Long-term temperature monitoring in a borehole drilled into the Nojima Fault, southwest Japan

Abstract Long-term monitoring of temperature distribution in an active fault zone was carried out using the optical fiber temperature-sensing technique. An optical fiber cable was installed in a borehole drilled into the Nojima Fault in Awaji Island, south-west Japan, and the temperature profile to a depth of 1460 m had been measured for 2.5 years (July 1997–January 2000). Although the obtained temperature records showed small temporal variations due to drifts of the measurement system all along the cable, local temperature anomalies were detected at two depths. One at around 80 m seems to correspond to a fracture zone and may be attributed to groundwater flow in the fracture zone. This anomaly had been stable throughout the monitoring period, whereas the other anomaly at around 500 m was a transient one. The water level in the borehole could be estimated from the diurnal temperature variations in the uppermost part of the borehole and may provide information on the hydrological characteristics of the fault zone, which is connected to the borehole through perforations on the casing pipe. Except for these minor variations, the temperature profile had been very stable for 2.5 years. The conductive heat flow calculated from this profile and the thermal conductivity measured on core samples increases with depth, probably resulting from errors in thermal conductivity due to sampling problems and/or from advective heat transfer by regional groundwater flow. Assuming that the middle part of the borehole (less fractured granite layer) is least affected by these factors, heat flow at this site is estimated to be approximately 70 mW/m².     

The effect of crystallization on the rheology and dynamics of lava flows

The dynamics of a lava flow is studied by a two-dimensional model describing a viscous fluid with Bingham rheology, flowing down a slope. The temperature in the flow is calculated assuming that heat is transferred through the plug by conduction and is lost by radiation to the atmosphere at the top of the flow. Taken into account is that the increasing crystallization takes place in the flow as a consequence of cooling. The lava viscosity and yield stress are expressed as a function of crystallization degree as well as of temperature: in particular it is assumed that yield stress reaches a maximum value above the solidus temperature, according to experimental data. Dynamical variables, such as velocity and thickness of the flow, are calculated for different values of the maximum crystallization degree and the flow rate. The model shows how the lava flow dynamics is affected by cooling and crystallization. The cooling of the flow is controlled by the increase of yield stress, which produces a thicker plug and makes the heat loss slower. The increasing crystallization has two opposing effects on viscosity: it produces an increase of viscosity, but at the same time produces an increase of yield stress and hence reduces the heat loss and keeps the internal temperature high. As a consequence, lava flows are significantly affected by the dependence of yield stress on temperature and scarcely by the maximum crystallization degree.     

Thermal impact of salt: Simulation of thermal anomalies in the gulf of Mexico

Salt and related structures have played important roles in controlling hydrocarbon accumulations in the Gulf of Mexico. Using a two-dimensional fluid flow/compaction model, which allows for both conduction and convection of heat, an examination is given of the effects on thermal patterns of the combined influence of multiple salt features, including diapirs, pillows, sheets and wedges. The focusing and defocusing of heat due to the higher thermal conductivity of salt are accounted for in the modeling. The results show that there could be as much as a 30°C anomaly above multi-salt bodies due to the focusing of heat by salt, and as much as 50°C temperature contrast between internal salt positions and sediments external to the salt in the deep part of a section. The magnitude of the thermal anomaly depends on the size (or width) of the salt and on the depth of the rooted salt. The modeled results provide estimates of the influence of salt in expanding the oil generation window by approximately half of the salt thickness.     

Temperature dependence of thermal conductivity and its impact on assessments of heat flux

The variability of sedimentary thermal conductivities with increasing temperature are explored for their impact on estimates of present-day heat flux and subsurface temperature gradient. For sand thicknesses less than about 10–20 km, or shale thicknesses less than about 40–80 km, the subsurface temperature is closely linearly proportional to the thermal resistance integral obtained in the absence of the temperature dependence of thermal conductivity. Estimates of heat flux should be increased (decreased) by about 5% for sands and decreased by about 1% for shales. For salt, because of the much shorter temperature range over which its thermal conductivity decreases, effects produced by the temperature dependence are more noticeable: heat flux should be increased by around 13%, salt thicknesses in excess of 5 km will yield major (around 30–100°C) changes in their temperature regimes solely as a consequence of the temperature-dependent thermal conductivity, and the linear increase of temperature with increasing thermal resistance is not an adequate approximation but has to be replaced with a more exact exponential increase.The impact of the variations, particularly in the case of salt, for geologic processes is briefly considered.     

