BSR热流的三维地貌校正和流体汇聚探测(英文)

从天然气水合物稳定区底界的地震似海底反射BSR(Bottom Simulating Reflector)深度计算得到的BSR热流包含了海底地貌(热流在凹地型会聚,在凸地形发散)和增生楔内部流体活动的影响。从BSR热流中移除地貌效应的贡献就能揭示出流体是否发生了汇聚。在难以使用解析方法计算地貌效应的复杂海底区域,三维有限元方法可以高精度的模拟地貌对背景热流的影响,从而可以对BSR热流进行地貌效应校正,得到平坦地形条件下的BSR热流,并进一步通过与背景热流值的对比,识别目前仪器所不能探测的流体汇聚区。在北卡斯卡底(Cascadia)俯冲边缘陆坡中部的研究区应用该方法,显示黄瓜岭(Cucumber Ridge)高地及其周围的海底热流正异常显著(高出背景热流值10-20%),同时这些区域在地震成像上与海底的裂隙系统相对应,指示了流体沿着这些高渗透率通道进行汇聚,并且很可能导致较高的水合物富集度。     

北京平原区西北部大地热流与深部地温分布特征

北京平原区蕴藏着丰富的中-低温水热型地热资源,其西北部分布着小汤山地热田和京西北地热田,两大地热田以南口—孙河断裂带为界.地热田及其外围地区基础的地热地质研究工作较少.为给地热学研究和地热资源精细勘探提供科学依据,本文基于前人23眼钻孔的温度测量数据以及近期完成的548件热导率和100件放射性生热率实测数据,研究了区域大地热流和0~4 km深部地温特征.结果表明：（1）研究区现今地温梯度为11.31~94.89℃·km^-1,平均值为31.79℃·km^-1;岩石热导率为0.895~5.111 W·（m·K）^-1,放射性生热率为0.257~2.305 μW·m^-3,大地热流为48.1~99.1 mW·m^-2,平均值为68.3 mW·m^-2,热流的分布受基底形态和断裂构造控制.研究区东部南口—孙河断裂带两侧小汤山和郑各庄地区为高热流异常区,中部马池口地区也存在局部高热流异常区.（2）在南口—孙河断裂带的不同位置,不同深度地层温度差异明显,体现出区域现今地温场不只受控于该活动断裂,更是多期次构造事件复合叠加的结果.（3）南口—孙河断裂带南侧存在两处有意义的较高地温异常区,分别为郑各庄异常区和马池口异常区,其中马池口异常区是未来地热开发利用有一定潜力的地区.

     

沁水盆地大地热流与地温场特征

分析了20口井的温度数据和39个岩石样品的热导率数据,计算了20个大地热流值.结果表明：沁水盆地具有偏高的大地热流背景,现今热流变化于44.8～101.8 mW/m2之间,平均62.7±15.2 mW/m2,现今地温梯度介于20.9～47.6 ℃/km之间,平均地温梯度28.2±10.3 ℃/km. 热流的分布与本区上、下主煤层含气量的分布特征相似,在一定程度上反映了现代热流继承了煤层气生气期的古地热背景.     

The effect of erosion on palaeoclimatic and topographic corrections to heat flow

The increase of surface temperature following a recent period of glaciation lowers the heat flow at shallow depths. At greater depths, increase of heat flow above the steady-state value might be expected, reflecting lowered surface temperature during the glacial period itself. Thus a plot of the climatic perturbation to heat flow against depth should have a sigmate form. The fact that measurable negative and positive deviation in heat flow (measurable amplitude of the sigmate variation) has not been observed in some deep boreholes may be explained by taking into account the erosion which accompanies ice ages. Quite small amounts of erosion during the period of lowered surface temperature result in perturbations to heat flow which are nearly constant, or decrease smoothly with depth, damping the sigmate variation and rendering it undetectable. Measured heat flow in this situation is not strongly dependent on depth but is nevertheless significantly different from the steady-state value.Ignoring the effect of erosion on topographic corrections in regions which have been subjected to valley glaciation may result in large errors in heat flow estimates, particularly for shallow measurements, such as in lakes.     

