An enhanced stochastic optimization in fracture network modelling conditional on seismic events     

《Computers and Geotechnics》2014

This paper presents an approach to modelling fracture networks in hot dry rock geothermal reservoirs. A detailed understanding of the fracture network within a geothermal reservoir is critically important for assessments of reservoir potential and optimal production design. One important step in fracture network modelling is to estimate the fracture density and the fracture geometries, particularly the size and orientation of fractures. As fracture networks in these reservoirs can never be directly observed there is significant uncertainty about their true nature and the only feasible approach to modelling is a stochastic one. We propose a global optimization approach using simulated annealing which is an extension of our previous work. The fracture model consists of a number of individual fractures represented by ellipses passing through the micro-seismic points detected during the fracture stimulation process, i.e. the fracture model is conditioned on the seismic points. The distances of the seismic points from fitted fracture planes (ellipses) are, therefore, important in assessing the goodness-of-fit of the model. Our aims in the proposed approach are to formulate an appropriate objective function for the optimal fitting of a set of fracture planes to the micro-seismic data and to derive an efficient modification scheme to update the model parameters. The proposed objective function consists of three components: orthogonal projection distances of the seismic points from the nearest fitted fractures, the amount of fracturing (fitted fracture areas) and the volumes of the convex hull of the associated points of fitted fractures. The functions used in the model update scheme allow the model to achieve an acceptable fit to the points and to converge to acceptable fitted fracture sizes. These functions include two groups of proposals: one for updating fracture parameters and the other for determining the size of the fracture network. To increase the efficiency of the optimization, a spatial clustering approach, the Distance-Directional Transform, was developed to generate parameters for newly proposed fractures. A simulated dataset was used as an example to evaluate our approach and we compared the results to those derived using our previously published algorithm on a real dataset from the Habanero geothermal field in the Cooper Basin, South Australia. In a real application, such as the Habanero dataset, it is difficult to determine definitively which algorithm performs better due to the many uncertainties but the number of association points, the number of final fractures and the error are three important factors that quantify the effectiveness of our algorithm.  相似文献   

2013年7月22日甘肃岷县-漳县M_S6.6地震震源破裂过程          下载免费PDF全文

孙蒙  王卫民  王洵  何建坤 《地球物理学报》2015,58(6):1909-1918

2013年7月22日,在甘肃岷县漳县交界处发生MS6.6地震,地震震中位置靠近临潭—宕昌断裂.本文通过构建有限断层模型,利用国家强震动台网中心提供的12条强地面运动三分量资料,通过波形反演方法来研究这次地震的震源破裂过程.结果显示这次地震是发生在甘东南地区岷县—宕昌断裂带东段附近的一次MW6.1级逆冲兼具左旋走滑破裂事件,最大滑动量约为80cm.发震断层走向及滑动性质与岷县—宕昌断裂吻合,推断本次地震与东昆仑断裂向北的扩展和推挤密切相关,是岷县—宕昌断裂进一步活动的结果.  相似文献   

Statistical fusion of two-scale images of porous media     

Azadeh Mohebi  Paul Fieguth  Marios A. Ioannidis 《Advances in water resources》2009

The reconstruction of the architecture of void space in porous media is a challenging task, since porous media contain pore structures at multiple scales. Whereas past methods have been limited to producing samples with matching statistical behavior, the patterns of grey-level values in a measured sample actually say something about the unresolved details, thus we propose a statistical fusion framework for reconstructing high-resolution porous media images from low-resolution measurements. The proposed framework is based on a posterior sampling approach in which information obtained by low-resolution (MRI or X-ray) measurements is combined with prior models inferred from high-resolution microscopic data, typically 2D. In this paper, we focus on two-scale reconstruction tasks in which the measurements resolve only the large scale structures, leaving the small-scale to be inferred. The evaluation of the results generated by the proposed method shows the strong ability of the proposed method in reconstructing fine-scale structures positively correlated with the underlying ground truth. Comparing our method with the recent method of Okabe and Blunt [12], in which the measurements are also used in the reconstruction, we conclude that our method is more robust to the resolution of the measurement, and more closely matches the underlying fine-scale field.  相似文献   

