供热规划区热储模型研究

地热尾水回灌作为一种处理手段和维持热储压力的一种方法，已在很多地热田有过实践，它对于开采第三系以上的热储层，控制地面沉降和环境保护有着重要的意义。本文针对低焓热储地热田研究了回灌的影响、回灌率、热储渗透率的分布，针对对井回灌开采供热系统做了理论分析，研究了回灌对维持热储压力的水平范围和冷峰面的作用，对井的合理井间距等，将对井模拟研究应用于天津地热田。     

回灌及回灌后开采对台兰河流域地下水位的影响

探讨不同的回灌及回灌后开采方式对地下水位的影响,将有助于对水资源的时空再调度并达到高效开发利用水资源。以新疆温宿县台兰河流域地下水库为例,在分析水文地质条件基础上构建了地下水流场数值模型,确定了回灌井及开采井、观测井的位置及回灌、回灌后开采方案,分析了HG1、HG2回灌井各自在全年回灌、汛期回灌时的地下水位变化情况,指出汛期回灌效果最佳;通过比较无回灌、开采无回灌、开采回灌、回灌无开采四种情况下地下水位变化情况,指出回灌后开采对区域地下水位影响显著,从而确定出HG1为最佳回灌井位。研究结果表明,摸清回灌及回灌后开采地下水的运动规律,将有利于台兰河流域地下水资源的优化调度。     

中低温孔隙地热田回灌试验研究

以天津武清地热田为例,探讨在孔隙介质地热田开展回灌的技术可行性,武清地热田主要开采层为第3系馆陶组砂岩,热付层温度76－86℃,1998年总开采量达到1.18Mm^3。经过数学模型预测该热储水位降深将在近期内趋于稳定。在无回灌条件下,如果以最大开采量持续开采,将导致5年内水位下降到105m。如果增加3眼回灌井,闰下降幅度将减缓15m。此外,计算了在回灌过程中各种不同情况下冷锋面的运移速度,并进一步探讨了示踪剂试验的可行性。     

中低温孔隙型地热田回灌试验研究

以天津武清地热田为例,探讨在孔隙介质地热田开展回灌的技术可行性,武清地热田主要开采层为第3系馆陶组砂岩,热储层温度76－86℃,1998年总开采量达到1.18Mn^-3,经过数学模型预测,该热储水位降深将在近期内趋于稳定,在无回灌条件下,如果以最大开采量持续开采,将导致5年内水位下降到105m,如果增加3眼回灌井,水位下降幅度将碱缓15m,此外,计算了在回藻过程中各种不同情况下冷锋面的运移速率,并进一步探讨了示踪剂试验的可行性。     

资源评价与数值模拟在对井回灌系统中的应用

主要针对低焓热水型地热热储，分析了对井系统种类参数依赖的因素，关系以及相关程度，回灌率的选取，渗透率在含水层中三维分布情况对开采区域的影响，回灌对维持热储压力的水平范围和回灌冷水的影响程度，对井的合理井间距等，并针对兰庄地热田地热地质的非均质，各向异性特点，研究了该区的地热地质构造特性，地下资源储量，水资源补给可能性，评价了该地区地热资源的开发潜力。     

天津市举办“全国地热回灌系统工艺设计与操作培训班”

随着我国地热资源开发速度的不断提高,有些地热田热储层的水位逐年下降,产生明显的开发效应,引起国内外地热同行的高度重视。地热水回灌能有效维持或恢复地热田的热储压力,对保持地热田的产热能力、稳定开采条件、预防因地热水开采而引起的地面沉降具有十分重要的意义。     

浅议孔隙型热储的回灌能力

河北平原的地热资源多数储存在第三系孔隙型热储层中,是目前我国地热资源开发的主要热储层之一。由于河北省对该热储层的开采规模扩大、开发利用水平偏低、资源浪费较严重,致使多个地热田的地热水位下降速率惊人。目前,有的地热田已面临资源枯竭的危险。因此,对孔隙型热储层实施地热尾水的回灌已势在必行。本文以第三系孔隙型热储层的回灌试验数据为基础,对孔隙型热储层的回灌能力及回灌的可行性进行初步的研究。     

回灌量与井深关系的试验研究

采用室内砂槽模型试验研究了回灌井回灌过程中水丘变化规律与井深对补给效率的影响,通过观测地下水位变化,分析了不同井深条件下水丘变化规律,测定了不同时刻的回灌流量、出流量及总回灌量,基于试验的有效性分析了井深变化对总回灌量的影响.结果表明,回灌井与水丘位置关系决定水丘壅堵的效应,单位井深回灌量最大值出现于包气带与包气带井潜水井的临界井深处.     

