混合域运动分层大气次声非线性传播仿真及其特征

声源识别与参数反演是次声探测应用的重点与难点,研究次声非线性传播模型及其特征是解决上述问题的关键点之一.典型的次声能量传播路径包括平流层及热层折射波波导,信号沿波导进入大气层时,大气密度随高度剧烈变化,波形呈现严重非线性失真与衰减.非线性效应使波形陡化及周期延长,且与依赖于频率的衰减效应相互作用,导致单一时域或频域仿真方法无法兼顾数值计算的稳定性与效率,本文采用时频混合域方法模拟运动分层大气中次声长程非线性传播,其中,Burgers非线性控制方程基于WENO（the weighted essentially non-oscillatory scheme）技术采用时间域变步长有限差分方法实现激波等非连续波的稳定传播,而信号衰减基于Sutherand-Bass系数于频率域进行计算.基于该方法,本文研究了次声沿不同波导路径传播的非线性形变,并分析了声源振幅、大气结构等对非线性特征的影响.结果表明,非线性效应与波导路径密切相关,非线性失真主要发生在信号向上进入大气层传播阶段,热层波导的非线性效应明显强于平流层;非线性与信号衰减之间具有相互抑制作用,而声源强度表现为两种作用的调节因子.最后,与实测数据对比则验证了本文方法的有效性及实用性.

     

基于深度残差傅里叶神经算子方法压制地震多次波

多次波是一种较为严重影响地震成像的干扰波,如何有效压制多次波是需要关注的地震资料处理关键问题之一. 本文基于傅里叶神经算子（FNO）和残差网络（ResNet）,提出了基于深度残差傅里叶神经算子（DRFNO）网络的多次波压制方法. DRFNO是一种弱约束模型 + 数据驱动的人工智能算法,包含一次波和多次波的全波场炮集为输入,其中真实一次波炮集为标签训练网络,输出为压制多次波后的一次波炮集. DRFNO的网络结构中考虑了地震波场的数据特点,结合波动方程正演模拟的物理机理,约束网络训练过程. 基于传统机器学习中的激活函数设置方法,该方法通过一个用于地震数据样本与标签预处理的激活函数（SDAF）,克服地震炮集数据中因同相轴能量差异导致神经网络无法训练的问题. 采用两套层状介质模型和Sigsbee2B复杂模型的模拟地震数据验证了DRFNO方法多次波压制处理的有效性,抗噪性和泛化能力. 最后,通过一套实际地震数据实例表明本文提出的DRFNO方法应用于压制实际复杂地震波场中多次波的良好效果.

     

北京平原区断裂构造重力异常识别研究

区域重力异常蕴含丰富的断裂构造特征信息.采用小波多尺度分解、归一化总水平导数垂向导数（NVDR_THDR）和剖面2.5D重力异常反演方法对北京平原区高精度区域重力资料进行了处理,获得了主要断裂构造平面位置、长度、规模、汇交关系及深浅延伸特征,分析了利用重力异常识别断裂的效果.结果表明：（1）北京平原区NE向断裂平面延展长度大、连续性强,NW向断裂分段性明显,连续性弱,但NW向断裂对NE向断裂有切割改造迹象.近EW或SN向断裂分布较为局限.（2）主控断裂平面和垂向延伸特征差异明显,顺义断裂、孙河断裂、永定河断裂等为盖层断裂;南口断裂、孙河断裂西段、二十里长山断裂和张喜庄断裂为基底断裂;黄庄—高丽营断裂南段、南苑—通县断裂、礼贤断裂、夏垫断裂和皮各庄断裂东段为地壳断裂.（3）利用NVDR_THDR峰值异常带的连续性、幅值、宽度及错切关系可有效识别断裂的平面展布特征,通过小波变换获得的不同深度等效层异常结合2.5D剖面反演可有效研究断裂在基岩内部的深浅延伸情况,但重力异常的垂向分辨能力弱,断裂在新生界内部延伸特征需结合其他地质资料进一步分析.

     

用重力测量技术观测城市地表下沉的实验研究

本文用重力测量技术对城市地表下沉进行了实验研究,从2016年3月到2017年5月在武汉市内地表下沉较大的部分城区进行了7期流动重力观测实验,并用D-InSAR观测的垂向位移进行了验证.数值结果表明重力观测每期整网平差后点值平均精度都小于10×10^-8m·s^-2,说明采用重力观测能在城市内获得高精度的区域重力变化.第7期相对于第1期的结果与D-InSAR在大致相同时间段内地表垂直位移结果比较表明,重力增加的大部分区域与D-InSAR观测到的地表下沉区域相一致,说明这些区域的重力增加主要是由地表下沉引起的.从第2到7期相对于第1期的重力变化说明在近12个月的时间内测区最大重力变化约40×10^-8m·s^-2,且局部区域的重力值是逐渐增加的,说明地表下沉是持续进行的.本实验结果说明重力观测技术能为城市地表下沉提供重力观测约束和机制解释.