Exploration of regional surface average heat flow from meteorological and geothermal series

We attempt to compute the Surface Average Heat Flow （SAHF） from long-term temperature observations of one hundred seventy-seven observational points at the depths of 0.8, 1.6, and 3.2 m, which were relatively evenly distributed in mainland China. We first employ Fourier transformation to remove the influence of atmospheric temperature variations from the observation series, which are classified into the type of the steady-state temperature monotonously increasing with depth （type I） and other three types. Then we compare our results obtained from the data of type I, of which the values are thought to equal to those of the mean borehole heat flow, with those obtained from traditional heat flow observations mainly distributed in North China Craton. In computations of the SAHF at the observation stations, we deduce the thermal diffusivity and volumetric specific heat of the soil by employing harmonic solutions of the heat conduction equation for the same moisture group as the first step, and then we determine the SAHF using Fourier＇s law. Our results indicate that the SAHF derived from shallow earth geothermal data can reflect the heat flow field to a large extent.     

Terrestrial heat flow and geothermal gradients in relation to hydrodynamics in the Alberta basin, Canada

Geothermal gradients in the Alberta part of the Western Canadian sedimentary basin have been studied on the basis of 55,244 bottom-hole temperature values from 28,260 petroleum exploration wells. Gradient estimates for different depth and stratigraphic intervals together with a study of the heat conductivity distribution indicate both regional heat flow variations and variations with depth. The regional hydrodynamics of the basin strongl influences both grad ifT gradient and heat flow increase with depth in water recharge areas to the west and decrease with depth in discharge areas to the north and east. The results indicate that heat flow in the central part of the basin should be approximately equal to the deep crustal heat flow.     

Numerical calculations of the perturbation of normal heat flow by topographic and local conductivity structure

A numerical method is used to investigate the effect of topographic and local thermal conductivity anomalies on near-surface heat flow for two-dimensional models. Heat flow associated with a sloping topographic structure is calculated. Also, the effects of a fault structure associated with the sloping topography are considered. Vertical and horizontal heat flow components are calculated alone; the surface of the earth as well as throughout the whole region of interest. The results indicate that surface heat flow is substantially affected by topographic relief and the horizontal heat flow component associated with topographic features can be large. Also, regional heat flow is greatly perturbed by local thermal conductivity anomalies and the effect of topographic features may be considerably modified by the subsurface structure.     

张裂型盆地地热参数的垂向变化与琼东南盆地热流分布特征

海洋热流数据是开展海洋地球动力学研究和油气资源评价的基础数据.为深入认识琼东南盆地的地热特征,本文首先利用耦合沉积作用与岩石圈张裂过程的数值模型分析了张裂型盆地主要地热参数的垂向变化特征;并通过钻孔资料的详细分析,获得了琼东南盆地44口钻孔的热流数据;结合海底地热探针获取的热流数据,对琼东南盆地地热特征及其主要影响因素进行了简要分析.结果表明:沉积作用的热披覆效应对表层热流有较明显的抑制作用,由于沉积物生热效应与披覆效应的共同作用,同一钻孔处海底表层热流与钻孔深度3000~4000 m处热流或与海底间的平均热流差异很小,可以一起用于分析琼东南盆地的热流分布特征;莺歌海组、乐东组热导率随深度变化小于黄流组及其下地层热导率的变化,钻孔沉积层平均热导率约为1.7 W·(m·K)-1,钻孔地层生热率一般低于2.5 μW·m-3,平均生热率为1.34 μW·m-3,平均地温梯度主要介于30~45 ℃/km,热流介于50~99 mW·m-2,陆架区热流主要集中于60~70 mW·m-2,深水区钻孔具有较高的地温梯度和热流值;从北部陆架与上陆坡区往中央坳陷带,热流值从50~70 mW·m-2,增高为65~85 mW·m-2,并且往东有升高趋势,在盆地东部宝岛凹陷、长昌凹陷与西沙海槽北部斜坡带构成一条热流值高于85 mW·m-2的高热流带.进一步分析认为,琼东南盆地现今热流分布特征是深部热异常、强烈减薄岩石圈的裂后冷却作用、晚期岩浆热事件、地壳与沉积层的生热贡献以及沉积作用的热披覆效应等多种主要因素综合作用的结果.     

