Oil／Gas Accumulation Characteristics and Exploration Methods of the Deltaic Lithologic Reservoirs in Northern Shaanxi Area

There are large deltaic systems in the Triassic Yanchang Formation in the northern Shaanxi area of the Ordos Basin, and developed two sets of good source-reservoir-caprock assemblages and many sets of oil-bearing beds. Exploration experience demonstrates that the formation and distribution of the reservoir were controlled by the generative depression of the Yanchang Formation, and deltaic reservoir sand body is the material basis for large-scale oilfields. In addition, secondary laumontite in a low permeable area was dissolved and then a high permeable area was formed. The updip lithologic variety of reservoir sand bodies is favorable to the formation of subtle lithologic traps, and the deltaic reservoirs are characterized by large multi-beds of oil-generation and abundant hydrocarbon resources. In this paper, the petroleum geologic settings of the studied area are analyzed, and the accumulation characteristics and exploration methods of lithologic reservoirs are summarized. It is of theoretical significance for the study of the exploration theories of lithologic reservoirs, and also expedites the exploration steps of deltaic reservoirs in the northern Shaanxi area.

河流、三角洲岩相一般特征研究

古河流-三角洲地带是油气有利的聚集地区,通过钻井数据与生产实际梳理河流-三角洲岩相规律;利用岩性、测井、物性等参数,结合微观影像、粒径分布等手段研究岩相特征。

西北江三角洲河网浮游植物叶绿素a粒径特征研究

为探索浮游植物叶绿素a粒径的时空变化及其影响因素,调查研究了西北江三角洲河网水域2021年枯水期(2月份和12月份)和丰水期(5月份和8月份)的水环境和浮游植物叶绿素a粒径特征。结果显示,叶绿素a总浓度呈现明显的季节差异,最高值出现在8月份,最低值出现在5月,分析原因主要与径流量的大小、水体pH和氧化还原电位的变化有关。叶绿素a总浓度的空间特征显示,广州周边站位的叶绿素a浓度明显偏高,主要与营养盐的空间分布格局和水体的交换能力有关。粒径特征的结果显示,小型和微型浮游植物是珠三角河网水体叶绿素a的主要贡献者,呈现交替优势。季节特征显示,2-5月份微型叶绿素a占主导地位,8月份和12月份小型叶绿素a占主导地位,分析原因主要与径流量的大小、水体pH和光照有关。空间特征显示,小型叶绿素a在8月份和12月份占比的最高值往往出现在河网中部的站位,微型叶绿素a占比的最高值往往出现在远离广州市的站位点,分析原因主要与溶解氧和硝酸盐含量有关。冗余分析结果表明pH、DO、水下光度、TP和硝酸盐含量是影响浮游植物粒径分布的主要影响因子。综上,物理因子包括径流量的大小和水体pH的变化影响叶绿素a粒径特征的季节变动,而化学因素如营养盐含量影响叶绿素a粒径特征的空间分布。

大尺度自成因机制与自成因地层学

在海平面升降、构造活动、沉积物供给等外部驱动作用下,沉积地层的叠置受自成因和他成因两种机制的控制。近年的认识表明,自成因机制可发生在沉积过程的各个时空尺度。不同于小尺度自成因机制仅发生在沉积系统的局部,大尺度自成因机制可在盆地范围内系统性地控制地层的发育,能够修饰甚至改变他成因过程。要想准确地探究地层的叠置样式与外部驱动条件之间的关系,必须有效地鉴别大尺度自成因与他成因过程。基于对大尺度自成因过程的认识,逐渐建立与发展了自成因地层学。它提出的自成因与他成因观、平衡响应与非平衡响应观为解析地层叠置样式与外部驱动条件之间的关系提供了新的视角。自成因地层学一方面对外部驱动条件分为稳定的(速率等作用方式保持不变)与不稳定的(速率等作用方式发生改变),由前者形成的地层叠加样式(或过程)称为自成因的,后者形成的地层叠加样式(或过程)称为他成因的。另一方面也将地层叠置样式分为稳定的(加积速率与进积速率的比值R_(agg)/R_(pro)保持不变)与不稳定的(R_(agg)/R_(pro)发生改变)。若稳定的外部驱动条件形成稳定的地层叠加样式,称为平衡响应,是自成因过程;稳定的外部驱动条件形成不稳定的地层叠加样式称为自成因的非平衡响应。此外,不稳定的外部驱动条件也可能形成稳定的地层叠加样式,称为他成因的非平衡响应。自成因地层学认为,由于自成因非平衡响应机制的普遍存在,地层的叠加过程通常表现得不稳定。相比而言,稳定的地层叠加样式仅在特殊情况下才能发生。传统成因地层学应当重视大尺度的自成因机制。

