Drag and inertia coefficients for a circular cylinder in steady plus low-amplitude oscillatory flows     

《Applied Ocean Research》2017

Computer simulations of steady plus low-amplitude oscillatory flow about a circular cylinder are reported at a fixed Reynolds number of 150 based on the steady component. The conventional Keleugan–Carpenter number based on the oscillatory component is fixed at π/5. The oscillation frequency is varied so as to study a wide spectrum of flows where inertial forces dominate at one end and viscous drag forces at the other as a function of the modified Keleugan–Carpenter number. The hydrodynamic force on the cylinder in-line with the flow direction is represented by Morison's equation and an extended version with three terms. The drag and inertia coefficients in Morison's equation are determined by least-squares fits to data directly computed from integration of skin friction and pressure distributions around the periphery of the cylinder. The root-mean-square value of the residue of reconstructed minus directly-computed forces varies between 2 and 41% depending on the flow parameters. Comparable results can be obtained with a semi-theoretical approach using inviscid inertia and quasi-steady viscous drag terms. Physical explanations for the variation of the force coefficients are provided and implications for pertinent flow–structure interactions are discussed.  相似文献   

Geothermometry and geobarometry of overpressured lower Paleozoic gas shales in the Jiaoshiba field,Central China: Insight from fluid inclusions in fracture cements     

《Marine and Petroleum Geology》2017

The Wufeng-Longmaxi organic-rich shales host the largest shale gas fields of China. This study examines sealed fractures within core samples of the Wufeng-Longmaxi shales in the Jiaoshiba shale gas field in order to understand the development of overpressures (in terms of magnitude, timing and burial) in Wufeng-Longmaxi shales and thus the causes of present-day overpressure in these Paleozoic shale formations as well as in all gas shales. Quartz and calcite fracture cements from the Wufeng-Longmaxi shale intervals in four wells at depth intervals between 2253.89 m and 3046.60 m were investigated, and the fluid composition, temperature, and pressure during natural fracture cementation determined using an integrated approach consisting of petrography, Raman spectroscopy and microthermometry. Many crystals in fracture cements were found to contain methane inclusions only, and aqueous two-phase inclusions were consistently observed alongside methane inclusions in all cement samples, indicating that fluid inclusions trapped during fracture cementation are saturated with a methane hydrocarbon fluid. Homogenization temperatures of methane-saturated aqueous inclusions provide trends in trapping temperatures that Th values concentrate in the range of 198.5 °C–229.9 °C, 196.2 °C-221.7 °C for quartz and calcite, respectively. Pore-fluid pressures of 91.8–139.4 MPa for methane inclusions, calculated using the Raman shift of C-H symmetric stretching (v₁) band of methane and equations of state for supercritical methane, indicate fluid inclusions trapped at near-lithostatic pressures. High trapping temperature and overpressure conditions in fluid inclusions represent a state of temperature and overpressure of Wufeng-Longmaxi shales at maximum burial and the early stage of the Yanshanian uplift, which can provide a key evidence for understanding the formation and evolution of overpressure. Our results demonstrate that the main cause of present-day overpressure in shale gas deposits is actually the preservation of moderate-high overpressure developed as a result of gas generation at maximum burial depths.  相似文献   

Identification and characterization of fluid escape structures (pockmarks) in the Estremadura Spur,West Iberian Margin     

《Marine and Petroleum Geology》2017

Located on the West Iberian margin, between Cabo Carvoeiro and Cabo da Roca, the Estremadura Spur is a trapezoidal promontory elongated in an east-west direction, extending until the Tore seamount. Recently a field with more than 70 pockmarks was discovered in the NW region of the Estremadura Spur outer shelf (Lourinhã Monocline). Pockmarks are the seabed culminations of fluid migration through the sedimentary column and their characteristic seabed morphologies correspond to cone-shaped circular or elliptical depressions. The characterization of these features and the understanding of the associated fluid escape process are the main objectives of this work. Here we characterize these structures to understand their structural and stratigraphic control based on: 1) Seismic processing and interpretation of the high resolution 2D single-channel sparker seismic dataset, 2) Bathymetric and Backscatter interpretation and 3) ROV direct observation of the seafloor.The analysis of the seismic profiles allowed the identification of six seismic units, disturbed by the migration and accumulation of fluids. The Estremadura Spur outer shelf has been affected by several episodes of fluid migration and fluid escape during the Pliocene-Quaternary that are expressed by a vast number of seabed and buried pockmarks. At present, the pockmarks are mainly inactive, as the seabed pockmarks are covered by recent sediments. It is concluded that the migration of fluids to the seabed occurred over the Pliocene-Quaternary, as indicated by the buried pockmarks at different depths below the seabed. The vertical stacking of various pockmarks suggests a cyclical fluid flow activity that can possibly be the result of the eustatic sea level variations and the subsequent changes of the hydrostatic pressure.  相似文献   

