基于云自适应遗传算法的深覆盖层上面板堆石坝渗流监控模型

针对库水位和降雨对面板堆石坝渗流的滞后效应,结合深覆盖层面板堆石坝的筑坝特点,在综合考虑覆盖层厚度、筑坝材料等对大坝渗流影响的基础上,建立了考虑滞后效应的深覆盖层面板堆石坝渗流安全监控模型,并在模型的求解中采用了云自适应遗传算法。实例应用表明,该模型能较好地反映库水位、降雨对渗流的滞后影响,模型精度与预报效果优于一般渗流统计模型,且云自适应遗传算法较好地弥补了传统遗传算法执行效率不高、易陷入局部最优解等不足。     

Thermal anomalies in lanzarote (Canary Islands)

About a hundred thermometers have been installed 3 m deep in an area of about 20 km² in the ? Montañas de Fuego ? (island of Lanzarote). The temperatures measured oscillate between 16°C and 350°C. In other wells 150 to 250 m deep a gradient of 0.2°C/m has been measured. This gradient is always found in a region of about 200 km² around the zones of the highest superficial anomalies.The local surface anomalies are related to the outflow of hot fluids through tectovolcanic fractures. At great depths these fluids probably form a convective system under impervious layers (hyaloclastites?). The heat transfer takes place by means of convection in a deep reservoir and in the superficial levels, but an intermediate zone with impervious layers must exist where heat is transmitted by conduction.     

Geophysical investigations of the Seferihisar geothermal area, Western Anatolia, Turkey

Self-potential (SP), magnetic and very low frequency electromagnetic (EM-VLF) surveys were carried out in the Seferihisar geothermal area to identify major and minor fault zones and characterize the geothermal system. The SP study provided useful information on the local faults and subsurface fluid flow. The main SP anomalies appear mostly along and near active fault zones in the area of the Cumalı, Tuzla and Doğanbey hot springs. Two of these anomalies near the Tuzla hot springs were further evaluated by SP modelling. Total magnetic field values increase from the Doğanbey to the Cumalı hot springs. Modelling performed on the magnetic data indicates that between these two spring areas are four different regions or units that can be distinguished on the basis of their magnetic susceptibility values. Fraser filtering of EM-VLF data also indicates that there are three significant conductive zones in the regions around the Cumalı, Tuzla and Doğanbey hot springs, and that they lie between important fault systems. The EM-VLF and total (stacked) SP data show that the conductive tilt anomalies obtained by Fraser filtering generally coincide with negative SP areas.According to our geophysical investigations, new exploratory wells should be drilled into the conductive zones located between the Cumalı and Tuzla hot springs. We further recommend that resistivity and magnetotelluric methods be carried out in the area to obtain additional information on the Seferihisar geothermal system.     

Thermal regime, groundwater flow and petroleum occurrences in the Cap Bon region, northeastern Tunisia

The Cap Bon region of northeastern Tunisia is part of a young continental margin that presents a thick column of sediments deposited mainly during Cretaceous and Miocene extended tectonic episodes. This sedimentary package is characterised by broad synclines alternating with NE–SW trending anticlines, and is affected by numerous NE–SW, NW–SE and E–W striking faults. Oligo-Miocene sandstones constitute the most important potential reservoir rocks in the region.The distribution of subsurface temperatures in the Cap Bon basin reflects local groundwater circulation patterns and correlates with the location of known oil and gas fields. The results of geothermal studies could therefore prove useful in the search for new hydrocarbon resources in the region. Subsurface temperatures were measured in deep oil exploration and shallow water wells. Local geothermal gradients range from 25 to 35 °C/km, showing higher values in the Korbous and Zennia areas, which correspond to zones of groundwater discharge and convergence in the Oligo-Miocene aquifer system, respectively.Analysis of thermo-hydraulic and geochemical data relative to the thermal springs in the Korbous region along the Mediterranean coast has made a useful contribution to geothermal prospecting for potential deep reservoirs. Positive geothermal gradient anomalies correspond to areas of ascending thermal waters (i.e. discharge areas), whereas negative anomalies indicate areas of infiltrating colder meteoric waters (i.e. recharge areas). The zones of convergence of upward-moving water and groundwater may be associated with petroleum occurrences.     

