新疆北部主要盆地二叠系烃源岩沉积环境与生烃特征

【作者】 苗建宇；

【导师】 曲志浩；

【作者基本信息】 西北大学 ， 矿产普查与勘探， 2001， 博士

【摘要】 新疆北部地区主要盆地系指位于新疆天山以北的准噶尔盆地、吐哈盆地和伊犁盆地。二叠系在这些盆地有着广泛的分布。油气勘探证实二叠系为新疆北部地区最重要的油气生成地层单元。本项研究不仅可从理论上探讨烃源岩沉积环境对有机质沉积和保存的控制，而且可以对盆地二叠系油气勘探前景作出客观的评价。因此，具有重大的理论意义和经济效益。研究工作对厘定的烃源岩层系首次依据烃源岩的沉积结构与构造、元素地球化学、古生物分布、岩石地球化学及油气有机地球化学等沉积特征，从多个角度，运用多种方法综合研究了新疆北部地区主要盆地二叠系烃源岩有机质沉积和保存的地质环境。 对区内各盆地烃源岩岩石地球化学元素研究结果表明，泥质岩类烃源岩大部分元素丰度与地壳泥（页）岩的克拉克值相近；湖相薄层碳酸盐岩类烃源岩大部分元素丰度则与地壳碳酸盐岩的克拉克值相差较大。首次提出大多数湖相薄层碳酸盐类烃源岩中有机质丰度之所以偏低，沉积环境对其改造作用相对强是其有机质丰度偏低的主要原因之一。采用烃源岩层段矿物组合、有机碳含量等分析，结合指示沉积环境pH值、Eh值地球化学墙的方法推断了各盆地烃源岩层段沉积时的pH值、Eh值。研究表明，各盆地有效烃源岩沉积的水介质条件总体为碱性、硫化物相还原环境。 运用元素比值法对烃源岩层段的Sr/Ba值、B/Ga值进行了分析对比，表明区内古盐度分布规律是：碳酸盐岩类烃源岩沉积时的水体古盐度高于泥质岩类烃源岩沉积时的水体古盐度；盆地（凹陷）中心的古盐度高于盆地（凹陷）边缘的古盐度；伊犁盆地的古盐度高于准噶尔和吐哈盆地的古盐度研究认为古气候控制了大气降水，间接控制了湖水注入量与蒸发量的相对关系及古水化学性质的变化，导致形成不同类型烃源岩的沉积，最终控制了烃源岩原始有机质的沉积、保存条件。依据烃源岩的沉积结构与构造，综合各门类化石分布特征研究表明，烃源岩沉积与古生物分布的形成特点是古生物化石保存较好的层段，大多沉积在粒度细、水动力条件弱的沉积环境中，间接说明烃源岩的沉积环境有利于沉积有机质的沉积、保存。运用荧光显微镜观察法及生物标志化合物分布等最新的研究手段进行测试，研究分析认为有机质丰度、显微组分赋存状态及组成主要受烃源岩沉积时的地质环境控制。通过对有机质在烃源岩中的赋存状态进行研究，发现有机质在烃源岩中具有顺层富集型、分散型及局部富集型三种不同的赋存状态，呈顺层富集型分布的烃源岩大多有机质丰度高、类型好。 采用我国通用的陆相烃源岩有机质丰度评价标准，对区内厘定的烃源岩层系分别进行了评价。通过各项方法研究了区内不同层段烃源岩有机质类型及热演化程度。认为烃源岩总的成烃特点是：继承性发育的较深的湖盆凹陷中心，有机质丰度高、类型好；而位于盆地边缘地带，有机质类型发育较差；现今各盆地二叠系烃源岩有机质已全部进入成熟期。综合烃源岩沉积的地质环境和烃源岩成烃特点进行分析，认为沉积环境控制了烃源岩有机质丰度高低和有机质类型的好差。其中沉积水体适时的盐度变化有利于原始有机质的沉积；具有一定水体深度的沉积相带是原始有机质沉积的良好场所；生物种群繁茂，原始有机质产率高是原始有机质丰富的主要原因；必要的有机质埋藏、保存条件是防止原始有机质破坏的重要基础。盆地构造演化则控制了烃源岩沉积的时期、面积、厚度分布及烃源岩有机质的成熟排烃时间。<WP=3>在上述研究基础上，进行了综合评价。认为准噶尔盆地玛湖、盆1井西及五彩湾凹陷应为烃源岩分布的最有利地区。准噶尔盆地昌吉、东海道子北凹陷，南缘山前断褶带、帐北断陷带、吉木萨尔及博格达山北缘地区，吐哈盆地台北凹陷、桃东沟南广大地区，伊犁盆地洼陷中心地区属烃源岩分布的有利地区。准噶尔盆地各凹陷边缘地带、吐哈盆地托克逊凹陷及伊犁盆地伊参1井等地区为烃源岩分布中等有利地区。吐哈盆地哈密拗陷、伊犁盆地伊宁拗陷周边及尼勒克以东地区归为较差烃源岩分布地区。更多还原

