N油田A油组钙质隔夹层地质特征及成因分析

在油田开发过程中,隔夹层控制油气水运动规律,对于寻找剩余油具有重要控制作用。本文以N油田TF组2段A油组为研究对象,通过薄片、岩心测试、测井、碳氧同位素等资料综合分析,研究其钙质隔夹层的分布特征、岩石学特征、物性特征、测井识别特征,并从沉积环境、物质来源、成岩作用相结合的角度分析钙质隔夹层的成因。研究表明,A油组纵向上发育的三套钙质隔夹层主要发育在前滨滩坝沉积微相,顶钙与底钙的岩性以砂质生屑质灰岩为主,中钙为钙质砂岩;三套钙质隔夹层中生物碎屑主要以腕足、腹足、有孔虫为主,含少量棘皮、瓣鳃、红藻、介形虫、苔藓虫等;成岩作用主要为胶结作用,胶结物类型包含早期方解石胶结物、中期铁方解石胶结物、晚期铁白云石胶结物;碳氧同位素分析表明,隔夹层中碳主要来自于沉积过程中的海水,同时有少量来自于大气淡水和有机酸,Ca~(2+)主要来源于生物碎屑,其次为钙长石溶解、铝硅酸盐矿物的水化作用。     

大兴安岭西坡比利亚谷银铅锌多金属矿床成因

比利亚谷银铅锌多金属矿床位于大兴安岭西坡的得尔布干成矿带,它是近些年来在该区新发现的一座大型银铅锌多金属矿床。该矿床矿体主要呈脉状、细脉浸染状、角砾状赋存于塔木兰沟组中—基性火山岩和满克头鄂博组酸性火山岩中的NW向断裂体系内。根据矿石的结构、构造以及矿物之间的共生组合、穿切关系,将成矿过程从早到晚划分为硅化石英+黄铁矿阶段（Ⅰ）、石英+黄铁矿+闪锌矿阶段（Ⅱ）、石英+黄铁矿+闪锌矿+方铅矿+辉银矿+黄铜矿±黝铜矿阶段（Ⅲ）、石英+黄铁矿+方解石+萤石±蛋白石阶段（Ⅳ）;详细的石英、闪锌矿流体包裹体研究揭示：成矿早阶段（Ⅰ、Ⅱ）石英中发育WL型、C型包裹体,包裹体完全均一温度为188~254℃,盐度（w（NaCl））为1.83%~4.79%,密度为0.81~0.94 g/cm³,属于中低温、低盐度的H₂O-NaCl-CO₂体系;成矿主阶段（Ⅲ）石英、闪锌矿中发育WL型包裹体,包裹体完全均一温度为160~188℃,盐度为3.69%~7.15%,密度为0.92~0.96 g/cm³,属于低温、中低盐度的H₂O-NaCl-CH₄体系;成矿晚阶段（Ⅳ）石英中发育WL型、L型包裹体,WL型包裹体完全均一温度为130~165℃,盐度为1.22%~3.53%,密度为0.93~0.95 g/cm³,属于低温、低盐度的H₂O-NaCl体系。流体包裹体H-O同位素地球化学特征揭示：早阶段流体的δ¹⁸O_H2O-SMOW值为-6.3‰~-5.9‰,δD_H2O-SMOW值为-163.4‰~-162.7‰;成矿主阶段流体的δ¹⁸O_H2O-SMOW值为-14.4‰,δD_H2O-SMOW值为-165.4‰~-162.0‰;成矿晚阶段流体的δ¹⁸O_H2O-SMOW值为-19.1‰,δD_H2O-SMOW值为-150.7‰;硫化物Pb同位素比值分别为²⁰⁶Pb/²⁰⁴Pb=18.435~18.513、²⁰⁷Pb/²⁰⁴Pb=15.579~15.675、²⁰⁸Pb/²⁰⁴Pb=38.283~38.603。这种特征揭示,该矿床成矿流体为低温、低盐度的H₂O-NaCl-CH₄体系,早期为残余岩浆水和大气降水混合、中—晚期大气降水逐渐增加;成矿物质源于壳幔混合源区;成矿过程以流体混合方式导致成矿元素聚集和沉淀,矿床成因类型为与陆相火山-次火山作用有关的低硫化型浅成热液铜（银）铅锌多金属矿床;其整体与大兴安岭西坡同类型矿床相似,成矿作用发生在早白垩世（131.3 Ma）,与古太平洋板块俯冲产生的弧后伸展环境相关。     