Reconstruction of the diagenesis of the fluvial-lacustrine-deltaic sandstones and its influence on the reservoir quality evolution——Evidence from Jurassic and Triassic sandstones, Yanchang Oil Field, Ordos Basin

The reservoir quality of Jurassic and Triassic fluvial and lacustrine-deltaic sandstones of the Yanchang Oil Field in the Ordos Basin is strongly influenced by the burial history and fa-cies-related diagenetic events. The fluvial sandstones have a highe' average porosity (14.8%) and a higher permeability (12.7×10-3 μm2) than those of the deltaic sandstones (9.8% and 5.8×10-3μm2, respectively). The burial compaction, which resulted in 15% and 20% porosity loss for Jurassic and Triassic sandstones, respectively, is the main factor causing the loss of porosity both for the Jurassic and Triassic sandstones. Among the cements, carbonate is the main one that reduced the reservoir quality of the sandstones. The organic acidic fluid derived from organic matter in the source rocks, the inorganic fluid from rock-water reaction during the late diagenesis, and meteoric waters during the epidiagenesis resulted in the formation of dissolution porosity, which is the main reason for the enhancement of reservoir-quality.

FUNDAMENTAL CHARACTERISTICS OF THE ANASTOMOSING FLUVIAL SYSTEM ON COMPLEX DELTAIC PLAIN

The anastomosing fluvial system was considered as the same term of the braided fluvial system. Smith and others have recognized the difference between them. They described the anastomosing fluvial system as 'a low energy complex of several interconnected channels of variable sinuosity crossing a wetland and forming many elongate vegetated islands', and established a depositional model of anastomosing fluvial system based on their

Testing optically stimulated luminescence dating on sand-sized quartz of deltaic deposits from the Sperchios delta plain, central Greece

This study reports on the first investigation into the potential of luminescence dating to establish a chronological framework for the depositional sequences of the Sperchios delta plain, central Greece. A series of three borehole cores(20 m deep) and two shallow cores(4 m deep), from across the delta plain, were extracted, and samples were collected for luminescence dating. The luminescence ages of sand-sized quartz grains were obtained from small aliquots of quartz, using the Single-Aliquot Regenerative-dose(SAR) protocol.The equivalent dose determination included a series of tests and the selection of the Minimum Age Model(MAM) as the most appropriate statistical model. This made it possible to confirm the applicability of quartz Optically Stimulated Luminescence(OSL) dating to establish absolute chronology for deltaic sediments from the Sperchios delta plain.Testing age results of the five cores showed that the deltaic sediments were deposited during the Holocene.A relatively rapid deposition is implied for the top14 m possibly as a result of the deceleration in the rate of the sea-level rise and the transition to terrestrial conditions, while on the deeper parts, the reduced sedimentation rate may indicate a lagoonal or coastal environment.

