Lacustrine basin unconventional resource plays: Key differences

There has been a revival in hydrocarbon source rock characterization and development associated with growing interest in unconventional resources, where these fine-grained organic-rich rocks act as both source and reservoir. To-date, the exploration focus on shale reservoirs has been largely on marine systems. Lacustrine source rocks for conventional resources are geographically important, dominating regions such as China, Indonesia, and Brazil's resource-base. However, they have been generally untested for unconventional resources.There are a number of key differences in the nature of these hydrocarbon systems that should be considered when assessing whether lacustrine systems may represent future unconventional opportunities in areas where the conventional resource-base is dominated by lacustrine-sourced oil. Among the key differences between these depositional systems is the greater sensitivity to high frequency climatic variability within lacustrine systems. Lacustrine systems are highly sensitive to changes in the balance between precipitation and evaporation, which may lead to rapid changes in lake level, potentially exceeding 600 m. These changes in depositional conditions are geologically rapid and may occur over periods of thousands of years. Such changes can reduce the areal extent of potentially thick source rock intervals to only those portions of a basin where a permanent deep lake was present. Thus the core unconventional target area may be geographically limited compared with their marine counterpart. Although potentially areally limited, a review of many lacustrine source rocks suggests that their thicknesses are often significantly greater than marine source rocks. An examination of the more distal portions of lacustrine systems, where better source rock potential is present reveals that there is generally limited connectivity between source and conventional reservoir. In these settings, such as the Wind River basin (Waltman Shale), the hydrocarbons remain trapped within the shales, potentially leading to over-pressured hydrocarbon charged systems. Such conditions suggest that although areally limited, viable unconventional targets may exist, if suitable reservoir conditions are present. Finally, the character of the oils produced is different in these settings, with lacustrine oils being waxy and displaying different hydrocarbon generation and cracking kinetics. High wax oils display distinct flow characteristics, being more viscous, and may offer different production challenges than their non-waxy marine equivalents. Additionally, differences in their cracking kinetics may indicate that the timing of gas generation for shale gas plays may differ significantly from marine systems.     

Seismic geomorphology,architecture and genesis of Miocene shelf sand ridges in the Pearl River Mouth Basin,northern South China Sea

Multiple stages of large-scale shelf sand ridges, including the shoreface-attached and the offshore types, have developed in the Miocene successions on the mid-shelf region of the Pear River Mouth Basin, northern South China Sea. Utilizing a high-quality 3D seismic data set, accompanying 2D seismic profiles and well logs, the morphology, architecture and genesis of these shelf sand ridges have been systematically investigated in this study. The ridges are of very large scale, with the largest one having a maximum height of 64 m, a width of more than 20 km and a length of 37 km within the 3D survey area. Being mound-shaped, they also display obvious asymmetry character, with the ridge crest preferentially located on the SE side. Three main internal components, including the ridge front, central ridge and the ridge tail, have been recognized through careful anatomy analysis of the two most well-imaged ridges, each displaying distinct expressions on seismic amplitudes and geometries. In the plan view, most of the shelf sand ridges are generally NE–SW oriented and widening to the SW direction. Scouring features can also be clearly observed along the SW direction, including scour depressions and linear sandy remnants. On well logs, the shelf sand ridges are represented by an overall coarsening-upward pattern. Intervals with blocky sandstones are preferentially present on higher locations due to a differential winnowing process controlled by shelf topography.Plenty of evidence indicates that these ridges were primarily formed by the reworking of forced regressive or lowstand deltaic deposits under a persistent southwesterly flowing current during the subsequent transgression. This very current is a composite one, which is speculated to consist of winter oceanic current, SCSBK (South China Sea Branch of Kuroshio) intrusion onto the shelf and internal waves propagating from the Luzon Strait. Tidal currents might have contributed to the SE growth of the ridge. In response to the reglaciation of Antarctic ice-sheet and the closure of Pacific-Indian ocean seaway in the middle Miocene, the intensification of the North Pacific western boundary current was considered to have potential links to the initiation of the shelf sand ridges at ∼12 Ma. The development of shelf ridges was terminated and replaced by rapid deltaic progradation at ∼5.5 Ma.     