Geology and fluid chemistry of the Fushime geothermal field, Kyushu, Japan

The Fushime geothermal field is located in a depression close to the coast line. The system is characterized by very high reservoir temperature (>350°C), and a high salinity production fluid. Geological analysis shows that the main reservoir in this field occurs in a fractured zone developed around a dacite intrusion located in the center of the field. High permeability zones recognized by drilling data are found to be associated with fault zones. One of these zones is clearly associated with a NW–SE trending andesite dike swarm which was encountered in some wells.Alteration in the system can be divided into four zones, in order of increasing temperature, based on calcium–magnesium aluminosilicate mineral assemblages: i.e., the smectite, transition, chlorite and epidote zones. The feed zone is located in the chlorite and epidote zones, which can be further divided into three sub-zones according to their potassium or sodium aluminosilicate mineralogy, from the center of the discharge zone: K-feldspar–quartz, sericite–quartz, and albite–chlorite zones.Chloride concentration of the sea-water is 19,800 mg/l, and Br/Cl mole ratio is 1.55. Based on geochemical information, the reservoir chloride concentration of this field ranges from 11,600 to 22,000 mg/kg. The Clres (Cl in reservoir), Br/Cl ratios and stable isotope data indicate that the Fushime geothermal fluid originated from sea-water and is diluted by ground water during its ascent. Some fluids produced from geothermal wells show low pH (about 4). It is thought that sulfide mineral (PbS, ZnS) precipitation during production produces this acidic fluid.     

小浪底水库大坝坝基渗漏影响分析

水库运行期间,坝体及坝基的渗漏不可避免,渗流对其稳定性影响较大,确定渗流量及主要渗漏部位尤显重要,以小浪底水库大坝为例,采用Feflow地下水数值模拟软件计算坝址区的地下水位,并与观测孔的实测水位进行拟合,反演获得坝址区各种材料的渗透参数值,并在此基础上,对坝基深厚覆盖层和断层等条件变化时的渗流量进行模拟预测。计算结果表明,坝基深厚覆盖层和断层对坝基的渗漏量影响明显,应加强坝基和断层的补强灌浆措施。     

基于一维波动理论的特厚覆盖层坝基动力特性研究

基于一维波动理论,考虑地震过程中基岩-覆盖层的相互作用以及上覆坝体的影响,对500m级特厚覆盖层坝基进行了动力反应分析,探讨了地震波在特厚覆盖层中的传播过程与规律性.计算结果表明,考虑基岩-上覆覆盖层相互作用的必要性明显,与不考虑相互作用的工况相比,覆盖层自由表面放大倍数增大约16%,后者缩减了土层的放大效应,使抗震计算趋于不安全;地震传播过程中覆盖层所含的软弱土层滤波效应明显,动反应随高程呈现出先衰减后增大的规律,覆盖层建基面的放大倍数小于1;在考虑上覆建筑物的影响时发现,随着建筑物高度的增加,覆盖层建基面地震动的放大倍数呈现逐渐减小的趋势,即在覆盖层上修建大坝后,建基面加速度峰值小于同一水平截面天然覆盖层地基的加速度峰值,说明修建大坝可加强覆盖层坝基的抗震稳定性.     

Magnetic anomalies associated with high temperature reservoirs in the taupo volcanic zone (New Zealand)

Distinct magnetic total force anomalies are associated with many, but not all, liquid-dominated geothermal reservoirs in the Taupo Volcanic Zone, which stand in thick, young (<0.7 Ma) volcanic host rocks. The anomalies are caused by demagnetised rocks (a result of hydrothermal alteration) in the upper 0.5–1 km section of the reservoirs; the phenomenon has been confirmed by core studies. Four different patterns of magnetic anomalies have been recognised. The most common type can be found over high-temperature systems where demagnetisation is confined to the main reservoir. Different anomaly patterns are associated with prospects characterised by subsurface outflows and reservoirs hosted in both normally and reversely magnetised rocks. A rather subdued and almost featureless pattern occurs over a few prospects where rocks lying outside the reservoir have also lost thei magnetisation by interaction with acidic, steam-heated water.     

Reservoir performance of the Geysers Field

The Geysers Field, located in Northern California, has an installed generating capacity of 502 MWe. Total withdrawal rate is approximately 8-5 million lb/h of steam from 95 wells. Four new generating plants are currently under construction, which will bring the installed capacity to 908 MWe by 1979.The reservoir rock consists of naturally fractured graywacke, a very competent rock with low interstitial porosity and permeability. The reservoir contains dry steam with an initial pressure of approximately 514 psia at sea level datum. Static pressure gradient is that of saturated steam to the total depths of wells drilled to date.The initial development at The Geysers Field occurred in an area which has two shallow dry steam anomalies. Recent studies have shown that the steam in these anomalies is being fed through fractures connecting them with the deeper regional fracture system.Development of the regional system has created two distinct pressure sinks. The larger of the two pressure sinks is in the oldest and most developed portion of the field. This sink has grown larger with the addition of new production capacity. There is no pressure interference between the two sinks, but pressure interference between wells in a given pressure sink is very rapid. Pressure behavior at observation wells in these sinks resembles an ideal single-phase system with constant pressure boundaries.The expansion of the field has been the result of continued exploratory drilling and testing of new step-out wells. Based on the successful exploratory wells drilled to date, it is estimated that the generating capacity of The Geysers could reach 1800 MW by the mid-1980s.     