Seismic and structural characterization of fluid escape pipes using 3D and partial stack seismic from the Loyal Field (Scotland,UK): A multiphase and repeated intrusive mechanism     

《Marine and Petroleum Geology》2017

The potential for fluid leakage from sub-surface reservoirs has important implications for CO2 storage, hydrocarbon reservoirs and water resources. Understanding the genesis, morphology, fluid flow mechanisms and extent of fluid escape from reservoirs allows for better risking of geological resources and storage potential. Here we describe in detail the structures of fluid escape pipes from the Loyal Field, observed from a 3D full and partial stack seismic dataset. The seismic imagery suggests that the fluid escape pipes are rooted at least in the main Paleocene reservoir and by-pass the reservoir seal to cross the post Lista Formation overburden up to the intra-Neogene units. The pipes extend for a few hundred meters to a few kilometres and show varying shape and structure from blow-out structures to incipient mud volcanoes. A detailed analysis of the seismic characteristics observed both from main baseline and partial stack data allows a division of the pipes into two families: (1) seeps and pipes following structural discontinuities and (2) pipes unrelated to the pre-existing structural features. The pipes internal seismic response, the reflector termination of the main conduits and the distribution of stacked bright reflectors suggest an upward migration mechanism (during pipe birth and development), requiring a cyclic switching from non-Darcy hydrofracturing (during overpressure) to Darcy flow lateral migration (during low-pressure stage).  相似文献   

Focused fluid flow and the sub-seabed storage of CO2: Evaluating the leakage potential of seismic chimney structures for the Sleipner CO2 storage operation     

《Marine and Petroleum Geology》2017

The integrity of the caprock of a storage formation is the most crucial parameter for the long-term performance of a geological CO₂ storage site. The Sleipner area in the Southern Viking Graben hosts the first and longest operating industrial scale CO₂ storage project, where CO₂ is injected in a saline aquifer of the Utsira Formation. Time-lapse seismic monitoring shows neither that CO₂ has left the Utsira Formation nor indications for fracturing of the caprock by the CO₂ injection activity, which is in agreement with previous numerical simulations. However, large chimney structures as close as 7 km from the injection point indicate that the caprock has been breached in the geological past, which may raise questions about the integrity of the caprock above the Sleipner CO₂ storage site. Here, we present seismically constrained numerical fluid flow simulations that evaluate the influence of chimney structures on the long-term performance of the CO₂ storage operation at Sleipner. The simulation could reproduce the spreading of the Sleipner CO₂ plume, which is controlled by the anisotropic permeability field of the Utsira Formation and the regional dip of the formation top. We have performed long-term plume evolution simulations, which show that the injected CO₂ will not reach the existing chimney structures assuming a realistic injection duration of 30 years. Our simulations indicate that an unrealistically long injection period between 92 and 140 years would be required for the CO₂ to reach the existing chimney structures. In this case, a comparably low chimney permeability of 10 mD may be sufficient to facilitate CO₂ migration from the storage formation to the seafloor, once the CO₂ has reached a chimney structure. However, the simulations indicate that it is very unlikely that the CO₂ may migrate along existing chimney structures at Sleipner. Our results highlight that the reconstruction of palaeo fluid flow systems and the identification of focused fluid conduits should be considered in the assessment of CO₂ storage sites.  相似文献   

