辽东湾葵花岛构造区浅层气分布特征、成因探讨及工程影响

揭示了葵花岛构造区浅层气规模小、埋藏浅、分布散、压力低、储层松散等分布特点,根据沉积环境和地质特征,推测浅层气为生物甲烷气,但并不完全排除是热生甲烷次生气藏的可能性,探讨了浅层气潜在的工程危害并提出相应防治措施,为今后海洋工程建设提供科学依据。     

山东半岛南部滨浅海区的海洋灾害地质

随着人类开发利用海洋的深入发展,世界各海洋国家都在实施新的海洋战略。作为自然灾害之一的海洋地质灾害,越来越受到人们的重视。根据2009年在山东半岛南部滨浅海区实测的3 000km的高分辨率浅地层剖面资料,识别出研究区主要潜在的海洋地质灾害因素,着重探讨了浅埋不规则基岩面、埋藏古河道、浅层气、浅层断层等灾害地质的埋藏特征和分布范围,编制了研究区灾害地质分布图,并分析了这些灾害地质的形成机制及危害性,该研究可为海洋资源开发及海洋工程建设提供科学依据。     

Composition of fluids expelled during compaction of Mississippi delta sediments

Fluids discharged from subaerial springs along faults on a sediment diapir near the mouth of the Mississippi River are derived from buried marine pore waters which have been extensively altered chemically by processes of bacterial respiration, mineral precipitation and, possibly, by fractionation due to the presence of clays of high exchange capacity. Vertical mass transport of dissolved components in many shallow marine sediments is controlled by long-term compaction, diffusion and bioturbation. In areas of rapid sediment deposition, however, these processes can be overwhelmed by catastrophic episodes of sediment failure, vertical mixing and upward discharge of water, gas and dissolved species.     

Possibility of Large Deposits of Gas Hydrates in Deeper Waters of India

The available geological and thermodynamic data, essential for the formation and accumulation of gas hydrates, have been integrated and broadly interpreted for the deeper waters of India. The preliminary studies indicate that, in all probability, vast gas hydrate resources exist in the shallow sediments under deep waters. The area of the Bay of Bengal and Arabian Sea, off the coast of India and Andaman Islands, have accumulated thick sediments, over 22 and 10 km, respec tively, during collision of the Indian Plate with the Tibetan Plate. Bottom Simulating Reflectors (BSRs), indicating the likely presence of gas hydrates, have been observed from multichannel and single-channel seismic reflec tion data west of the Andaman Islands and Kerala-Konkan offshore. The Indian continental shelf, slope, and rise areas have, at places, shown the presence of gas-charged sediments and gas seeps through faults. There are commercial oil and gas fields in the shallow waters of both the east and west coasts of India. These are indicative of generation of both biogenic as well as thermogenic gases in the offshore areas of India. For the first time, an attempt has been made to estimate in-place gas hydrate resources under deep waters of India beyond 600 m water depth to the legal continental shelf boundary, and to the Andaman Islands. The gas hydrate resources appear to be vast, and require extensive exploratory efforts for their precise mapping and quantitative assessment.     

Distribution and origin of shallow gas in deep-sea sediments of the Ulleung Basin, East Sea (Sea of Japan)

A synthesis of high-resolution (Chirp, 2–7 kHz) subbottom profiles in the Ulleung Basin reveals patchy distribution of shallow (<90 m subbottom depth) gassy sediments in the eastern basin plain below 1,800-m water depth. The shallow gases in the sediments are associated with acoustic turbidities, columnar acoustic blankings, enhanced reflectors, dome structures, and pockmarks. Analyses of gas samples collected from a piston core in an earlier study suggest that the shallow gases are thermogenic in origin. Also, published data showing high amounts of organic matter in thick sections of marine shale (middle Miocene to lower Pliocene sequence) and high heat flow in the basin plain sediments are consistent with the formation of deep, thermogenic gas. In multi-channel deep seismic profiles, numerous acoustic chimneys and faults reflect that the deep, thermogenic gas would have migrated upwards from the deeper subsurface to the near-seafloor. The upward-migrating gases may have accumulated in porous debrites and turbidites (upper Pliocene sequence) overlain by impermeable hemipelagites (Quaternary sequence), resulting in the patchy distribution of shallow gases on the eastern basin plain.     

