are also carried out in the paper based on results from regional tectonics, volcanic geology and lithology, as well as data from geothermal displays, geochemistry, geophysics, and shallow borehole temperature measurements. The study reveals several promising areas of HDR geothermal resource in China, including Tengchong of Yunnan province, Qiongbei of Hainan province, Changbaishan of Jilin province, Wudalianchi of Heilongjiang province, and the Southern Tibet area. A 3D static heat conduction model was developed to study the underground temperature gradient characteristics of the Rehai geothermal field in Tengchong and the Yangbajing geothermal field in Tibet. The model adopted is a geological block 10 km deep from the ground surface and 50 km wide in each of the horizontal directions (2500 km² area). The numerical simulation results in evaluations on the quantities of the HDR geothermal resource in Rehai and Yangbajing geothermal fields. The paper shows that there is abundant HDR geothermal resource with large exploitation value in China. If developed with a power capacity of 1×10⁸ kW, the Rehai and Yangbajing fields along would be able to generate electricity for 1560 years.     

A fractal model for the coupled heat and mass transfer in porous fibrous media

This paper developed a mathematical model for the coupled heat and mass transfer in porous media based on the fractal characters of the pore size distribution. According to Darcy’s law and Hagen–Poiseuille’s law for liquid flows, the diffusion coefficient of the liquid water, a function of fractal dimension, is obtained theoretically. The liquid flow affected by the surface tension and the gravity, the water vapor sorption/desorption by fibers, the diffusion of the water vapor and the phase changes are all taken into account in this model. With specification of initial and boundary conditions, distributions of water vapor concentration in void spaces, volume fraction of liquid water, distribution of water molecular content in fibers and temperature changes in porous fibrous media are obtained numerically. Effects of porosity of porous fibrous media on heat and mass transfer are analyzed. The theoretical predictions are compared with experimental data and good agreement is observed between the two, indicating that the fractal model is satisfactory.