漳州热田(市区)干热岩增强型地热系统梯级综合利用方案初步评估

通过漳州热田市区高温中心干热岩增强型地热系统高科技、高端、高能位地热能梯级综合利用方案初步评估,探讨地表地热显示良好、研究程度较高地区干热岩增强型地热系统项目开发综合利用方案及经济、社会效益,从中积累经验,以便在全国范围内推广应用。     

增强型地热系统（EGS）的人工热储技术

文章分析了增强型地热系统（干热岩）发电原理,研究该系统建立人工热储的关键技术,包括人工致裂、监测、裂隙网络的连通、封闭水流循环、热储系统建模等。最后分析了芬顿山、Hijiori、苏尔士大型试验电站的人丁热储应用实例。     

海南陵水地区深层干热岩地热发电项目的勘查选址

本文以海南陵水地区深层干热岩地热发电项目勘查选址报告为基础,论述了海南岛地热构造及地质条件、勘探及选址工作以及开发干热岩地热发电对地质环境造成的影响。通过已有资料,结合全岛地热条件对全国首个干热岩实验电站的下一步工作提出几点建议。     

干热岩增强型地热系统备选靶区选址标准的探讨

通过干热岩增强型地热系统备选靶区选址标准提出背景的阐述,充分体现出制定干热岩增强型地热系统备选靶区标准的重要性;在此基础上制定出5条干热岩增强型地热系统备选靶区选址标准,提供有关部门、单位开发综合利用干热岩地热资源勘查、评估、选址、开采钻探、项目利用规划与设计等参考。     

增强型地热系统水力压裂与声发射监测室内实验研究

增强型地热系统（enhanced geothermal system, EGS）以干热岩热能的开采和利用为目的,正逐渐成为世界各国的重点研究对象。除了建立EGS野外试验场开展实际场地研究和技术示范外,亦有必要开展相关的室内实验研究,研究或验证相关关键技术,为野外场地建设提供理论基础和技术支持。本课题组自主研发了模拟地下真实环境的实验系统,开展了尺寸为400 mm × 400 mm × 400 mm的花岗岩水力压裂实验,通过声发射事件监测到的声发射数据,分析了裂缝的扩展规律,并进行了初步的水力连通实验,探讨了各采出井的流量分配,研究了从注入井到生产井的水力连通特性。结果可为数值模拟提供基础数据,为野外试验场地的建设提供参考。     

增强型地热系统水力压裂与双井连通实验仿真研究

增强型地热系统（Enhanced Geothermal System, EGS）作为未来新能源和清洁能源利用的一个重要方向,受到了世界各国的广泛关注。一直以来,野外试验场的工程实践和数值模拟分析是进行EGS研究的两种主要方式。本文通过实验室规模的小型试验系统,对EGS的水力压裂、裂隙监测、生产井定位和注水测试进行了仿真,成功实现了注入井−热储层−生产井的水力连通,分别以定井口压力和定注水流量进行水力测试。试验结果表明,热储层的裂隙开度会随着水力特性而发生变化,注水压力较大时热储层的裂隙具有更大的开度和渗流能力。从提升热储层经济性的角度考虑,实践中应当在较大注水压力时对热储裂隙结构进行加固处理。     

澳大利亚的干热岩发电

干热岩或称工程型地热系统（EGS）是一种没有水或蒸汽的热岩体,主要是各种变质岩或结晶岩体。一般埋藏在距地表2000-6000m的深处,温度在150-650℃之间。干热岩的分布很广,各大陆地下均有丰富的干热岩资源。开发潜力最大的地方通常是新的火山活动地带或地壳已经变薄的地区。干热岩是潜力巨大的本土资源,其开发不受地域的限制。     

增强型地热系统(EGS)资源开发利用研究

EGS资源蕴藏量巨大、利用效率高、系统稳定,是洁净绿色新能源,对其合理开发利用可以应对当前面临的能源需求、能源安全和环境保护的挑战.EGS开发利用是一项复杂的系统工程.目前,EGS的研究开发工作主要在一些发达国家展开,我国尚未开展这方面的研究.我国EGS储藏量巨大,具有发展优势及开发利用的价值.     

