【作者】 卢占武；

【导师】 高锐；

【作者基本信息】 中国地质科学院 ， 构造地质学， 2007， 博士

【摘要】 羌塘盆地地处青藏高原北部,位于巨型油气聚集带—特提斯构造域的东段,是青藏高原内部海相地层保存最完整、最具油气远景的盆地。众多的地球物理资料表明羌塘盆地可能是印度板块与亚洲板块碰撞交锋的地域,南北向挤压应力影响着盆地内部的构造变形样式。传统的油气勘探方法,对地壳深部构造资料利用甚少。事实上,盆地的深部结构影响着盆地的演化,也影响着油气的运移和保存。因此,深入分析羌塘盆地岩石圈结构,探寻岩石圈构造对油气资源的影响,即是地球科学研究的前沿问题,同时也是青藏高原油气资源调查与评价的迫切任务。作者在参加《青藏高原油气资源战略选区调查与评价》项目工作的基础上形成本文。(一)论文的主要内容:论文主要分为四个部分:第一部分:羌塘盆地岩石圈结构综合研究。根据已有的深部地球物理资料,经系统分析,本文概括出羌塘盆地岩石圈结构具有以下特征:羌塘盆地处于印度板块与欧亚板块的碰撞交锋的前缘,俯冲的印度板块与欧亚板块岩石圈地幔在羌塘盆地下方相遇,面对面碰撞汇聚并回流到地幔;地壳减薄,在盆地南北两个缝合带下都存在不同尺度的Moho错断。南侧的拉萨地体和北侧的可可西里地体正向羌塘盆地下挤入;盆地下方大规模的低速体可能是源自温度升高,也可能是地幔物质上涌的结果。在地壳、地幔的部分构造薄弱区可能存在热物质流动的通道,发生大量的物质交换;岩石圈地幔断离后,软流圈地幔物质上涌,地壳发生近东西向的伸展减薄作用。第二部分:羌塘盆地基底及其盖层结构研究。由于复杂地表地质条件和恶劣工作条件的影响,羌塘盆地油气勘探技术尚未取得大的突破,盆地基底及其盖层结构特征并不十分清楚。本论文在完成地震数据采集试验和处理试验的基础上,得到在羌塘盆地进行二维反射地震资料采集和处理的技术方法,并提出了对羌塘盆地基底的初步认识。(1)采集方案:单井激发,井深不能少于15 m,尽量避免使用组合井。最佳药量为16-18kg;排列长度应大于7000 m,记录长度不少于10 s;合理施放大炮(100kg药量);布设交叉剖面。(2)仪器设备:配备大功率、多功能车载钻机。可以保证在多种地质条件下钻进,确保激发井深。先进的采集仪器以保证获得高品质地震数据。(3)现场监控:配备高性能的现场监控设备,连夜对当日采集的原始资料进行处理,提供监控剖面。对监控剖面进行评价,指导次日采集,是保证质量的必须措施。(4)数据处理:要对地震资料进行精细处理与特殊处理。精细静校正处理过程中需要有针对性地使用有效的静校正方法。综合应用三种地表静校正方法的静校正组合技术和无射线层析成像静校正方法在羌塘盆地应用效果较好;去噪处理时要仔细分析对比,避免在去噪的同时损失大量的有效信号。试验证明自适应噪音压制法和针对不同的噪声分别采用不同的去噪手段的精细去噪能够大大提高剖面的分辨率;采用速度谱解释,与常速扫描、变速扫描和沿层速度分析等方法结合,找出速度变化规律,通过自动剩余静校正迭代处理,建立较准确的速度模型,提高常规速度的分析精度。通过新采集的地震剖面和对原有地震数据的重新处理,我们获得了可用于构造解释的剖面,在对这些剖面进行对比分析后,对羌塘盆地基底及其盖层结构提出了一些初步认识:羌塘盆地的反射地震剖面在纵向上可分为三部分,上部褶皱变化较剧烈,以TWT2.0 s为界限,可能为中生代地层,TWT 4.5s-6s之间的反射可能为盆地的结晶基底的反映,其上为趋于平缓的古生代地层,其下为元古界。地震剖面上解释出9条多呈北西西向或北西向展布的断裂,对羌塘盆地的基底构造起控制作用;隐伏的中央隆起带向东至少延伸至约89°42′。由西向东中央隆起带的跨度由近61km逐渐减小为40km左右。中央隆起将盆地分为南羌塘盆地和北羌塘盆地。中央隆起区盆地的基底较浅、向两侧逐渐加深;基底的变形控制着盆地浅部地层的面貌,盆地浅部的弧形隆起与基底的隆起具有一定的继承性。第三部分探讨了盆地的深部结构对基底及其上覆盖层的影响。主要探讨了缝合带对盆地基底的影响;中央隆起对盆地基底及其盖层的影响;南北向挤压作用对南、北羌塘盆地的改造等内容。认为在班公-怒江缝合带北侧,盆地基底明显受到印度板块岩石圈的向北运动的作用力的影响,基底上部地层受俯冲时产生的拖曳作用而表现为不连续的弧状反射;对比南、北羌塘盆地反射地震剖面,北羌塘盆地的构造变形程度较南羌塘盆地弱。羌塘盆地遭受南北向的构造挤压,导致盆地构造层发生不同程度、不同形式的构造变形,可能由于中央隆起带的阻挡、调节作用,北羌塘盆地变形强度减弱。第四部分主要是在以上工作的基础上,对羌塘盆地油气资源远景进行初步的探讨:羌塘盆地地壳深处热作用明显,在浅处表现为水热活动及岩浆岩分布,具备了油气田形成和演化所必需的温度条件。中生代地层褶皱变形较强,可以考虑变形相对较弱的古生代地层作为油气勘探另一个重要目的层;羌塘盆地内发育的半地堑构造,作为油气储存的场所,对油气勘察具有战略价值;北羌塘盆地的构造变形程度较南羌塘盆地弱,从而利于油气的保存;羌塘盆地还存在深层油气形成的可能。受欧亚板块和印度板块的碰撞挤压,羌塘盆地的岩石圈发生了不同尺度不同规模的变形,形成的一系列断裂-裂隙系统,为非生物成因的油气由深部向地壳上部运移提供了良好通道。(二)论文的主要结论在羌塘盆地进行了详尽二维反射地震采集方法试验,提出了在羌塘盆地进行前期二维地震勘探的可行性方案。利用新采集的和重新处理的地震资料,形成了横跨羌塘盆地主体的反射地震长剖面,并对其进行构造解释,这在羌塘盆地的地震工作中尚属首次。在此基础上,作者得出了一些主要结论如下:(1)羌塘盆地岩石圈结构认为南北向挤压的动力学机制、在缝合带下发生Moho错断、地壳减薄以及深部热作用明显是羌塘盆地岩石圈结构的主要特征。(2)羌塘盆地基底及盖层结构研究羌塘盆地反射地震剖面有“纵向三分”的特点。上部中生代地层褶皱变化较剧烈,以TWT2.0 s为界限,其下的古生代地层趋于平缓,TWT 4.5s-6s之间的强反射可能反映了盆地的结晶基底,其下为元古界;中央隆起附近基底埋深较浅,向两侧盆地内部逐渐加深,临近班公-怒江缝合带基底最深;南羌塘盆地受班公-怒江缝合带影响较大,构造变形强烈;通过反射地震剖面解释出盆地内部的9条断裂。这些断裂多呈北西西向或北西向展布,控制了盆地的基底构造格架。(3)羌塘盆地二维反射地震采集方法研究单井激发,井深不能少于15 m,尽量避免使用组合井;最佳药量为16-18kg;排列长度应大于7000 m,记录长度不少于10 s;合理施放大炮(100kg药量);布设交叉剖面。是在羌塘盆地进行前期二维地震勘探的可行性方案。(4)羌塘盆地油气资源远景的探讨羌塘盆地是较强热作用使盆地具备了油气田形成和演化所必需的温度条件;羌塘盆地内部古生代地层变形相对较弱,可以考虑作为油气勘探另一个目的层;羌塘盆地内发育的半地堑构造,是羌塘盆地中良好的油气聚集单元,对油气勘察具有战略价值;北羌塘的变形相对较弱,油气保存条件要好于南羌塘。更多还原

【Abstract】 Located in the northern Qinghai-Tibetan Plateau and the eastern tectonic realm of Tethys, where is the accumulation zones of the huge oil and gas in the world, Qiangtang basin is a region of the most hydrocarbon potential, and the most intact marine strata in the northern Qinghai-Tibetan plateau. Geophysical data indicate that the Qiangtang basin may be the collision zone between the Indian plate and the Asian plate, and the north-south compressional stress affects the tectonic deformation pattern of the basin. The previous method of oil and gas exploration has used little deep crustal structure