Assessing the relative contributions of the flood tide and the ebb tide to tidal channel network dynamics

Flood and ebb currents provide different contributions to the initiation and evolution of tidal channel networks, generating diverse network structures and channel cross-sections. In order to separate the effects of these contributions, a physical model of a sloping tidal-flat basin was set up in the laboratory. Depending on the degree of tidal asymmetry imposed offshore, either flood or ebb currents can be enhanced. The experimental results show that the ebb current has a higher capability to initiate and shape tidal networks than the flood current. Headward erosion is mainly induced by the ebb flow. The slightly inclined flat surface tends to reduce the energy of the flood current and to enhance the ebb current, thus prolonging the duration of morphodynamic activity as well as sediment motion. Overall, flood-dominated tides favour the formation of small-scale channel branches in the upper basin zone, while long lasting ebb-dominated tides result in more complex, wider and deeper tidal networks. © 2019 John Wiley & Sons, Ltd.     

Scattering pattern analysis and true-amplitude generalized Radon transform migration for acoustic transversely isotropic media with a vertical axis of symmetry

In multi-parameter ray-based anisotropic migration/inversion, it is essential that we have an understanding of the scattering mechanism corresponding to parameter perturbations. Because the complex nonlinearity in the anisotropic inversion problem is intractable, the construction of true-amplitude linearized migration/inversion procedures is needed and important. By using the acoustic medium assumption for transversely isotropic media with a vertical axis of symmetry and representing the anisotropy with P-wave normal moveout velocity, Thomsen parameter δ and anelliptic parameter η, we formalize the linearized inverse scattering problem for three-dimensional pseudo-acoustic equations. Deploying the single-scattering approximation and an elliptically anisotropic background introduces a new linear integral operator that connects the discontinuous perturbation parameters with the multi-shot/multi-offset P-wave scattered data. We further apply the high-frequency asymptotic Green's function and its derivatives to the integral operator, and then the scattering pattern of each perturbation parameter can be explicitly presented. By naturally establishing a connection to generalized Radon transform, the pseudo-inverse of the integral operator can be solved by the generalized Radon transform inversion. In consideration of the structure of this pseudo-inverse operator, the computational implementation is done pointwise by shooting a fan of rays from the target imaging area towards the acquisition system. Results from two-dimensional numerical tests show amplitude-preserving images with high quality.     

基于Seislet-TV双正则化约束的地震随机噪声压制方法

人工地震数据总是受到随机噪声的干扰,地震数据时-空变的特性使得常规去噪方法处理效果并不理想,容易导致有效信号的损失.目前广泛应用的预测滤波类方法存在处理时变数据能力不足的问题.随着压缩感知理论的不断完善,稀疏变换阈值算法能够解决时变地震数据噪声压制问题,但是常规的稀疏变换方法,如傅里叶变换,小波变换等,并不是特殊针对地震数据设计的,很难提供地震数据最佳的压缩特征,同时,常规阈值算法容易导致去噪结果过于平滑.因此开发更加有效的时-空变地震数据信噪分离方法具有重要的工业价值.本文将地震数据信噪分离问题归纳为数学基追踪问题,在压缩感知理论框架下,利用特殊针对地震数据设计的VD-seislet稀疏变换方法,结合全变差(TV)算法,构建seislet-TV双正则化条件,并利用分裂Bregman迭代算法求解约束最优化问题,实现地震数据的有效信噪分离.通过理论模型和实际数据测试本文方法,并且与工业标准FXdecon方法进行比较,结果表明基于seislet-TV双正则化约束条件的迭代方法能够更加有效地保护时-空变地震信号,压制地震数据中的强随机噪声.     

