【作者】 曹婷婷；

【导师】 徐思煌；

【作者基本信息】 中国地质大学 ， 能源地质工程， 2011， 硕士

【摘要】 我国南方海相地层沉积厚度大,发育有多套主力烃源岩,是我国目前油气勘探的重要领域之一。然而长期的热演化和强烈的构造运动改造,使得这些烃源岩中有机质的数量和质量发生了较大的变化,传统的烃源岩评价方法在该地区的应用面临很多困难,尤其是氯仿沥青“A”、氢指数等地化指标受高演化作用的影响会出现误差。本文就是针对高演化海相烃源岩而提出的新的烃源岩评价方法。本次研究以四川盆地南江杨坝地区下寒武统为研究对象,结合油气地球化学的基本原理,综合运用区域地质与野外记录资料,在烃源岩传统评价的基础上,以优质烃源岩的形成条件为基础,阐明了影响海相烃源岩发育的主要控制因素,同时提出了一套利用元素地球化学数据评价烃源岩优劣的方法。取得的主要研究成果如下：1、在野外露头踏勘、采样的基础上,以油气地球化学及元素地球化学为指导,分析了南江杨坝剖面下寒武统中有机质的特征,同时结合分析测试数据,阐述了下寒武统中筇竹寺组、仙女洞组、阎王碥组及石龙洞组中常量元素、微量元素以及碳同位素的变化规律。研究认为在南江杨坝剖面下寒武统中筇竹寺组平均TOC大于1%,属于传统意义上优质烃源岩发育的层段；仙女洞组、阎王碥组和石龙洞组所有样品中的TOC都小于0.4%,在烃源岩传统评价标准中属于非烃源岩。地层中各组的有机质类型较好,以Ⅰ型腐泥型为主,同时在长期的热演化作用下,有机质成熟度高,普遍处于高-过成熟阶段。此外,结合测试结果来看：筇竹寺组岩性以黑色炭质页岩为主,其样品中常量元素总体较高,且尤其以Al、Ba、Ca、P、Cu、Zn、K、Na及S这些与生物生长发育相关的元素含量最高；微量元素V、Cr、Ni、U及Mo这五种金属元素在筇竹寺组底部的含量最高,到筇竹寺组的中、上部,V、U、Mo元素的含量都有明显的减少,而Cr、Ni元素含量变化却不甚明显；同时稀土元素模式图反映出轻稀土元素较富集,重稀土元素略有亏损的特征。仙女洞组以鲕粒灰岩及砂屑灰岩为主,测试结果反映常量元素Al、Ba、Fe、P、Ti、K、Na及S元素含量明显较低；同时微量元素V、Cr、Co、Ni、U、Mo、Th及Pb的含量也明显很低；稀土模式曲线略呈水平。阎王碥组多发育粉砂质泥岩,其中阎王碥组底部,常量元素的含量均有增大的趋势,但向上常量元素含量仍然较低,微量元素的含量变化趋势与常量元素较相似,在阎王碥组底部除了Pb元素含量则有减少的现象外,其它微量元素含量总体上都有降低的趋势,而到了该组中、上部,各项微量元素含量均较低,阎王碥组稀土模式曲线也略呈水平。石龙洞组主要发育白云岩,总体上各个样品中的常量元素及微量元素的含量均较低；此外该组中稀土元素模式曲线则呈略微的右倾现象,即：较富集轻稀土元素。同时,研究区碳同位素呈现两次旋回的特征。2、通过对野外剖面的测量,并结合室内总有机碳及元素分析测试的结果,以元素示踪原理为指导,揭示研究区海相烃源岩形成的主控因素。本文从古生产力、古氧相、埋藏效率及热液作用这四个方面入手,利用Baxs及无机碳同位素(δ13Ccarb)来指示海洋古生产力；V/Cr、Ni/Co、U/Th及稀土元素的La/Yb及6 Ce反映有机质沉积时的氧化还原环境；Mo元素含量指示有机碳的埋藏效率；Ba/Sr比值来指示海底热液作用对有机质富集的影响。通过分析后发现,研究区下寒武统筇竹寺组下部古生产力很高,有机质沉积在厌氧的环境中,有机碳埋藏量也很高,具备形成优质烃源岩的条件；仙女洞组及阎王碥组古生产力低,沉积环境偏向贫氧-富氧相,不利于有机质的保存,同时有机碳埋藏量也较低；石龙洞组底部尽管有机碳埋藏效率相对较低,但仍具有较高的古生产力及缺氧的沉积环境。从这个角度分析后认为,较高的古生产力,缺氧的沉积环境以及较高的埋藏效率为优质烃源岩的形成与发育提供了良好的环境。此外,海底的热液流体也影响着有机质的富集,从而控制着优质烃源岩的发育。3、元素地球化学特征能够反映烃源岩发育的环境,影响有机质的富集,这与反映有机质丰度的有机碳含量密切相关。本文在此理论的指导下,分析了与总有机碳含量、无机碳同位素及有机碳同位素相关的元素,并以三者为因变量,优选的元素含量为自变量,建立起三个拟合公式,其中影响生物生长的营养元素Baxs、Mnxs、Fexs,海水盐度Srxs及影响有机质保存条件的Uxs、Vxs、Nixs及Znxs都被选入用来评价有机质的丰度和沉积、保存环境。同时对选取的Moxs、Znxs、Fexs、Mnxs、Vxs、Nixs、Znxs、Srxs及Baxs这9个元素,进行因子分析,得到一个多元素组合的综合因子计算公式,这个公式包括了沉积岩中有机质从形成、到沉积、埋藏过程中元素变化的总体信息,反映有机质沉积环境的变化及有机质的分布、聚集规律,可以用来评价烃源岩的优劣。从分析结果来看,下寒武统筇竹寺组的下部综合因子得分较高,反映其有机质沉积数量多,保存条件优越,具备优质烃源岩发育的条件；筇竹寺组顶部、仙女洞组及阎王碥组底部综合因子得分处于0-1之间,可发育一般烃源岩；而阎王碥组中、上部及石龙洞组综合因子得分低,基本处于0以下,有机质数量少,埋藏条件差不利于发育烃源岩。4、利用元素地球化学特征评价烃源岩为评价高演化海相烃源岩提供了一条新的思路,其与传统烃源岩评价结果存在一定的统一性,但仍存在一些差异。目前可以将其作为我国南方高演化地区传统烃源岩评价的重要补充。更多还原

【Abstract】 Marine source rock is currently one of the important oil and gas exploration areas.It has thick sediment, develop several sets of main source rocks. However,the quality and quantity of organic matter of these hydrocarbon source rock changed a lot, suffered long-term thermal evolution and transformation of violent tectonic movement.the traditional method of hydrocarbon source rock evaluation of the application in the region face many difficulties, especially chloroform Bitumen "A", hydrogen index and so the evolution of indicators by the effects of high error will appear. This article is for the highly evolved marine source rocks and the proposed new method for evaluating source rock.In this paper the lower Cambrian of Yangba Profile in Nanjiang, Sichuan has been studied. Taking the basic principle