A Large-scale Tertiary Salt Nappe Complex in the Leading Edge of the Kuqa Foreland Fold-Thrust Belt, the Tarim Basin, Northwest China

The tectono-stratigraphic sequences of the Kuqa foreland fold-thrust belt in the northern Tarim basin, northwest China, can be divided into the Mesozoic sub-salt sequence, the Paleocene-Eocene salt sequence and the Oligocene-Quaternary supra-salt sequence. The salt sequence is composed mainly of light grey halite, gypsum, marl and brown elastics. A variety of salt-related structures have developed in the Kuqa foreland fold belt, in which the most fascinating structures are salt nappe complex. Based on field observation, seismic interpretation and drilling data, a large-scale salt nappe complex has been identified. It trends approximately east-west for over 200 km and occurs along the west Qiulitag Mountains. Its thrusting displacement is over 30 km. The salt nappe complex appears as an arcuate zone projecting southwestwards along the leading edge of the Kuqa foreland fold belt. The major thrust fault is developed along the Paleocene-Eocene salt beds. The allochthonous nappes comprise large north-dipping faulting monoclines which are made up of Paleocene-Pliocene sediments. Geological analysis and cross-section restoration revealed that the salt nappes were mainly formed at the late Himalayan stage (c.a. 1.64 Ma BP) and have been active until the present day. Because of inhomogeneous thrusting, a great difference may exist in thrust displacement, thrust occurrence, superimposition of allochthonous and autochthonous sequences and the development of the salt-related structures, which indicates the segmentation along the salt nappes. Regional compression, gravitational gliding and spreading controlled the formation and evolution of the salt nappe complex in the Kuqa foreland fold belt.

Efectiveness and petroleum geological signifcance of tectonic fractures in the ultra‑deep zone of the Kuqa foreland thrust belt:a case study of the Cretaceous Bashijiqike Formation in the Keshen gas feld

The buried depth of the gas-producing reservoir in the Kuqa foreland thrust belt of the Tarim Basin exceeds 6000 m.The average matrix porosity of the reservoir is 5.5%,and the average matrix permeability is 0.128×10^(−3)μm^(2).In order to reveal the characteristics and efectiveness of ultra-deep fractures and their efects on reservoir properties and natural gas production,outcrops,cores,thin section,image logs and production testing data are used to investigate the efectiveness of tectonic fractures in ultra-deep reservoirs in the Kuqa foreland thrust zone,and the corresponding geological signifcance for oil and gas exploration and development are discussed.Tectonic fractures in the thrust belt include EW-trending high-angle tensile fractures and NS-trending vertical shear fractures.The former has a relatively high flling rate,while the latter is mostly unflled.Micro-fractures are usually grain-piercing-through cracks with width of 10-100 microns.In the planar view,the efective fractures are concentrated in the high part and wing zones of the long axis of the anticline,and along the vertical direction,they are mainly found in the tensile fracture zone above the neutral plane.The adjustment fracture zone has the strongest vertical extension abilities and high efectiveness,followed by the nearly EW longitudinal tensile fracture zone,and the netted fracture zone with multiple dip angles.The efectiveness of fracture is mainly controlled by fracture aperture and flling degrees.Efective fractures can increase reservoir permeability by 1-2 orders of magnitude.The higher part of the anticline is associated with high tectonic fracture permeability,which control enrichment and high production of natural gas.The netted vertical open fractures efectively communicate with pores and throats of the reservoir matrix,which forms an apparent-homogenous to medium-heterogeneous body that is seen with high production of natural gas sustained for a long term.