Seed germination traits of two plant functional groups in the saline deltaic ecosystems

Aims Salt stress resulting from soil salinization is one of the driving forces of the land degradation throughout the world.The modern Yellow River delta is one of the most saline areas in China.Phytoremediation can be an effective way to restore the salinized ecosystems,which requires selecting appropriate plant species.This study explored the germination responses of common plant species from contrasting habitats in the Yellow River delta to varying salinity,offering experimental information for ecosystem restoration in the Yellow River delta.Methods In this study,15 common plant species from the Yellow River delta were divided into two groups(high-salinity and low-salinity groups)by their natural habitats using Canonical Correlation Analysis.Seeds of each species were treated with five salinity levels(0,5,10,20 and 30 ppt),using a randomized complete block design,and germinated seeds were counted and removed daily for 28 days to calculate the final germination proportion and mean time to germination.The germination responses of seeds to salinity treatments were compared between the two groups.Important Findings In relation to salinity,seed germination behavior of the test species was closely related to the salinity level of the habitats over which they were distributed.Species from the habitats with higher salinity had generally higher final germination proportion but shorter mean time to germination than those from the habitats with lower salinity in all of five salinity treatments used.The final germination proportion and mean time to germination of low-salinity group species were more sensitive to salinity than those of high-salinity group species.Selecting the species with high final germination proportion and short mean time to germination is important for restoration of salinized land.

Dramatic changes in the horizontal structure of mangrove forests in the largest delta of the northern Beibu Gulf, China

The horizontal structure of mangrove forests is an important characteristic that reflects a significant signal for coupling between mangroves and external drivers.While the loss and gain of mangroves has received much attention,little information about how the horizontal structure of mangrove forests develops from the seedling stage to maturity has been presented.Here,remote sensing images taken over approximately 15 years,UVA images,nutrient elements,sediments,and Aegiceras corniculatum vegetation parameters of the ecological quadrats along the Nanliu Delta,the largest delta of the northern Beibu Gulf in China,are analyzed to reveal changes in the horizontal structure of mangroves and their associated driving factors.The results show that both discrete structures and agglomerated structures can often be found in A.corniculatum seedlings and saplings.However,the combination of seedlings growing into maturity and new seedlings filling in available gaps causes the discrete structure of A.corniculatum to gradually vanish and the agglomerate structure to become stable.The aggregated structure of seedlings,compared to the discrete structure,can enhance the elevation beneath mangroves by trapping significantly more sediments,providing available spaces and conditions for seedlings to continue growing.Furthermore,by catching fine sediments with enriched nutrients,the survival rate of A.corniculatum seedlings in the agglomerated structure can be much higher than that in the discrete structure.Our results highlight the significance of the agglomeration of A.corniculatum,which can be beneficial to coastal mangrove restoration and management.

地震沉积学在东海陆架盆地西湖凹陷河流-三角洲相储集层刻画中的应用

针对东海陆架盆地西湖凹陷渐新统花港组河流-三角洲相储集层横向变化快、常规切片属性形态差、储集层预测难度大、难以满足岩性油气藏的后续勘探开发的问题应用分频解释、反演-常规-90°相移联合构建地震岩性体、非线性切片、古地貌恢复、多属性融合等特色技术对传统地震沉积学方法进行优化。研究发现花港组发育辫状河、曲流河和浅水三角洲3类沉积体,垂向沉积演化受中期基准面旋回和古地貌联合控制。在中期基准面旋回上升阶段的早—中期以辫状河道沉积为主,发育垂向叠置型砂体;在上升半旋回晚期和下降半旋回的早期以曲流河沉积为主,发育孤立型砂体;在中期基准面下降半旋回的中—晚期以浅水三角洲沉积为主,发育迁移型中—厚层砂体。限定性古地貌对砂体展布具有控制作用,非限定性古地貌对砂体展布影响较小。在储集层刻画的基础上,提出断层封堵型和储集层上倾尖灭型构造岩性圈闭是西湖凹陷下一步滚动挖潜的主力方向。