Muscovite surface structure imaged by fluid contact mode AFM     

Y. Kuwahara 《Physics and Chemistry of Minerals》1999,26(3):198-205

The surface structure of muscovite was imaged using an atomic force microscope (AFM) in contact mode in water. The following three types of AFM images were observed: (1) those showing clearly the arrangement of hexagonal rings of SiO₄ tetrahedra; (2) those showing a hexagonal array of bright spots separated by a distance of about 5.3 Å; and (3) those changing gradually from image (2) to image (1). Image (1) successfully provides information on the tetrahedral tilt and basal surface corrugation that are particularly characteristic of dioctahedral micas. The mean unit cell dimensions for the muscovite surface measured from Image (1) were slightly longer than those of the bulk structure, due to the rehydration of the tetrahedral sheet and/or surface relaxation. Image (2) was made by varying the scan angles, even on the same surface in which Image (1) was obtained. Image (3) has information on a single plane rather than on two or more planes involving steps, kinks and so on. Therefore, what is depicted in Images (2) and (3) is not the arrangement of interlayer K ions but the basal plane of the tetrahedral sheet. Some structural relaxation of the tetrahedral sheet surface was also observed. Gradual expansion and contraction of hexagonal rings were randomly found on the muscovite surface. The surface relaxation results from a tetrahedral rotation and/or tilting after cleaving, since significant variations of both distances and bond angles between adjacent SiO₄ tetrahedra on the surface were found.  相似文献   

地质结构控渗效应初探   总被引：4，自引：0，他引：4  

张辉 《工程地质学报》1999,7(2):135-140

将地质控制论与岩体水力学相结合,认为地质结构对岩体渗流具有最直接的控制作用。考虑岩体渗流的特点,对地质结构进行了合理分级。总结性提出地质结构控渗的四大效应:分级优先效应、分流交叉效应、非饱和效应和耦合效应。初步探讨了这四大效应的基本内容、相互关系及工程意义。  相似文献   

中国大陆23个震例流体异常时空分布特征研究   总被引：1，自引：0，他引：1  

简春林  晏锐  黄辅琼 《地震》2006,26(1):99-106

将1966~1999年中国大陆发生的188例M_S≥5.0地震震例中, 单次震例流体异常项数≥10项的23次地震的446项流体异常取出, 并将其按时序和分区进行时、 空分布统计分析。 结果表明, 除西北地区与震例相关的流体异常数量明显偏少外, 在西南、 华北、 东南3个地区, 不论是按时序还是按分区的时、 空统计, 都有较为清晰的各自阶段性; 与中国震例中流体异常的总体分布特征和各自分区异常分布特征之间有较好的一致性。  相似文献   

沉积盆地中地质流体运动与油气成藏   总被引：2，自引：0，他引：2  

曾溅辉 《海相油气地质》2005,10(1):37-42

沉积盆地内地质流体运动的驱动力主要有压实作用、地下水重力作用、构造作用和进入盆地中的热流。在不同的驱动力作用下,地质流体可有离心流、向心流、穿越流以及幕式和集中式等不同的运动特征,对油气成藏的影响亦存在差异。在压实作用驱动下,油气藏围绕盆地生油中心成环状分布。在重力作用驱动下,油气主要聚集在地下水的低势区,如盆地的斜坡和中心,或地下水中下游的靠盆地一侧。构造作用驱动下的油气运移比较复杂,油气主要聚集在冲断层一侧,但也可以长距离运移到斜坡带聚集。  相似文献   

太湖水龄分布特征及“引江济太”工程对其的影响   总被引：1，自引：5，他引：1  

黄春琳  李熙  孙永远 《湖泊科学》2017,29(1):22-31

太湖作为典型的风生流湖泊,风场对水体运输和交换的过程起着重要的作用.基于环境水动力学模型EFDC源程序建立了染色剂模型以及水龄模型,借助水龄研究太湖水体的长期输运过程和更新速率特征,从而为太湖的调水工程管理提供科学依据.本文在研究春、夏、秋、冬季不同风场作用下太湖的水龄季节性分布特征的基础上,结合太湖实测风速、流量数据及"引江济太"工程调水运行的现状,着重分析了望虞河枢纽调水运行以及新沟河工程对太湖水龄分布的影响.数值试验的模拟结果表明:太湖水体交换受季风影响明显,春、夏季的水龄相对较大、水体交换较差;靠近湖流入口处的地方水龄较小,远离入口的地方水龄较大;水流流向与风向一致时水龄减小,水循环加快,反之则减慢.望虞河引水引工程能够减小贡湖及湖心区的水龄,加快贡湖湖区及湖心区的水循环;新沟河工程引水能够减小梅梁湖区的水龄,改善该湖区的水质.引水工程的实施对加快整个太湖的水循环做出重要贡献.  相似文献