Three-dimensional discrete element numerical simulation of Paleogene salt structures in the western Kuqa foreland thrust belt

Taking the Paleogene salt strata in the west of Kuqa foreland thrust belt as study object, the deformation features of salt structure in the compression direction and perpendicular to the compression direction were examined to find out the control factors and formation mechanisms of the salt structures. By using the three-dimensional discrete element numerical simulation method, the formation mechanisms of typical salt structures of western Kuqa foreland thrust belt in Keshen and Dabei work areas were comprehensively analyzed. The simulation results show that the salt deformation in Keshen and Dabei work areas is of forward spread type, with deformation concentrated in the piedmont zone;the salt deformation is affected by the early uplift near the compression end, pre-existing basement faults, synsedimentary process and the initial salt depocenter;in the direction perpendicular to the compression direction, salt rocks near the compression end have strong lateral mobility with the velocity component moving towards the middle part, and the closer to the middle, the larger the velocity will be, so that salt rocks will aggregate towards the middle and deform intensely, forming complex folds and separation of salt structures from salt source, and local outcrop with thrust faults. Compared with 2 D simulation, 3 D simulation can analyze salt structures in the principal stress direction and direction perpendicular to the principal stress, give us a full view of the formation mechanisms of salt structures, and guide the exploration of oil and gas reservoirs related to salt structures.

Influence of Salt Beds on the Segmentation of Structure and Hydrocarbon Accumulation in Qiulitag Structural Belt,Tarim Basin,China

Seismic information and balanced profile technology were used to reveal the influence of the salt bed in segmentation of structure and hydrocarbon accumulation in Qiulitag structural belt in Tarim basin. From west to east, the shortening of strata above the salt beds gradually decreases, while, the shortening below the salt beds gradually increases, which shows that the segmentation of structure integrated the seismic profile. There is great difference of the deformation of strata below and above the salt beds between the west segment and the east segment. The analysis of the distribution of oil/gas fields and the hydrocarbon properties indicates the similar segmentation to the structure segmentation. The salt beds in relatively shallow layers change the stress condition from basement of Kuqa foreland basin, which leads to the segmentation of Qiulitag structural belt. Because the salt beds in the west segment came into being earlier than those in the east segment, the west segment captures hydrocarbon from two sets of source rock, while the east segment can only capture hydrocarbons from one set of source rock. So, the salt beds play an important role in the segmentation of structure and hydrocarbon accumulation.

Oil and gas source and accumulation of Zhongqiu 1 trap in Qiulitage structural belt, Tarim Basin, NW China

Well Zhongqiu 1 obtained highly productive oil-gas stream in the footwall of Zhongqiu structure, marking the strategic breakthrough of Qiulitag structural belt in the Tarim Basin. However, the oil and gas sources in Zhongqiu structural belt and the reservoir formation process in Zhongqiu 1 trap remain unclear, so study on these issues may provide important basis for the next step of oil and gas exploration and deployment in Qiulitage structural belt. In this study, a systematic correlation of oil and gas source in Well Zhongqiu 1 has been carried out. The oil in Well Zhongqiu 1 is derived from Triassic lacustrine mudstone, while the gas is a typical coal-derived gas and mainly from Jurassic coal measures. The oil charging in Well Zhongqiu 1 mainly took place during the sedimentary period from Jidike Formation to Kangcun Formation in Neogene, and the oil was mainly contributed by Triassic source rock;large-scale natural gas charging occurred in the sedimentary period of Kuqa Formation in Neogene, and the coal-derived gas generated in the late Jurassic caused large-scale gas invasion to the early Triassic crude oil reservoirs. The Zhongqiu 1 trap was formed earlier than or at the same period as the hydrocarbon generation and expulsion period of Triassic-Jurassic source rocks. Active faults provided paths for hydrocarbon migration. The source rocks-faults-traps matched well in time and space. Traps in the footwall of the Zhongqiu structural fault have similar reservoir-forming conditions with the Zhongqiu 1 trap, so they are favorable targets in the next step of exploration.

Mechanisms of abnormal overpressure generation in Kuqa foreland thrust belt and their impacts on oil and gas reservoir formation