天津基岩热储对井系统回灌与示踪剂试验研究

地热回灌效应，与热储构造关系密切。在WR45对井系统抽水试验中发现在回灌井和开采井之间不存在明显的水力联系，地质条件分析也显示在这两眼井之间热储层连通性较差。为了探明回灌井和生产井之间连通渠道，1998年至1999年冬季在WR45进行示踪剂试验。结果表明生产井中可监测示踪剂浓度主要与热储层的地质和水文条件有关。     

天津地热对井回灌系统中的同位素示踪技术

为深入分析地热回灌开采中回灌水的运移规律、求证热储参数，本文选取二组中元古界雾迷山组地热对井，分别注入放射性同位素巧^35S（T12=87天）、^125I（T12=60天）进行示踪试验，并分别于第130天、51天检出峰值，以此数据计算出热储层的渗透系数、导水系数等有关参数，与传统的抽水试验算出的结果吻合良好。注入示踪剂在地层中的运移方向也与抽水试验观测到的结果完全一致，且形象直观，检出精度更高。同位素示踪技术能为进一步深入研究热储层在回灌前后压力场、温度场、水化学场的变化特征提供大量基本数据，也为天津乃至华北地区地热资源实施循环开发提供有效的技术保障。     

Magma: A potential source of fuels

Recent calculations and measurements indicate that basaltic magma is a new, extensive source for fuels (hydrogen, carbon monoxide, and methane). The fuel production processes have been found to occur in nature as well as the laboratory and as a result, our work indicates that current concepts of geothermal energy can be broadened beyond producing only steam and heat. When magma is considered as a geothermal resource, its use for the direct production of fuels should be included. It is possible to generate several mole percent hydrogen when water-rich fluid is equilibrated with the ferrous and ferric iron in magma. This paper describes the basis of the fuel production processes, the fuel yields for injected water and water plus natural organic matter (biomass), and the increased geothermal resources that would be made available by these processes.     

Sustainable geothermal utilization – Case histories; definitions; research issues and modelling

Sustainable development by definition meets the needs of the present without compromising the ability of future generations to meet their own needs. The Earth's enormous geothermal resources have the potential to contribute significantly to sustainable energy use worldwide as well as to help mitigate climate change. Experience from the use of numerous geothermal systems worldwide lasting several decades demonstrates that by maintaining production below a certain limit the systems reach a balance between net energy discharge and recharge that may be maintained for a long time (100–300 years). Modelling studies indicate that the effect of heavy utilization is often reversible on a time-scale comparable to the period of utilization. Thus, geothermal resources can be used in a sustainable manner either through (1) constant production below the sustainable limit, (2) step-wise increase in production, (3) intermittent excessive production with breaks, and (4) reduced production after a shorter period of heavy production. The long production histories that are available for low-temperature as well as high-temperature geothermal systems distributed throughout the world, provide the most valuable data available for studying sustainable management of geothermal resources, and reservoir modelling is the most powerful tool available for this purpose. The paper presents sustainability modelling studies for the Hamar and Nesjavellir geothermal systems in Iceland, the Beijing Urban system in China and the Olkaria system in Kenya as examples. Several relevant research issues have also been identified, such as the relevance of system boundary conditions during long-term utilization, how far reaching interference from utilization is, how effectively geothermal systems recover after heavy utilization and the reliability of long-term (more than 100 years) model predictions.     

