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深水重力流沉积发育特征与形成机制研究:以东非海域鲁武马盆地上始新统深水沉积为例
鲁银涛
学位类型博士
导师秦蕴珊 院士
2017-05
学位授予单位中国科学院大学
学位授予地点北京
学位专业海洋地质
关键词鲁武马盆地 深水沉积 结构单元 发育特征
摘要深水沉积砂岩储层在现今的油气勘探过程中,扮演着越来越重要的角色,一系列巨型、大型深水油气田的发现,吸引着众多研究者对其开展深入研究。相应地,经过几十年的发展,深水沉积理论基础和研究手段不断进步,其在油气勘探过程中也获得了越来越多的突破。众多国际油气公司也瞄准了该勘探领域,投入大量工作量进行深水沉积油气勘探工作,即使在深水区域,也获得了巨大的收益。未来很长一段时间,深水油气储量、产量增长将继续在全球油气储量、产量中占有举足轻重的地位,是石油公司的必争之地。在这个背景下,东非海域鲁武马盆地近年来获得了巨型天然气发现,成为了深水油气勘探的热点区域。同时,在油气勘探工作的带动下,在东非海域获取了大量的地震、钻井等基础地质、地球物理资料,为东非海域深水沉积研究提供了优越的条件。
通过深水沉积理论和野外地质考察建立的模式,结合研究区内的基础资料,特别是高分辨率的三维地震资料,对东非海域深水沉积体系展开了识别刻画研究,特别是对东非海域始新统深水沉积体系进行了细致的识别刻画,并对其成因、物源、演化特征等进行了分析。
研究认为,研究区第三系的深水沉积体系由多个峡谷、水道体系进行输送物质,物源来自古鲁武马三角洲。由于东非陆架相对较窄,陆坡相对陡倾,所以整个深水沉积体系发育相对顺直,且输送的颗粒物均属于较粗粒类型,属于近源陡坡型富砂质深水沉积体系,并定义研究区第三系发育的深水沉积体系整体为“线源型近源陡坡富砂质深水沉积体系”。
本文研究目标-上始新统深水沉积体系主要发育在研究区的中部,该沉积体系内部可分为6期水道形态的沉积体系,自第1期到第6期,自西北向东南发育。这6期水道的走向和形态均相当,相互呈大致平行的状态,相邻期次之间发育明显的边界,特别对于水道沉积体系而言,晚期沉积体系对早期沉积体系有侵蚀作用。在第3期至第6期水道末端,发育有水道末端扇,呈朵叶体状。但是1期水道和2期水道末端的朵体没有明显的特征,可能被侵蚀或者由于晚期沉积体系的叠加而不易识别,同时第1期水道和第2期水道的末端部分也无法完整追踪,在均方根振幅属性图上没有展现完整形态。将这几个朵体标注为3号朵体、4号朵体、5号朵体和6号朵体。
通过地震资料和测井资料,对不同深水沉积结构单元的地球物理响应特征进行了分析,认为不同的典型的沉积结构单元在地球物理资料上,有不同的响应特征。地震剖面上,深水水道复沉积表现为U型或V型,与其内部的独立水道反射特征相似,但是规模上,水道复合体比内部的独立水道大许多倍。垂向上,水道复合体的底部和下部与顶部的反射特征有明显的差别,反映底部和中下部的滑塌-碎屑流沉积,而底部和下部的反射特征也有差异,底部表现为低振幅、不连续、杂乱的反射特征,而下部地震反射的反射特以强振幅、不连续-弱连续的地震反射特征。在测井曲线上,水道表现为箱型的低GR特征,同时,电阻曲线显示电阻率值为异常高值,泥质含量很低,水道砂岩段的砂地(NGR)比可达0.97;朵体在地震剖面上表现为相对平缓、连续的强反射特征,测井相表现为锯齿状逐渐升高的高频震荡GR曲线和锯齿状逐渐降低的高频震荡GR曲线,反映了正粒序特征,发育在薄层互层内,岩性往往从砂岩过渡到粉砂岩、泥岩,粒度自下而上逐渐变小,指示着流体能量逐渐变弱,与水道末端扇和朵体所处的开放环境相吻合,砂地比相对较低,大约0.58。
研究区内始新统深水重力流沉积虽然也有多种因素的控制,但是最重要的因素为东非海域的地震活动。水道-朵体沉积这种深水重力流沉积与构造抬升之间的直接关系反映了构造控制了水道-朵体的物源补给和深水沉积体系的活动规律。鲁武马三角洲体系为始新统巨型深水重力流沉积提供了物质来源。构造隆升时间与深水水道-朵体复合体的发育时间相吻合。在下始新统沉积的碳酸盐岩碎屑流和钙质胶结砂岩物源来自西部的陆架区域和三角洲区域,指示该区在始新世之前经历了强烈的构造隆升作用。由于构造隆升和相对海平面的降低,早渐新世陆架碳酸盐岩和钙质胶结砂岩可能发生滑塌,而这些碳酸盐岩碎屑被高能量的浊流和碎屑流流体通过水道复合体搬运至深水区域。
研究区内朵体的延伸方向与水道延伸方向相比,全都有自北东向向东南向略微转向的特征,平面上水道到朵体呈“U”型拐角。这种特征指示水道和朵体复合体西北部相对高的地形限制了水道和朵体的空间展布区域。水道向朵体转变的过渡点的规模和形状可能也是造成水道轴向到朵体轴向发生弯曲的原因之一。
