Simulation of Power Production from Dry Geothermal Well Using Down-hole Heat Exchanger in Sabalan Field,Northwest Iran

In this research, a simulation was performed for evaluating power production from an abandoned geothermal well as an enhanced geothermal system by injecting a secondary fluid. Abandoned wells, due to lack of fluid or very low transmissivity, are regarded among the low-to moderate-temperature resources that have the potential for heat production without any cost for deep drilling. Accordingly, they are taken as suitable sources of energy. In the present paper, an abandoned geothermal well at Meshkinshahr geothermal field in Sabalan district, northwestern Iran, with 3176 m depth was simulated. The bottom-hole temperature of 148 °C, as well as well casing size, and real thermal gradient for well were applied in the model. A 3D heat transfer simulation model was designed by considering a coaxial pipe as a down-hole heat exchanger between surrounding rocks of the well and injected fluid. Injected fluid to the well with specified pressure and temperature receives heat from rocks surrounding the well, until it reaches the bottom of the well and converts to vapor. The vapor returns to the surface from inner pipe with very low heat loss during its return. The inner pipe is isolated by a thin layer having a low heat conductivity to prevent heat loss from the returned fluid. It was observed that obtained heat in the well depends on temperature profile of the well, injection velocity, and fluid mass flow rate. The model results were optimized by selecting suitable parameters such as inlet injection speed and fluid flow rate to achieve the highest temperature of the fluid returned from the well. A binary power plant was also modeled to determine the extractable power using returned fluid as input using ammonia and isobutene, as working fluids in binary cycle. Finally, electric power of 270 kW was generated from well NWS3 using designed down-hole heat exchanger.     

Asthenosphere flow and plate motions

Summary. A dynamical theory of flow in the asthenosphere is developed by treating it as a thin layer of Newtonian viscous fluid, pushed horizontally by the dense sinking slabs attached to some plates and by the differences in heating under continental and oceanic crust. Two-dimensional lubrication theory is adapted to give the world-wide effects of inflow to the asthenosphere at the slabs, outflow to the plates at mid-ocean ridges, and the horizontal forces applied at the slabs. The resulting torque balance for the plates is better than any previously published, and leads one to conclude that the asthenosphere's viscosity is least at the top.     

粘性泥石流阻力和运动方程验证分析

现有的粘性泥石流阻力方程可以大致归纳为三类：一类是将泥石流视为固液两相流,通过理论分析建立的泥石流阻力运动方程;二类是认为粘性泥石流符合宾汉姆流体阻力方程;三类是依据泥石流体具有基本符合库伦公式的剪切强度,将泥石流视为固体颗粒散体重力流,在理论分析基础上建立的阻力和运动方程。用粘性泥石流动力学实验数据对三类阻力运动方程进行了验证,结果表明第三类阻力和运动方程与实际接近。     

Mantle convection under simulated plates: effects of heating modes and ridge and trench migration, and implications for the core—mantle boundary, bathymetry, the geoid and Benioff zones

Summary. Numerical convection models are presented in which plates are simulated by imposing piecewise constant horizontal velocities on the upper boundary. A 4 × 1 box of constant viscosity fluid and two-dimensional (2-D) flow is assumed. Four heating modes are compared: the four combinations of internal or bottom heating and prescribed bottom temperature or heat flux. The case with internal heating and an isothermal base is relevant to lower mantle or whole mantle convection, and it yields a lower thermal boundary layer which is laterally variable and can be locally reversed, corresponding to heat flowing back into the core locally. When scaled to the whole mantle, the surface deflections and gravity and geoid perturbations calculated from the models are comparable to those observed at the Earth's surface. For models with migrating ridges and trenches, the flow structure lags well behind the changing surface 'plate'configurations. This may help to explain the poor correlation between the main geoid features and plate boundaries. Trench migration substantially affects the dip of the cool descending fluid because of induced horizontal shear in the vicinity of the trench. Such shear is small for whole mantle convection, but is large for upper mantle convection, and would probably result in the Tonga Benioff zone dipping to the SE, opposite to the observed dip, for the case of upper mantle convection.     