基于时空矩阵图析土地覆盖演变——以中国珠江三角洲为例

[目的]在快速城市化的三角洲地区,气候变化与土地覆盖演变是高度相关的。因此,图析土地覆盖的演变过程,从而探讨人类活动对城市系统的影响,并评估城市抵抗自然灾害的能力至关重要。[方法]从空间和时间维度系统分析了珠江三角洲(简称珠三角)的土地覆盖演变模式,以揭示土地利用政策对珠三角地区的空间影响,并为应对气候变化和城市可持续发展提出建议。[结果]建立了一种利用R Studio、完全基于开放数据、通过时空矩阵在区域尺度图析土地覆盖演变过程的方法。利用开放的欧洲航天局气候变化倡议土地覆盖图和美国地质勘探局高程地图数据,分析了1992—2015年世界上城市化速度最快的地区之一珠三角的演变模式。通过在相对精细的时间颗粒度上来量化土地覆盖演变模式,揭示了珠三角不同地区对应不同发展阶段的各自变化强度与变化趋势。此外,低海拔海岸带的土地覆盖演变幅度较大,特别容易受到海平面上升、风暴增强等气候变化引发的灾害的影响。[结论]结果表明:2001—2002年,深圳和东莞土地覆盖演变幅度最大,2008年开始呈减小趋势;其他周边城市的土地覆盖年变化幅度具有更加稳定的特征。所提出的时空矩阵可以帮助决策者更好地了解三角洲地区土地覆盖的时空演变,有助于制定针对性的规划战略,以增强脆弱沿海地区的抗灾韧性。

渤海新近系浅水三角洲沉积体系与大型油气田勘探

新近纪渤海具有构造稳定、沉降缓慢、湖泊水域范围大、内部无分割、地形平缓、坡度小等特点,广泛发育浅水三角洲,从而形成渤海海域新近系良好的储盖组合和优越的油气成藏条件。浅水三角洲砂岩储层由于受河流作用的控制,砂体具有明显的方向性,存在明显的分叉现象,与曲流河相比,砂体连通性较好,砂体等厚图呈典型的朵叶状。湖相厚层泥岩普遍发育,与浅水三角洲砂体组成多套垂向优质储盖组合。浅水三角洲发育于渤海新近纪至今处于生烃的峰期主力富烃凹陷的有利区带,新构造运动造成新近纪以来凹陷主力源岩生烃峰期与新构造运动的同步耦合,为渤海大型浅水三角洲成因的优质储层油气成藏创造了优越条件,可以形成大型油气田。因此,重视并充分挖掘渤海浅水三角洲储层类型油气藏的勘探潜力将是追求浅层优质油藏、进一步增储上产的方向所在。

扇三角洲沉积体系及其与油气聚集关系

扇三角洲沉积体系是断陷盆地中极为发育的一种沉积体系，主要由扇三角洲平原组合、扇三角洲前缘组合和前三角洲沉积构成，可识别出9种成因相。受沉积物供给速率、可容空间增长速率及盆缘断裂产状等因素控制可划分出退积型、加积型、前积型、陡坡型和缓坡型5种扇三角洲类型。位于扇三角洲平原的辫状分流河道砂体及其位于扇三角洲前缘的与之有成因联系的水下分流河口坝、洪水型重力流砂体等物性好，可以构成优质储层。含油性勘探成果亦证实各主力油层段平面上主要分布于扇三角洲前缘及分流间湾区，小部分位于扇三角洲平原区。受埋藏深度和成岩场的影响，不同地区、不同层位主力油层段的物性与岩性相关性各异。因此，应用沉积体系分布与油气聚集规律挖掘剩余油层及进行远景区预测是有效的与可行的。

三角洲前缘水下分流河道储集层构型及剩余油分布

以吉林扶余油田J19密井网区为例,结合现代浅水三角洲沉积模式,综合应用岩心、测井等资料,对三角洲前缘水下分流河道单砂体内部构型进行了精细解剖。水下分流河道内部构型要素主要可分为前积体和前积层2种,前积层根据被破坏程度的不同又可分为保留型、破坏型和混合型,随湖平面升降及沉积物供给速率与可容纳空间增加速率的比值不同,前积体可分为进积型、退积型和加积型,各自具有不同的成因及沉积演化模式。应用岩电标定、公式拟合、密井网、对子井等资料对前积层和前积体进行了定量识别描述,建立了水下分流河道单砂体内部的三维构型模型。剩余油分析表明:前积层对剩余油的垂向分布有较强的控制作用,而在前积体内部剩余油主要在前积体的上倾方向富集。