研究区上始新统深水沉积顺直的特征与陆坡坡度和其携带的沉积物有关。鲁武马盆地的陆坡相对较短、较陡。除陆坡坡度外,钻井获取的测井曲线揭示了水道内的岩性主要为砂岩,具有较强的侵蚀性,可能也是另一个造成研究区上始新统水道沉积体系如此顺直的原因。
鲁武马盆地东部深水区物源主要来源于鲁武马三角洲和陆架区域,而三角洲和陆架区域的碎屑岩主要来自西部陆上的莫桑比克褶皱带,该褶皱带内的片麻岩、花岗岩等富含长石的结晶岩是沉积岩的母岩,这些结晶岩被风化剥蚀,随鲁武马河向东注入海洋,首先形成鲁武马三角洲和陆架沉积,在特定的时期,由于构造事件等,发育事件性的重力流沉积,重力流携带三角洲和陆架上的大量碎屑物质沿峡谷、水道向东运移至鲁武马深盆区,在流体的能量减弱后,沉积在水道、朵体等沉积结构单元内,形成深水重力流砂岩。所以,究其根本,是东非大陆的莫桑比克褶皱带为鲁武马盆地深水重力流沉积提供了物源。
其他摘要Deep water sediment clastic reservoirs plays a more and more important role in petroleum exploration nowadays. More and more discoveries in this exploration region, attract researchers interests in it. On the other hand, the progress of the theory and technology on deep water sediment during decades, brought out more and more oil and gas discoveries. Most of the international oil and gas companies aimed to his exploration region, and deployed plenty of exploration activities all around the world. The giant and huge reserves guaranteed considerable revenue for these companies, even most of the reserves distributed in deep and ultra-deep water area. It is predicted that the deep water reserves and productions will be continue increasing in future for a long time, and occupy a very important status in petroleum exploration. Thus, more and more investment from these companies will pour into deep water region. During this period, Rovuma Basin in East African offshore revealed great exploration potential and reserves. As a "hot pot" of petroleum exploration, plenty of seismic data, well data and other geological and geophysical data were acquired in this area, provided advances for the deep water sediment research in this area.
Based on the deep water sediment theory and the modeling from outcrop in field trip, combining with the dataset in study area, especially high resolution 3D seismic data, we identified and analyzed deep water sediment system in East African offshore. We focus on the deep water sediment system which developed in Late Eocene, including its origin, source supply, evolution feature and et al.
