Effects of fracture lineaments and in-situ rock stresses on groundwater flow in hard rocks: a case study from Sunnfjord, western Norway

Systematic field mapping of fracture lineaments observed on aerial photographs shows that almost all of these structures are positively correlated with zones of high macroscopic and mesoscopic fracture frequencies compared with the surroundings. The lineaments are subdivided into zones with different characteristics: (1) a central zone with fault rocks, high fracture frequency and connectivity but commonly with mineral sealed fractures, and (2) a damage zone divided into a proximal zone with a high fracture frequency of lineament parallel, non-mineralized and interconnected fractures, grading into a distal zone with lower fracture frequencies and which is transitional to the surrounding areas with general background fracturing. To examine the possible relations between lineament architecture and in-situ rock stress on groundwater flow, the geological fieldwork was followed up by in-situ stress measurements and test boreholes at selected sites. Geophysical well logging added valuable information about fracture distribution and fracture flow at depths. Based on the studies of in-situ stresses as well as the lineaments and associated fracture systems presented above, two working hypotheses for groundwater flow were formulated: (i) In areas with a general background fracturing and in the distal zone of lineaments, groundwater flow will mainly occur along fractures parallel with the largest in-situ rock stress, unless fractures are critically loaded or reactivated as shear fractures at angles around 30° to σ_H; (ii) In the influence area of lineaments, the largest potential for groundwater abstraction is in the proximal zone, where there is a high fracture frequency and connectivity with negligible fracture fillings. The testing of the two hypotheses does not give a clear and unequivocal answer in support of the two assumptions about groundwater flow in the study area. But most of the observed data are in agreement with the predictions from the models, and can be explained by the action of the present stress field on pre-existing fractures.     

塔里木盆地岩石圈热-流变学结构和新生代热体制

塔里木盆地是我国特大型沉积盆地,也是“西气东输”工程的重要战略基地。利用盆地区大量的地温及岩石热物性参数并结合地热学知识分析了塔里木盆地的现代地温场、热演化和岩石圈热-流变学结构,并进一步讨论了地热场和岩石圈性质对成盆、成烃和成藏的意义。研究结果表明塔里木盆地现今平均大地热流为45mW/m2,平均地温梯度为18~20℃/km;整体上具有低温冷盆的特征。地温场的展布具有明显的横向差异,不同构造单元的地温场特征相差较大:坳陷部位具有较低的地温,隆起区具有较高的地热特征。热演化模拟表明盆地自成盆以来经历了从震旦纪—奥陶纪高热流(“热”盆)、志留纪—晚古生代热衰减(“热”盆向“冷”盆过渡)、中生代稳定的热演化(低热流“冷”盆阶段)、新生代岩石圈挠曲热演化等阶段。“热”岩石圈厚度为205~230km,有效弹性厚度(Te)达66±7km,脆-韧性转换深度为25~28km,岩石圈总强度为1.6×1013~7.8×1013N/m。盆地区的岩石圈表现为地温低、强度高的刚性块体,具有整体变形特征。受印度-欧亚大陆碰撞的远程效应影响,塔里木盆地作为刚性块体进行应力传递,盆地周边产生强烈变形,表现山脉的急剧隆升和盆地边缘的快速挠曲沉降。这一动力学过程造成地层内部流体趋于流向山前隆起带,并对油气成藏和分布具有重要的控制作用。     

利用毛管压力曲线分形分维方法研究流动单元

利用取心井铸体薄片获得的图像资料和毛管压力曲线,通过图像分形几何学方法以分维数的形式定量地表征出了复杂的微观孔隙喉道结构特征,发现能够很好地划分和评价孔隙岩石中油、气、水的渗流差异,可以用于储层微观流动单元表征。文中阐述了岩石微观孔隙喉道结构分形的理论基础、计算方法和应用于表征流动单元的依据。建立了中国西部砾岩低渗透油藏微观孔隙喉道分维数与孔隙度、渗透率之间计算图版,据此在油藏中利用常规测井资料获得的孔隙度、渗透率参数计算微观孔隙喉道分维数,开展全油藏流动单元划分与评价,取得了良好的效果。研究结果表明,利用毛管压力曲线分形分维方法研究储层微观流动单元是一种很有效的途径。     

晶体及矿物颗粒大小对岩土材料力学性质的影响

岩石常见较大的晶体或者矿物颗粒,混凝土中是骨料,通过团簇模拟大颗粒的力学行为、团簇可以破裂。根据设计的相同数量、相同位置、不同半径的大颗粒数值单轴压缩试验,在虚拟试验条件下,考察了颗粒大小对材料力学响应的影响。通过分析颗粒材料的破裂形态、裂纹扩展过程、应力-应变曲线和破裂能量演化规律发现：大颗粒具有明显的增强特性,有阻止裂纹扩展的作用,破裂多绕大颗粒发展;增强幅度随颗粒半径的增加呈单增趋势,半径较小时,增强效果不明显。     

Identification of diffusion parameters in a nonlinear convection–diffusion equation using the augmented Lagrangian method

Numerical identification of diffusion parameters in a nonlinear convection–diffusion equation is studied. This partial differential equation arises as the saturation equation in the fractional flow formulation of the two-phase porous media flow equations. The forward problem is discretized with the finite difference method, and the identification problem is formulated as a constrained minimization problem. We utilize the augmented Lagrangian method and transform the minimization problem into a coupled system of nonlinear algebraic equations, which is solved efficiently with the nonlinear conjugate gradient method. Numerical experiments are presented and discussed. This work was partially supported by the Research Council of Norway (NFR), under grant 128224/431.     