     

淮南深地实验室分布式光纤地震立体台阵观测数据分析

在淮南深地实验室布设了水泥固结的传感光缆,结合竖井中已有通信光缆,利用分布式光纤地震传感技术(DAS)构建了高密度的三分量立体台阵,开展了为期一年的连续观测.通过分析地下870 m的背景噪声记录,发现其日间变化幅度较小,这表明深地实验室受气压、温度和人类活动等的影响较小.然而,在低频段观测到明显增强的噪声,这给低频信号研究带来了一定困难.在连续记录中,识别出了多个地方震和区域震信号,尤其是获得了高质量的玛多地震P波信号.与共址地震仪数据的一致性表明DAS波形记录的可靠性.通过三分量DAS记录识别了Rayleigh面波信号,并利用多重滤波技术测量得到其群速度频散曲线;利用DAS应变率记录与共址宽频带地震仪的速度记录比值获得了相速度信息.两种方法测得的面波频散数据可用于研究速度结构.这些初步结果展现了深地实验室提供的超静环境以及三分量立体DAS台阵观测的优势,为后续进一步研究提供参考.

     

Characteristics of petroleum accumulation in syncline of the Songliao basin and discussion on its accumulation mechanism

The relation between oil and water in reservoirs with low and ultra-low permeability is very complicated. Gravitational separation of oil and water is not obvious. Normal reservoirs are located in depression and structural high spot, oil and water transitions are located in their middle. Stagnation is the key fact of oil-forming reservoir in the axis of a syncline based on the research of oil, gas and water migration manner, dynamics and non-Darcy flow in the Songliao basin. In low and ultra-low permeable reservoir, gas and water migrate easily through pore throats because their molecules are generally smaller than the pore throats; but the minimum diameter of oil droplets is larger than pore throats and they must be deformed to go through. Thus, gas and water migrate in advance of oil, and oil droplets remain behind. Pressure differential and the buoyancy force in a syncline reservoir are a main fluid driving force; and capillary force is the main resistance to flow. When the dynamics force is less than resistance, oil is immobile. When the buoyancy force is less than the capillary force, a gravitational separation of oil and water does not occur. The reservoir in the mature source rock of a syncline area with the low and ul- tra-low permeability belongs to an unconventional petroleum reservoir.     

Physical characteristics of high-rank coal reservoirs in different coal-body structures and the mechanism of coalbed methane production

The physical characteristics of coal reservoirs are important for evaluating the potential for gas desorption, diffusion, and seepage during coalbed methane (CBM) production, and influence the performance of CBM wells. Based on data from mercury injection experiments, low-temperature liquid nitrogen adsorption, isothermal adsorption, initial velocity tests of methane diffusion, and gas natural desorption data from a CBM field, herein the physical characteristics of reservoirs of high-rank coals with different coal-body structures are described, including porosity, adsorption/desorption, diffusion, and seepage. Geometric models are constructed for these reservoirs. The modes of diffusion are discussed and a comprehensive diffusion-seepage model is constructed. The following conclusions were obtained. First, the pore distribution of tectonically deformed coal is different from that of normal coal. Compared to normal coal, all types of pore, including micropores (<10 nm), transitional pores (10–100 nm), mesopores (100–1000 nm), and macropores (>1000 nm), are more abundant in tectonically deformed coal, especially mesopores and macropores. The increase in pore abundance is greater with increasing tectonic deformation of coal; in addition, the pore connectivity is altered. These are the key factors causing differences in other reservoir physical characteristics, such as adsorption/desorption and diffusion in coals with different coal-body structures. Second, normal and cataclastic coals mainly contain micropores. The lack of macropores and its bad connectivity limit gas desorption and diffusion during the early stage of CBM production. However, the good connectivity of micropores is favorable for gas desorption and diffusion in later gas production stage. Thus, because of the slow decline in the rate of gas desorption, long-term gas production can easily be obtained from these reservoirs. Third, under natural conditions the adsorption/desorption properties of granulated and mylonitized coal are good, and the diffusion ability is also enhanced. However, for in situ reservoir conditions, the high dependence of reservoir permeability on stress results in a weak seepage of gas; thus, desorption and diffusion is limited. Fourth, during gas production, the pore range in which transitional diffusion takes place always increases, but that for Fick diffusion decreases. This is a reason for the reduction in diffusion capacity, in which micropores and transitional pores are the primary factors limiting gas diffusion. Finally, the proposed comprehensive model of CBM production under in situ reservoir conditions elucidates the key factors limiting gas production, which is helpful for selection of reservoir stimulation methods.     