珠江口盆地西江凹陷南部文昌组层序地层及沉积体系研究

珠江口盆地西江凹陷南部包括两个相邻洼陷：西江36洼和番禺4洼,钻探结果却揭示了截然不同的油气勘探前景,其中,番禺4洼探明储量已过亿吨,而西江36洼却未有商业发现,导致勘探上对西江36洼烃源潜力有所顾虑。为了揭示这种差异油气地质条件产生的原因,亟待开展两个洼陷的对比研究。以主要烃源层系文昌组为切入点,通过开展精细的层序-沉积研究,进一步系统评估西江36洼烃源潜力。依据地震、钻井及分析化验等资料,在西江36洼与番禺4洼文昌组共识别了6个三级层序。西江36洼和番禺4洼文昌组发育扇三角洲、辫状河三角洲、湖底扇及湖泊沉积等沉积相类型,垂向上沉积相带具有旋回特征。伴随裂陷不同阶段和边界断层活动差异,陡坡带和缓坡带三角洲沉积体系规模呈现差异演化特征,而湖盆和半深湖-深湖相规模总体呈现出先增大后减小的规律。沉积相带在横向上也具有明显的迁移特征,表现为文六段时期先在西江36洼开始沉积,文五段开始再扩展到番禺4洼,同时文一段时期西江36洼湖盆已经消失,只在番禺4洼沉积充填。进一步对比两个洼陷各三级层序反映优质烃源岩条件的半深湖-深湖规模及物源供给量,结果显示在文六段至文四段时期两个洼陷烃源条件基本一致。鉴于该层段作为番禺4洼的主力源岩,其巨大的生烃潜力已经被勘探所证实,因此认为不能低估具有相似烃源条件的西江36洼生烃潜力。     

Numerical investigation of the control factors driving Zhe-Min Coastal Current

During the northeast monsoon season, Zhe-Min Coastal Current(ZMCC) travels along the Chinese mainland coast and carries fresh, cold, and eutrophic water. ZMCC is significantly important for the hydrodynamic processes and marine ecosystems along its path. Thus, this bottom-trapped plume deserves to be further discussed in terms of the major driving factor, for which different opinions exist. For this purpose, in this study, a high resolution Semi-implicit Cross-scale Hydroscience Integrated Syste...     

黄河口及邻近海域鱼卵、仔稚鱼群落结构及多样性的年间变化

为了解黄河口及邻近海域鱼卵、仔稚鱼的群落结构动态,分别于2014年、2015年、2017年和2018年的6月利用大型浮游生物网对黄河口及邻近海域进行4个航次的表层水平拖网调查。根据鱼卵、仔稚鱼的种类组成、数量分布等群落结构特征,运用生物多样性指数、聚类分析和皮尔逊相关性矩阵分析等方法对该海域鱼卵、仔稚鱼的资源分布进行了综合研究。结果表明,4年调查共采获鱼卵3 829粒,仔稚鱼234尾,隶属于7目14科15属。鱼卵的主要优势种为鳀（Engraulis japonicus）和短吻红舌鳎（Cynoglossus joyeri）,仔稚鱼的主要优势种为斑鰶（Konosirus punctatus）和虾虎鱼科未定种Gobiidae sp.。生物多样性各指数均以2015年最高,2018年最低。利用R语言对鱼卵、仔稚鱼年间种类组成相似性进行聚类,将4个调查年份划分为3组,各分组之间主要的分歧种均为鳀。生物多样性各指数与环境因子之间皮尔逊相关性分析表明,盐度与鱼卵、仔稚鱼生物多样性的关系较为密切。分析认为,黄河口及邻近海域鱼卵、仔稚鱼群落分布和多样性的年间变化特征体现了鱼类对环境变异的响应。     

黄河三角洲潮间带大型底栖无脊椎动物群落结构与分布特征

为了解黄河三角洲潮间带大型底栖无脊椎动物现状,于2019年5月分别对建国后黄河入海口4个流路区域20个潮间带站位进行了采样调查.调查共采集到大型底栖无脊椎动物5纲16目37科60种,主要优势种有托氏（虫昌）螺(Umbonium costatum)、泥螺(Bullacta exarata)、光滑河篮蛤(Potamocor...     

