New insights into the carbonate karstic fault system and reservoir formation in the Southern Tahe area of the Tarim Basin

As worldwide hydrocarbon exploration has extended from shallowly to deeply buried strata, reservoir quality has attracted substantial and persistent interest in petroleum geology. In particular, deeply buried strata (>5500 m) in the Tarim Basin have attracted considerable attention because carbonate reservoirs that have experienced fracture or dissolution have also been shown to demonstrate considerable hydrocarbon potential. Therefore, it is necessary to determine how these reservoirs are developed and distributed in detail from both scientific and practical standpoints.In this paper, we address this issue using a case study in the southern Tahe area, which is contained within the largest Palaeozoic marine oilfield in China. In the northern Tahe area, mega-paleokarst systems developed in the Ordovician strata; however, the reservoir quality in the southern part of the Tahe area is relatively poor because it is covered by insoluble formations during karstification. Observations of cores and analyses of images of well logging demonstrate that these reservoirs are dominated by caves, vugs and fractures that have developed near faults. We speculate that the faults penetrating insoluble formations represent the main dissolution passages that originally developed these karstic fault systems. Additionally, we analyse a series of outcrops, seismic data, and structures to characterize the spatial geometry of these major faults and their surrounding fractures in detail. Most of these are strike-slip faults, and their subsequent reservoirs can be divided into three categories based on their development, including dendritic, sandwich and slab reservoirs. Recent studies demonstrate that karstic fault reservoirs are most common traps in the study area. Although various types of carbonate karstic fault reservoirs are represented in this region, the dendritic karstic fault reservoir is the most hydrocarbon-rich.Guided by these initial results, 108 wells were drilled from 2013 to 2014, producing 485 thousand tons of oil and yielding success ratios greater than 89%. The average production of dendritic reservoirs is 37.4 tons per day (t/d), while those of sandwich and slab types are 20.2 t/d and 14.0 t/d, respectively. These results represent significant references for future hydrocarbon exploration and the development of similar deeply buried karstic fault reservoirs in the Tarim Basin and elsewhere.     

Geochemistry and origin of organic-rich sediment veins in fractured granitic basement,Helmsdale, Sutherlandshire,UK

Black sediment veins up to 2 cm width penetrate the Caledonian Helmsdale Granite in the vicinity of the Helmsdale Fault, onshore Moray Firth. The black colour and geochemistry of the veins reflect a high content of organic carbon. Both Devonian and Jurassic shales are conceivable available sources, but sterane compositions relate the organic matter to the Jurassic shales. A content of extractable organic matter higher than in the shales suggests that the carbon in the veins represents oil rather than mechanically mobilized shale. The oil was present during sediment vein emplacement. The veins were emplaced forcefully, which may reflect high fluid pressure associated with post-Jurassic movement on the Helmsdale Fault.     

东太平洋CC区西区表层沉积物黏土矿物和地球化学特征

本文以太平洋CC区西区12个表层沉积物样品作为研究对象,对其粒度、化学组分和矿物成分进行分析,讨论其沉积环境和物质来源。研究区地处深海,主要以深海黏土和硅钙质黏土为主,含有少量的硅质黏土、黏土质硅质软泥和黏土质钙质软泥。黏土矿物成分主要是蒙皂石和伊利石,含有部分的高岭石和绿泥石。黏土矿物组成表明,区内沉积物主要是陆源,由高空气流携带而来,南极底流和热液活动对其物源的来源有一定影响。沉积物地球化学特征也表明,物源以陆源为主,稀土元素分布曲线和北太平洋表层海水稀土曲线类似,且表现出强的Ce亏损,表明生物活动导致的生物沉降对表层沉积物也有一定的影响。     

Examining fault architecture and strain distribution using geospatial and geomechanical modelling: An example from the Qaidam basin,NE Tibet

