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971.
972.
The stability of river channels and their suitability as habitat for aqueous organisms is strongly controlled by the rate of bedload transport. Quantification of bedload transport rates in rivers is difficult, not only because of the temporal variation in transport, but also because of the cross‐channel variation in transport. The objectives of this study were: (i) to determine the effect of cross‐channel variation in bedload transport on the uncertainty of width‐integrated transport rates; and to use this knowledge (ii) to improve guidelines for bedload sampling. This was done through a thorough statistical evaluation of stochastic and systematic uncertainties involved in bed‐load transport measurements. Based on this evaluation, new guidelines are presented for determination of the number of samples and sampling positions across the channel that are required for bedload measurements in several types of sand‐bed rivers and gravel‐bed rivers. The guidelines relate to bedload measurements made with pressure‐difference (Helley‐Smith type) samplers that require numerous bedload samples of short duration at several positions across the channel. The results show that generally more sampling positions across the channel are required in gravel‐bed rivers than in sand‐bed rivers. For gravel‐bed rivers with unknown cross‐channel distribution of transport, at least 10 sampling positions are recommended, whereas for most sand‐bed rivers five positions suffice. In addition, at least 12 short‐duration samples are required at each position to obtain bedload estimates with uncertainties below 20%. If the same level of uncertainty is desired in the case of high spatial and temporal variation in transport rates, the number of short‐duration samples needed per sampling position increases to 40. 相似文献
973.
Flow dynamics at the origin of thin clayey sand lacustrine turbidites: Examples from Lake Hazar,Turkey 下载免费PDF全文
Sophie Hage Aurélia Hubert‐Ferrari Laura Lamair Ulaş Avşar Meriam El Ouahabi Maarten Van Daele Frédéric Boulvain Mohamed Ali Bahri Alain Seret Alain Plenevaux 《Sedimentology》2017,64(7):1929-1956
Turbidity currents and their deposits can be investigated using several methods, i.e. direct monitoring, physical and numerical modelling, sediment cores and outcrops. The present study focused on thin clayey sand turbidites found in Lake Hazar (Turkey) occurring in eleven clusters of closely spaced thin beds. Depositional processes and sources for three of those eleven clusters are studied at three coring sites. Bathymetrical data and seismic reflection profiles are used to understand the specific geomorphology of each site. X‐ray, thin sections and CT scan imagery combined with grain‐size, geochemical and mineralogical measurements on the cores allow characterization of the turbidites. Turbidites included in each cluster were produced by remobilization of surficial slope sediment, a process identified in very few studies worldwide. Three types of turbidites are distinguished and compared with deposits obtained in flume studies published in the literature. Type 1 is made of an ungraded clayey silt layer issued from a cohesive flow. Type 2 is composed of a partially graded clayey sand layer overlain by a mud cap, attributed to a transitional flow. Type 3 corresponds to a graded clayey sand layer overlain by a mud cap issued from a turbulence‐dominated flow. While the published experimental studies show that turbulence is damped by cohesion for low clay content, type 3 deposits of this study show evidence for a turbulence‐dominated mechanism despite their high clay content. This divergence may in part relate to input variables, such as water chemistry and clay mineralogy, that are not routinely considered in experimental studies. Furthermore, the large sedimentological variety observed in the turbidites from one coring site to another is related to the evolution of a sediment flow within a field‐scale basin made of a complex physiography that cannot be tackled by flume experiments. 相似文献
974.
Alan D. Chapman 《International Geology Review》2017,59(5-6):664-701
ABSTRACTThe Pelona–Orocopia–Rand and related schists of southern California are an archetypal example of an exhumed shallow subduction complex. ‘The schist’ comprises mainly trench materials underthust beneath continental arc rocks during Late Cretaceous–early Cenozoic collision of one or more oceanic plateaux with southern California. The arc-on-trench relationship, without intervening mantle or lowermost crust, implies that significant subduction erosion accompanied shallow subduction. Upsection increases in metamorphic grade (~150 ± 100°C/km) and spatial variations in age and peak temperature provide an ~50 million year long record of tectonic underplating within a cooling system. Evidence for palaeoseismic events in earliest formed and hottest (locally transitional granulite grade) schists provides a possible field-based record of episodic tremor and slow slip events such as detected in several modern shallow subduction zones. Structural ascent of the schist was achieved in distinct Late Cretaceous–early Eocene and late Oligocene–early Miocene extensional pulses, the first during collapse of gravitationally unstable upper plate assemblages and accompanied by trench-directed (top-NE) lower plate extrusion and the second corresponding temporally, spatially, and in character with core complex formation in the SW United States. The line between schist and core complex belts is blurred by the recent discovery of schist within 40 km of the nearest core complex and containing synkinematic Miocene intrusions, a hallmark of SW U.S. core complexes. The history of schist assembly, metamorphism, and exhumation provides the most complete field-based record of thermo-mechanical processes, subduction erosion and tectonic underplating in particular, that operated during a shallow subduction event. Future cross-disciplinary investigations of, and comparisons between, the schist and other possible ancient (e.g. Swakane gneiss, Sanbagawa belt, Qiangtang terrane) and modern (e.g. Cascadia, SW Japan, central Mexico, Chile) shallow subduction zones will yield new insights into the tectonic and petrologic processes that operate within such systems. 相似文献
975.