information. In fact, deep structure of the basin affects not only evolution of the basin, but also the formation and migration of the oil and gas. Therefore, analysing the lithosphere structure of the Qiangtang basin and searching the effect of the lithosphere structure on oil and gas resources, are the forefront of earth science research, and also the urgent task of perspective evaluation of oil and gas resource.The author completes the paper on the basis of participates in seismic data acquisition and data processing in the project《The investigation and evaluation of strategic precinct of oil and gas resources in the Tibetan Plateau》.(1)The main contents:This paper can be divided into 4 parts by contents. The first part: Researches on the lithosphere structure in the Qiangtang basin. After the data analysis to the previous deep geophysical data, the author summarized the following characteristics of the lithosphere structure in the Qiangtang basin:The Qiangtang basin is located in the front of collision between the Indian plate and Eurasian plate. The subducted Indian plate met with the mantle of Eurasian plate beneath the Qiangtang basin, and entered in the mantle after face-to-face collision. The crust and lithosphere become thin obviously, and the Moho offset occurs in different scales under two sutures on southern and northern boundary of basin, respectively. Lhasa Block to the north basin and the Hoh Xil Block to the south of basin are squeezing into the Qiangtang basin; the large scale low velocity bodies occur beneath the basin has been interpreted to be originated from the going-up of temperature or upwelling of the mantle. There may be channels for the flowing of hot material in partial structural weakness of the crust and mantle, where the large material exchange; after the lithospheric mantle breaking off, the rheosphere mantle upwelling, and the crust was extended near EW direction, and the north-south extensional tectonics occurred in the basin.The second part: Study on the basement and covers of the Qiangtang basin. Because of the complex geology conditions and tough work environment, the oil and gas exploration in the Qiangtang basin has not achieved the breakthrough so far. How the basement and covers of the Qiangtang basin is still unclear. On the basis of the completion of seismic data acquisition and processing tests, a 2D seismic data acquisition and processing techniques in the Qiangtang basin has been obtained:1) Data Acquisition: Exploding in the single well and more than 15 m well-depth must be adopted, the combination of wells is avoided to be used in exploding. The optional explosive is about 16-18kg; The explosive and well depth are guaranteed as the premise, the spread length of more than 7000 m and record length of more than 10s can ensure the effective reflection of basement; Reasonable big explosive (100 kg ) can increase downward energy and improve resolution, and can obtain effectively the basement reflection. At the mean time, the reflection energy of a relatively stable layer can be enhanced to provide standard stratum for residual static correction in the processing. To track changes of the structure of the same area in different directions and interpret the structure stratum of the area, the cross section is needed to emplace.2) Equipment: Drilling is the most important. The high power and vehicle-mounted rig must be equipped. Two MN rigs with 300 horsepower, made in German used in 2004 and a rig with 260 horsepower was used in 2006.They