Artificial tracers for geothermal reservoir studies

Safe disposal of thermally spent geothermal brines that contain environmentally hazardous constituents is commonly obtained by reinjection. The reinjection process also serves to maintain reservoir pressure, enhance thermal recovery, and eliminate possible compactional subsidence. To avoid premature thermal breakthrough of reinjected fluids, tracer tests are employed for detection and evaluation of preferential path networks. In this paper some promising tracers that have not received much attention in geothermal reservoir studies are discussed, and a comprehensive tabulation of field sites of artificial tracer utilization is presented. Chemical and transport processes responsible for tracer retention by the formation of reservoir solids, as well as available tracer detection techniques, are emphasized.     

Turbidity and suspended solids variations downstream of a regulating reservoir

A controlled reservoir release from Llyn Celyn to the Afon Tryweryn, Wales, U.K., has been used to study suspended load and turbidity variations. Turbidity was monitored continuously at two sites and 235 suspended solids samples were obtained at these and three additional sites during the passage of the release wave. The results are compared with data for a natural tributary flood event. The reservoir release data relate to sediment source depletion and reflects changing sources along the channel. Close to the dam, fine organic matter dominates the seston which scanning electron microscopy revealed to be predominantly allochthonous organic matter, with algal fragments and inorganic diatom frustules, derived from the periphyton of the channel bed. Coulter Counter analysis showed the seston to be relatively coarse with a median particle-size of 20 μm. Within 3 km of the dam, however, minerogenic particles dominate the sediment load of which more than 90 per cent is finer than 10 μm. This represents the flushing of channel-bed accumulations derived from tributary sources. The relationships between suspended sediment concentration and turbidity during the release are characterized by a marked, anticlockwise hysteresis. This contrasts with the clockwise hysteresis for the tributary flood event, but the different relationships cannot be explained by particle-size variations alone; seston composition also appears to be an important control.     

基于GF-1影像的洞庭湖区水体水质遥感监测

湖泊水质监测是有效开展湖泊水环境综合管理与水污染防治实施的基础,也是湖泊藻华风险评估与生态安全建设的重要依据。本文基于GF-1号影像对2014-2016年洞庭湖水体的叶绿素a浓度、悬浮物浓度和透明度展开遥感监测,结果表明：叶绿素a主要集中在水流速度较慢的安乐湖、大小西湖和东洞庭湖西部地区,其他区域水体扰动力大,叶绿素含量a较低。透明度从北到南递增,与悬浮物浓度的分布趋势相反,符合常规监测规律。东洞庭湖水质较南洞庭湖和西洞庭湖差,水污染程度处于全湖最高水平。GF-1数据可精确反映叶绿素a浓度、悬浮物浓度和透明度指数的空间变化规律,也为后续高分遥感影像湖泊水质监测的应用研究提供了重要参考。     

Impact of NaSO4 dominated ionic strength on trace metal removal products in vertical flow bioreactors

Vertical flow bioreactors (VFBR) are often used as a component of passive treatment systems (PTS) to treat mine drainage. One of the primary purposes of VFBR is to remove trace metals from mine drainage and retain them in the organic substrate. Elevated ionic strength may impact the performance of VFBR and affect their ability to remove trace metals. A paired-comparison study was performed to determine how products of trace metal removal may change when ionic strength is elevated due to increased concentrations of common contributors to TDS, specifically sodium and sulfate. A sequential extraction procedure (SEP) and acid-volatile sulfide/simultaneously extracted metals analyses (AVS/SEM) were used to determine dominant Cd, Mn, Ni, Pb, and Zn removal products in bench-scale VFBR. Elevated ionic strength resulted in more Pb being retained in the substrates as an insoluble sulfide and less Mn being removed via adsorption to the substrates. An increase in ionic strength had a greater impact on adsorption when sulfate reduction was inhibited, with percentages of Mn and Zn removed via this mechanism decreasing by at least half. This finding could be particularly significant at the start of VFBR operation when adsorption is expected to be the primary removal mechanism.     