of petroleum geochemistry and basing on field records,the Geochemical testing of trace elements as well as carbon and oxygen isotope is used to illustrate the mainly facts of developing marine source rock, proposing a set of method of element geochemical for evaluating source rock. The main results and conclusions are as follows:1. According to the observation and sampling of fieldwork, the characteristics of organic matter, major elements, trace elements and carbon isotopes are analyzed in the Lower Cambrian of Yangba profile in Nanjiang,Sichuan.Qiongzhusi group which the average TOC is greater than 1%, is the high-quality hydrocarbon.Other groups have a low content of organic carbon,belong to non-source rock. Organic matter type is sapropelic, high maturity each group.In addition, the testing results show that the major elements constant of black carbonaceous shale, especially Al, Ba, Ca, P, Cu, Zn, K, Na and S which related to biological growth is higher in Qiongzhusi group, trace elements,such as V, Cr, Ni, U and Mo, also has higher content in the bottom of Qiongzhusi group, the upper part, V, U, Mo content of the elements are significantly reduced, REE diagram also shows a more enriched in light rare earth elements and heavy rare earth element characteristics of a slight loss.Xiannvdong group developed oolitic limestone and calcarenite. The results reflect the content of major elements,such as Al, Ba, Fe, P, Ti, K, Na and S, are decreased heavily,while the contents of trace elements V, Cr, Co, Ni, U, Mo, Th and Pb are reduced, rare earth model curves keep slightly level.Yanwangbian group mainly developed silty mudstone, the content of major elements have a tendency to increase in the bottom, while still low in the upper. The trends of trace elements is similar to major element.In addition to Pb, there is declining. Rare earth model curves slightly level.Shilongdong group developed dolomite. Generally, the content of major elements and trace elements are lower, the mode curve of the rare earth element showed that a more enriched in light rare earth elements.In addition,the carbon isotope have two cycles.2. Based on the theory of element track, the key control element of marine source rock formation in region of interest is researched by the measurement of field profile, combining with the result of interior analysis test about total organic carbon and element. We start with the paleo-productivity, fossil oxygen facies, burial efficiency and hydrothermal activity to denote the ocean paleo-productivity by Baxs, reflect the oxido reduction environment at the time the OM sediment by V/Cr, Ni/Co, U/Th and the rare-earth element including La/Yb andδCe, indicate the burial efficiency of organic carbon by Mo, instruct the submarine hydrothermal solution action’s influence to the OM accumulation by Ba/Sr.The analysis result indicate that the lower of Qiongzhusi formation in lower Cambrian has a high paleo-productivity, the OM sediment in an anaerobic environment, the burial quantity of organic carbon is high, and the geobiology condition is