Effects of sea states on seafloor compliance studies

Gas hydrates affect the bulk physical properties of marine sediments, in particular, elastic parameters. Shear modulus is an important parameter for estimating the distribution of hydrates in the marine sediments. However, S-wave information is difficult to recover without proper datasets. Seafloor compliance, the transfer function between pressure induced by surface gravity waves and the associated seafloor deformation, is one of few techniques to study shear modulus in the marine sediments. The coherence between recorded time series of displacement and pressure provides a measure of the quality of the calculated transfer function, the seafloor compliance. Thus, it is important to understand how to collect high coherence datasets. Here we conducted a 10-month pilot experiment using broadband seismic sensors and differential pressure gauges. We found that data collected in shallow water depth and during rough seas gave high coherence. This study is the first time long-term data sets have been employed to investigate seafloor compliance data quality and its dependence on sea state. These results will help designing future large-scale compliance experiments to study anomalously high shear moduli associated with the presence of gas hydrate or cold vents, or alternatively anomalously low shear moduli, associated with partial melt and magma chamber.     

High-resolution seismic imaging of gas accumulations and seepage in the sediments of the Ria de Aveiro barrier lagoon (Portugal)

Methane is a powerful greenhouse gas and an important energy source. The global significance and impact in coastal zones of methane gas accumulation and seepage in sediments from coastal lagoon environments are still largely unknown. This paper presents results from four high-resolution seismic surveys carried out in the Ria de Aveiro barrier lagoon (Portugal) in 1999, 2002 and 2003. These comprise three chirp surveys (RIAV99, RIAV02, RIAV02A) and one boomer survey (RIAV03). Evidence of extensive gas accumulation and seepage in tidal channel sediments from the Ria de Aveiro barrier lagoon is presented here for the first time. This evidence includes: acoustic turbidity, enhanced reflections, acoustic blanking, domes, and acoustic plumes in the water column (flares). The stratigraphy and structural framework control the distribution and extent of gas accumulations and seepage in the study area. In these shallow systems, however, tidal altitude variations have a significant impact on gas detection using acoustic methods, by changing the raw amplitude of the enhanced seismic reflections, acoustic turbidity, and acoustic blanking in gas-prone areas. Direct evidence of gas escape from drill holes in the surrounding area has shown that the gas present in the Ria de Aveiro consists of biogenic methane. Most of the gas in the study area was probably generated mainly in Holocene lagoon sediments. Evidence of faults affecting the Mesozoic limestones and clays underlying some of the shallow gas occurrences, and the presence of high-amplitude reflections in these deeper units raise the possibility that some of this gas could have been generated in deeper sedimentary layers, and then migrated upward through the fractured Mesozoic strata.     

Seismic Characterisation of Gas-rich Near Surface Sediments in the Arkona Basin, Baltic Sea

Gas in sediments has become an important subject of research for various reasons. It affects large areas of the sea floor where it is mainly produced. Gas and gas migration have a strong impact on the environmental situation as well as on sea floor stability. Furthermore, large research programs on gas hydrates have been initiated during the last 10 years in order to investigate their potential for future energy production and their climatic impact. These activities require the improvement of geophysical methods for reservoir investigations especially with respect to their physical properties and internal structures. Basic relationships between the physical properties and seismic parameters can be investigated in shallow marine areas as they are more easily accessible than hydrocarbon reservoirs. High-resolution seismic profiles from the Arkona Basin (SW Baltic Sea) show distinct ‘acoustic turbidity’ zones which indicate the presence of free gas in the near surface sediments. Total gas concentrations were determined from cores taken in the study area with mean concentrations of 46.5 ml/l wet sediment in non-acoustic turbidity zones and up to 106.1 ml/l in the basin centre with acoustic turbidity. The expression of gas bubbles on reflection seismic profiles has been investigated in two distinct frequency ranges using a boomer (600–2600 Hz) and an echosounder (38 kHz). A comparison of data from both seismic sources showed strong differences in displaying reflectors. Different compressional wave velocities were observed in acoustic turbidity zones between boomer and echosounder profiles. Furthermore, acoustic turbidity zones were differently characterised with respect to scattering and attenuation of seismic waves. This leads to the conclusion that seismic parameters become strongly frequency dependent due to the dynamic properties of gas bubbles.     