Three-dimensional thermal structure of the Chinese continental crust and upper mantle

We invert S-wave velocities for the 3D upper-mantle temperatures, in which the position with a temperature crossing the 1300℃ adiabat is corresponding to the top of the seismic low velocity zone. The temperatures down to the depth of 80 km are then calculated by solving steady-state thermal conduction equation with the constraints of the inverted upper-mantle temperatures and the surface temperatures, and then surface heat flows are calculated from the crustal temperatures. The misfit between the calculated and observed surface heat flow is smaller than 20% for most regions. The result shows that, at a depth of 25 km, the crustal temperature of eastern China (500―600℃) is higher than that of western China (<500℃). At a depth of 100 km, temperatures beneath eastern and southeastern China are higher than the adiabatic temperature of 1300℃, while that beneath west China is lower. The Tarim craton and the Sichuan basin show generally low temperature. At a depth of 150 km, temperatures beneath south China, eastern Yangtze craton, North China craton and around the Qiangtang terrane are higher than the adiabatic temperature of 1300℃, but is the lowest beneath the Sichuan basin and the regions near the Indian-Eurasian collision zone. At a depth of 200 km, very low temperature occurs beneath the Qinghai-Tibet Plateau and the south to the Tarim craton.     

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3000~4000m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2.5μW·m-3,平均生热率为1.34μW·m-3,平均地温梯度主要介于30~45℃/km,热流介于50~99mW·m-2,陆架区热流主要集中于60~70mW·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50~70mW·m-2,增高为65~85mW·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85mW·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.     

FINITE-ELEMENT ANALYSIS OF SHALLOW TEMPERATURE ANOMALIES*

Finite-element analysis has been used in calculating shallow temperature anomalies due to both the presence of salt domes and near-surface faults. The results of the numerical analysis are in good agreement with field observations reported earlier by Poley and van Steveninck. The calculations show how surface emissivity must be responsible for the pronounced temperature anomalies above salt domes. Faulting is a mechanism that disorders the layering sequence of sedimentary deposits. If the disordered sedimentary layers show notable differences in heat conductivity, the layers are thick enough and the displacements along the fault plane large enough, temperature anomalies close to the free surface may be apparent because of the surface-emissivity mechanism. In order to explain certain characteristic temperature anomalies where a fault reaches or approaches the free surface, an additional mechanism has to be assumed; namely a distortion of texture, and consequently a change in the heat conductivity of the rock material surrounding the fault plane. The consequences of both a reduced and an increased heat conductivity of the surroundings of a near-surface fault have been calculated, and they show remarkable agreement with temperature anomalies observed in various parts of the world.     

Moving salt sills and hydrocarbon maturity

Salt sills have been observed in the Gulf Coast. The contrast in the thermal conductivity between salt and detrital sediments means that a salt sill focuses heat around its leading edge, resulting in the devlopment of an anomalous temperature pattern in the vicinity of the salt sill. The consequent anomaly in thermal maturity pattern for hydrocarbons is related to four parameters: the salt sill thickness; the subsurface depth of the sill; the inclination of the sill; and the salt speed through the sediments. The excess maturity in the vicinity of the salt sill is shown to be dominantly dependent on the velocity of the salt sill. The positional influence of the hydrocarbon maturity relative to the salt is also examined and it is shown that the alteration of sedimentary burial paths by the inserted salt also causes a thermal anomaly. Both thermal focusing of heat by salt and sediment burial to a different thermal regime caused by passage of inserted salt produce thermal maturity effects comparable in magnitude, and neither may be ignored.The work here was supported by the Industrial Associates of the Basin Analysis Group at the University of South Carolina.     