Heat flow and the geothermal potential of Egypt

Preliminary heat flow values ranging from 42 to 175 mW m^–2 have been estimated for Egypt from numerous geothermal gradient determinations with a reasonably good geographical distribution, and a limited number of thermal conductivity determinations. For northern Egypt and the Gulf of Suez, gradients were calculated from oil well bottom hole temperature data; east of the Nile, and at three sites west of the Nile, gradients were calculated from detailed temperature logs in shallow boreholes. With one exception, the heat flow west of the Nile and in northern Egypt is estimated to be low, 40–45 mW m^–2, typical of a Precambrian Platform province. A local high, 175 mW m^–2, is probably due to local oxidational heating or water movement associated with a phosphate mineralized zone. East of the Nile, however, including the Gulf of Suez, elevated heat flow is indicated at several sites, with a high of 175 mW m^–2 measured in a Precambrian granitic gneiss approximately 2 km from the Red Sea coast. These data indicate potential for development of geothermal resources along the Red Sea and Gulf of Suez coasts. Water geochemistry data confirm the high heat flow, but do not indicate any deep hot aquifers. Microearthquake monitoring and gravity data indicate that the high heat flow is associated with the opening of the Red Sea.     

Wave-induced topographic formstress in baroclinic channel flow

Large-scale zonal flow driven across submarine topography establishes standing Rossby waves. In the presence of stratification, the wave pattern can be represented by barotropic and baroclinic Rossby waves of mixed planetary topographic nature, which are locked to the topography. In the balance of momentum, the wave pattern manifests itself as topographic formstress. This wave-induced formstress has the net effect of braking the flow and reducing the zonal transport. Locally, it may lead to acceleration, and the parts induced by the barotropic and baroclinic waves may have opposing effects. This flow regime occurs in the circumpolar flow around Antarctica. The different roles that the wave-induced formstress plays in homogeneous and stratified flows through a zonal channel are analyzed with the BARBI (BARotropic-Baroclinic-Interaction ocean model, Olbers and Eden, J Phys Oceanogr 33:2719–2737, 2003) model. It is used in complete form and in a low-order version to clarify the different regimes. It is shown that the barotropic formstress arises by topographic locking due to viscous friction and the baroclinic one due to eddy-induced density advection. For the sinusoidal topography used in this study, the transport obeys a law in which friction and wave-induced formstress act as additive resistances, and windstress, the effect of Ekman pumping on the density stratification, and the buoyancy forcing (diapycnal mixing of the stratified water column) of the potential energy stored in the stratification act as additive forcing functions. The dependence of the resistance on the system parameters (lateral viscosity ε, lateral diffusivity κ of eddy density advection, Rossby radius λ, and topography height δ) as well as the dependence of transport on the forcing functions are determined. While the current intensity in a channel with homogeneous density decreases from the viscous flat bottom case in an inverse quadratic law ~δ ^–2 with increasing topography height and always depends on ε, a stratified system runs into a saturated state in which the transport becomes independent of δ and ε and is determined by the density diffusivity κ rather than the viscosity: κ/λ ² acts as a vertical eddy viscosity, and the transport is λ ²/κ times the applied forcing. Critical values for the topographic heights in these regimes are identified.     