Based on overview for mechanism of abnormaloverpressure generation in sedimentary basins, an insightdiscussion is made by the authors for the distribution, fea-tures and generation mechanisms of abnormal overpressurein the Kuqa foreland thrust belt. The abnormal overpressurein the Kelasu structure zone west to the Kuqa forelandthrust belt was primarily distributed in Eogene to lowerCretaceous formations; structural compression and struc-tural emplacement as well as the containment of Eogenegyps-salt formation constituted the main mechanisms for thegeneration of abnormal overpressure. The abnormal over-pressure zone in the eastern Yiqikelike structure zone wasdistributed primarily in lower Jurassic Ahe Group, resultingfrom hydrocarbon generation as well as structural stressother than from under-compaction. Various distributionsand generating mechanisms have different impacts upon theformation of oil and gas reservoirs. K-E reservoir in the Ke-lasu zone is an allochthonous abnormal overpressure system.One of the conditions for reservoir accumulation is the mi-gration of hydrocarbon (T-J hydrocarbon source rock) alongthe fault up to K-E reservoir and accumulated into reservoir.And this migration process was controlled by the abnormaloverpressure system in K-E reservoir. The confined abnor-mal overpressure system in the Yiqikelike structure zoneconstituted the main cause for the poor developing of dis-solved porosity in T-J reservoir, resulting in poor physicalproperty of reservoir. The poor physical property of T-J res-ervoir of Yinan 2 structure was the main cause for the ab-sence of oil accumulation, but the presence of natural gasreservoir in the structure.

库车前陆褶皱—冲断带盐构造差异变形和分段性特征探讨

通过野外地质调查、GIS分析、三维可视化分析、盐相关构造变形样式的探讨、平衡剖面分析以及缩短量和缩短率的估算,表明库车前陆褶皱—冲断带盐构造具有明显的差异变形和分段性特征。差异变形主要表现为纵向上不同层次变形的差异性以及平面上构造变形的分带性与分段性。段与段的分界一般为走滑断层,在野外可见大量断层三角面、擦痕、阶步、错断的山脊和河谷等现象,地貌GIS分析可以揭示一些构造分段的细节特征,三维可视化反映了隐伏的残留盐枕的分段性。不同的段具有迥然不同的构造变形样式,平衡剖面分析可以估算出不同段落缩短量和缩短率的明显差异。盐构造差异变形和分段性的形成一方面受控于天山造山带的分段性活动过程,还和盐岩层本身的沉积学特征及盐体展布格局有关,同时还明显受到基底构造的控制,与基底古隆起、基底断裂及古构造断坡的发育密切相关。

库车前陆褶皱—冲断带前缘大型盐推覆构造

塔里木盆地北部库车前陆褶皱-冲断带构造-地层层序可划分为中生界盐下层序、古新统一始新统盐层层序和渐新统一第四系盐上层序。盐岩层序的岩性主要为灰白色、浅灰色盐岩、膏岩、泥灰岩和紫红色碎屑岩,厚110～3000 m。盐岩层的存在使库车前陆褶皱-冲断带发育-系列盐相关构造,其中最引人注目的是盐推覆构造。野外地质调查、地震资料解释、遥感资料和钻井资料揭示,沿库车前陆褶皱-冲断带前缘西秋立塔克山发育大型盐推覆构造,总体呈近东西走向,并略呈往西南凸出的弧形展布,沿走向延伸超过200km,由北往南逆冲推覆距离达30km以上。主断层沿古新统-始新统盐岩层发育,外来推覆体由古新统-始新统盐层层序和渐新统-第四系盐上层序组成,表现为受断层控制的单面山,逆冲推覆在原地中生代-新生代地层之上。地质分析和剖面复原结果表明,盐推覆构造主要形成于新近纪末期以来的喜马拉雅晚期阶段,现今仍具有强烈的活动性。由于不均匀推覆作用,在盐推覆构造的不同地段,逆冲推覆距离、冲断层产状、外来岩系和原地岩系的叠置关系以及盐相关构造的发育都有较大差异,显示出走向上分段性特点。库车前陆褶皱-冲断带前缘盐推覆构造的形成演化受区域挤压作用、重力滑动和重力扩展作用控制。