Numerical analysis for cooling effect of open boundary ripped-rock embankment on Qinghai-Tibetan railway

At present, the Qinghai-Tibetan railway is being built, and it will pass across more than 550-km perma-frost regions. Therefore, the key to the stability of therailway embankment lies in solving the permafrost problem. Because global warming and existence of railway tend to degrade the permafrost in these re-gions[1], more difficulties and problems are induced in the construction and maintenance of railway. In the area where the mean annual air temperature is higher than a certain value, the …     

Terrestrial heat flow in Japan

Terrestrial heat flow, Q=K×ΔT/ΔZ cal/cm² sec has been determined at 51 localities (39 on land and 12 in the sea) in and around the Japanese Islands. The average values of observed heat flow in land and sea are 1.53µ cal/cm²sec and 1.48µcal/cm²sec respectively. These value do not differ greatly from the world’s averages. The outstanding features of the heat flow distribution are as follows:a) High heat flow region (Q>2.0µcal/cm²sec) exists in the Inner Zone of the Honshu Arc. This region of high heat flow is more distinct in the northeastern Japan than in the southwestern Japan.b) The High heat flow region seems to extend, through the Fossa Magna area, down to the Izu-Mariana Arc.c) It is also probable that a similar high heat flow zone exists in the inner side of the Kurile Arc.d) These zones of high heat flow precisely coincide with the zones of the Cenozoic orogeny in the area concerned.e) Far off the coast of the northeastern Japan, the area at about 150° E may be a high heat flow region.f) Low heat flow (Q<1.0µcal/cm²sec) prevails in the Pacific coast side of the northeastern Japan and in the oceanic area directly east of it, including the area of the Japan Trench.g) The region bounded by the above mentioned high and low heat flow regions has heat flow which is more or less normal. Based on these measurements, a « steady state ” temperature distribution in the crust has been calculated for each of the above regions of high, low and intermediate heat flow, and it was found that there is a large temperature differences between the bottom of the crust of the high and low heat flow regions: the temperature at the Moho boundary in the high heat flow regions should be as high as some 800～1000°C (d=27 km), whereas that under the low heat flow region should be only about 200°C (d=23 km). The high general temperature at the Moho under the high heat flow region seems to favor a production of magma in the upper mantle. Calculated Moho temperatures disfavor the hypothesis that the Moho boundary is due to phase transition.     

珠江口盆地大地热流特征及其与热岩石圈厚度的关系

沉积盆地现今热流特征是岩石圈构造-热演化过程的综合反映和盆地热史恢复的必要约束条件,其总体变化趋势与热岩石圈厚度密切相关.本文根据新收集的珠江口盆地19口钻井温度数据,新增计算了19个大地热流数据,其中12个数据位于深水区（水深大于300 m）,丰富了该盆地深水区钻井地热数据.结合前人研究成果,绘制了该盆地的大地热流图,并分析了其热流分布特征.在此基础上通过求解一维热传导方程,计算得到36口井位处的热岩石圈厚度,量化了盆地大地热流与热岩石圈厚度间的关系.结果显示,珠江口盆地大地热流值介于24.2~121.0 mW·m^-2,平均71.8±13.6 mW·m^-2,新增盆地深水区钻井平均热流值高达84.5±4.4 mW·m^-2.大地热流分布整体上从陆架区到陆坡区升高,而热岩石圈厚度整体分布趋势与大地热流相反.大地热流与热岩石圈厚度间存在良好的指数相关性.     

Modeling the influence of MgSO4 invariant points on multiphase reactive transport process during saline soil evaporation

In the present work, we modeled a laboratory experiment where a sand column saturated with a MgSO₄ solution is subject to evaporation. We used a compositional formulation capable of representing the effect of geochemistry on flow and transport for concentrated solutions under extreme dry conditions. The model accounts for the water sink/sources terms due to hydrated mineral dissolution/precipitation and the occurrence of invariant points, which prescribe the water activity. Results show that the occurrence of the invariant points at the top of the domain could affect the vapor flux at the column top and salt precipitation along the column. In fact, the invariant points occurrence could explain the spatial fluctuation on the salt precipitates formation. Results also suggest that the complex hydrochemical interactions occurring during soil salinization, including osmotic effects, are crucial not only to understand the salt precipitation, but also the evaporation rate.     