The study area developed multiple deep water sediment systems in Tertiary, composed of several canyon-channel systems, which acted sediment path for the current and sediment materials. The source supply could be from paloe-Rovuma deltas. Because of narrow shelf and steep slope in East African continent margin, the deep water sediment systems were quit straight, while transported and deposited coarse grained sediment. The deep water sediment system belongs to proximal sand rich sediment system developed in steep slope, which could be defined to "linear proximal sand-rich deep water system in steep slope environment".
Upper Eocene sediment system, which is located in the center of study area, could be divided into 6 stages. From 1st to 6th, the sediment system flowed from west to east, with the migration direction from north to south. These 6 channel systems developed similar feature, parallel to each other. There was obvious margin and boundary between two adjacent channels, where the younger channel incised the elder channel. Among the 6 channels, 4 of which develop with a lobe, correspondingly marked as lobe-3, lobe-4, lobe-5 and lobe-6, while lobe-1, love-2 are missing. Part of channel-1, channel-2, and channel-3 are also missing.
Different elements in deep water system have different geophysical response. On seismic profiles, deepwater channel complex deposits expressed U- or V-shaped feature. The lower part of deepwater channel complex deposits corresponds to low-amplitude, poor-continuity and chaotic seismic reflection signatures, probably indicating slump-debris flow deposits, while the upper part is characterized by strong-amplitude, poor to moderate continuity seismic reflection signatures. The well logging curves of channel sand were characterized by low box-shaped Gammar (GR) value and high resistivity value. The shale content is quite low, which could achieve a Net Gross Ratio (NGR) of 0.97. Lobes expressed flat, continuous and high amplitude features in seismic sections, while serrated shape of ascending amplitude and high frequency in GR curve and descending amplitude and also high frequency in resistivity curve in well logging data. This feature indicated normal grading character, which reflected deceasing energy of the deep water current. This feature represented the open environment in the mouth splays and lobes which located in the basin floor. The NGR generally dropped down to 0.58 in lobes.
Several factors controlled or effected the deep water sediment system in study area, however, in which the main factor should be seismicity in East Africa. The development of channel-lobe system related to the tectonic uplifting, which implied tectonic movements controlled the source supply and deep water current activities. The paleo-Rovuma deltas provided abundant source for giant Eocene sediment system. The uplifting episodes response to the development of channel-lobe complexes. The carbonate debris low and calcite cement sandstone from west indicate the strong uplifting during Eocene. The carbonate and calcite cement sandstone could collapse in this tectonic background, transported to the basin floor by high energy turbidity currents and debris flows.
Comparing with the straight channels, the lobes expressed different strike from Northeast to Southeast, where showed U shape on the plain view from channel to lobe. The feature implied the high geometry of Northwest of complex constrained the accommodation space for channels and lobes. The transitional point between channel and lobe also played a important role for the blend feature developed here.
The straight feature also related to the steep slope and coarse clasts in turbidity currents. The steep slope usually caused steep deep water systems because of high energy. Meanwhile, the coarse clasts were apt to incise the seafloor and deepen the channel, also caused the straight feature of this system.
The paleo-Rovuma Deltas provided source for the deep water sediment system, however, the clasts of Rovuma Delta supplied from Mozambique Fold in the west. Based on lithologic analysis, the granite and gneiss is the parent rock for the sandstones. These crystallized rock experienced uplifting movements and weathering activities during Eocene. Thus, the huge amount of clasts were transported to the offshore in the east area, then the Rovuma Delta formed firstly. During special period, the gravity current occurred in this area under the tectonic events, which caused the unstable environment. The gravity current easily transported the plenty of clasts from shelf and deltaic area to the basin floor along the canyons and channels. The clasts will deposit in channels and lobes when the current energy decreased finally. Thus, the Mozambique Fold provided the source for deep water sediment system basically.
学科领域海洋地质学
语种中文
文献类型学位论文
条目标识符http://ir.qdio.ac.cn/handle/337002/136564
专题海洋地质与环境重点实验室
作者单位中国科学院海洋研究所
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鲁银涛. 深水重力流沉积发育特征与形成机制研究:以东非海域鲁武马盆地上始新统深水沉积为例[D]. 北京. 中国科学院大学,2017.
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