中国东部晚更新世以来的海水进退

我国东部滨海平原及其以东的浅海陆架,是第四纪冰川时期海岸线往复迁移的地带.要掌握海水的进退边界及反复过程,必须在沉积层序学和年代学的广泛研究基础上,依据古滨线沉积和残留地貌标志,与世界典型地区的海面变化模式进行对比,才能获得冰川性海面变化及构造型海面变化在我国东部海面升降及海水进退过程中互相影响、相互消长的时空表现.     

An insight into shallow gas hydrates in the Dongsha area,South China Sea

Previous studies of gas hydrate in the Dongsha area mainly focused on the deep-seated gas hydrates that have a high energy potential, but cared little about the shallow gas hydrates occurrences. Shallow gas hydrates have been confirmed by drill cores at three sites(GMGS2 08, GMGS2 09 and GMGS2 16) during the GMGS2 cruise, which occur as veins, blocky nodules or massive layers, at 8–30 m below the seafloor. Gas chimneys and faults observed on the seismic sections are the two main fluid migration pathways. The deep-seated gas hydrate and the shallow hydrate-bearing sediments are two main seals for the migrating gas. The occurrences of shallow gas hydrates are mainly controlled by the migration of fluid along shallow faults and the presence of deep-seated gas hydrates.Active gas leakage is taking place at a relatively high-flux state through the vent structures identified on the geophysical data at the seafloor, although without resulting in gas plumes easily detectable by acoustic methods.The presence of strong reflections on the high-resolution seismic profiles and dim or chaotic layers in the subbottom profiles are most likely good indicators of shallow gas hydrates in the Dongsha area. Active cold seeps,indicated by either gas plume or seepage vent, can also be used as indicators for neighboring shallow gas hydrates and the gas hydrate system that is highly dynamic in the Dongsha area.     

浅地层剖面资料处理中的地层厚度校正（英文）

浅地层剖面测量是海洋工程勘察、灾害地质调查和大陆架海洋地质科学研究的重要手段,资料解译的准确程度将对地质调查和研究成果的可靠性造成直接影响。由于发收分置型浅地层剖面仪的激发装置与接收装置是分开的,当调查区域的水深过浅时,将其近似为自激自收的单道地震系统会导致地层的畸变,水深越浅地层畸变率越大。根据浅地层剖面仪的基本原理,推导出了浅部地层厚度畸变校正公式,为用C-View软件更准确地解译此类浅地层剖面资料提供了参考。海底沉积物的声速直接影响浅地层剖面地层厚度解译的准确性,利用卢博等建立的适用于中国东南近海的声速经验公式,在某人工岛构造调查中,根据地质钻孔获取的孔隙度参数计算各沉积层的平均声速,建立相应的声速结构剖面,对地层厚度进行校正,取得较好的效果,用孔隙度预测声速的方法参数容易获取,能够提高浅地层剖面资料的解译精度,使地层的厚度更接近于实际,具有一定的实用意义。     

澳大利亚波拿巴盆地北部中新统硅质碎屑与碳酸盐混合沉积特征及控制因素

波拿巴盆地油气资源十分丰富.新生界千余米的浅海碳酸盐岩背景下,中新统底部发育一套12～52 m硅质碎屑与碳酸盐混合沉积,其中硅质碎屑作为潜在的良好储集体,尚未引起足够重视.综合运用录井、测井及三维地震等资料,认为盆地北部研究区内该套混合沉积是由陆棚浅海台地生物滩、坝碳酸盐和三角洲平原和前缘硅质碎屑混合而成,以相在空间上...     