Insulating effect of coals and organic rich shales: implications for topography-driven fluid flow, heat transport, and genesis of ore deposits in the Arkoma Basin and Ozark Plateau

ABSTRACT Sedimentary rocks rich in organic matter, such as coal and carbonaceous shales, are characterized by remarkably low thermal conductivities in the range of 0.2–1.0 W m^?1 °C^?1, lower by a factor of 2 or more than other common rock types. As a result of this natural insulating effect, temperature gradients in organic rich, fine‐grained sediments may become elevated even with a typical continental basal heat flow of 60 mW m^?2. Underlying rocks will attain higher temperatures and higher thermal maturities than would otherwise occur. A two‐dimensional finite element model of fluid flow and heat transport has been used to study the insulating effect of low thermal conductivity carbonaceous sediments in an uplifted foreland basin. Topography‐driven recharge is assumed to be the major driving force for regional groundwater flow. Our model section cuts through the Arkoma Basin to Ozark Plateau and terminates near the Missouri River, west of St. Louis. Fluid inclusions, organic maturation, and fission track evidence show that large areas of upper Cambrian rocks in southern Missouri have experienced high temperatures (100–140 °C) at shallow depths (< 1.5 km). Low thermal conductivity sediments, such as coal and organic rich mudstone were deposited over the Arkoma Basin and Ozark Plateau, as well as most of the mid‐continent of North America, during the Late Palaeozoic. Much of these Late Palaeozoic sediments were subsequently removed by erosion. Our model results are consistent with high temperatures (100–130 °C) in the groundwater discharge region at shallow depths (< 1.5 km) even with a typical continental basal heat flow of 60 mW m^?2. Higher heat energy retention in basin sediments and underlying basement rocks prior to basin‐scale fluid flow and higher rates of advective heat transport along basal aquifers owing to lower fluid viscosity (more efficient heat transport) contribute to higher temperatures in the discharge region. Thermal insulation by organic rich sediments which traps heat transported by upward fluid advection is the dominant mechanism for elevated temperatures in the discharge region. This suggests localized formation of ore deposits within a basin‐scale fluid flow system may be caused by the juxtaposition of upward fluid discharge with overlying areas of insulating organic rich sediments. The additional temperature increment contributed to underlying rocks by this insulating effect may help to explain anomalous thermal maturity of the Arkoma Basin and Ozark Plateau, reducing the need to call upon excessive burial or high basal heat flow (80–100 mW m^?2) in the past. After subsequent uplift and erosion remove the insulating carbonaceous layer, the model slowly returns to a normal geothermal gradient of about 30 °C km^?1.     

山地绿洲边界层特征的数值模拟

使用美国NCAR新版MM5V35非静力平衡模式, 采用三重嵌套的降尺度方法, 通过设计理想的地形和山地绿洲, 模拟研究了山地绿洲环流及边界层特征。山地绿洲的地面感热通量和潜热通量与周围沙漠差异较大, 对形成沙漠绿洲环流有明显贡献。在无山地绿洲的情况下, 地形仅对感热通量有影响, 对潜热通量影响不大。山地绿洲可以使绿洲上空的干冷气流通过下沉气流向下层输送, 在山地绿洲上空形成下沉干冷气流的边界层特征, 它可以抑制由地形形成的向上输送的暖湿气流, 改变地形形成的边界层特征。地形引起的环流是低层复合, 高空辐散。绿洲引起的环流是低空辐散, 高空复合。两种环流呈完全相反的情况。山地绿洲的气候效应可以抑制山地地形的气候效应。     

Dynamic modelling of passive margin salt tectonics: effects of water loading, sediment properties and sedimentation patterns