can work in a variety of geological conditions. Where vehicle can’t arrive, the portable diesel rigs were available. The advanced acquisition equipment is a guarantee in acquiring a high quality seismic data. The 408 seismograph has many advantages to ensure the good effect in the Qiangtang area, such as light cables, multiple receivers, acquisitions of higher resolution;3) Field Monitoring:Outfitting the field monitoring equipment with high-performance. Processing raw data and provide monitoring profiles in time are helpful to guiding next work, which is a necessary measure to ensure quality.4) Data processing: The seismic data needs fine processing and special processing. Fine static correction procedure must focus on the effective static correction method. Comprehensive application technique of the three surface static correction method and non-ray tomography static correction are fairly effective on the processing of seismic data from the Qiangtang basin; Carefully analyzing signals and noises is helpful to avoid the loss of useful signals during removing noises. The tests showed that the adaptive noise suppression and the various noise removal means used for different noises can greatly improve the fine resolution of the profile; Explaining the velocity spectrum, combining with constant-velocity scanning, scanning velocity and the layer velocity analysis can identify effectively the velocity changes. Though creating more accurate velocity model and using an automated residual static correction, the precision of conventional velocity is enhanced.Through processing of the new and the old seismic data, we obtained the profile for the structure explanation. Some new understandings to the tectonic framework of the Qiangtang basin are obtained after analyzing and explaining the seismic profiles:The reflection seismic profile from the Qiangtang basin may divide into three sections in ordinate direction, the upper Mesozoic strata from 0 to 2.0 s (TWT) appears the intensive fold deformation. The reflections from 4.5s to 6s may represent the basement of basin. The flat Paleozoic stratum lies on the basement and Proterozoic stratum is under the basement; the central uplift divides the basin into the south Qiangtang basin and the north Qiangtang basin. There are 9 faults in the basin distributing in NWW or NW direction, which control the tectonic framework of the Qiangtang Basin; the central uplift extends eastward at least to 89°42 ’. The span of the central uplift from west to east gradually decreases from 61km to 40km.The basement of central uplift is shallower and become deeper gradually to both sides. The deformation of the basement control the basal outlook of the shallow stratum in the basin, the shallow arcuate dome and the basement uplift have the continuity to some extent.The third part: How the deep structure influence on the basement and covers is discussed in the part. In the northern Bangong - Nujiang suture zone, the basement of the basin is affected obviously by northward movement of lithosphere of the Indian plate, the upper basement appears a discontinuous arc-shaped reflection caused by the subduction; The tectonic deformation in the northern Qiangtang basin is weaker than that in the southern Qiangtang basin according to the seismic reflection profiles. The Qiangtang basin suffered from the tectonic compression in the north-south direction, resulting in the structural deformation with various degrees and forms. The deformation of the north Qiangtang basin is weak because