漳州热田的对流热流和传导热流的研究

漳州地热系统属对流型地热系统.漳州热田是我国东南沿海地区目前所见热田中温度最高（121.5℃）的一个.地表热流值的研究表明,热田中心具有最大的实测热流值（359mw/m²）.本文根据热田内152个钻孔的测温资料和56块岩石样品的热导率数据,采用三种不同方法计算出漳州热田及其邻近地区的大地热流值,并讨论了热流值分布的特点.     

Geothermal map of Mexico

Silica temperatures were calculated for 326 water samples from hot and warm springs located throughout Mexico as an attempt to estimate heat flow. Available heat flow data (Smith, 1974; Smith et al., 1979) for northern Mexico were related to silica temperature data to obtain the appropriate constants for the regional conditions according to Swanberg and Morgan's equation (1979, 1980). The constants obtained are similar to those obtained for the United States, therefore heat flow can be estimated on the basis of silica temperature data. By contouring calculated temperatures a map is obtained where the main geothermal provinces are shown.     

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。     

Heat flow and ground water movement in the Bohemian cretaceous basin (Czechoslovakia)

Sub-surface temperature fields may be considerably affected by active ground water systems, thereby seriously hampering the interpretation of heat flow data. Quantitative evaluation of the convective component of heat transfer is thus very important in cases such as large sedimentary basins with vast underground water circulation. We propose in this study a simple model of horizontal aquifer. This model was used to examine the effect of the lateral convection on the surface heat flow near the recharge zone of basinal margins. The perturbation of the heat flow field above the aquifer was calculated for various aquifer geometry and various flow velocities and the regional scale dependence of the perturbation on the hydraulic properties of the aquifer was demonstrated. The model was applied to the Bohemian Cretaceous Basin and it was shown that within a few kilometres from the recharge zones the observed surface heat flow may be underestimated by up to several tens of percent. The procedure was tested in two locations in this area, in an attempt to make hydrogeological corrections to the measured heat flow values in several boreholes.     

Numerical simulations of mantle flow around slab edges

A simple kinematic-dynamic model of mantle flow around the slab-edge is constructed in order to understand the flow complexity there. The flow velocity on the top and the small boundary region around the shallow plate boundary is kinematically imposed in order to achieve a subduction-like feature and the flow in other part is dynamically calculated. The geometry of the plate mimics the region around the junction of Aleutian Islands and Kamchatka, that are examples of the convergent-transform fault plate boundaries. In a simple model in which the overlying plate is almost stationary, the lateral flow from the mantle under the subducting slab to the mantle under the neighboring plate is of minor importance, once the slab penetrates into the high viscosity layer where the downward flow encounters the resistance. Similar situation was found when the trench is advancing, that is, the trench moves toward the overlying plate. For the case with retreating trench, that is, the trench moves toward the subducting plate, a lateral flow exists even after the slab penetrates into the high viscosity layer, although its magnitude is significantly smaller than that of the plate velocity. The presence of a low viscosity layer just beneath the subducting plate may promote the emergence of lateral flow. A significant lateral flow is observed when the high temperature anomaly, that is, buoyant and low viscosity block carried by the movement of subducting plate, approaches the slab. These results may have important implications for the possible existence of trench parallel flow in the sub-slab mantle.     

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.     

中国第一批大地热流数据

本文叙述了观测大地热流的方法和仪器, 其中包括在钻孔中测定温度的半导体热敏电阻井温仪和在室内测定岩芯标本热导率的装置.给出了最近几年在华北地区11个地点的16个钻孔中取得的温度和热导率数据以及计算热流值的结果.初步讨论了热流值分布与本区复杂地质条件之间的关系, 如中国北部及东部地区热流值与世界同类型地质单元相比较具有较高值和较大分散性的可能解释.      

基于热流变运动学模型的长白山熔岩流数值模拟

热流变运动学模型是熔岩流复杂流动过程模拟的一种方法,其通过热量系统和地形的计算来模拟熔岩流的流动速度、温度变化和流动距离等.本文以气象站期碱流岩的野外调查数据为依据,应用该模型对其进行模拟研究.通过对模拟结果的分析发现,速度变化趋势与地形坡度变化趋势一致,但随着流动过程中黏度的增大,地形影响作用逐渐减小.在热量系统中,...