The control of wind strength on the barchan to parabolic dune transition

The evolution of barchan-to-parabolic dunes can be driven by vegetation establishment, which may be linked to climate change and/or human activity. However, little is known of the impact of changes in wind strength on vegetation development and the resulting impacts on the evolution of dune morphology and sedimentological characteristics. To address this issue, we studied the morphology and grain-size characteristics of barchan, barchan-to-parabolic and parabolic dunes in the Mu Us Desert in north China, which was combined with an analysis of changes in normalized difference vegetation index (NDVI) and climatic variables during 1982–2018. The results reveal a trend of increasing growing-season NDVI which was related to a significant decrease in drift potential (DP). Therefore, we suggest that the initiation of dune transformation was caused by the reduced wind strength which favored the establishment and development of vegetation. To reveal the response of sedimentological reorganization during the processes of dune transformation, grain-size characteristics along the longitudinal profile of the three different types of dunes were examined. The decreasing wind strength led to the transport of fine sands on the upper part of the windward face of the dunes, resulting in a progressive coarsening of the grain-size distribution (GSD) and a reduction in dune height at the crest area. No distinct trend in sorting and mean grain-size was observed on the windward slope of the barchan-to-parabolic dune, indicating that the sand in transit had little influence on the GSD. Conversely, progressive sorting and coarsening of the sand occurred towards the crest of the parabolic dune. This indicates that vegetation development limited the transport of sand from upwind of the dune, and affected a shift in the dune source material to the underlying source deposits, or to reworked pre-existing aeolian deposits, and resulted in the trapping of sand in the crest area. © 2020 John Wiley & Sons, Ltd.     

Bedrock erosion due to hoeing as tillage technique in a hilly agricultural landscape,southwest China

Tillage on hillslopes may not only induce severe soil erosion, but may also cause bedrock erosion under certain conditions. Yet, little is known about bedrock erosion by tillage in a hilly agricultural landscape, southwest China. The aim of this study is to quantify the translocation of rock fragments derived from bedrock fragmentation by hoeing under different conditions, including slope gradient, hoeing depth and soil-covered thickness using a gravel tracing method. The reliability of the gravel tracing method was confirmed by the bedrock dyeing tracing method. Hoeing depth is a significant factor affecting the translocation rate of rock fragments (Q_r ). Meanwhile, under the condition of overlying soil layers (0.06−0.10 m thick), the values of Q_r were significantly smaller with a reduction of 20.7−25.6%, compared with rock fragmentation by hoeing for bare bedrock. However, slope gradient was found to have insignificant effects on Q_r . Fractured bedrock moved as individual small fragments, which was mainly controlled by the hitting force of the hoe, while soil moved in the shape of lumps, which was dominated by both drag force of the hoe and gravity. This study suggests that hoeing into soil-covered bedrock can diminish bedrock erosion while providing soil matrix for shallow soil layers. Our work presents a quantitative assessment of bedrock erosion by hoeing and an underlying insight into characteristics of bedrock erosion by tillage operations in hilly agricultural regions with mudstone and shale, southwest China. © 2020 John Wiley & Sons, Ltd.     

Decadal link between longitudinal morphological changes in branching channels of Yangtze estuary and movement of the offshore depo-center

In estuaries, the morphology of inland and offshore areas usually evolves synergistically. This study examines the decadal link between longitudinal changes in morphology of branching channels and movement of the offshore depo-center (where sediment deposition rate is maximum) of the Yangtze River estuary, under intense human interference. Integrated data analysis is provided on morphology, runoff discharge, and ebb partition ratio from 1950 to 2017. Channel-volume reductions and change rates between isobaths in branching channels reflect the impact of estuarine engineering projects. Ebb partition ratio and duration of discharge ≥ 60 000 m³ s^-1 act as proxies for the water excavating force in branching channels and runoff intensity. It is found that deposition occurs in the lower/upper sub-reaches (or further downstream/upstream channels) of the inland north/south branching channels, and the offshore depo-center moves southward or southeastward, as runoff intensity grows; the reverse occurs as runoff intensity declines. This is because the horizontal circumfluence in the Yangtze estuary rotates clockwise as ebb partition ratios of the north/south branching channels increase/decrease for increasing runoff, and conversely rotates anticlockwise for decreasing runoff. Land reclamation activities, the Deepwater Channel Project, and the Qingcaosha Reservoir have impacted greatly on longitudinal changes of morphology in the North Branch and the South Passage and on ebb partition ratio variations in the North/South Channel and the North/South Passage. Dam-induced runoff flattening has enhanced deposition in the upper/lower sub-reaches of the north/south branching channels and caused northward movement of the offshore depo-center, except in areas affected by estuarine engineering projects. Dam-induced longitudinal evolution of branching channel morphology and offshore depo-center movement will likely persist in the future, given the ongoing construction of large cascade dams in the upper Yangtze and the completion of major projects in the Yangtze estuary. © 2020 John Wiley & Sons, Ltd.     