库车前陆褶皱冲断带中段第三系盐枕构造

本文旨在探讨库车前陆褶皱冲断带盐枕构造的类型、分布、成因机制及其与油气聚集的关系。通过地震反射剖面的解释和石油地质条件综合分析 ,认为库车前陆褶皱冲断带由北而南依次发育残留盐枕、非稳态盐枕和稳态盐枕等 3类盐枕构造 ,沿克拉苏构造带和西秋立塔克构造带呈长条形带状分布 ,其成因受重力滑动、重力扩展、区域挤压和塑性流动作用的联合控制。从盐枕构造的演化序列和分布特征看 ,该区盐枕构造的主要特点表现为 :北部盐枕形成较早 ,稳定性差 ,出现残留盐枕 ,盐枕规模较小 ;南部盐枕形成较晚 ,稳定性较强 ,形态相对完整 ,规模较大。库车前陆褶皱冲断带盐枕构造与油气聚集密切相关 ,伴随盐枕构造的形成 ,发育大量盐相关油气圈闭构造 ,沿盐枕构造成带状分布 ,同时盐枕构造巨厚的盐岩层为油气聚集提供了良好的封闭条件。

库车再生前陆逆冲带的构造特征与成因

库车再生前陆逆冲带自北而南分为以下５个构造带：①北部边缘冲断──隐伏构造楔；②斯的克背斜带；③北部线 性背斜带；④拜城背驮凹陷；⑤丘里塔格前缘带。全体形成前锋向南的冲断变形楔。各构造带中发耷多种型式的断坪／断坡 台阶状逆断层相关褶皱：断层转折褶皱、断层传播褶皱、滑脱褶皱、断层传播──滑脱混生褶皱、双重逆冲构造。在不同构 造带发育不同时代的生长地层，指示了各构造带不同的构造变形年代。斯的克背斜带变形时期最早，始于中新世 （２４．５Ｍａ），北部线性为形始于中新世中期（１６．９Ｍａ），拜城凹陷的大宛其背变形始于上新世中期（３．９Ｍａ），丘里塔格前锋 带的亚肯背斜变形始于更新世早期（１．８Ｍａ）．可见构造变形自北向南自中新世至第四纪逐渐变新。这一道冲带是印－藏板 块陆－陆碰撞远距离构造效应的内陆变形产物。

库车前陆褶皱冲断带前缘滑脱层内部变形特征

古近系库姆格列木组和新近系吉迪克组膏盐层构成了库车前陆褶皱冲断带的区域滑脱层。在褶皱冲断带前缘,膏盐层发生塑性流动,其内部形成多种构造样式。根据野外考察、地震剖面解释和钻井资料识别出的膏盐层内部构造变形样式主要包括盐枕、盐墙、盐推覆、鱼尾构造、盐焊接(断层焊接)、盐缩颈、透镜状增厚和盐垛等盐构造。盐构造在形成时间上具有一定的演化序列,库车前陆褶皱冲断带总体表现为由北向南迁移,前缘秋里塔格构造带则是从西往东迁移,盐推覆、盐焊接、盐枕等构造形成时间较早,盐墙形成较晚,东秋地区的盐构造形成时间整体较西段和中段晚,规模也较小。

库车前陆褶皱—冲断带前缘盐构造分段差异变形特征

库车前陆褶皱-冲断带前缘秋里塔格构造带发育大量盐构造,其类型丰富多样。根据野外露头、钻井和地震资料识别出的盐构造样式主要有盐推覆、盐枕、盐墙、盐焊接、鱼尾构造、盐撤凹陷、突发构造、断层传播褶皱、断层转折褶皱和三角带构造等。秋里塔格构造带盐构造变形表现出明显的分段差异变形特征,其中西段却勒地区以古隆起(盐下)—盐枕(盐层)—逆冲推覆构造(盐上)为主;中段西秋地区以构造斜坡(盐下)—盐墙(盐层)—断层传播褶皱、向斜(盐上)为主;东段东秋地区则以断层转折褶皱(盐下)—盐推覆(盐层)—断层传播褶皱(盐上)为主。造成这种盐构造分段差异变形的主要控制因素包括基底断裂、含盐层系、构造转换带和变形空间等方面的差异性,其中基底构造和含盐层系的差异性起主导作用。