中原油田区域内废弃井共2090口,经筛选可利用井有355口。根据这些废弃井不同的井身结构、水层位置、水泥返高等条件,确定了针对性的选井选层方法和废弃井改造工艺方案。配套研发优选了新型套管端部密封止水工具、套管鱼顶修复专用工具、套管切割方案和热储层酸洗方案,形成了废弃井改造的完井工艺系列技术和产能测试工艺技术。开展了马古6井现场改造实验,成功实施了井口恢复、储层解堵和试水测试,验证了改造方案和工艺配套技术的可行性和可靠性。 相似文献
976.
基于浅层探冰雷达的东南极内陆地区冰盖内部等时层提取 总被引:2,自引:1,他引:1
中国第32次南极考察内陆队首次使用雪地车载浅层探冰雷达取得了中山站至昆仑站全程1 300 km 的浅层冰盖数据,通过MATLAB对数据进行FFT转换、背景滤波、改变叠加次数去噪和基于曲波变换的图像处理,使用Reflexw对MATLAB处理后数据进行地形校正、二次背景滤波和平滑滤波等处理,成功提取了冰盖浅层等时层并得出了等时层的平均深度、最大深度和波动情况。最后进行了数据的连接,展示了LGB69冰芯处等时层的分布并与冰芯数据结合大体对应了相应等时层的年代和事件。给出了Dome A附近的等时层分布情况。为东南极中山站至昆仑站沿途的物质积累率计算提供重要的数据支撑。 相似文献
977.
天然气水合物被誉为最有研究价值和开采价值的清洁能源,已经成为当今世界能源研究的热点。但到目前为止还未形成成熟稳定的天然气水合物开采技术体系,仍处于研究和试采阶段。陆域冻土天然气水合物开采与海域天然气水合物开采相比相对比较容易,在钻进过程中能够形成较稳定的孔壁。天然气水合物开采的主要方法有热激法、降压法、置换法和化学抑制剂法。SAGD(Steam Assisted Gravity Drainage)技术也叫蒸汽辅助重力驱油技术,在重油、油砂开采中得到了迅速发展,取得了非常有效的成果,被认为是目前重油开采最有效的方法。对SAGD技术应用到陆域冻土天然气水合物开采中进行理论分析研究,经过分析发现将SAGD技术应用到天然气水合物开采中是可行的,但确定两口水平井之间的距离是关键,且在应用时要将上部井变为生产井,下部井变为注汽井。 相似文献
978.
979.
伊朗Y油田主力产层F油层属于典型的高温、高压、高产、有腐蚀性流体产出的油田。为了保障该油田的长效、高效、安全生产,需要对完井工艺及管柱保护进行防腐研究。采取完井时下入带封隔器的完井管柱,并在封隔器之上的油套环空注入防腐封隔液;室内对引进的2种环空封隔液体系进行了互溶性、高温稳定性、杀菌性等基础理化性能及对井下管材的腐蚀性的实验及评价。评价结果表明,CaCl2型环空封隔液高温稳定性较差,浸泡腐蚀速率值高值为0.062 mm/a,电偶腐蚀速率值高值为0.078 mm/a,均大于设定的腐蚀速率值0.05 mm/a。而引进的NaCl KCl型环空封隔液高温稳定性较好,浸泡腐蚀速率值高值为0.014 mm/a,电偶腐蚀速率值高值为0.037 mm/a,均低于设定的腐蚀速率值0.05 mm/a。鉴于此情况,对引进的CaCl2型环空封隔液进行改进并优化设计,确定合适的CaCl2型环空封隔液体系。优化设计后的CaCl2型环空封隔液高温稳定性良好,浸泡腐蚀和电偶腐蚀速率值均低于设定的腐蚀速率值,综合性能达到了现场应用要求。 相似文献
980.
永安油田永553区块目的层为沙四段,以含砾砂岩、砾岩为主,为低孔低渗油藏。前期施工井存在钻进速度慢、开采程度低、经济效益差等特点。针对永553低渗区块开发现状及开发难点,对该区块进行了一体化(IPM)钻井方案设计,并对钻井设计进行了优化。通过优化钻井技术,钻井提速明显,提高了井身质量,延长了油井寿命。永553低渗区块IPM钻井项目的成功实施,说明IPM钻井模式对于提高油井质量、节约钻井成本、提高经济效益是行之有效的。 相似文献