一种波速结构的两步优化反演策略          下载免费PDF全文

师黎静  陶夏新  赵纪生  路建波 《地球物理学报》2009,52(8):2105-2112

借助虚拟反演思路,通过对各种遗传算子不同匹配方式的比较研究,指出了对于频散曲线反演浮点数编码与轮盘赌选择的匹配方式离线性能最好,提出了一种两步优化反演策略.该两步策略利用浮点数编码、轮盘赌选择、浮点数均匀交换与变异算子匹配组成基本遗传算法框架,在此框架基础上施加免疫启发策略和免重复计算加速策略,多次运行,对每次运行结果继续施加模拟退火算法使其至少达到局部最优,最后取得最优解.免疫启发策略充分利用最佳个体的信息加速进化进程,通过对每代的最佳个体施加一服从标准正态分布的随机数来加强对邻近区域的局部搜索,通过标准差的调整也兼顾了对邻近区域以外区域的搜索,将局部搜索和全局搜索有机地结合起来,同时还最大限度地降低了对遗传算法自身进化进程的干扰;免重复计算策略大大减少了正演计算次数,节约了计算成本,提高了反演效率.两步反演策略避免了多次平均法的缺陷,提高了反演结果的稳定性和精度,降低了非惟一性.  相似文献   

MT-重力模拟退火联合反演研究   总被引：8，自引：1，他引：7       下载免费PDF全文

陈华根  李嘉虓  吴健生  于鹏 《地球物理学报》2012,55(2):663-670

为了合理互补不同地球物理场的优势和特点,本文研究了MT与重力模拟退火联合反演的技术.在分析MT与重力联合反演的必要性和可行性后,讨论并研究了主要技术难点及解决方法.重点解决了模型扰动、MT与重力界面不一致的处理、目标函数的加权联合问题,提出MT-重力模拟退火反演(MT-GSA)算法.在此基础上进行了理论模型试验和实际资料处理,取得了较好的效果.  相似文献   

Assessment of the performance of WEPP in purple soil area with simulated rainfall experiments   总被引：1，自引：0，他引：1  

Bin Fu  Yukuan Wang  Pei Xu  Kun Yan 《山地科学学报》2012,9(4):570-579

The water erosion prediction project(WEPP) model is a popular water erosion prediction tool developed on the basis of the physical processes of water erosion.Although WEPP has been widely used around the world,its application in China is still insufficient.In this study,the performance of WEPP used to estimate the runoff and soil loss on purple soil(Calcaric Regosols in FAO taxonomy) sloping cropland was assessed with the data from runoff plots under simulated rainfall conditions.Based on measured soil properties,runoff and erosion parameters,namely effective hydraulic conductivity,inter-rill erodibility,rill erodibility,and critical shear stress were determined to be 2.68 mm h-1,5.54 × 106 kg s-1 m 4,0.027 s m 1 and 3.5 Pa,respectively,by using the recommended equations in the WEPP user manual.The simulated results were not good due to the low Nash efficiency of 0.41 for runoff and negative Nash efficiency for soil loss.After the four parameters were calibrated,WEPP performed better for soil loss prediction with a Nash efficiency of 0.76.The different results indicated that the equations recommended by WEPP to calculate parameters such as erodiblity and critical shear stress are not suitable for the purple soil areas,Sichuan Province,China.Although the predicted results can be accepted by optimizing the runoff and erosion parameters,more research related to the determination of erodibility and critical sheer stress must be conducted to improve the application of WEPP in the purple soil areas.  相似文献   

广东肇庆星湖仙女湖区水生植被的演变   总被引：5，自引：1，他引：4  

陈学年  郭玉娟 《湖泊科学》2005,17(4):334-339

通过在人工构建湿地“小宇宙”系统开展受控模拟实验,研究湿地湿生植物对水环境中磷的吸收和去除规律．本 次研究,选择对比四种不同类型挺水植物和浮叶植物,在不同体系环境条件下(如溶解氧、pH)对水环境中磷吸收和去 除．模拟实验通过对比四种不同类型的水生植物系统,结果显示,不同类型湿生植物对环境中磷的吸收强度和作用方式 有较大的差别．总体来看,实验体系水体中正磷酸盐浓度下降趋势大致呈现的“三阶段”变化模式,即：坡降期、陡降期、平 台期,不同期内磷去除率分别为：35．53%、29．98%和7．20%．  相似文献   