Carbon isotope composition and comparison of Lower Triassic marine carbonate rocks from Southern Longmenxia section in Guang’an,Sichuan Basin

The Early Triassic was a period of ecological restoration for the earth's system after the end-Permian mass extinction.Geochemical records linked to the variations in marine ecosystems during this period have attracted the interest of geologists for many years.Based on petrographic analysis of samples and evaluations of their reliability as proxies for original seawater,this study investigated the carbon and oxygen isotopic compositions of 350 carbonate rock samples from the Lower Triassic(and adjacent strata)in the southern Longmenxia section of Guang'an,eastern Sichuan Basin.The results indicate that the Triassic carbonate rocks from the southern Longmenxia section favorably preserved the original seawater'sδ~(13)C signal.Furthermore,carbon and oxygen isotopic compositions are found to be poorly correlated,with a determination coefficient as low as 0.0205 and only 44 rock samples show results of Mn/Sr2 and/orδ~(18)0-6.5‰.The complete carbon isotopic curve for the Lower Triassic is established using the data from the remaining 306 samples with Mn/Sr2 and/orδ~(18)O-6.5‰.This curve presents favorable comparability on a global scale,specifically in theδ~(13)C minima near the Permian-Triassic boundary,at the top of the Jia1 and within the the Jia3,as well as in theδ~(13)C maxima at the tops of the Ye1 and Ye4,at the base of the Jia2 and at the top of the Ye3.The peaks and troughs corresponding to these maxima and minima all reflect global signals.By comparing these results to previous research on coeval carbon isotopic curves established within the chronostratigraphic framework,the ages of these critical evolution points are determined.The results show that the Ye1 roughly corresponds to the Griesbachian substage;the Ye2 through Ye4 correspond to the Dienerian substage;Jial corresponds to the Smithian substage;from the Jia2 to the lower part of the Jia4 correspond to the Spathian substage;and the middle and upper parts of the Jia4 belongs to the Aegean Substage of the Middle Triassic.Around the boundary between the Jial and Jia2(which represents the Smithian-Spathian boundary(SSB)),the value ofδ~(13)C increases rapidly from-0.911‰to 3.679‰.The span during which the seawater's carbon isotope experiences this drastic change may be less than36 kyr.The oxygen isotope,which is more sensitive to sedimentary environmental changes,exhibits changes prior to the carbon isotope near the SSB,indicating a significant increase in the salinity of the seawater before a sharp rise in the carbon isotope;this event leads to the formation of evaporites and dolomites.     

Numerical simulation and data assimilation of the water-energy cycle over semiarid northeastern China

The default fractional vegetation cover and terrain height were replaced by the estimated fractional vegetation cover, which was calculated by the Normalized Difference Vegetation Index(NDVI) of Earth Observing System Moderate-Resolution Imaging Spectroradiometer(EOS-MODIS) and the Digital Elevation Model of the Shuttle Radar Topography Mission(SRTM) system. The near-surface meteorological elements over northeastern China were assimilated into the three-dimensional variational data assimilation system(3DVar) module in the Weather Research and Forecasting(WRF) model. The structure and daily variations of air temperature, humidity, wind and energy fields over northeastern China were simulated using the WRF model. Four groups of numerical experiments were performed, and the simulation results were analyzed of latent heat flux, sensible heat flux, and their relationships with changes in the surface energy flux due to soil moisture and precipitation over different surfaces. The simulations were compared with observations of the stations Tongyu, Naiman, Jinzhou, and Miyun from June to August, 2009. The results showed that the WRF model achieves high-quality simulations of the diurnal characteristics of the surface layer temperature, wind direction, net radiation, sensible heat flux, and latent heat flux over semiarid northeastern China in the summer. The simulated near-surface temperature, relative humidity, and wind speed were improved in the data assimilation case(Case 2) compared with control case(Case 1). The simulated sensible heat fluxes and surface heat fluxes were improved by the land surface parameterization case(Case 3) and the combined case(Case 4). The simulated temporal variations in soil moisture over the northeastern arid areas agree well with observations in Case 4, but the simulated precipitation should be improved in the WRF model. This study could improve the land surface parameters by utilizing remote sensing data and could further improve atmospheric elements with a data assimilation system. This work provides an effective attempt at combining multi-source data with different spatial and temporal scales into numerical simulations. The assimilation datasets generated by this work can be applied to research on climate change and environmental monitoring of arid lands, as well as research on the formation and stability of climate over semiarid areas.