柴达木盆地第三系烃源岩与膏盐岩赋存关系研究

发布时间：2018-05-31 11:36

本文选题：柴达木盆地第三系 + 膏盐岩与烃源岩　；参考：《西北大学》2017年硕士论文

【摘要】：柴达木盆地第三系膏盐层与烃源岩共生沉积的现象广泛存在。认识湖水咸化与有机质的堆积的关系、认识膏岩层与烃源岩在横向分布与纵向接触上的关系,对探究富烃凹陷分布具有重要的理论和实践意义。综合前人研究成果的基础上,通过系统的野外地质调查及岩心观察,应用岩石薄片鉴定、扫描电镜与能谱分析等手段,对柴达木盆地第三系地层、沉积等基础地质、烃源岩的地化特征和膏盐岩的岩石学特征进行了探讨;结合测井资料,调查了膏盐岩发育的井位和层位,划分盐韵律,认识其沉积序列纵横向的变化;分析了膏盐岩与烃源岩展布规律与形成环境,初步阐述了二者赋存关系等问题。认识到柴达木盆地野外露头中顺层与穿层产出的薄层石膏属于次生盐类矿物,对相邻岩层沉积时的咸化环境具有指示意义。柴西下干柴沟组上段中的石盐在测井曲线上的主要特点为大井径(淡水泥浆中)、高声波时差、低自然伽马(小于泥岩的三分之一)等,石膏显示出低自然电位、高电阻率等主要特点。发现膏盐岩测井曲线上表现出盐岩(A段)、膏岩与泥膏岩(B段)、砂泥岩(C段)的交互出现的盐韵律,从咸化中心至外围依次展布以ABC型、AB型、B型为主的沉积序列,逐渐过渡至BC型,最终以砂泥岩为主,且盐岩有逐渐减薄的趋势。下干柴沟组膏盐岩层展布范围主要集中在狮子沟地区。柴西各层位烃源岩(由E31至N22)逐渐变差,而整体基本属于未成熟—成熟热演化阶段。将柴达木盆地水体咸化程度划分为淡水至超咸水共五类,借以代表碎屑岩至膏盐岩类,绘制柴达木盆地西部咸化程度范围与烃源岩展布叠合图。发现有效烃源岩边界与半咸水环境边界存在较好的相关性,但烃源岩沉积中心与咸化中心并不完全吻合。表明盐度是烃源岩展布的主要影响因素之一,但并不能完全制约烃源岩的分布。综合分析认为,膏盐岩(半咸水至超咸水环境)与烃源岩在平面的展布具有较好的叠合关系,膏盐岩和烃源岩均分布在柴西南沉积中心处,受到凹陷的控制;膏盐岩与烃源岩在纵向剖面上直接接触,常常表现为频繁互层;随着咸化程度的升高,其对烃源岩质量的影响表现为“先促进、后抑制”的规律。
[Abstract]:The symbiotic deposition of Tertiary gypsum salt layer and source rock exists widely in Qaidam Basin. It is of great theoretical and practical significance to understand the relationship between salinization of lake water and accumulation of organic matter, as well as the relationship between the transverse distribution and longitudinal contact of gypsum rock and source rock. On the basis of previous research results, through systematic field geological investigation and core observation, and by means of thin slice identification, scanning electron microscope and energy dispersive analysis, the basic geology of Tertiary strata and sedimentation in Qaidam Basin is studied. The geochemical characteristics of the source rocks and the petrological characteristics of the gypsum salt rocks are discussed, the well sites and horizons developed in the gypsum salt rocks are investigated in combination with the logging data, the salt rhythm is divided, and the longitudinal and horizontal variations of the sedimentary sequences are recognized. The distribution law and formation environment of gypsum salt rock and source rock are analyzed. It is recognized that the thin layer gypsum produced in the outcrop of Qaidam Basin belongs to the secondary salt minerals and is of significance to the salinization environment of adjacent strata. The main characteristics of the salt in the upper section of Xiaganchaigou formation in the west of Qaixi are large well diameter (fresh water mud, high acoustic time difference, low natural gamma (less than 1/3 of mudstone), etc., and gypsum shows low natural potential. High resistivity and other main characteristics. It is found that the salt rhythms of salt rock formation A, gypsum rock and mudstone B member B, sand mudstone member C) appear on the log curve of gypsum salt rock, and the sedimentary sequence of ABC type AB type B is distributed from the center to the periphery of salting. Gradually transition to BC type, finally mainly sand and mudstone, and salt rock has a trend of gradual thinning. The distribution of gypsum rock in Xiaganchaigou formation is mainly concentrated in Shizigou area. The source rocks (from E31 to N22) in western Qaixi gradually become worse, while the whole rocks belong to the stage of immature and mature thermal evolution. The salinization degree of water body in Qaidam Basin is divided into five categories: fresh water and super brackish water, so as to represent clastic rock to gypsum salt rock, and to draw a map of the range of salinization degree and the distribution of hydrocarbon source rocks in western Qaidam Basin. It is found that there is a good correlation between the boundary of the effective source rock and the boundary of brackish water environment, but the sedimentary center of the source rock is not completely consistent with the salinization center. The results show that salinity is one of the main factors affecting the distribution of source rock, but it can not completely restrict the distribution of source rock. The comprehensive analysis shows that the gypsum salt rock (brackish to ultra-brackish water environment) has a good superposition relation with the distribution of source rock in the plane. Both the gypsum salt rock and source rock are distributed in the center of southwestern Qaihai sedimentary area and are controlled by the depression. The direct contact between gypsum salt rock and source rock in longitudinal profile often shows frequent interlayer, and with the increase of salinization degree, the influence of gypsum salt rock on source rock quality is "promoted first, then suppressed".
【学位授予单位】：西北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P618.13

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