上覆压力对深厚覆盖层地基渗透及渗透稳定性的影响

为了研究不同上覆压力对深厚覆盖层中管涌型土层的渗透及渗透稳定性影响,利用土体渗流—应力耦合装置,在施加不同上覆压力(0、0.3、0.5、0.7 MPa)的条件下,对缺级配砂砾石进行渗透破坏试验。结果表明,随着上覆压力的增大,土体在渗透破坏过程中,局部的渗透特性变化和渗流场分布均存在差异性,反映了细土颗粒被运移和填充孔隙的情况不同,从而影响了水力坡降在局部的分配情况;上覆压力的增大使得土体稳定渗流阶段和渗透破坏阶段的渗透性出现不同程度的减小,临界坡降和破坏坡降的变化与上覆压力之间存在相同形式的非均匀变化关系。     

刘家峡大坝坝基渗压系数变化及影响因素分析

详细分析坝基渗压系数变化 ,渗压系数与库水位关系。幕前观测孔 U7- 1 渗压系数接近常量 ,与库水位线性相关具有同步性。分析了坝基渗压分布与坝前泥沙淤积铺盖防渗性、帷幕灌浆、渗水断层裂隙分布关系     

Reservoir characteristics and development plan of the Oguni geothermal field, Kyushu, Japan

Geothermal power development at the Oguni field, central Kyushu, is planned to begin in the year 2001 with a double flash system generating 20 MW_e. The Oguni reservoir has been delineated by systematic geothermal surveys, well tests and reservoir engineering studies. The fractured reservoir is horizontally layered and divided into northern and southern portions. Both of them have NaCl dominant fluids ranging from 200 to 240°C. The northern reservoir covers a large area including the Takenoyu Fault Zone and has a relatively high permeability (kh≈80–230 darcy-m). By contrast, the southern reservoir covers a relatively small area and has limited transmissivity. The southern reservoir has a higher pressure (1 MPa) than the northern reservoir, indicating little connectivity between them. Based on numerical calculations, as well as the surface topography and environmental aspects, the production and reinjection zones have been separated, and a large part of the necessary fluid will be produced from the northern reservoir along the Takenoyu Fault and a small part will be taken from the southern reservoir. The separated water will be reinjected into the northernmost part of the northern reservoir, in order to prevent a cold sweep problem for production.     

The southern boundary of Larderello geothermal field

The southern area of the Larderello geothermal field presents some typical characteristics of the peripheral areas of vapor-dominated systems where the reservoir passes from confined to unconfined conditions. In the natural state, steam rising from depth in upflow zones migrates laterally towards the zones where the reservoir becomes unconfined, partly condensing and partly feeding natural manifestations. Two different zones are recognizable: (a) Monterotondo, where the vapor-dominated system and the cold external aquifers are separated by a low permeability “barrier” and the physical conditions change strongly over short distances. (b) Lagoni Rossi-Carboli, where the two systems are connected, at shallow depth, through thin, isolated, permeable channels and interfere with one another. The physical conditions there vary gradually with distance. The gas content in the fluid produced increases with the distance from the upflow zones, but at a lower rate in the vicinity of confinement boundaries than in zones in which the reservoir is confined throughout. The accumulation of gas is avoided by the venting to the atmosphere of the laterally migrating steam. Water recharge increased to a significant rate only when the reservoir pressure declined and water influx took the place of the original steam outflow through the shallow permeable formations.     

Assessment of reservoir heterogeneity by using produced water chemistry in SAGD

The key challenge of extracting oil from oil sand reservoirs is the viscosity of the oil which is typically between 100 000 and several million cP. To reduce the viscosity of the oil, high pressure, high temperature steam, typically between about 185 and 250 °C, is injected into the reservoir by using recovery processes such as the steam‐assisted gravity drainage (SAGD) process. In this process, steam heats the bitumen and as a consequence, its viscosity drops to about 5 cP and it readily flows under gravity within the reservoir. One key issue that has not gained much attention with respect to SAGD process evolution are steam–rock reactions, water geochemistry, and how the produced water composition varies as the process evolves. Here, we examine how the produced water composition varies in SAGD operations. For the first time, we show that the produced water composition can be used to detect shale barriers and contact of the steam chamber with the overburden. As yet, the produced water composition is not used to understand in situ process development but as we show here, this could be a rich data source for understanding process dynamics. Copyright © 2016 John Wiley & Sons, Ltd.     