The investigation of complex geological setting is still dominated by traditional geo-data collection and analytical techniques, e.g., stratigraphic logging, dip data measurements, structural ground mapping, seismic interpretation, balance section restoration, forward modelling, etc. Despite the advantages of improving our understanding in structural geometry and fault architecture, the geospatial modelling, applying computer-aided three-dimensional geometric design, visualization and interpretation, has rarely been applied to such complex geological setting. This study used the Lenghu fold-and-thrust belt (in Qaidam basin, NE Tibetan Plateau) to demonstrate that the application of geospatial and geomechanical modelling could improve our understanding and provide an effective technique for investigating the fault architecture and strain distribution. The three-dimensional configuration of the Lenghu fold-and-thrust belt was initially derived from traditional analysis techniques, such as regional stratigraphic logging, cross section construction, meso-scale ground mapping and landsat image interpretation. The high-resolution field data and landsat image were integrated to construct the geospatial model, which was subsequently used to quantitatively investigate the fault throw changes along the Lenghu thrust fault zone and to understand its control on the lateral structural variation. The geospatial model was then restored in three dimensions to reveal the kinematic evolution of the Lenghu fold-and-thrust belt. Geomechanical modelling, using a Mass-Spring algorithm, provided an effective three-dimensional tool for structural strain analysis, which was used to predict the strain distribution throughout the overall structure, e.g., normal faults with throws ranging from meters to tens of meters in the hanging-wall. The strain distribution predicted by geomechanical modelling was then validated by the natural normal faults in the hanging-wall. The high accordance between the strain prediction and statistics of natural normal faults demonstrates good applicability of geospatial and geomechanical modelling in the complex geological setting of the Lenghu fold-and-thrust belt. The geospatial models and geomechanical models, therefore, can provide a robust technique for analyzing and interpreting multi-source data within a three-dimensional environment. We anticipate that the application of three-dimensional geospatial modelling and geomechanical modelling, integrating both multi-source geologic data and three-dimensional analytical techniques, can provide an effective workflow for investigating the fault architecture and strain distribution at different scales (e.g., ranging from regional-to meso-scale).     

Identification of important marine areas using ecologically or biologically significant areas (EBSAs) criteria in the East to Southeast Asia region and comparison with existing registered areas for the purpose of conservation

The biodiversity of East to Southeast (E–SE) Asian waters is rapidly declining because of anthropogenic effects ranging from local environmental pressures to global warming. To improve marine biodiversity, the Aichi Biodiversity Targets were adopted in 2010. The recommendation of the Subsidiary Body on Scientific, Technical and Technological Advice (SBSTTA), encourages application of the ecologically or biologically significant area (EBSA) process to identify areas for conservation. However, there are few examples of the use of EBSA criteria to evaluate entire oceans. In this article, seven criteria are numerically evaluated to identify important marine areas (EBSA candidates) in the E–SE Asia region. The discussion includes 1) the possibility of EBSA criteria quantification throughout the E–SE Asia oceans and the suitability of the indices selected; 2) optimal integration methods for criteria, and the relationships between the criteria and data robustness and completeness; and; 3) a comparison of the EBSA candidates identified and existing registered areas for the purpose of conservation, such as marine protected areas (MPAs). Most of the EBSA criteria could be quantitatively evaluated throughout the Asia-Pacific region. However, three criteria in particular showed a substantial lack of data. Our methodological comparison showed that complementarity analysis performed better than summation because it considered criteria that were evaluated only in limited areas. Most of the difference between present-day registered areas and our results for EBSAs resulted from a lack of data and differences in philosophy for the selection of indices.     

新元古代沂沭海峡地震引发的软沉积物变形及其微量元素信息*

新元古代沂沭海峡位于郯庐断裂带昌邑—大店断层西侧宽60~90,km、长300,km的区域内,其分布范围基本与郯庐断裂带中段一致。新元古代,该海峡盆地先后沉积了青白口系、南华系及震旦系的滨—浅海相陆源碎屑、泥质及碳酸盐沉积物,其岩石地层称之为土门群。本次研究从该海峡盆地土门群佟家庄组(由石英砂岩、泥灰岩和页岩组成,属南华系)、浮来山组(由细—粉砂岩夹页岩组成,属震旦系)及石旺庄组(主要由碳酸盐岩组成,下部夹页岩,属震旦系)中鉴别出了一系列地震触动软沉积物形成的变形构造,包括液化砂墙和砂脉、负载构造、火焰构造、球枕构造、软布丁构造、底辟构造、滑塌褶曲和同沉积断层等。它们是地震事件的记录——震积岩。新元古代中晚期(约800—600,Ma)沂沭海峡盆地拉张裂陷是它们形成的动力机制。根据石旺庄组中的微亮晶方解石脉与地震成因的变形构造(如负载、火焰、软布丁及同沉积断层等)共(伴)生的事实,并结合模拟地震试验结果分析,认为微亮晶方解石脉很可能是地震引发的饱和灰泥(方解石微粒)液化脉。微量化学元素分析结果表明,这些震积岩中的w(La)/w(Sc)和 w(La)/w(Th)值高于上地壳平均值和正常沉积层,而w(Th)/w(Sc)值则较低,深源微量元素Ni和Cr的含量也高于上地壳平均值及正常沉积层。这些微量元素特征是当时的盆地基底不稳定、快速沉积且伴有深部物质元素混入的反映,强地震很可能是快速沉积和促进深源物质混入的主要动力。土门群中发育的一系列地震引起的软沉积物变形(震积岩),再次证明了古郯庐断裂带的存在,由它们记录的地震事件也是晋宁运动乃至Rodinia超大陆的裂解的响应。     