We investigate the evolution of passive continental margin sedimentary basins that contain salt through two‐dimensional (2D) analytical failure analysis and plane‐strain finite‐element modelling. We expand an earlier analytical failure analysis of a sedimentary basin/salt system at a passive continental margin to include the effects of submarine water loading and pore fluid pressure. Seaward thinning sediments above a weak salt layer produce a pressure gradient that induces Poiseuille flow in the viscous salt. We determine the circumstances under which failure at the head and toe of the frictional–plastic sediment wedge occurs, resulting in translation of the wedge, landward extension and seaward contraction, accompanied by Couette flow in the underlying salt. The effects of water: (i) increase solid and fluid pressures in the sediments; (ii) reduce the head to toe differential pressure in the salt and (iii) act as a buttress to oppose failure and translation of the sediment wedge. The magnitude of the translation velocity upon failure is reduced by the effects of water. The subsequent deformation is investigated using a 2D finite‐element model that includes the effects of the submarine setting and hydrostatic pore pressures. The model quantitatively simulates a 2D approximation of the evolution of natural sedimentary basins on continental margins that are formed above salt. Sediment progradation above a viscous salt layer results in formation of landward extensional basins and listric normal growth faults as well as seaward contraction. At a later stage, an allochthonous salt nappe overthrusts the autochthonous limit of the salt. The nature and distribution of major structures depends on the sediment properties and the sedimentation pattern. Strain weakening of sediment favours landward listric growth faults with formation of asymmetric extensional depocentres. Episodes of low sediment influx, with partial infill of depocentres, produce local pressure gradients in the salt that result in diapirism. Diapirs grow passively during sediment aggradation.     

Instabilities of fluid conduits in a flowing earth — are plates lubricated by the asthenosphere?

Summary A laboratory and theoretical study of the stability of conduits of buoyant fluid in a viscous shear flow has been conducted. The object of the study is to explain the formation of discrete islands in island chains such as the Hawaiian Emperor seamount chain, and to investigate a new method by which the variation of shear with depth in the mantle may be determined. The conduits were made by injecting oil into a more viscous oil of greater density. Initially a growing chamber of lower viscosity oil formed near the injector, but when the chamber got sufficiently large it rose as a buoyant spheroid. Behind this trailed a vertical cylindrical conduit through which fluid could continue to rise to the surface as long as the source continued. If the more viscous fluid was sheared laterally the conduit was gradually rotated to a more horizontal position. The diameter of the conduit increased with time due to a decreasing component of gravitational force along the axis of the conduit. When the conduit was tilted to more than 60° with the vertical, it began to go unstable by developing bumps which ultimately initiated a new chamber which rose to a new spot. In addition, if the Reynolds number of the conduit was greater than approximately ten, an axisymmetric wavy instability appeared in the walls of the conduit and the conduit had to be tilted less before a new chamber was initiated. If shear under the Pacific plate has to tilt buoyant mantle plumes to as much as 60° to form the relatively regular island chains associated with hot spots, most of the shear would be found in a zone with a vertical extent of less than 200 km.     

绿洲和沙漠下垫面状态对大气边界层特征影响的数值模拟

采用两维高分辩率边界层数值模式,并与一个包括植被和土壤层的生物一大气能量传输模式(BATS)耦合,模拟研究绿洲和沙漠下垫面状态对大气边界层特征的影响。结果表明,沙漠中的绿洲对大气产生"冷湿效应",使之上空形成冷湿气柱;绿洲之间的沙漠对大气呈"暖干效应",使上空形成热干气柱。在水平平流的作用下,在绿洲下游的沙漠边缘形成降水峰值,有利于降水,但沙漠区下游的绿洲则相对于整个绿洲区降水偏少,不利于形成降水。     

Electrical conductivity models for the continental crust based on laboratory measurements on high-grade metamorphic rocks

Summary. Deep electrical conductivity soundings are increasingly being used as an additional source of information regarding the nature of the lower continental crust. However, a lack of relevant laboratory-based conductivity measurements makes interpretation of such soundings difficult. Laboratory measurements have been made on saturated and unsaturated samples of possible lower crustal rock types subjected to confining pressures up to 0.4 GPa, temperatures up to 300°C, and with variable pore fluid pressure up to the confining pressure. Extrapolation of these results suggests that the surprisingly high conductivities deduced for depths of approximately 20 km in certain stable continental areas may result from a combination of basic rock type and high pore fluid pressures, for whereas the conductivities measured in acid rock types can be explained in terms of conduction through the pore fluid alone, the conductivities measured in basic rock types imply enhanced conduction presumably through the matrix or along grain boundaries. The lower conductivities deduced from field experiments for the upper crust may be due to more acid rock types and/or lower pore fluid pressures, perhaps due to hydration reactions. In areas where the high conductivity layer is coincident with a low velocity layer an explanation in terms of changing pore fluid pressure, i.e. low to high, with increasing depth seems more likely.     