Prediction of boiling, scaling and formation conditions in geothermal reservoirs using computer programs tequil and geofluids

Predictions of boiling, scaling, and solubility of gases are important to the exploitation of geothermal resources. These chemical phenomena are strong functions of the composition, temperature and pressure of the working fluid and are therefore difficult to predict from prior experience or tabulated data. Thermodynamic models of geothermal brine behavior recently developed by the authors are introduced and used to study various problems involved in geothermal energy production. The models have been extensively tested. Results of comparisons with laboratory measurements indicate that predictions are very close to experimental data for a wide range of conditions. Comparisons with field data also show remarkable agreement. Here the models are also applied to the prediction of breakout and scale formation in geothermal wells. Good agreement is obtained with actual well performance.     

Use of slim holes with liquid feedzones for geothermal reservoir assessment

Production and injection data from slim holes and large-diameter wells at four geothermal fields (Oguni, Japan; Sumikawa, Japan; Takigami, Japan; Steamboat Hills, U.S.A.) were analyzed in order to establish relationships (1) between injectivity and productivity indices, (2) between productivity/injectivity index and borehole diameter, and (3) between discharge capacity of slim holes and large-diameter wells. The productivity and injectivity indices for boreholes with liquid feedzones are more or less equal. Except for the Oguni boreholes, the productivity and injectivity indices display no correlation with borehole diameter. Thus, the productivity index (or, more importantly, the injectivity index in the absence of discharge data) from a slim hole with a liquid feed can be used to provide a first estimate of the probable discharge capacity of a large-diameter geothermal production well. The large-diameter wells at the Oguni, Sumikawa and Steamboat Hills geothermal fields have a more or less uniform inside diameter, and the discharge capacity of these wells (with liquid feedzones) can be predicted using Pritchett's “scaled maximum discharge rate” in conjunction with discharge data from slim holes. Because of the non-uniform internal diameter for large-diameter Takigami wells, it is not possible to use a simple scaling rule to relate the discharge capacities of slim holes and large-diameter wells at Takigami; therefore, a numerical simulator was used to model the available discharge data from Takigami boreholes. The results of numerical modeling indicate that the flow rate of large-diameter Takigami production wells with liquid feedzones can also be predicted using discharge and injection data from slim holes.     

Geothermal reinjection experience

Reinjection into geothermal reservoirs is discussed and the experience gained by reinjection experiments in 44 geothermal fields is reviewed. Reinjection started purely as a disposal method, but has more recently been recognised as an essential and important part of reservoir management. Only a small part of the thermal energy in place in geothermal reservoirs can be recovered if reinjection is not applied. Thermal breakthrough has been observed in few geothermal reservoirs but has in all cases been found to be a manageable part of field operation. Silica scaling in surface equipment and injection wells is a delicate aspect of the reinjection process in most high-temperature geothermal fields, but silica scaling in the reservoir has not been considered a problem. Reinjection of low-enthalpy geothermal fluid into sandstone has not been successful, for reasons that are poorly understood. The location of injection wells in relation to production wells influences the ratio of injected fluid recovered in production wells. For peripheral injection, about one third of the injected fluid is commonly recovered, whereas injection within the production area results in a higher ratio of recovered fluid. Subsidence is in general of small concern in geothermal operations and micro-gravity has proved a valuable tool to estimate the recharge to geothermal reservoirs.     

Modeling studies for production potential of Chingshui geothermal reservoir

The Chingshui geothermal power plant was decommissioned in 1993 due to a continued decline in production. Although some geothermal exploration and field investigation had been exercised, the production potential of the reservoir is still not well understood. In this paper, numerical modeling approaches for characterization of the geothermal reservoir, investigation of reservoir production performance, and evaluation of exploitation scheme design are presented. At first, a site-scale refined grid numerical model was developed for simulating the natural state of Chingshui geothermal reservoir. Through the model, the production potential of the geothermal reservoir was estimated and the availability of water resources was assessed. We further built production model to simulate the production history during 1981–1993. From the production model, we can conclude that the abnormal drop of the reservoir production capacity is mainly caused by carbonate scaling. Potential production schemes with different reinjection designs were evaluated through the model. Simulation results indicated that a sustainable hot water production capacity of Chingshui geothermal reservoir is about 200 t/h without reinjection, and 300 t/h or even higher with reinjection which is enough for a 3 MWe power plant. The simulation results indicate that reinjection provides an effective approach for maintaining reservoir pressure during hot water/steam production.     