advantage to develop superior source rock. The paleo-productivity of Xiannvdong formation and Yanwangbian formation is low. The sedimentary environment deviates to be poor oxygen-rich oxygen facies which is disadvantage to the conservation of OM, and the quantity of organic carbon is little. The burial efficiency of the bottom of Shilongdong formation is relatively low, while the paleo-productivity is big and the sedimentary environment is anoxic. Analyzing from this point, more paleo-productivity, anoxic environment and high efficient burial rate provide good environment for the formation and development of superior source rock. Otherwise, the submarine hydrothermal fluid also affects the accumulation of OM and controls the development of superior source rock.3. The element geochemistry can reflect the environment of source rock, affect the concentration and has a closely correlation to the organic carbon content which reflects the abundance of OM. Under the direction of this theory, the elements which are correlated to TOC, inorganic carbon isotope and organic carbon isotope are analyzed to build three fitting equations with the TOC, inorganic carbon isotope and organic carbon isotope as variable and optimized element content as argument. The nutrient elements affecting the growth of biology such as Baxs、Mnxs、Fexs, the sea water salinity element Srxs,and the elements affecting the conservation condition of OM such as Uxs、Vxs、Nixs、Znxs are chosen to evaluate the abundance and deposition, conversation environment of OM. At the same time, factor analysis is conducted to the elements including Moxs、Uxs、Fexs、Mnxs、Vxs、Nixs、Znxs、Srxs and Baxs to obtain a compositive factor calculation equation combined by multi-element which includes total information about the change of trace element of the OM in sedimentary rock in the process from formation to deposition and bury. It reflects the changes of the OM sedimentary environment and the rules of OM distribution and accumulation. It can be used to evaluate the superior and inferior of the source rock.The analysis result indicates that the lower of Qiongzhusi formation in lower Cambrian has a higher compositive factor score which reflects that the sediment quantity is more, the reservation condition is advantageous and superior source rock can develop. The compositive factor score of top Qiongzhusi formation, Xiangnvdong formation and low Yanwangbian formation is between 0 and 1 which shows ordinary source rock may develop. Whereas the compositive factor score of the middle and top of Yanwangbian formation and Shilongdong formation is smaller than 0 which shows the OM quantity is little and the bury condition is so bad that it’s unfavorable for the source rock development.4. It is a new clue to evaluate highly evolved marine source rock by the characteristic of element geochemistry. It has some unity to the result of traditional source rock evaluation, but some differences still exist. This method can be used as an important addition to the source rock evaluation of highly evolved area in southern China.更多还原