长江源区五道梁的土壤热状况研究

活动层土壤热状况是寒区陆面物理过程研究的重要内容之一。利用五道梁能量收支观测站1993年9月～2000年12月份实测辐射及土壤热通量资料结合五道梁气象站1961-2010时段的气象资料分析了近50 a来该地区活动层土壤的热状况。结果表明：五道梁地区土壤热通量有显著的年际、年代际变化;20世纪60～80年代,土壤热通量小于0.0 W/m²,活动层土壤以放热为主,自90年代以来,土壤热通量大于0.0 W/m²,活动层土壤以吸热为主。过去50 a中该地土壤热通量呈现增大趋势,平均每10 a土壤热通量增大0.31 W/m²。土壤热通量随净辐射的增大而增大。土壤热平衡系数的变化特点与土壤热通量的变化特点一致。60～80年代,活动层土壤热平衡系数<1,该地区冻土相对比较稳定,而自90年代以来此间土壤热平衡系数<1,表明该地多年冻土呈现出退化迹象。活动层土壤热平衡系数可表示为气温、地表温度及水汽压的函数。     

Numerical modelling of rise and fall of a dense layer in salt diapirs

Numerical models are used to study the entrainment of a dense anhydrite layer by a diapir. The anhydrite layer is initially horizontally embedded within a viscous salt layer. The diapir is down-built by aggradation of non-Newtonian sediments ( n = 4, constant temperature) placed on the top of the salt layer. Several parameters (sedimentation rate, salt viscosity, perturbation width and stratigraphic position of the anhydrite layer) are studied systematically to understand their role in governing the entrainment of the anhydrite layer. High sedimentation rates during the early stages of the diapir evolution bury the initial perturbation and, thus, no diapir forms. The anhydrite layer sinks within the buried salt layer. For the same sedimentation rate, increasing viscosity of the salt layer decreases the rise rate of the diapir and reduces the amount (volume) of the anhydrite layer transported into the diapir. Model results show that viscous salt is capable of carrying separate blocks of the anhydrite layer to relatively higher stratigraphic levels. Varying the width of the initial perturbation (in our calculations 400–800 m), from which a diapir triggers, shows that wider diapirs can more easily entrain an embedded anhydrite layer than the narrower diapirs. The anhydrite layer is entrained as long as rise rate of the diapir exceeds the descent rate of the denser anhydrite layer. We conclude that the four parameters mentioned above govern the ability of a salt diapir to entrain an embedded dense layer. However, the model results show that the entrained blocks inevitably sink back if the rise rate of the diapir is less than the rate of descent of the anhydrite layer or the diapir is permanently covered by a stiff overburden in case of high sedimentation rates.     

Seasonal variations of the near surfacelayer parameters over the Antarctic ice sheet in Princess Elizabeth Land,East Antarctica

Analysis of sensible heat flux(Qh),latent heat flux(Qe),Richardson number(Ri),bulk transport coefficient(Cd) and katabatic winds are presented by using the meteorological data in the near surface layer from an automatic weather station(AWS) in Princess Elizabeth Land,East Antarctica ice sheet and the data of corresponding period at Zhongshan station in 2002.It shows that annual mean air temperature at LGB69 is-25.6°C,which is 16.4°C lower than that at Zhongshan,where the elevation is lower and located on the coast.The temperature lapse rate is about 1.0°C/110 m for the initial from coast to inland.The turbulence heat flux at LGB69 displays obvious seasonal variations with the average sensible heat flux-17.9 W/m2 and latent heat flux-0.9 W/m2.The intensity(Qh+Qe) of coolling source is-18.8 W/m2 meaning the snow surface layer obtains heat from atmosphere.The near surface atmosphere is near-neutral stratified with bulk transport coefficients(Cd) around 2.8×10-3,and it is near constant when the wind speed higher than 8 m/s.The speed and the frequency of easterly Katabatic winds at LGB69 were higher than that at Zhongshan Station.     