Experimental Study on Mine Spoils During Superficial Geochemistry Processes

Based on the mineral and chemical compositions of spoils taken from the Shilu Cu-Mo deposit and Hetai gold deposit, the leaching and batch experiments were made on spoils taken from these two deposits using the leaching column designed by the authors. The experimental results showed that it is not always true that the mine drainage is acidic. Its acidity depends on acid-buffering capacity of gangue, host rock and its alteration mineral assemblage. The composition of the drainage water is related with the interaction between superficial or underground water and solid materials in the spoils, including minerals, hydroxides and amorphous substances. The leaching extent of the element is related with its occurrence form in the deposit. The preferential flow results in leaching-out of heavy metals in large amounts. So it is important to prevent the generating of preferential flow in the system. The results will provide very important grounds for the comprehensive management of land and ecological rehabilitation of the mine site.     

熔体结构与酸性熔岩的某些特征

在流纹质岩浆中,存在两种不混溶的熔体,一种熔体富SiO_2贫FeO,另一种则相反。从熔体结构的角度看,前一种熔体富桥氧,后者则富自由氧。水的解聚作用可以改变流纹质岩浆的结构,即降低它的聚合程度,因此,含水流纹岩浆的粘度低于玄武岩浆的粘度,从而使流纹岩中流纹构造发育。 实际工作中应避免混淆流纹岩与酸性熔结凝灰岩。     

随机扩散水质模型研究

考虑湖泊中影响总磷沉积过程的众多生态因子的变化过程,假定湖泊中总磷沉积过程由标准布朗运动驱动,建立了一个总磷浓度的随机扩散方程,推广确定性富营养化Vollenweider水质模型为随机扩散模型,获得了总磷浓度过程的解析解,进而求出了总磷浓度过程的均值和方差,指出了一种依据沉积系数调控湖泊中总磷浓度的方法。模型被应用于巢湖总磷浓度过程的模拟。     

Autogenic avulsion,channelization and backfilling dynamics of debris‐flow fans

Alluvial fans develop their semi‐conical shape by quasi‐cyclic avulsions of their geomorphologically active sector from a fixed fan apex. On debris‐flow fans, these quasi‐cyclic avulsions are poorly understood, partly because physical scale experiments on the formation of fans have been limited largely to turbidite and fluvial fans and deltas. In this study, debris‐flow fans were experimentally created under constant extrinsic forcing, and autogenic sequences of backfilling, avulsion and channelization were observed. Backfilling, avulsion and channelization were gradual processes that required multiple successive debris‐flow events. Debris flows avulsed along preferential flow paths given by the balance between steepest descent and flow inertia. In the channelization phase, debris flows became progressively longer and narrower because momentum increasingly focused on the flow front as flow narrowed, resulting in longer run‐out and deeper channels. Backfilling commenced when debris flows reached their maximum possible length and channel depth, as defined by channel slope and debris‐flow volume and composition, after which they progressively shortened and widened until the entire channel was filled and avulsion was initiated. The terminus of deposition moved upstream because the frontal lobe deposits of previous debris flows created a low‐gradient zone forcing deposition. Consequently, the next debris flow was shorter which led to more in‐channel sedimentation, causing more overbank flow in the next debris flow and resulting in reduced momentum to the flow front and shorter runout. This topographic feedback is similar to the interaction between flow and mouth bars forcing backfilling and transitions from channelized to sheet flow in turbidite and fluvial fans and deltas. Debris‐flow avulsion cycles are governed by the same large‐scale topographic compensation that drives avulsion cycles on fluvial and turbidite fans, although the detailed processes are unique to debris‐flow fans. This novel result provides a basis for modelling of debris‐flow fans with applications in hazards and stratigraphy.     

等效水力隙宽和水力梯度对岩体裂隙网络非线性渗流特性的影响

等效水力隙宽和水力梯度是影响岩体裂隙网络渗流特性的重要因素。制作裂隙网络试验模型,建立高精度渗流试验系统;求解纳维-斯托克斯方程,模拟流体在裂隙网络内的流动状态,研究等效水力隙宽和水力梯度对非线性渗流特性的影响。结果表明,当水力梯度较小时,等效渗透系数保持恒定的常数,流体流动属于达西流动区域,流量与压力具有线性关系,可采用立方定律计算流体流动;当水力梯度较大时,等效渗透系数随着水力梯度的增加而急剧减少,流体流动进入强惯性效应流动区域,流量与压力具有强烈的非线性关系,可采用Forchheimer方程计算流体流动。随着等效水力隙宽的增加,区别线性和非线性流动区域的临界水力梯度呈幂函数关系递减。当水力梯度小于临界水力梯度时,控制方程可选立方定律;当水力梯度大于临界水力梯度时,控制方程可选Forchheimer方程,其参数A和B可根据经验公式计算得到。其研究结果可为临界水力梯度的确定及流体流动控制方程的选取提供借鉴意义。