南祁连盆地木里坳陷部署的多个天然气水合物钻孔钻遇不同程度的水合物与油气显示伴生现象,指示该地区具有良好的油气勘探前景,有必要对已发现油气显示进行来源分析.由于水合物钻孔深度有限,针对DK-9孔4组油气显示样品,在开展现有烃源岩油源对比基础上,选取中侏罗统、上三叠统各5组代表性低熟烃源岩样品进行热模拟实验,模拟深部烃源岩生、排烃过程,将新生烃类再次与油气显示进行对比,进一步探究油气显示来源.结果显示,油气显示可分为两类(Ⅰ和Ⅱ),第Ⅰ类油气显示遭受生物降解作用,成熟度稍高,第Ⅱ类油气显示成熟度稍低;现有烃源岩主要分为三种类型(Ⅰ—Ⅲ),分别对应深度163.30～207.42 m、207.42～348.50 m、357.90～586.50 m.结合常规油源对比、热模拟实验与地质条件分析,最终推测第Ⅰ类油气显示主要与第Ⅰ类烃源岩同源;第Ⅱ类油气显示主要与第Ⅱ类烃源岩同源,此外可能还有第Ⅲ类烃源岩或更深层烃源岩的贡献,即其母质来源既与中侏罗统烃源岩有关又与上三叠统烃源岩有关.

通过开展南祁连盆地木里坳陷天然气水合物基础地质剖面调查工作,对石炭系、二叠系、三叠系、侏罗系共四套层系5条剖面的炭质泥岩、泥岩等样品进行了系统采样与分析,在此基础上深入研究四套层系的有机质丰度、有机质类型和有机质成熟度等地球化学特征,分析及对比各层系的有机地球化学指标,以探讨不同层系烃(气)源岩为天然气水合物提供的气源条件.结果表明:石炭系-二叠系有机质丰度偏低,TOC(总有机碳含量)普遍小于0.4％,为非和差烃源岩,有机质类型主要为Ⅱ型和Ⅲ型,有机质成熟度为过成熟,生烃能力较差,难以成为天然气水合物潜在气源岩.三叠系样品TOC值普遍大于1％,氯仿沥青"A"平均为0.89‰,以很好和好烃源岩为主,并含少量差和非烃源岩,有机质类型以Ⅲ型为主,含少量Ⅱ2型,镜质体反射率Ro值为0.74％～0.98％,整体上处于成熟阶段,生气能力较强,可作为天然气水合物主要潜在气源岩.侏罗系以很好、好和中等烃源岩为主,并含部分差烃源岩,有机质类型主要为Ⅱ型和Ⅲ型,Ro值为0.62％～0.97％,整体上处于成熟阶段,可作为天然气水合物次要潜在气源岩.

Natural gas hydrate, oil and gas were all found together in the Qilian Mountain permafrost area, northeast of Qinghai-Tibet Plateau, China. They are closely associated with each other in space, but whether they are in any genetic relations are unknown yet. In this paper, a hydrocarbon gas-generation series, gas-fluid migration series and hydrocarbon gas-accumulation series are analyzed to probe the spatial, temporal and genetic relationships among natural natural gas hydrate, oil and gas. The subsequent results show that natural gas hydrate, oil and gas actually form a natural gas hydrate-oil-gas system. Based on the Middle Jurassic and the Upper Triassic hydrocarbon gas-generation series, it is divided into four major sub-systems in the study area: (1) A conventional Upper Triassic gas-bearing sub-system with peak hydrocarbon gas-generation in the late Middle Jurassic; (2) a conventional Middle Jurassic oil-bearing sub-system with low to mature hydrocarbon gas-generation in the late Middle Jurassic; (3) a natural gas hydrate sub-system with main gas source from the Upper Triassic gas-bearing sub-system and minor gas source from the Middle Jurassic oil-bearing sub-system as well as little gas source from the Middle Jurassic coal-bed gas and the microbial gas; (4) a shallower gas sub-system with microbial alteration of the main gas source from the Upper Triassic gas-bearing sub-system. This natural gas hydrate-oil-gas system and its sub-systems are not only theoretical but also practical, and thus they will play an important role in the further exploration of natural gas hydrate, oil and gas, even other energy resources in the study area.

哈拉湖地区目前基本属于地质空白区,有关天然气水合物形成及分布的研究较少,尤其针对该地区天然气水合物储层研究与认识较为有限。青徳地2井（QH-2）位于南祁连盆地哈拉湖坳陷西部,为坳陷内首口天然气水合物调查深井,钻遇第四系、新近系—古近系和三叠系。以青徳地2井三叠系主要储集岩层段岩心为研究对象,通过岩石薄片观察以及孔隙度、渗透率、密度、铸体薄片等物性测试,结合测井资料开展哈拉湖坳陷储层特征研究,结果表明:青德地2井三叠系储层分布较广,厚度巨大,但储集性能整体较差,绝大部分属非常规储集层,且整体裂隙较不发育,较难形成类似木里地区固结岩层中的裂隙型水合物及孔隙型水合物,而该区冻土层下存在厚层第四系松散沉积物及裂隙相对发育的古近系—新近系,可为天然气水合物形成提供良好的储集空间。