天山南缘与北缘前陆冲断带构造地质特征对比及油气勘探建议

在区域构造、盆地演化与沉积充填特征分析的基础上,对天山南、北缘地震大剖面进行了精细构造变形几何学与年代学的解析。揭示出中—新生代以来天山南、北缘虽然具有相似的构造演化过程、沉积充填特征和油气地质条件,但是受沉积地层介质的力学性质差异和印—藏碰撞远距离效应的空间位置差异的影响,天山南、北缘新生代构造变形启动的时间与构造变形样式存在明显的差异,并在一定程度上导致油气聚集的不同。新生代天山隆升并向两侧扩展,冲断构造沿滑脱层向克拉通盆地内传播,构造形成的时间从造山带向克拉通方向依次变晚。库车前陆冲断带的构造变形时间早于准南,因此库车冲断带内构造圈闭的油气充注时间长、充满程度高,容易形成高丰度大型气藏。库车冲断带盐下发育多个切过中生界煤系烃源岩的逆冲断层,它们不仅控制了多个褶皱侧向上台阶状叠置,形成盐下堆垛的构造样式,而且成为深部中生界油气向浅层运移聚集的通道;膏盐岩保证了盐下构造圈闭的完整性和封盖条件。准南冲断带主要的构造变形样式是层间滑脱与构造位移量反向冲断的楔形构造,水平滑脱断层封隔了上、下含油气系统,限制深部油气向中浅层运移;大型背斜内部发育多个小型叠置的楔形构造,破坏了构造圈闭的完整性。因此准南山前东端隐伏的燕山期古构造与二、三排新生代构造核部以及库车秋里塔格西段中生界印支期古构造和克拉苏—依奇克里克新生代较早形成的构造带是成藏的有利部位;库车盐下储盖组合是油气富集的有效构造层,准南深层中生界中的大型、完整的构造圈闭是油气勘探大突破的场所。

库车新生代构造性质和变形时间

库车构造位于南天山古生代碰撞造山带之南，为塔里木盆地最北的一个构造带。它自北而南可分为边缘逆冲（ 隐伏构造楔） 、斯的克背斜带、北部线性背斜带、拜城盆地、南部背斜带。每个背斜带又包含有若干逆冲断层相关褶皱，它们是断层转折褶皱、断层传播褶皱、滑脱褶皱、断层传播 滑脱混生褶皱、双重逆冲构造、突发构造、三角带构造。底部逆冲断层向南变浅，堆叠逆冲岩席向南变薄，总体上形成一个向南的逆冲构造楔。逆冲断层在斯的克背斜带侵位最早（２５ Ｍａ） ，在北部线性背斜带为１６９ Ｍａ，拜城盆地中的大宛其背斜为３６ Ｍａ，南部背斜带为５３ Ｍａ（ 北部） 和１８ Ｍａ（ 南部） ，变形作用向南变新。库车构造是印 藏板块碰撞的内陆构造响应。

塔里木盆地北缘库车前陆褶皱──冲断构造分析

库车前陆褶皱－冲断带是以断坪－断坡式的台阶状逆断层作为滑动机制的盖层薄皮推覆构造，它们在剖面上形成一个向南变薄尖灭的推覆构造楔，底部沿脱面在北侧深南侧浅，推覆变形也是自北向南传递。依据其构造形态和变形特点可分为五个构造亚带：（1）南天山前缘楔状构造带；（2）库姆格列木－依奇克里克断层扩展褶皱构造带：（3）吐格尔明－吉迪克断层弯曲褶皱构造带：（4）秋里塔格断层扩展褶皱与断层弯曲褶皱叠加构造带；（5）库车－亚肯生长断层弯曲褶皱构造带。

库车再生前陆盆地的构造演化

库车再生前陆盆地位于塔里木盆地的北缘 ,其沉积和构造特征具有典型的前陆盆地性质。库车再生前陆盆地开始形成于吉迪克组沉积早期 (距今 2 5Ma) ,叠置于晚二叠世 -三叠纪前陆盆地之上 ,是始新世末印度 -西藏碰撞的远距离构造效应所致。其中的前陆逆冲带是由浅部和深部两个层次的构造组成的 ,其构造特征具有不一致性和不协调性。库车再生前陆逆冲带内的台阶状逆断层及其相关褶皱都是伴随着中新世以来的造山运动形成的 ,由山前向盆地以背驮式渐次连续扩展 ,自渐新世晚期一直持续到现在。印度 -西藏碰撞作用引起的陆内俯冲及壳内拆离