封闭地热系统水平井采热储层内渗流与传热的有限元模拟

地热能是储量巨大、分布广泛且供给稳定的清洁能源.地热发电对经济发展和环境保护都具有重要意义.然而, 现有地热电站广泛采用的开放性采热模式易导致发电设备结垢与腐蚀、循环水流量不足与波动、自耗功率高等问题.采用传热工质与地热储层分离的封闭性采热模式, 不但能根治上述问题, 而且提升了选择传热工质和设计传热循环的灵活性.本研究采用有限元方法数值模拟水平井采热的封闭地热系统中自然对流强化储层内渗流与传热的动力学过程, 系统分析了水平井温度、水平井位置、储层渗透率、水平井周围渗透率强化改造范围及储层厚度-宽度比等关键因素对采热热流和采热年限的影响, 从而为适用于地热发电的大型封闭地热系统设计和工程实践提供理论指导和基础数据.模拟结果表明, 在水平井周围半径10 m区域内进行渗透率强化改造就能够启动和强化自然对流, 大幅提高未强化改造区域的地热开采; 水平井从储层采热的先后次序由自然对流区域逐渐拓展控制, 开发厚地热储层并将水平井设置在储层高处能够提高采热效率并延长采热年限; 驱动自然对流的水平井-储层温差与采热热流不成正比但正相关; 地热储层内存在的稳态背景自然对流对水平井采热有显著贡献.

     

Temperature and heat flux spectra in the turbulent buoyancy subrange

The physical nature of motions with scales intermediate between approximately isotropic turbulence and quasi-linear internal gravity waves is not understood at the present time. Such motions play an important role in the energetics of small scales processes, both in the ocean and in the atmosphere, and in vertical transport of heat and constituents. This scale range is currently interpreted either as a saturated gravity waves field or as a buoyancy range of turbulence.We first discuss some distinctive predictions of the classical (Lumley, Phillips) buoyancy range theory, recently improved (Weinstock, Dalaudier and Sidi) to describe potential energy associated with temperature fluctuations. This theory predicts the existence of a spectral gap in the temperature spectra and of an upward mass flux (downward buoyancy and heat fluxes), strongly increasing towards large scales. These predictions are contrasted with an alternate theory, assuming energetically insignificant buoyancy flux, proposed by Holloway.Then we present experimental evidences of such characteristic features obtained in the lower stratosphere with an instrumented balloon. Spectra of temperature, vertical velocity, and cospectra of both, obtained in homogeneous, weakly turbulent regions, are compared with theoretical predictions. These results are strongly consistent with the improved classical buoyancy range theory and support the existence of a significant downward heat flux in the buoyancy range.The theoretical implications of the understanding of this scale range are discussed. Many experimental evidences consistently show the need for an anisotropic theory of the buoyancy range of turbulence.     

Relations between basal condition,subglacial hydrological networks and geothermal flux in Antarctica

When modelling the Antarctic ice sheet, the velocity of the ice flow is linked to its temperature. Depending on the thermal rate, the flow rate may vary between deformation and sliding. In this study, we focus on the geothermal flux because it is the least well-known component of the heat equation, and because it constrains the temperature at the bottom of the ice sheet. We used available geological data to build a map of the geothermal flux, which was found to increase from 51 mW/m² in East Antarctica to 68 mW/m² in West Antarctica. These values were integrated in the computation of a basal temperature map. The available map of hydrological networks clearly shows more melted areas in West Antarctica than in the earlier results. So we suggest that the model should be forced with higher geothermal flux values, over 85 mW/m² in this sector. This increase is in good agreement with published results which found a geothermal flux three times higher in West Antarctica. Finally, we computed the bottom melt rate over the ice sheet area which has a mean value of 3.5 mm/yr resulting in a lost of melted ice equal to 1% of the total mass balance.     

Radioactive heat generation and heat flow in the Indian shield

Using a laboratory gamma-ray spectrometer, 160 rock samples from different heat flow sites in India have been analysed for their U, Th and K contents. Heat generation has been estimated for the significant rock types. Of the six regions covered by this study, correction due to heat generation contrast and geologic structure was found necessary and has been applied in two regions. Heat flow/heat generation plots for two regions in the southernmost part of the shield follow the line characteristic of a normal continental heat flow province. The plots for the other four regions indicate a heat flow province with an intercept of 0.92 HFU and a slope of 14.8 km. From data available at present, these parameters are higher compared to those from the other shields. The higher parameters imply a higher temperature and heat flow at the Moho, indicating a region of “hotter” upper mantle in the Indian shield.     