Extraction of heat from multiple-fractured dry hot rock

A brief summary of theoretical solutions for the extraction of heat from multiple-fractured dry hot rock is presented. The analysis is based on an infinite series of parallel vertical fractures of uniform aperture and separated by blocks of homogeneous and isotropic impermeable rock with a uniform spacing between fractures. Cold water enters at the bottom of the fractures and the solutions are given in terms of dimensionless parameters from which the exiting water temperature at the top of the fractures can be determined. An example of the application of the theory is given to demonstrate how a multiple, fractured system provides a more efficient mechanism for heat extraction than a single fracture in dry hot rock.     

Modeling heat extraction from hot dry rock in a multi-well system

A mathematical model is developed for describing the heat energy extracted from a hot dry rock in a multi-well system. The solutions for the water temperature, accounting for a geothermal gradient in a geothermal reservoir, are given in the Laplace domain and computed by numerical inversion, the modified Crump method. The results show that the heat extraction effectiveness is affected significantly by the well spacing, well radius, reservoir thickness, and pumped flow rate in a multi-well system. The water temperature decreases with increasing pumping rate and increases with the well spacing, well radius, and reservoir thickness. The geothermal gradient affects only the early time heat extraction effectiveness significantly and has direct impact on the water temperature all the time if the vertical thickness of geothermal reservoir is large. The present solution is useful for designing and simulating the heat extraction project of geothermal energy exploitation in a multi-well system.     

Development of hot dry rock technology at the Hijiori test site

Since 1985, the New Energy and Industrial Technology Development Organization (NEDO) has conducted a Hot Dry Rock project at the Hijiori test site, Yamagata prefecture. The objective of this project is to develop and test technologies such as borehole logging, hydraulic fracturing, fracture mapping and reservoir evaluation, which are essential for the development of a Hot Dry Rock power generation system. In 1991, heat was successfully extracted from a shallow reservoir at a depth of 1800 m for three months using one injection well (SKG-2) and three production wells (HDR-1, HDR-2 and HDR-3). About 80% of the injected water was recovered from these production wells. The thermal output of hot water and steam reached about 8 MW. Since 1992, a deep reservoir at a depth of 2200 m has been developed. In 1995 and 1996, heat extraction tests were conducted using one injection well (HDR-1) and two production wells (HDR-2 and HDR-3). A long-term circulation test, lasting about two years, is planned to evaluate the reservoir, starting in 2000.     

Drilling for hot dry rock reservoirs

The drilling group evaluated techniques suitable for drilling inclined boreholes, of controlled geometry, to reach temperatures of 200–250°C in crystalline rock. They concluded that there is no fundamental reason why holes for HDR projects cannot be drilled and completed successfully using techniques already available, and that further development work should aim at risk and cost reduction rather than new techniques. They stressed the need for meticulous planning and careful engineering in any HDR drilling operation.     

Progress in hot dry rock exploitation

The term hot dry rock (HDR) has been used to describe the exploitation of the thermal energy contained in rocks that have a sufficiently high temperature but contain insufficient fluids to enable the heat to be extracted. The attraction of such a resource is that it is probably available everywhere, but at varying depths. International activity has focused on the problem of circulating fluids through the rock and extracting the heat by conduction from the rock to the fluid. The initial concepts were based on creating individual cracks to interlink two wells approximately 500 m apart. The necessary heat exchange area was to be achieved by using multiple systems of interconnections in parallel. The results from the field work have shown that the interlinking is dominated by stimulated natural joints and the degree of normal dilation that can be achieved is limited by the orientation of the natural discontinuity with the pre-existing stresses and, hence, the shear stress on the joint. The normal dilation is important because it controls the resistance to flow between the wells. The shear mechanism controls the far-field water losses and the direction of growth of the more permeable interwell region and has obvious implications for the proposed geometry of any system. The cost of drilling has been shown to be comparable to deep drilling for other purposes and the development of deviated holes in strong crystalline rocks has been shown to be possible. The progress of the stimulation has been mapped successfully by locating the microseismic events generated by shearing but the relationship of the microseismically active areas and the heat transfer region has yet to be identified. No adverse environmental problems have been identified; the produced fluids are generally benign and the microseismicity is well below any threshold of damage. The goal of a universally available heat source free of stack emissions and waste products that does not consume finite reserves of minerals and hydrocarbon demands substantial investment in the research to determine if it is attainable. The major field programmes should have reached their preliminary conclusions by the middle of 1986.     