Geometry of half-grabens containing a mid-level viscous décollement

In this work, we explore by means of analogue models how different basin-bounding fault geometries and thickness of a viscous layer within the otherwise brittle pre-rift sequence influence the deformation and sedimentary patterns of basins related to extension. The experimental device consists of a rigid wooden basement in the footwall to simulate a listric fault. The hangingwall consists of a sequence of pre-rift deposits, including the shallow interlayered viscous layer, and a syn-rift sequence deposited at constant intervals during extension. Two different geometries exist of listric normal faults, dip at 30 and 60° at surface. This imposes different geometries in the hangingwall anticlines and their associated sedimentary basins. A strong contrast exists between models with and without a viscous layer. With a viscous décollement, areas near the main basement fault show a wide normal drag and the hangingwall basin is gently synclinal, with dips in the fault side progressively shallowing upwards. A secondary roll-over structure appears in some of the models. Other structures are: (1) reverse faults dipping steeply towards the main fault, (2) antithetic faults in the footwall, appearing only in models with the 30° dipping fault and silicone-level thicknesses of 1 and 1.5 cm and (3) listric normal faults linked to the termination of the detachment level opposite to the main fault, with significant thickness changes in the syn-tectonic units. The experiments demonstrate the importance of detachment level in conditioning the geometry of extensional sedimentary basins and the possibility of syncline basin geometries associated with a main basement fault. Comparison with several basins with half-graben geometries containing a mid-level décollement supports the experimental results and constrains their interpretation.     

A New Model for Heat Flow in Extensional Basins: Estimating Radiogenic Heat Production

Radiogenic heat production (RHP) represents a significant fraction of surface heat flow, both on cratons and in sedimentary basins. RHP within continental crust—especially the upper crust—is high. RHP at any depth within the crust can be estimated as a function of crustal age. Mantle RHP, in contrast, is always low, contributing at most 1 to 2 mW/m² to total heat flow. Radiogenic heat from any noncrystalline basement that may be present also contributes to total heat flow. RHP from metamorphic rocks is similar to or slightly lower than that from their precursor sedimentary rocks. When extension of the lithosphere occurs—as for example during rifting—the radiogenic contribution of each layer of the lithosphere and noncrystalline basement diminishes in direct proportion to the degree of extension of that layer. Lithospheric RHP today is somewhat less than in the distant past, as a result of radioactive decay. In modeling, RHP can be varied through time by considering the half lives of uranium, thorium, and potassium, and the proportional contribution of each of those elements to total RHP from basement. RHP from sedimentary rocks ranges from low for most evaporites to high for some shales, especially those rich in organic matter. The contribution to total heat flow of radiogenic heat from sediments depends strongly on total sediment thickness, and thus differs through time as subsidence and basin filling occur. RHP can be high for thick clastic sections. RHP in sediments can be calculated using ordinary or spectral gamma-ray logs, or it can be estimated from the lithology.     

塔克拉玛干沙漠夏季晴空对流边界层大涡模拟

为了探索塔克拉玛干沙漠夏季晴空对流边界层湍流结构和热对流运动规律,利用沙漠腹地探空及地表通量观测资料,开展了晴空对流边界层的大涡模拟研究。结果表明：（1）沙漠夏季晴空条件下,对流边界层湍能主要由地表热力浮力对流产生,机械剪切对边界层湍能的贡献较小,小尺度湍涡对湍能的耗散随高度呈减弱趋势,边界层湍能变化呈现间歇性特点。（2）沙漠夏季晴空边界层中存在着有组织的热对流泡现象,热泡最大上升速度可超过4.0 m·s^-1;沙漠热对流运动一般呈羽状和网状分布特征,在上升运动区周围伴随有大片的下沉辐散区域。（3）地表感热和逆温层顶盖强度是控制和影响沙漠对流边界层发展的两个重要因素,感热增大,对流边界层变暖且高度升高;感热减小,对流边界层变冷且高度降低。在感热不变的条件下,逆温层顶盖强度越强,越不利于对流边界层发展,反之则相反。     