水盐梯度下黄河三角洲湿地植被空间分异规律的定量分析

三角洲湿地植被的形成和分布同时受水深、土壤含盐量两个环境因子的作用。采用模糊数学排序方法分析了黄河三角洲湿地植被在水深、土壤含盐量两个环境梯度下的空间分异规律。结果表明,由TWINSPAN划分而得到的8个植被类型在模糊数学排序图中有各自的分布范围,界线明显。以穗状狐尾藻(Myriophyllum spica-tum)等水生植物为优势种的群落分布在排序图的左上部,为黄河三角洲湿地高水深、低盐分地区;以柽柳(Tam-arix chinensis)、翅碱蓬(Suaeda heteroptera)等典型盐生植物为优势种的群落分布在排序图的右下部,为黄河三角洲的低水深、高盐分地区;其他以芦苇(Phragmites australis)、荻(Triarrhena sacchariflora)、旱柳(Salix matsudana)等为优势种的群落分布在排序图的中部。利用Gini-Simpson指数,在模糊数学排序图中分析了植物物种多样性随水深、土壤含盐量梯度的空间变化,结果表明,高水深、低盐分和低水深、高盐分地区植物物种多样性均较低,而二者过渡区域植物物种多样性较高。

环渤海海平面上升与三角洲湿地保护

环渤海地区三角洲是我国滨海重要的湿地发育区 ,在淤泥质滩地型湿地上发育着众多的动、植物群落 ,成为若干珍稀水禽的栖息地。从地面垂直形变与潮位资料等分析 ,黄河三角洲和辽河三角洲的地面下降速率为 3～ 4mm/a和 3.5～ 4.5mm/a,而相对海平面上升速率为 4 5～ 5 .5mm/a和 5～ 6mm/a,预计至 2 0 5 0年总体的相对海平面上升量可达 40～ 5 5cm。海平面上升对三角洲湿地的影响首先是直接淹没大片农田、油井和市区 ,其次是加剧海岸线的侵蚀与后退 ,还有风暴潮与洪涝灾害的加剧。针对三角洲湿地生态系统所面临的生态风险与人为活动干扰 ,有必要采取更加科学合理的保护与开发模式。本文介绍了生境更新与湿地调整的管理策略 ,以及淤长型滨海湿地的滚动开发模式。交替采用“渐进”与“跃进”的滚动开发 ,可保持湿地总量的动态平衡 ,有利于三角洲的可持续发展。

成岩作用对河流—三角洲相砂岩储层物性演化的影响——以延长油区上三叠统延长组长2砂岩为例

延长油区上三叠统长 2地层河流相—三角洲相砂岩储层的物性明显受埋藏—成岩作用事件的影响。埋藏压实作用是导致砂岩孔隙丧失的主要原因 ,造成的平均孔隙度丧失为 17.8%。其中黑云母的早期成岩蚀变是造成原生孔隙丧失的一个重要原因。胶结作用造成的平均孔隙度丧失为 7.1%。其中碳酸盐胶结物和次生石英加大是造成砂岩物性降低的主要胶结物。碎屑颗粒周围绿泥石薄膜的存在阻止了一部分石英次生加大及碳酸盐胶结物的沉淀 ,使一部分原生粒间孔隙得以保存。晚期成岩阶段有机质分解形成的酸性流体及表生成岩作用阶段的大气降水是形成次生孔隙的主要原因 ,从而使长

四川盆地元坝地区上三叠统须家河组的潮控河口湾与潮控三角洲沉积

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