Novel insights on the impact of top water on Steam‐Assisted Gravity Drainage in a point bar reservoir

As efforts are made to efficiently exploit and recover bitumen resources in Canada, increasingly more complex reservoirs in the Athabasca area continue to challenge the application of Steam‐Assisted Gravity Drainage (SAGD) technology. Several studies have been done to investigate the impact of heterogeneities/complexities such as shale barriers, lean zones, and top and bottom water on the performance of the SAGD process. However, the literature is deficient for point bar deposits with top water zones, a common occurrence in oil sands systems. This study, by using thermal reservoir simulation, examines SAGD performance in a point bar deposit reservoir where an overlying top water and an inclined heterolithic strata (IHS) is present. The results show that where the top water is unconfined and steam injection pressure is higher than that of the top water zone, there is a loss of thermal energy, but the top water does not impact steam chamber development. At steam injection pressure lower than that of the top water zone, top water continuously drains into the reservoir and constrains the size of the chamber. However, the IHS zone helps to delay drainage of the top water into the chamber when steam is injected at underbalanced conditions. Finally, under proper steam injection pressure conditions, top water production can be considerably delayed.     

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.     

Sustainability of the Hatchobaru geothermal field, Japan

The Hatchobaru power plant Unit No. 1 (55 MW) has been operating since 1977 and Unit No. 2 (55 MW) since 1990. The mean capacity factor of the power plant has reached about 90%. Considering that the long-term operation of the plant, over 30 years for Unit No. 1 and nearly 20 years for Unit No. 2, has been maintained with such a high capacity factor, sustainable development in terms of economic production has been achieved. To maintain a stable operation, systematic reservoir monitoring and reservoir simulation studies have been conducted. The monitoring of changes in reservoir pressure, temperature and gravity indicates that the reservoir is currently approaching a stable state. Results of a simulation study suggest that the sustainable power output of the Hatchobaru reservoir is approximately 120 MW, and each productive fault has the capacity to produce enough steam to generate from 11 to 55 MW. Therefore, it would be possible to maintain the rated power output of 110 MW by optimizing well alignments so that the mass production can be kept within the sustainable productivity of each fault, and the injected water does not cool the production zones.     

Geophysics in geothermal prospecting

Geophysical prospecting of high temperature geothermal reservoirs aims at identifying either fluid trapping structures or anomalies related to the properties of the hydrothermal fluid and rock to fluid interactions. Two types of reservoir environments can be characterized: (i) sedimentary reservoirs when a carbonate reservoir is generally capped by a dominantly argillaceous, hydraulically impervious and thermally insulating cover, and (ii) volcanic and volcano-sedimentary reservoirs associated with hydrothermally altered areas. Based on the aforementioned exploration goals and reservoir settings, a wide spectrum of geophysical methods can be applied whose selection is largely commanded by local geological conditions and expected reservoir morphology. Major geophysical techniques are reviewed and their potential, as to geothermal reservoir prospecting issues, discussed.     

Results of a 3D seismic survey at the Travale (Italy) test site

In the last 15 years geothermal exploration in Tuscany, Italy, has addressed deep reservoirs (depth ≥ 3000 m), hosted within complex geological systems, such as metamorphic formations and/or intrusive bodies. Reservoir productivity is linked to fractured and permeable zones that are rather confined and not uniformly distributed. In this context, the seismic methods represent one of the most reliable geophysical techniques for locating potential drilling targets. A 3D seismic survey has been acquired at the Travale test site, and its results have been used to develop a geological and structural model of the site, and to identify and characterize fractured zones inside the deep geothermal reservoir. A correlation between a high-amplitude reflector (H marker) and fractured contact-metamorphic rocks has been highlighted. More than 70% of the total geothermal fluid production at the Travale area comes from this seismic marker.     

Distribution of hydrothermal mineral zones in the Cerro Prieto geothermal field of Baja California, Mexico

Our ongoing studies of water-rock interaction at Cerro Prieto have now been extended to include samples from 40 wells. We have confirmed the regular sequence of progressive hydrothermal alteration zones previously described, and have mapped these alteration zones across the geothermal field. Our earlier work showed the relationships between hydrothermal mineralogy, temperature and permeability, in that alteration occurs at lower temperature in sandstone than in the less permeable shales. The effects of chemical parameters such as silica activity and differences in CO₂ fugacity have also become apparent when mineral assemblages are compared in sandstones from different wells at the same temperature. A rather complete picture of the shape of the reservoir and the nature of its boundaries is developing, and we have begun to identify patterns in the observed hydrothermal mineral zonations which are characteristic of different temperature gradients. We infer such different gradients to be indicative of different parts of the hydrothermal flow regime. In certain wells mineral zones are closely spaced, indicating steep thermal gradients, while in others they are much farther apart. We believe that patterns characteristic of recharge, discharge and upwelling zones as well as areas of primarily horizontal flow can be recognized.The geothermal circulation system at Cerro Prieto appears to be rather young and shows no indication of retrograde reactions due to cooling. The pattern of fluid flow does not seem to be significantly affected by faults, stratigraphic horizons or by the presence of a cap-rock. The mineral zones define a thermal dome which is apparently fed from the east and spreads westward.