Permeability–porosity relationships of subduction zone sediments

Permeability–porosity relationships for sediments from the northern Barbados, Costa Rica, Nankai, and Peru subduction zones were examined based on sediment type, grain size distribution, and general mechanical and chemical compaction history. Greater correlation was observed between permeability and porosity in siliciclastic sediments, diatom oozes, and nannofossil chalks than in nannofossil oozes. For siliciclastic sediments, grouping of sediments by percentage of clay-sized material yields relationships that are generally consistent with results from other marine settings and suggests decreasing permeability as percentage of clay-sized material increases. Correction of measured porosities for smectite content improved the correlation of permeability–porosity relationships for siliciclastic sediments and diatom oozes. The relationship between permeability and porosity for diatom oozes is very similar to the relationship in siliciclastic sediments, and permeabilities of both sediment types are related to the amount of clay-size particles. In contrast, nannofossil oozes have higher permeability values by 1.5 orders of magnitude than siliciclastic sediments of the same porosity and show poor correlation between permeability and porosity. More indurated calcareous sediments, nannofossil chalks, overlap siliciclastic permeabilities at the lower end of their measured permeability range, suggesting similar consolidation patterns at depth. Thus, the lack of correlation between permeability and porosity for nannofossil oozes is likely related to variations in mechanical and chemical compaction at shallow depths. This study provides the foundation for a much-needed global database with fundamental properties that relate to permeability in marine settings. Further progress in delineating controls on permeability requires additional carefully documented permeability measurements on well-characterized samples.     

南海东沙群岛以北海底沙波稳定性分析

利用在南海东沙群岛北部至西北海域为工程目的所采集的海底地形测量、底质取样、海底底流测量资料,以及以往的区域地质、地球物理资料,采用沉积学、构造学和海洋水动力学综合研究方法,对该区海底沙波形成及稳定性进行了综合分析。认为该区海底沙波是在目前水动力环境下所形成,为今生,海底表层沉积物为晚更新世地层受到冲刷改造的再沉积。沙波形成主要受潮流底流的水动力作用控制,并与构造抬升有关。沙波具有一定的活动性,主要由SE向NW方向移动,且活动性逐渐减弱。北区段海底沙波稳定,中区段海底沙波较稳定,它们对海底工程建设不会造成影响;而南区段海底沙波较为活动,当沙波发生较大规模移动时,对海底工程建设会造成一定影响。     

南海北部湾海洋工程地质特征

根据地球物理、声学探测及海底取样等实测资料详细分析,发现北部湾油气勘探开发区具有近岸、水浅等优越自然条件以及复杂的海洋工程地质特征。海底地形地貌较为复杂,存在潮流沙脊与潮沟、海底沙坡、埋藏古河道、浅层气、埋藏古陡坡、滑塌断层及可能的砂土液化层等潜在灾害地质因素,对海上构筑物存在直接或潜在的危险性。尤其在东部,海底坎坷不平,活动性的潮流消脊、侵蚀沟槽、海底沙波及浅层气等很发育,是海底工程建设的危险区,应引起高度重视。     

Shallow gas depth-contour map of the Skagerrak-western Baltic Sea region

A shallow gas depth-contour map covering the Skagerrak-western Baltic Sea region has been constructed using a relatively dense grid of existing shallow seismic lines. The digital map is stored as an ESRI® shape file in order to facilitate comparison with other data from the region. Free gas usually occurs in mud and sandy mud but is observed only when sediment thickness exceeds a certain threshold value, depending on the water depth of the area in question. Gassy sediments exist at all water depths from approx. 20 m in the coastal waters of the Kattegat to 360 m in the Skagerrak. In spite of the large difference in water depths, the depth of free gas below seabed varies only little within the region, indicating a relatively fast movement of methane in the gas phase towards the seabed compared to the rate of diffusion of dissolved methane. Seeps of old microbial methane occur in the northern Kattegat where a relatively thin cover of sandy sediments exists over shallow, glacially deformed Pleistocene marine sediments. Previous estimates of total methane escape from the area may be correct but the extrapolation of local methane seepage rate data to much larger areas on the continental shelf is probably not justified. Preliminary data on porewater chemistry were compared with the free gas depth contours in the Aarhus Bay area, which occasionally suffers from oxygen deficiency, in order to examine if acoustic gas mapping may be used for monitoring the condition of the bay.     