Elastic wave velocities and permeability of cracked rocks

Cracks play a major role in most rocks submitted to crustal conditions. Mechanically, cracks make the rock much more compliant. They also make it much easier for fluid to flow through any rock body. Relying on Fracture Mechanics and Statistical Physics, we introduce a few key concepts, which allow to understand and quantify how cracks do modify both the elastic and transport properties of rocks. The main different schemes, which can be used to derive the elastic effective moduli of a rock, are presented. It is shown from experimental results that an excellent approximation is the so-called non-interactive scheme. The main consequences of the existence of cracks on the elastic waves is the development of elastic anisotropy (due to the anisotropic distribution of crack orientations) and the dispersion effect (due to microscopic local fluid flow). At a larger scale, macroscopic fluid flow takes place through the crack network above the percolation threshold. Two macroscopic fluid flow regimes can be distinguished: the percolative regime close to the percolation threshold and the connected regime well above it. Experimental data on very different rock types show both of these behaviors.     

珠江口悬浮泥沙迁移数值模拟

建立了珠江口海域三维悬浮泥沙的非饱和输沙数学模型,并与珠江口三维水动力斜压模型耦合,对悬沙迁移分布进行了模拟。模型由4个点的逐时实测含沙量过程进行了验证。各点模拟含沙量与实测含沙量吻合较好,表层分布与同期珠江口悬沙分布遥感图像基本一致.模拟结果表明,珠江口海域悬沙分布分层明显,河口附近水域大多为底层含沙量大于表层,但在盐淡水交汇处出现中层含沙量最小的情况总体上,自各个口门输出的泥沙受沿岸流作用向西南万向输送明显。大多数河口落潮时相对涨潮时含沙量等值线外移,反映珠江口水域悬浮泥沙主要来自河流。     

The vertical attenuation of light in Charlotte Harbor, a shallow, subtropical estuary, south-western Florida

The relative contribution of different components to the attenuation of photosynthetically active radiation was determined in the Charlotte Harbor estuarine system based on laboratory and in situ measurements. Agreement between laboratory and in situ measurements of the attenuation coefficient (k_t) was good (r² = 0·92). For all in situ measurements (n = 100), suspended, non-chlorophyll matter accounted for an average of 72% of k_t, dissolved matter accounted for 21%, suspended chlorophyll for 4%, and water for the remaining 3%.For individual determinations, suspended non-chlorophyll matter, dissolved matter, suspended chlorophyll, and water, each accounted for as much as 99%, 79%, 21%, and 18% of k_t. Attenuation by suspended matter was greatest near the mouth of the northern tidal rivers and was variable over the rest of the estuarine system. Attenuation by dissolved matter was greatest in the brackish tidal rivers and decreased with increasing salinity. Attenuation due to dissolved matter was positively correlated with water color. The source of the color was basin runoff. Wavelength transmittance changed along the salinity gradient. Maximum transmittance shifted from 500 to 600 nm in gulf waters to 650 to 700 nm in colored, brackish waters. Dissolved matter was primarily responsible for the large attenuation at short wavelengths (400–500 nm).     

西藏高原达则错湖泊铀富集特征

达则错位于班怒构造带的次级盆地中,湖水最深为36 m,平均深度为20.8 m。湖表水体矿化度17.27~20.27 g/L,平均为19.46 g/L,水化学类型为(CO₃+HCO₃)·SO₄-Na型,属弱度碳酸盐型咸水湖;在垂向上,由浅及深矿化度略有增加,水化学类型不变。湖表水体铀浓度264~324μg/L,平均铀浓度为286μg/L,8 m、18 m和28 m深度铀浓度平均值分别为288μg/L、290μg/L和300μg/L。湖底沉积物铀含量为2.31~4.08μg/g,平均铀含量为3.16μg/g,略高于我国东海大陆架海底沉积物的铀含量。达则错湖水的铀元素来自于周边岩体和地层,通过河水迁移到湖泊中。在河口混合带,铀酰离子部分吸附于悬浮物上,到湖区以碳酸铀酰的形式存在于水体中,沉淀于湖底的悬浮物铀含量没有明显增加。