库车再生前陆盆地的构造与油气

库车再生前陆盆地位于塔里木盆地的北缘 ,其沉积和构造特征具有典型的前陆盆地性质。盆地中三叠系、侏罗系烃源岩发育 ,具有多套储盖组合 ,是塔里木盆地重点勘探地区之一。研究表明 :(1)断层活动与生烃、排烃时期是否匹配是确定断层封闭性的关键 ,断层活动期 ,断面具有较强的输导能力 ,断层停止活动 ,断层对流体有较强的遮挡作用 ;(2 )断层相关褶皱是最有利的构造圈闭 ;(3)突破断层对油气藏主要起破坏或改造作用 ;(4)导油构造缺乏是深部勘探失利的关键。在构造与油气关系研究的基础上 ,确定库车再生前陆盆地中的北部背斜油气聚集带和拜城阳霞向斜北油气聚集带是目前最有利的勘探目标。

库车褶皱冲断带克拉苏三角带及其油气潜力

塔里木盆地库车褶皱冲断带克拉苏构造带在古近系膏盐岩之下发育克拉苏三角带 .克拉苏三角带发育时代约在中新世中期 ,位于古近系膏盐岩和侏罗系煤系之间 ,为Ⅱ类三角带 .上新世时 ,该三角带底部被突破 ,库车褶皱冲断带前缘扩展至秋里塔格构造 .克拉苏三角带的发展与超压封套的发生有关 ;突破层位在伊 -蒙混层向伊利石的转换边界 .克拉苏三角带深层是有利的油气勘探目标 .

冲断构造带深层变形的空间分布规律——以库车坳陷克拉苏构造带为例

传统上认为前陆冲断带内部的背斜构造具有"成排成带分段"的特征,在表观认识和宏观尺度上讲,容易理解这一特征,并且通过"成排成带分段"的解剖,直接为含油气区带评价和地震解释方案的落实提供指导作用。随着前陆冲断带深层结构的精细解剖和三维空间内构造变形的准确刻画,发现前陆冲断带深层构造变形的分布并非成排成带分段的特征,褶皱构造的发育与分布明显受前陆冲断构造位移量及各个断层位移量的大小所控制,各个断层控制的逆冲岩席在垂向上相互叠置、侧向上交叉对接、走向上错落有致,3D立体空间内由多个次级弧形体组成鳞片状分布。本文以中国天然气勘探最为成功、勘探资料最为详实的库车坳陷克拉苏构造带为例,通过地震剖面精细构造解释,揭示出构造变形的运动学特征及其构造位移量在传播过程中的分异和转换,进而控制冲断带内部构造岩席的生长发育和空间展布特征,并在3D立体空间内揭示冲断岩席受构造位移量的控制而成鳞片状分布的规律,控制这一分布规律的主控因素是冲断构造位移量与冲断岩席长度之间定量的几何关系。这一认识提升了油气藏评价和构造圈闭描述的精度。

塔里木盆地库车前陆褶皱带中段盐相关构造特征与油气聚集

塔里木盆地北部库车前陆褶皱带古新统—始新统发育盐岩层系,将库车前陆褶皱带构造变形和圈闭样式分为三层,即盐上构造、盐层(盐间)构造和盐下构造。盐上构造包括盐上背斜、盐上道冲断层及断层相关褶皱、盐上背冲断块构造、强制褶皱、盐上逆冲断层遮挡构造和盐推覆构造等;盐层(盐间)构造主要包括盐枕构造、盐间断褶构造、盐焊接构造和外来盐席等;盐下构造主要有背冲断块构造、断层相关褶皱、叠瓦冲断带和双重构造等。库车前陆褶皱带盐构造的形成可能受挤压作用、重力滑动和重力扩展作用多重控制。笔者等讨论了盐相关构造油气成藏条件和模式,认为库车前陆褶皱带盐岩层变形与丰富的圈闭构造形成密切相关,烃源岩主要位于盐下,盐岩层作为优质盖层构成石油和天然气藏最优越的遮挡条件,断裂对盐下、盐间和盐上油气成藏都起重要控制作用,但盐下是最有利的油气聚集场所。