动电测井实验研究Ⅱ:伴随动电场和界面动电场

动电效应指孔隙介质中与固/液界面的双电层和孔隙流体渗流有关的弹性-电磁耦合现象,探索基于动电效应的勘探和测井新方法则是石油工业重点关注的研究方向之一.本文对流体饱和孔隙介质中的动电效应进行了实验测量研究,记录到了不同模型井中伴随声波的动电转换信号和界面动电转换信号,对比分析了这两种动电信号的产生条件及传播特性,验证了理论分析结果,并进一步研究了动电信号的分波成分及其与声波信号的关系,探讨了声源激发模式、电极接收方式及数据处理方法对动电信号的影响,为动电测井仪器设计奠定实验基础.     

Spatiotemporal changes of land desertification sensitivity in northwest China from 2000 to 2017

Sensitivity assessment is useful for monitoring land desertification.Research into how to prevent and control desertification is also important.In the arid region of northwest China,desertification is becoming worse and is a serious problem that affects local sustain-able development.Based on remote-sensing and geographic information system technology,this study establishes a"soil-terrain-hydrology-climate-vegetation"desertification sensitivity comprehensive evaluation system to reflect the spatiotemporal changes of land desertifica-tion,and proposes a spatial distance model to calculate a desertification sensitivity index.The spatiotemporal change characteristics of land desertification sensitivity in northwest China are quantitatively assessed from 2000 to 2017.Moreover,the main driving factors are ana-lyzed using the geographical detector method.The results show the following.(1)Terrain,soil,climate,vegetation and hydrology affect and restrict each other,and constitute the back-ground conditions of the distributions and changes of sensitivity to desertification in northwest China.(2)Desertification sensitivity generally displays a low distribution characteristic on the periphery of the area and a high one in the interior.The low-sensitivity regions are mainly in the five major mountain ranges(Altai Mountains,Tianshan Mountains,Kunlun Mountains,Altun Mountains and Qilian Mountains),while the high-sensitivity regions are mainly in re-gions such as the Junggar Basin,the Tarim Basin and the Inner Mongolia Plateau,as well as the Taklimakan Desert,Badain Jaran Desert and Tengger Desert.The spatial distribution of desertification sensitivity is obviously regional,and the high-and low-sensitivity regions have clear boundaries and a concentrated distribution.(3)With regard to spatiotemporal evolution,changes in desertification sensitivity since 2000 have been predominantly stable,and the overall sensitivity has displayed a slowly decreasing trend,indicating that potential desertifi-cation regions are decreasing annually and that some achievements have been made in the control of regional desertification. (4) Soil and climate play a direct role in the driving factors of desertification in northwest China, and these have been found to be the most important in-fluential factors. Vegetation is the most active and basic factor in changing the sensitivity. In addition, topography and hydrology play a role in restricting desertification changes. So-cio-economic factors are the most rapid factors affecting regional desertification sensitivity,and their impacts tend to be gradually increasing. In general, desertification has been effec-tively controlled in northwest China, and positive results have been achieved in such control.However, against the backdrop of intensified global climate change, increasingly prominent human activities and new normals of socio-economic development, the monitoring, assess-ment and control of desertification in China still have a long way to go.     

Development of Climate and Earth System Models in China: Past Achievements and New CMIP6 Results

The Earth-Climate System Model (ECSM) is an important platform for multi-disciplinary and multi-sphere integration research, and its development is at the frontier of international geosciences, especially in the field of global change. The research and development (R&D) of ECSM in China began in the 1980s and have achieved great progress. In China, ECSMs are now mainly developed at the Chinese Academy of Sciences, ministries, and universities. Following a brief review of the development history of Chinese ECSMs, this paper summarized the technical characteristics of nine Chinese ECSMs participating in the Coupled Model Intercomparison Project Phase 6 and preliminarily assessed the basic performances of four Chinese models in simulating the global climate and the climate in East Asia. The projected changes of global precipitation and surface air temperature and the associated relationship with the equilibrium climate sensitivity under four shared socioeconomic path scenarios were also discussed. Finally, combined with the international situation, from the perspective of further improvement, eight directions were proposed for the future development of Chinese ECSMs.     

Seismoelectric measurements in a porous quartz‐sand sample with anisotropic permeability

Seismoelectric coupling coefficients are difficult to predict theoretically because they depend on a large numbers of rock properties, including porosity, permeability, tortuosity, etc. The dependence of the coupling coefficient on rock properties such as permeability requires experimental data. In this study, we carry out a set of laboratory measurements to determine the dependence of seismoelectric coupling coefficient on permeability. We use both an artificial porous “sandstone” sample, with cracks, built using quartz‐sand and Berea sandstone samples. The artificial sample is a cube with 39% porosity. Its permeability levels are anisotropic: 14.7 D, 13.8 D, and 8.3 D in the x‐, y‐, and z‐directions, respectively. Seismoelectric measurements are performed in a water tank in the frequency range of 20 kHz–90 kHz. A piezoelectric P‐wave source is used to generate an acoustic wave that propagates through the sample from the three different (x, y, and z) directions. The amplitudes of the seismoelectric signal induced by the acoustic waves vary with the direction. The highest signal is in the direction of the highest permeability, and the lowest signal is in the direction of the lowest permeability. Since the porosity of the sample is constant, the results directly show the dependence of seismoelectric coefficients on permeability. Seismoelectric measurements with natural rocks are performed using Berea sandstone 500 and 100 samples. Because the Berea samples are nearly isotropic in permeability, the amplitudes of the seismoelectric signals induced in the different directions are the same within the measurement error. Because the permeability of Berea 500 is higher than that of Berea 100, the amplitude of the seismoelectric signals induced in Berea 500 is higher than those in Berea 100. To determine the relative contributions of porosity and permeability on seismoelectric conversion, we carried out an analysis, using Pride (1994) formulation and Kozeny–Carman relationship; the normalized amplitudes of seismoelectric coupling coefficients in three directions are calculated and compared with the experimental results. The results show that the seismoelectric conversion is related to permeability in the frequency range of measurements. This is an encouraging result since it opens the possibility of determining the permeability of a formation from seismoelectric measurements.     