Time-frequency decomposition of seismic signals via quantum swarm evolutionary matching pursuit

Matching pursuit belongs to the category of spectral decomposition approaches that use a pre-defined discrete wavelet dictionary in order to decompose a signal adaptively. Although disengaged from windowing issues, matching point demands high computational costs as extraction of all local structure of signal requires a large size dictionary. Thus in order to find the best match wavelet, it is required to search the whole space. To reduce the computational cost of greedy matching pursuit, two artificial intelligence methods, (1) quantum inspired evolutionary algorithm and (2) particle swarm optimization, are introduced for two successive steps: (a) initial estimation and (b) optimization of wavelet parameters. We call this algorithm quantum swarm evolutionary matching pursuit. Quantum swarm evolutionary matching pursuit starts with a small colony of population at which each individual, is potentially a transformed form of a time-frequency atom. To attain maximum pursuit of the potential candidate wavelets with the residual, the colony members are adjusted in an evolutionary way. In addition, the quantum computing concepts such as quantum bit, quantum gate, and superposition of states are introduced into the method. The algorithm parameters such as social and cognitive learning factors, population size and global migration period are optimized using seismic signals. In applying matching pursuit to geophysical data, typically complex trace attributes are used for initial estimation of wavelet parameters, however, in this study it was shown that using complex trace attributes are sensitive to noisy data and would have lower rate of convergence. The algorithm performance over noisy signals, using non-orthogonal dictionaries are investigated and compared with other methods such as orthogonal matching pursuit. The results illustrate that quantum swarm evolutionary matching pursuit has the least sensitivity to noise and higher rate of convergence. Finally, the algorithm is applied to both modelled seismograms and real data for detection of low frequency anomalies to validate the findings.     

2015年四川乐山金口河M5.0地震孕震构造条件分析

2015年1月14日乐山金口河M5.0地震发生在历史地震强度较低的川南山区与四川盆地交界一带。基于四川区域地震台网的震相报告与波形资料,采用双差定位法对地震序列进行重新定位,同时,采用CAP波形反演方法及HASH方法反演了主震及序列中8次M_L≥2.0地震的震源机制解。另外,利用Coulomb3计算了主震发生后库仑应力改变量,得到的结果如下：①重新定位结果显示,金口河M5.0地震位于（103.18°E,29.32°N）,震源深度16.6km,略深于波形反演结果（12km）。序列分布在NNW向天全-荥经断裂和NE向西河-美姑断裂的交汇部位,余震序列在空间上呈NE向展布。②M5.0主震的机制解为节面Ⅰ：走向350°/倾角46°/滑动角107°,节面Ⅱ：走向146°/倾角47°/滑动角73°,表现为走向NW（NNW）、中等倾角的逆冲型运动方式。序列中其余8次M_L≥2.0余震大多以走向NE的逆冲型地震为主,个别为走滑或正断层类型。主震和大部分余震的节面方向不一致,主震节面方向与余震长轴方向也不一致。③主震后库仑应力改变量显示,余震主要发生在主震引起的库仑破裂应力增加的区域。综合分析推测,NNW向天全-荥经断裂为本次地震主震的发震构造,倾向NE的机制解节面Ⅰ指出了该断裂的几何产状;M5.0主震发生后,立即触发了其旁侧的NE向西河-美姑断裂,并激发了多次余震。