Magnetic anisotropy produced by magma flow: theoretical model and experimental data from Ferrar dolerite sills (Antarctica)

Volcanic rocks forming sills, dykes or lava flows may display a magnetic anisotropy derived from the viscous flow during their emplacement. We model a sill as a steady-state flow of a Bingham fluid, driven by a pressure gradient in a horizontal conduit. The magma velocity as a function of depth is calculated from the motion and constitutive equations. Vorticity and strain rate are determined for a reference system moving with the fluid. The angular velocity and the orientation of an ellipsoidal magnetic grain immersed in the fluid are calculated as functions of time or strain. Magnetic susceptibility is then calculated for a large number of grains with a uniform distribution of initial orientations. It is shown that the magnetic lineation oscillates in the vertical plane through the magma flow direction, and that the magnetic foliation plane changes periodically from horizontal to vertical. The results are compared with the magnetic fabric of Ferrar dolerite sills (Victoria Land, East Antarctica) derived from low-field susceptibility measurements.     

城市不同下垫面的能量平衡及温度差异模拟

城市能量平衡是研究城市热岛效应的物理基础。利用北京市教学植物园2010年的实测数据,设置不同类型下垫面(植被覆盖类型:林地、草地和不透水层覆盖类型:道路、房屋),利用局地尺度城市气象参数化方案模拟并分析了相同气象条件和净辐射通量输入下,不同类型下垫面的显热、潜热通量及蒸散降温效应的差异。结果显示:(1)不同类型下垫面的各能量支出项有明显差异,植被覆盖区域和不透水层覆盖区域的波文比年均值分别为0.28和4.60,且在植被生长季差异较大;(2)城市扩展过程中道路、房屋替换林地、草地的过程,也是显热增加而潜热减少的过程。植被层向不透水层转换的过程中,显热通量年均增加32.74W/m²,潜热通量减少38.87W/m²,储热通量增加7.95W/m²;(3)理论上,植被蒸散的年降温效应使单位面积植被覆盖区域的气温比不透水层区域可低2.63℃。     

Salt tectonics driven by differential sediment loading: stability analysis and finite-element experiments

At many continental margins, differential sediment loading on an underlying salt layer drives salt deformation and has a significant impact on the structural evolution of the basin. We use 2‐D finite‐element modelling to investigate systems in which a linear viscous salt layer underlies a frictional‐plastic overburden of laterally varying thickness. In these systems, differential pressure induces the flow of viscous salt, and the overburden experiences updip deviatoric tension and downdip compression. A thin‐sheet analytical stability criterion for the system is derived and is used to predict conditions under which the sedimentary overburden will be unstable and fail, and to estimate the initial velocities of the system. The analytical predictions are in acceptable agreement with initial velocity patterns of the numerical models. In addition to initial stability analyses, the numerical model is used to investigate the subsequent finite deformation. As the systems evolve, overburden extension and salt diapirism occur in the landward section and contractional structures develop in the seaward section. The system evolution depends on the relative widths of the salt basin and the length scale of the overburden thickness variation. In narrow salt basins, overburden deformation is localised and characterised by high strain rates, which cause the system to reach a gravitational equilibrium and salt movement to cease earlier than for wide salt basins. Sedimentation enhances salt evacuation by maintaining a differential pressure in the salt. Continued sedimentary filling of landward extensional basins suppresses landward salt diapirism. Sediment progradation leads to seaward propagation of the landward extensional structures and depocentres. At slow sediment progradation rates, the viscous flow can be faster than the sediment progradation, leading to efficient salt evacuation and salt weld formation beneath the landward section. Fast sediment progradation suppresses the viscous flow, leaving salt pillows beneath the prograding wedge.