An inverse problem methodology to identify flow channels in fractured media using synthetic steady-state head and geometrical data     

R. Le Goc  J.-R. de Dreuzy  P. Davy 《Advances in water resources》2010

We present a methodology for identifying highly-localized flow channels embedded in a significantly less permeable medium using steady-state head and geometrical data. This situation is typical of fractured media where flows are often strongly channeled at the scales of interest (10 m–1 km). The objective is to identify both geometrical and hydraulic characteristics of the conducting structures. Channels are identified in decreasing order of importance by successive optimizations of an objective function. The identification strategy takes advantage of the hierarchical flow organization to restrict the dimension of the solution space of each individual optimization step. The characteristics of the secondary channels are strongly determined by the main flow channels. The latter are slightly modified by the secondary channels through the addition of a regularization term to the main channel characteristics in the objective function. As the objective function is strongly non-convex with numerous local minima, inversion is performed using a stochastic algorithm (simulated annealing). We assess the possibilities of the hierarchical identification strategy on simple synthetic steady-state flow configurations where hydraulic data are made up of 25 regularly spaced heads and of the boundary conditions. Those flow structures that are dominated by at most two simple channels can be identified with these head data only. Configurations comprising up to three complex and interconnected channels can still be identified with additional geometrical information including the distances of piezometers to their closest channel. The capabilities of the hierarchical identification strategy are limited to flow structures dominated by at most three equivalent flow channels. We finally discuss the perspectives of application of the method to transient-state data obtained on a more restricted number of piezometers.  相似文献   

Effects of Caragana Korshinskii Kom. Cover on runoff,sediment yield and nitrogen loss     

Guan-Hua ZHANG  Guo-Bin LIU  Guo-Liang WANG 《国际泥沙研究》2010,25(3):245-257

Soil erosion is serious in the Loess Plateau of China. Deposition of the eroded sediment in lakes or rivers may lead to eutrophication, because the sediment carries a lot of nutrients. Field experiments were conducted to study soil erosion and loss of nitrogen (N) from a 15o hillslope with 30% (low) or 80% (high) coverage of the shrub Caragana korshinskii Kom. A bare soil plot was used for the comparison. The results showed that Caragana korshinskii cover significantly reduced runoff and soil erosion. In comparison to the bare soil plot, the vegetation covered plots had about 20% less runoff and 65% less sediment. In general, the concentration of N in both runoff water and the eroded sediment decreased with time and approached a steady value. However, the species of nitrate nitrogen (NO3) was exceptional which increased with time slightly. The soil erosion caused an N loss of about 250 mg/m2 for the bare soil plot, the low coverage of Caragana korshinskii reduced the N loss by 20% and the high coverage of Caragana korshinskii reduced the N loss by 40%. Moreover, the amount of total N in eroded sediment was 2 to 3 times higher than the value in runoff water. In the total N loss, the organic N was about 75-80%. Nevertheless, inorganic N in runoff water was 5 to 10 times higher than the value in eroded sediment. The species of NO3 was obviously higher than the species of ammonium nitrogen (NH4). NO3 was the main species of inorganic N loss and was about two thirds of total. The organic N was the main species of N in the eroded sediment.  相似文献   

密度和速度随机分布共网格模型的重力与地震联合反演   总被引：4，自引：3，他引：1       下载免费PDF全文

于鹏  戴明刚  王家林  吴健生 《地球物理学报》2008,51(3):845-852

针对重力与地震联合反演存在的问题,结合已有的研究成果,本文研究实现了速度和密度随机分布共网格单元模型的建模技术,以适应密度和速度剧烈变化的复杂模型及联合反演的计算要求.重力正演利用了该网格的二度半体模型,并进一步改进了地震走时的二维射线追踪计算方法,以适用于速度随机分布的网格介质.结合改进的模拟退火算法,实现了这种共网格条件下的重力与地震资料的同步联合反演.模型试验证明了重力与地震联合反演可以准确确定复杂物性界面的密度和速度结构,适用于物性界面不完全一致和物性变化剧烈的复杂模型,并且联合反演结果要优于单独的重力反演.带先验信息约束下的实际资料的联合反演,进一步证明了该方法的适用性和效果,可提高反演精度并减少多解性.  相似文献