天然气水合物的上界面——硫酸盐还原-甲烷厌氧氧化界面

定义了海域天然气水合物成矿带的上界面。指出在地球深部存在最原始的、从根本上不依靠光合作用来生存的生命系统。根据对ODP岩心样品中微生物数量的统计,海底以下沉积层中的生物数量可能占据全球原核生物总量的70%,其生物总碳量和地球表面所有植物的碳总量相当。地球内部如此巨大的生物总量应该在地壳中的气体分布等方面起着重要作用。甲烷在地壳层中广泛存在,并主要是微生物成因的。微生物产甲烷的途径主要有两个,一是二氧化碳还原,另一个是醋酸盐发酵。相应地,参与产甲烷的微生物菌群主要是产甲烷菌和食醋酸菌。甲烷在沉积层中的厌氧氧化是一个不争的事实。该过程发生在海底以下一个非常局限的区带,称为硫酸盐还原-甲烷厌氧氧化区带。通常,这个区带很窄,仅为一个面,因此,硫酸盐还原-甲烷厌氧氧化区带又称硫酸盐还原-甲烷厌氧氧化界面。这是一个基本的生物地球化学界面,在功能上它起到屏蔽甲烷向海底和大气逸散的作用,是一个巨大的甲烷汇。甲烷的厌氧氧化同样是一个由微生物介导的过程,参与此过程的微生物主要是食甲烷古菌和硫酸盐还原菌。硫酸盐还原-甲烷厌氧氧化界面在海洋沉积层中一般深可达海底以下上百米,浅可至海底。此界面为天然气水合物的上界面,该界面以上没有甲烷...     

A Sound Approach to Soft Sediment Resolution

The last few years has seen a surge in research activities directed towards investigating properties and dynamics of young marine, limnic and fluvial sediments. It is by now a well established fact that the sequence of sediments ranging from concentrated benthic suspension over fluid mud to un-consolidated material summarized as liquid sediments (LS), act as carriers for a wide range of pollutants discharged or migrated into waterways. Knowledge of the transport and fate of LS allows determining the transport and fate of adsorbed constituents (e.g., heavy metals, pesticides, PCBs, PAHs). To assess the environmental impact of LS, efforts have to be made to better understand the processes in relation to hydrodynamics and the chemical and physical properties of the layers. Since physical laws limit the resolution and detection power of conventional seismo-acoustic systems in respect of LS, alternative measurement, data analysis and processing approaches have to be found. Adapted acoustic procedures initially developed for shallow water marine environments to extreme shallow water regimes using matched field inversion techniques can reveal geoacoustic parameters including density, compressional wave speed and attenuation as a function of depth and time. The paper outlines the effects of sediment mobility upon the environment followed by a short overview of techniques commonly used to investigate sediments and other freshwater/marine events. The problems faced and limitations of existing systems are briefly outlined. Results obtained with recently developed and refined geoacoustic inversion methods are presented highlighting their potential for long-term study of physical properties and dynamics of LS.     

广东大亚湾海域潜在的地质灾害类型及其分布规律

根据大量地质一地球物理实测资料,分析了大亚湾海底潜在地质灾害因素,特别是基底断层、沙波、浅埋基岩、陡坎、异常堆积区等与海洋工程关系密切的地质灾害的类型、分布特征、形成机制及危害性,为海洋开发与海底工程设计提供科学依据。     

浅地层剖面测量在海洋井场调查中的应用和解释

浅地层剖面测量广泛应用于各种海洋工程项目中,对于查明海底沉积结构、沉积环境和浅部潜在的地质灾害因素等具有不可或缺的作用。海洋井场调查是海洋油气勘探开发中一个重要过程,其调查结果将对平台插桩安全和钻探作业顺利进行产生很大影响。因此,需要充分了解浅剖技术原理、资料的质量影响因素和资料的解释过程,以及如何与钻探资料相结合,以满足井场调查的要求。