【Abstract】 The major basins in North Xinjiang include the Junggar basin,Turfan-hami basin and Yili basin , where located on North Xinjiang Tianshan mountain .The Permian system has the extensive distribution in these basins. The oil and gas are explored to confirm that the Permian system provide for the most of oil and gas in North Xinjiang.. This research not only can be inquire into the controlling of depositional environment in hydrocarbon source rocks to organic matters depositing and preserving on theory but can be made the objective evaluations to the Permian system oil and gas exploration foreground in the basins. Therefore it is possessed of great theory meaning and economic performance. According to depositional structure and characteristics such as construction,element geochemistry, palaeophyte distribution, rock geochemistry and oil and gas geochemistry etc in hydrocarbon source rocks for the first time, and from many angles, using many kinds of methods, the study on hydrocarbon source rocks stratum to be collated and stipulated has been syntheticaly discussed about geology environment with deposits and preserves of organic matters of Permian system hydrocarbon source rocks of major basins in North Xinjiang. The researches resulted about rock geochemistry element of hydrocarbon source rock in each basin are indicated that the most of elements abundance in mudstone source rock is closed with the clarke value of the earth’s crust mudstone ( shale ), it is demonstrated that the depositional environment is weak relatively to his transformation effect . But most of element abundance of thin layer of carbonate rock source rock in the lake differ from greatly with the clarke value of earth’s crust carbonate rock, it is explaned that depositional environment is relatively stronger to his transformation effect. Therefore it is advanced for the first time why organic matters abundance are lower partially in the carbonate source rock of thin layer in most of lakes to the mudstone., which the depositional environment is transformed to act on strong to be one of major cause . By means of hydrocarbon source rock stratum mineral combinations and organic carbon content to combine the methods of the instruction depositional environment in geochemistry wall the pH’s value and Eh’s value are infered during the deposit of hydrocarbon source rock in each basin.The study indicates that the water medium condition is overall for basicity and sulphide environment in effective hydrocarbon source rock deposited in the each basin． Using the element specific value law the Sr / Ba value and the B / Ga value of hydrocarbon source rock are analysed and contrasted .The palaesalinity distribution in this area is that the palaesalinity of the water body during depositing of carbonate source rock is more than the mudsource rock and the palaesalinity of the basin center is more than border and the palaesalinity of YiLi basin is more than the Junggar ,Turfan- hami basin overall. It is thinked that atmosphere precipitation has been controlled of palaeclimate and the change with relations of boil-off and pouring into and ancient water chemistry quality of the lake water indirectly, which lead to forming the deposit of different type hydrocarbon source rocks and the deposit and preserve condition of original matters finally. Juging by depositing structure and construction in the hydrocarbon source rock and <WP=5>syntheticaly researching on distribution characteristics of fossils demanstrate that depositing of the hydrocarbon source rock and the better layer of fossils preserved are the depositional environment that the deposit is mostly thin at the size and the water motive force condition is weak. Therefore the depositional environment of hydrocarbon source rock is favour of deposit and preserve of organic matters indirectly. Applying the newest research means such as fluorosccpic to observe and the biomarker distributes to test it is thinked that the organic matters abundance and organic matters macerral o更多还原