The U.S. hot dry rock project

Early attempts to hydraulically fracture and connect two wells drilled at the Hot Dry Rock (HDR) site at Fenton Hill in New Mexico produced a large volume of fractured rock, but no connection. Microearthquakes triggered by fracturing indicated that the stimulated rock zones grew in unexpected directions. Consequently one of the wells was sidetracked at a depth of 2.9 km. It was redrilled into the zones of most intense microseismic activity, and flow connections were achieved. Hydraulic communication was improved by supplemental stimulation using recently developed high temperature and high pressure open hole packers. Preliminary testing indicates a reservoir with heat production capability which greatly surpasses that attained in the earlier Phase I reservoir. Longer term testing in 1987 and 1988 will provide more complete information on reservoir behaviour.     

Maximum tolerable reservoir impedances for hot dry rock

The finite hydraulic impedance of the natural and artificial fractures that constitute the water flow paths in hot dry rock reservoirs is shown to influence the cost of generating electricity from such resources in two ways. First, pumps, and hence power, will be required to circulate water through the fracture system. Second, the pressure difference across the reservoir cannot be increased indefinitely to improve the energy extraction rate as too high a pressure at the injection borehole will cause unacceptable losses of the circulating water.     

Passive cooling by evapo-reflective roof for hot dry climates

A dynamic mathematical model for an evapo-reflective roof to improve space cooling in buildings for hot arid climates has been developed. The proposed roof design is composed of a concrete ceiling over which lies a bed of rocks in a water pool. Over this bed is an air gap separated from the external environment by an aluminium plate. The upper surface of this plate is painted with a white titanium-based pigment to increase reflection of a radiation to a maximum during the day. At night, the temperature of the aluminium sheet falls below the temperature of the rock bed mixed with water. Water vapour inside the roof condenses and falls by gravity. This heat pipe effect carries heat outwards and cold inwards. Heat exchange is improved by radiation between two humid internal surfaces. The efficiency of this cooling system is studied using finite difference method. Numerical calculations performed for different external temperatures and solar radiation show that the cooling produced by such a system is significant. As a result of this, the mean air temperature in the room may be kept a few degrees above the minimum nocturnal outdoor temperature throughout the day. However, the maximum indoor air temperature was observed at sunset. This could further be lowered by allowing ventilation of the building in the evening. The work is continuing.     

Stimulation and flow processes in hot dry rock reservoirs

There was less agreement among the stimulation and flow processes group than in the other groups, reflecting the fact that this aspect remains the major uncertainty in the understanding of HDR systems. The differences arose from the different emphasis placed by the various research teams on the role of artificial as opposed to natural fractures. There was, however, general agreement that the flow in HDR reservoirs is predominantly laminar. It was also agreed that impedance can be reduced only by enlarging fractures apertures; the best way forward, however, depends on resolution of the “artificial” versus “natural” fracture controversy. This will require further theoretical work in close association with prolonged circulation in the major deep field experiments.     

Borehole measurements in the field of hot dry rock experiments

The logging group examined the value of different types of borehole logging in the context of HDR developments and considered the limitations of current techniques and the scope for further development. They recommended that the main development effort should concentrate on methods of fracture detection, both at the borehole wall and in the far field. They further recommended that such work would best be done as part of a collaborative international effort.