Methane-derived authigenic carbonates from active hydrocarbon seeps of the St. Lawrence Estuary,Canada

Nearly 2000 pockmarks with diameters ranging from a few tens of meters up to 700 m are present on the seafloor of the St. Lawrence Estuary in eastern Canada. Coring of some pockmarks resulted in the recovery of various-sized and shaped carbonate concretions in a predominantly silty mud matrix. Petrographic and geochemical data on four authigenic carbonate concretions are reported as well as data from shell material in the unconsolidated sediment. Video observations and echo-sounder images indicate that the sampled pockmarks are actively gas venting. The video images show significant look-alike microbial mats in areas where gas is venting. The carbonate concretions are primarily made up of carbonate cements with varying percentage of shell fragments, micrite particles and fine-grained clastics. Orthorhombic crystal morphology and diagenetic fabrics including isopachous layers and botryoids characterize the aragonite cement. Oxygen isotopes ratios for the cement crusts do not record any thermal anomaly at the site of precipitation with δ¹⁸O_VPDB ratios (+3‰) in equilibrium with cold (5 °C) deep marine waters, whereas significant negative δ¹³C_VPDB ratios (−9.9 to −33.5‰) for cement and shell material within concretions indicate that the carbonates largely derive from the microbial oxidation of methane. The δ¹³C_VPDB ratios of aragonite shells (−2.7 to −5.6‰) taken from unconsolidated sediments at some distance from the concretions/vents show variable dilution of HCO₃⁻ with negative δ¹³C_VPDB ratios derived from microbial oxidation of methane with isotopically normal (0‰) marine bicarbonate. These results are in agreement with other lines of evidence suggesting that pockmarks formed through the recent and still active release of gas from a reservoir within the Paleozoic sedimentary succession.     

Diurnal variation of nitric oxide emission flux from a mangrove wetland in Zhangjiang River Estuary,China

The diurnal variation of nitric oxide (NO) emission fluxes from a Kandelia obovata and Avicennia marina mangrove wetland were studied in the Zhangjiang River Estuary Mangrove National Nature Reserve using a dynamic chamber-based technique and a chemiluminescent analyzer. Results from field experiments show that NO emission from K. obovata and A. marina sampling sites reached maximal values of 1.07 ng N m⁻² s⁻¹ and 1.23 ng N m⁻² s⁻¹, respectively after the night tide. Meanwhile NO emission maintained at a steady lower level in daytime for both wetland sites. In laboratory experiments, NO emission from the mangrove wetland soil samples treated with simulated tides in the darkness exhibited higher values than those in the light, therefore it seems that tides and darkness could increase NO emission from mangrove wetlands, while intensive light, high temperature, and dryness in the daytime decreased NO emission. Compared with K. obovata soil samples, the diurnal average NO emission rate of the A. marina site was significantly higher, which was closely related to relatively higher diurnal average CO₂ emission rate, soil available nitrogen content and soil net nitrification rate of the A. marina site. Moreover, soil samples of the A. marina site were more responsive to simulated tides and the addition of nitrogen than those of the K. obovata site.     

端元分析模型在长江口邻近海域沉积物粒度数据反演方面的应用

海洋沉积物粒度分布曲线往往同时具有多个峰,而且同一类型沉积物因时间和空间上的不同其粒度分布曲线峰的位置也不同,沉积物粒度分布多峰的特点反映了沉积物不同的输运形式和沉降过程[1,2].因此,在沉积物的粒度分布数据中保存了有关沉积物输运和沉降的信息,而获得这些信息对于揭示沉积区域水动力特性、沉积物输运和沉降规律具有重要的意义.     

闽江河口区湿地生态旅游环境容量研究

本文讨论了生态旅游环境容量的定义及内涵，分析了生态旅游环境容量的特征及构成，在此基础上估算了闽江河口区湿地生态旅游环境容量．结果表明：闽江河口区湿地生态旅游环境容量的限制因子是鳝鱼滩自然保护区生态旅游环境空间容量．鳝鱼滩旅游步行道可分成南路和北路，北路为水路游线，南路为陆路游线．北路游线环境空间日容量为800人次／d，南路游线环境空间日容量为1144人次／d．鳝鱼滩湿地生态旅游环境空间年容量为451202人次／a．这一环境容量可作为闽江河口区湿地生态旅游活动环境容量的最高限制量．