Analysis on Environmental Pollution in China’s Coastal Ecosystem

In recent years, with the rapid development of China’s economy, the coastal environment is facing large pressure. However, the coastal environment pollution has not attracted much attention as air pollution and land water pollution. Based on the data on economic development and marine ecosystem environmental pollution which collected from the National Bureau of Statistics and China’s coastal marine environmental monitoring, the paper analyzes the overall coastal ecosystem environment pollution in China as well as the four sea areas the Bohai Sea, the Yellow Sea, the East China Sea and South China Sea. The paper finds that the coastal marine environment pollution differ in different sea areas, taking the seawater quality, over-standard pollutants, water quality of rivers entering seas and coastal marine environmental disasters, such as red tide as index. Couple of policy suggestions provided based on research findings.     

Distribution of petroleum hydrocarbons in soils and the underlying unsaturated subsurface at an abandoned petrochemical site,North China

Contamination characteristics of petroleum hydrocarbons in soils and the underlying unsaturated subsurface were analysed by investigating and sampling at different depth of five boreholes named SH1 through SH5 at a typical petrochemical site, North China. Topsoil volatile organic gas measurement revealed that SH‐3 was the center of one pollution plume. Soil samples analysis showed that aromatic hydrocarbons and chlorinated hydrocarbons were major pollutants. Their maximum concentration was found at 6.5 and 14.6 m of SH‐2, 13 m of SH‐5, and 18.5 m of SH‐3. These pollutants are mostly accumulated on the interface between two different lithological layers, especially between the sand and silt clay layers. Denitrifying and iron reducing were main biogeochemical processes in this site. Under the influence of groundwater level fluctuation, free NAPLs passed through the boundary and dissolved into the lower groundwater. Knowledge of these associations between contaminant distributions and affecting factors could have implications for soil and groundwater pollution prevention and control. Copyright © 2013 John Wiley & Sons, Ltd.     

Prospective scenarios of the saltwater intrusion in an estuary under climate change context using Bayesian neural networks

In recent decades, saltwater intrusion over some low-lying coastal regions was deteriorated by rising sea-level and decreasing streamflow in the context of climate change. Though physically-based hydrodynamic models are the most detailed means to simulate salinity processes, they are commonly restricted by data insufficiency issues both in spatial resolution and temporal lasting. This motivates us to build a statistical model enable simulation and scenario analysis for coastal salinity change with limited observations. A Bayesian neural network (BNN) model is built hereby to simulate salinity. It offers more precise estimation compared with the conventional artificial neural network. Meanwhile, the model gives the uncertainty behaviors of the final salinity simulation which is not available for other methods. Future scenarios of salinity change are constructed and analyzed in different time periods on the basis of the validated BNN model. Results indicate that the water quality over lower Pearl River is degrading along with more significant uncertainties. Further analysis suggests that streamflow alteration has a more direct impact on salinity variations than the sea-level change does. The method allows a profound analysis of the potential influence on water quality degradation in coastal and low-lying regions in support of water management and adaptation toward global climate change.     

甘肃永登5.8级地震前兆异常特征及天祝-古浪5.4级地震中短期预报

综合分析了 1 995年 7月 2 2日甘肃永登 5 .8级地震前兆异常时空分布特征 ,主要表现为异常数量多、分布广、密度大、震后响应性异常显著 ,且时空分布具有成组性、空间分布具有相对稳定性。这可能与该区中强震成丛活动方式有关。此研究结果在 1 996年 6月 1日甘肃天祝 -古浪 5 .4级地震中短期预报中发挥了作用     

蓄水初期三峡水库草堂河水-气界面CO2和CH4通量日变化特征及其影响因素

为查明三峡水库蓄水初期典型支流水-气界面CO_2和CH_4通量的日变化特征,采用LGR在线分析仪-通量箱法,于2015年9月初在库腹一级支流草堂河回水区开展连续24 h的定位观测.结果表明,24 h监测期内,支流库湾水-气界面CO_2通量变幅为-81.642~180.991 mg/(m~2·h),呈"昼吸夜放"特征,均值为17.346 mg/(m~2·h),总体为释放特征;CH_4全天均表现为释放状态,释放通量均值为0.064 mg/(m~2·h),呈"昼弱夜强"变化.相关分析结果表明,CH_4和CO_2释放通量与风速呈正相关,与表层水温、溶解氧浓度、叶绿素a浓度呈负相关,说明风速物理扰动、浮游植物光合作用是控制草堂河水-气界面气体通量最重要的环境因素.同时,干-支流相互作用形成的特殊水环境(如异重流、水温分层)也与水-气界面温室气体通量过程密切相关,但是其作用机制更为复杂,应开展进一步系统观测和深入研究.     

基于高分辨率遥感影像的建筑物轮廓信息提取

针对许多领域对建筑物信息更新的迫切要求,提出并发展了一套完整的基于高分辨率遥感影像的建筑物二维轮廓快速提取流程。首先介绍一种利用数学形态学理论进行边缘检测和边缘连接的新方法,然后利用了模式识别和图像分析领域的相关技术(区域标识和特征量测等)进行建筑物二维信息的提取。最后通过Quickbird影像进行了方法验证,试验证明该流程可以快速有效的提取建筑物轮廓信息。