Analysis of tracer test data, and injection-induced cooling, in the Laugaland geothermal field, N-Iceland

The Laugaland geothermal system in N-Iceland is hosted by low-permeability fractured basalt and its productivity is limited by insufficient recharge, even though substantial thermal energy is in-place in the 90–100 °C hot rocks of the system. The purpose of a 2-year reinjection experiment, completed in late 1999, was to demonstrate that some of this energy could be extracted economically through long-term reinjection. A comprehensive monitoring program was implemented as part of the project, including three detailed tracer tests. More than 1400 tracer samples were collected during the tests. Tracer return data indicate that the injected water travels through the area bedrock by two modes: first, along direct, small volume flow-paths, such as fractures or interbeds; second, by dispersion and mixing throughout a large volume of the reservoir. Based on the tracer test results, and assuming 15 l/s average future reinjection, the temperature of water produced is predicted to decline by 1–3 °C in 10 years. It can be asserted, in spite of measurement uncertainties, that the 2-year reinjection experiment did not cause a temperature decline greater than about 0.5 °C, conforming to predictions. It is estimated that future reinjection at 15 l/s will enable an increase in energy production amounting to about 24 GWh_th/year, which equals roughly of the average yearly energy production at Laugaland during the last decade. Reinjection has continued after the experiment and is already an important part of the management of the Laugaland geothermal system.     

Geothermal exploitation of the dogger in the paris basin maintenance, renewal and reliability of the geothermal loop

For a project to be profitable the geothermal loop, a complex system within which many physical and chemical phenomenea occur, must be in good working order. The reliability of this system depends on the general design of the installation, the quality of materials used and organisation set up for monitoring, maintenance and replacement of materials. The experience gained from many incidents has enabled a number of rules to be defined that should be applied to project design. In the same way, this experience has made it possible to select the materials, or types of materials, which should be used, and those which should be avoived. The paper gives many examples, and a table showing the life of the principal materials, drawn up form the results of a survey. For the monitoring, maintenance and replacement of the geothermal loop, a range of devices must be installed to enable. permanent observation of the geothermal loop. periodical maintenance of materials. immediate intervention in the case of production stoppage Several companies have created units for carrying out these services. The progress made during the last five years in the three areas of general design of the loop, materials, and organisation of monitoring and maintenance enables geothermal power stations to reach an annual rate of availability greater than 95%.     

The geothermal system of Ischia Island (southern Italy): Critical review and sustainability analysis of geothermal resource for electricity generation

In this paper we analyze the main available data related to the geothermal system of Ischia Island, starting from the first geothermal exploration in 1939. Our aim is to define a conceptual model of the geothermal reservoir, according to geological, geochemical, geophysical and stratigraphic data. In recent times, the interest on geothermal exploitation for electricity generation in Italy is rapidly increasing and the Ischia Island is one of the main targets for future geothermal exploitation. Nowadays, one of the main economic resources of the island is the tourism, mainly driven by the famous thermal springs; so, it is crucial to study the possible interaction between geothermal exploitation and thermal spring activities. To this aim, we also analyze the possible disturbance on temperature and pressure in the shallow geothermal reservoir, due to the heat withdrawal for electric production related to small power plant size (1–5 MWe). Such analysis has been performed by using numerical simulations based on a well known thermofluid-dynamical code (TOUGH2^®). Obtained results show that such geothermal exploitation generates a perturbation of temperature and pressure field which, however, is confined in a small volume around the well. At shallow level (0–100 m) the exploitation does not produce any appreciable disturbance, and can be made compatible with thermal spring exploitation. Moreover, such results are crucial both for the evaluation of volcanological processes in the island and for the general assessment of geothermal resource sustainability.     

两相流与溶液化学平衡相结合的地热井结垢模拟研究

水热型地热系统和干热岩增强型地热系统在运行一段时间后都有可能出现井筒和管道设备结垢现象,困扰和阻碍着地热资源的高效低成本开发.由于温度和压力变化导致CO2从地热水中逸出,进而使得CaCO3析出结垢,是地热生产井堵塞的主要原因.将两相流动换热计算与水溶液物理化学模拟相结合,针对地热井内CaCO3垢进行流动换热与化学组分变...