Porosity, permeability, and fluid flow in the Yellowstone geothermal system, Wyoming

Cores from two of 13 U.S. Geological Survey research holes at Yellowstone National Park (Y-5 and Y-8) were evaluated to characterize lithology, texture, alteration, and the degree and nature of fracturing and veining. Porosity and matrix permeability measurements and petrographic examination of the cores were used to evaluate the effects of lithology and hydrothermal alteration on porosity and permeability. The intervals studied in these two core holes span the conductive zone and the upper portion of the convective geothermal reservoir. Variations in porosity and matrix permeability observed in the Y-5 and Y-8 cores are primarily controlled by lithology. Y-8 intersects three distinct lithologies: volcaniclastic sandstone, perlitic rhyolitic lava, and non-welded pumiceous ash-flow tuff. The sandstone typically has high permeability and porosity, and the tuff has very high porosity and moderate permeability, while the perlitic lava has very low porosity and is essentially impermeable. Hydrothermal self-sealing appears to have generated localized permeability barriers within the reservoir. Changes in pressure and temperature in Y-8 correspond to a zone of silicification in the volcaniclastic sandstone just above the contact with the perlitic rhyolite; this silicification has significantly reduced porosity and permeability. In rocks with inherently low matrix permeability (such as densely welded ash-flow tuff), fluid flow is controlled by the fracture network. The Y-5 core hole penetrates a thick intracaldera section of the 0.6-Ma Lava Creek ash-flow tuff. In this core, the degree of welding appears to be responsible for most of the variations in porosity, matrix permeability, and the frequency of fractures and veins. Fractures are most abundant within the more densely welded sections of the tuff. However, the most prominent zones of fracturing and mineralization are associated with hydrothermal breccias within densely welded portions of the tuff. These breccia zones represent transient conduits of high fluid flow that formed by the explosive release of overpressure in the underlying geothermal reservoir and that were subsequently sealed by supersaturated geothermal fluids. In addition to this fracture sealing, hydrothermal alteration at Yellowstone appears generally to reduce matrix permeability and focus flow along fractures, where multiple pulses of fluid flow and self-sealing have occurred.     

Reservoir lifetime and heat recovery factor in geothermal aquifers used for urban heating

Simple models are discussed to evaluate reservoir lifetime and heat recovery factor in geothermal aquifers used for urban heating. By comparing various single well and doublet production schemes, it is shown that reinjection of heat depleted water greatly enhances heat recovery and reservoir lifetime, and can be optimized for maximum heat production. It is concluded that geothermal aquifer production should be unitized, as is already done in oil and gas reservoirs.Nomenclature a distance between doublets in multi-doublet patterns, meters - A area of aquifer at base temperature, m² drainage area of individual doublets in multidoublet patterns, m² - D distance between doublet wells, meters - h aquifer thickness, meters - H water head, meters - Q production rate, m³/sec. - r _e aquifer radius, meters - r _w well radius, meters - R _g heat recovery factor, fraction - S water level drawdown, meters - t producing time, sec. - T aquifer transmissivity, m²/sec. - v stream-channel water velocity, m/sec. - actual temperature change, °C - theoretical temperature change, °C - water temperature, °C - heat conductivity, W/m/°C - _r rock heat conductivity, W/m/°C - _aC_a aquifer heat capacity, J/m³/°C - _aC_r rock heat capacity, J/m³/°C - _WC_W water heat capacity, J/m³/°C - aquifer porosity, fraction     

Temperature/flow statistics and thermomechanics of low-temperature geothermal systems in Iceland

A survey of low-temperature geothermal activity in Iceland shows that there is a strong positive correlation between the temperature and the mass flow of the systems. The relation is very clearly displayed by the thermal systems in Central Northern Iceland. Subdividing the temperature interval from 20/dgC to 100°C into 8 intervals of equal length and plotting the average system flow in each interval against the average temperature of the interval we find that the mass flow increases with the temperature. At the lower end this relation is the result of a conductive cooling of the thermal water as it ascends to the surface. At temperatures above 50°C convective effects appear to be the dominant cause. A very simple lumped element analysis of the low-temperature systems results in reasonable estimates of important flow parameters. The convective downward migration of fracture spaces along the walls of mafic dikes appears to be a dominant thermomechanical process in the development of the low-temperature systems in Northern Iceland.