of the obstruction or absorption of the central uplift, and thus benefit to the preservation of oil and gas.The fourth part: The author gives a preliminary discussion on the oil and gas prospects in the Qiangtang basin on the basis of the above work:The obvious thermal feature occurs in the deep crust, indicated by the thermal activity and the magmatic distribution in the shallow level in the Qiangtang basin. This is the necessary temperature conditions for the formation and evolution of oil and gas fields. The deformation of Mesozoic strata is intensive, the Paleozoic strata with the relatively weak deformation can be regarded as another important layer for oil and gas exploration; The half-graben structures developed in the Qiangtang basin have the strategic value for oil and gas survey; Contrasting the south Qiangtang and the north Qiangtang basin, oil and gas prospects in the north Qiangtang is better than that in the south Qiangtang. There is a possibility that oil and gas may exist in the deep Qiangtang basin. Because of the collision of the Indian plate with Eurasian plate, the lithosphere of the Qiangtang basin has developed the intensive deformations, and has formed a series of fault-fracture system. They provide a good channel for migration of non-biogenic gas from the deep in the high temperature and pressure conditions to the upper low temperature and pressure conditions.(2) Main results A feasible program valid in prophase of the seismic exploration was brought forward in the article, by detail gathering tests on the 2D seismic reflection data completed in Qiantang basin. Using new and reprocessed seismic data, the author made out a long seismic profile across the Qiangtang basin body, which is the first time in the seismic exploration history of this area. On the basis of the above works, the author gives some main results:1) Lithosphere structure of Qitangtang basin: North-South compression、Moho break-off under sutures、thinned crust and obvious thermal action are main lithospheric characters of Qiangtang basin.2)Structure of basement and covers of Qiangtang basin: It behaves three parts in depth on the seismic reflection profiles. The upper Mesozoic strata from 0 to 2.0 s (TWT) appear the intensive fold deformation. The reflections from 4.5 s to 6 s may represent the basement of basin. The flat Paleozoic stratum lies on the basement and Proterozoic stratum is under the basement. 9 faults in the basin distributing in NWW or NW direction control the tectonic framework of the Qiangtang basin.3) Study on the 2-D reflection seismic acquisition method in the Qiangtang basin: Exploding in the single well with more than 15 m well-depth, 16-18kg optional explosive; more than 7000 m spread length and more than 10s record length; reasonable big explosive (100 kg) and the cross section are effective acquisition technique for prophase exploration in Qiangtang basin.4) Oil and gas prospects for the Qiangtang basin: The obvious thermal actions occurring in the deep crust afford the necessary temperature conditions for the formation and evolution of oil and gas fields; With the relatively weak deformation, the Paleozoic strata can be regarded as another important layer for oil and gas exploration; The half-graben structures developed in the Qiangtang basin have the strategic value for oil and gas survey; Contrasting the south Qiangtang and the north Qiangtang basin, oil and gas prospects in the north Qiangtang are better than that in the south Qiangtang for weak deformation.更多还原