东昆仑东段杨树沟金矿地质特征及找矿方向

杨树沟金矿位于东昆仑成矿省伯喀里克-香日德印支期金、铅、锌、铁、石墨（铜、稀有、稀土）成矿带的东段.矿体严格受近东西向、北东向断裂构造控制.成矿类型为构造蚀变岩型金矿床,成矿时代为印支早期.矿区中已发现的金矿带深部及矿区东南部断裂发育地区具有较好的找矿空间,下一步工作应针对含矿构造破碎带,采用探矿工程与化探工作相结合等手段开展矿区东南部及深部找矿工作,寻找金矿体,争取该矿区找矿的更大突破.     

东昆仑南缘韧性剪切带变形特征及其形成时代的限定

中生代巴彦喀拉-松潘甘孜地体向东昆仑地体斜向俯冲,在东昆仑南缘形成一条巨型的韧性剪切带。剪切带中发育的旋转碎斑、书斜构造、解理阶步、云母鱼、S-C组构、不对称褶皱、雁列脉等宏微观构造,显示剪切带兼具右行和左行的特征,且右行早于左行剪切,但总体以左行剪切为主。对西大滩糜棱岩化花岗岩和小南川未变形花岗岩进行了LA-ICP-MS锆石UPb测年,西大滩岩体侵位于199.3±2.2Ma,小南川岩体形成于196.4±1.3Ma。西大滩与小南川岩体中的锆石为典型的岩浆锆石,其年龄代表了岩体侵位的时代。鉴于2个岩体的变形程度完全不同,东昆仑南缘在199~196Ma之间发生了左行韧性剪切。     

西沙海域南部多边形断层的发现及其分布特征与控制因素

根据新采集的三维地震资料,在西沙海域南部发现了多边形断层,其发育分布具有层控特征明显、在富泥地层中发育、多方位走向、纵向断距小、平面延伸长度小且形态为不规则多边形等特征。由于研究区东西两侧应力条件的差异,导致多边形断层发育特征的差异明显。通过对多边形断层发育控制因素的分析,认为地层岩性(特别是西沙海域上构造层的远源细粒沉积物)是其发育的主控因素之一,同时水道砂岩、成岩作用及构造作用等也是影响其发育分布的因素。多边形断层可以作为流体运移的通道,它与下部构造断层连接可将深部烃源岩中的油气运移到上部储层中聚集,或继续向上运移到浅部地层中形成天然气水合物。     

运用SDM方法研究2001年昆仑山口西MS8.1地震破裂分布:GPS和InSAR联合反演的结果

2001 年11月14日昆仑山口西M_S8.1地震是有现代仪器记录以来发生在青藏高原区域最大地震之一,对研究青藏高原的运动学模式具有重要意义.从地震发生至今,不同研究者运用不同资料和方法获取的地震破裂分布还存在一定差异.基于此,本文采用GPS和InSAR资料数据,参考最新研究成果,构建更为合理的断层几何模型,运用SDM方法反演本次地震的破裂分布.在反演中充分考虑不同数据权重的影响及InSAR数据中存在的整体偏移.结果显示本次地震断层性质以左旋走滑为主,最大破裂位错为~6.9 m,分布在35.76°N、93.40°E附近,地震较大破裂区域主要分布在地下20 km以内.同时,反演的位错分布在断层浅部与地质考察得到的地表破裂分布较为吻合.在与前人相关研究的对比中,显示本文结果的可靠性是较高的,例如,近地表破裂包络线与地表考察结果相近,地下破裂分布特征与前人提出的3次子地震事件相一致等,再一次佐证了此次地震由多次子地震事件组成的研究结论.