The Qilian Mountain permafrost is the only place where gas hydrate occurs onshore China at present and its gas hydrate distribution is very complex and irregular. What patterns affecting the accumulation of gas hydrate or what process controlling the formation of gas hydrate are not clear in the study area. Aiming at a gas hydrate geological system, the geological process of gas hydrate formation was studied, based on geological data and analytical results obtained from drilling wells in the Qilian Mountain permafrost. As a result, three stages for the geological process of gas hydrate formation are put forward in the study area. During the late Mid-Jurassic, the upper Triassic generated and provided a major gas source for gas hydrate, secondarily in combination with gas associated with oil generated from the middle Jurassic. The main gas source migrated upward via faults of F-1 and F-2, partly and occasionally mixed with the coal-bed methane and the microbial methane produced in the shallow strata. It was blocked jointly by thrust faults and thick mudstone or oil shale to be initially accumulated in gas reservoir. From Cretaceous to Pleistocene, the sedimentary strata experienced erosion and the initial gas accumulation turned into residual gas after series of the Qinghai-Tibet plateau uplift. Since the early middle Pleistocene, glaciations formed a gas hydrate stability zone (GHSZ) and the residual gas was coupled with GHSZ to form gas hydrate subsequently. Hence three patterns for the coupling of the residual gas with GHSZ are summarized in the study area. When the residual gas happened to lie within GHSZ, the residual gas directly formed gas hydrate, which was indicated by the drilling results that gas anomalies were encountered within GHSZ as well as occurrences of gas hydrate in the field. When the residual gas was below GHSZ, the residual gas would continually migrate into GHSZ to form gas hydrate, which was indicated by the drilling results that gas anomalies had ever been encountered even if below GHSZ as well as occurrences of gas hydrate within GHSZ in the field. When the residual gas was above GHSZ, the residual gas remained or escaped, which was indicated by the drilling results that gas anomalies even with a high pressure abnormity were encountered in the shallower strata above GHSZ without occurrences of gas hydrate within GHSZ in the field.

通过对南祁连盆地哈拉湖坳陷天然气水合物科学钻探试验QH-1孔、QH-2孔不同层段内岩心顶空气中各烃类气体含量及甲烷碳同住素值的统计,对比研究了岩心中烃类气体组分含量随不同深度的变化特征,剖析了组分含量与岩性、裂隙或破碎带之间的对应关系,探讨烃类气体的成因,指出了烃类气体对岩性、裂隙或破碎带、天然气水合物异常的地质指示意义.结果 显示:顶空气高含量区间段对泥岩有一定的指示作用,岩心中一定深度范围内多处钻遇石膏晶体,石膏出露层段与顶空气高含量区间段较为吻合,烃类气体可能主要以吸附(游离)的方式被封存在泥岩中,石膏起到了一定的封堵作用;裂隙或破碎带内岩心顶空气组分含量相对较高,显示裂隙或破碎带对烃类气体的聚集有一定控制作用;与南祁连盆地木里地区相比,钻探区虽然达到了天然气水合物稳定带条件,但未能钻获到天然气水合物,推测气体浓度较低为原因之一;钻孔岩心顶空气中甲烷气体主要以热解成因为主,并含部分混合成因气.

通过对南祁连盆地木里坳陷石炭系、二叠系、三叠系、侏罗系等4套层系5条剖面的野外测量及室内地质分析,明确了该区天然气水合物潜在气源岩的岩性特征、沉积相类型及沉积演化过程.石炭系—二叠系整体以出露中厚层砂岩夹薄层泥岩为主要特征,沉积浅海陆棚相、滨岸相和三角洲相,由于断层发育致使局部地层厚度减薄且泥质岩大部分缺失,可能难以成为天然气水合物潜在气源岩;上三叠统整体以发育中薄层泥岩与中薄至中厚层砂岩互层为主要特征,沉积相类型为潮坪相、湖泊相和河流相,泥岩累积厚度较大,是天然气水合物主要潜在气源岩;中侏罗统整体上以发育厚层泥岩、砂岩为主要特征,沉积相类型为辫状河相、三角洲相和湖泊相,是天然气水合物次要的潜在气源岩.研究结果为南祁连盆地木里坳陷天然气水合物气源岩研究提供了重要地质依据.

Three gravity cores (LZK1, ZKA4, and CSJA6) from the incised Yangtze paleo-valley comprise a thick sequence of the post-glacial deposit. Nineteen genera (26 species) of the benthic foraminifers are described from these cores, with detailed down-core foraminiferal variations to investigate their paleoenvironmental implications. Three foraminiferal assemblages are recognized for the lower, middle, and upper parts of the cores respectively. The lower part is dominated by Ammonia beccarii var. and Florilus decorus with lower abundance and diversity. In the middle part, the foraminifers are abundant and diverse, dominated by both Ammonia beccarii var. and Elphidium advenum. Cavarotalia annectens, Pararotalia nipponica, and porcellaneous benthic foraminiferal forms are always present, sometimes abundant. The upper part is characterized by the Ammonia beccarii-Elphidium magellanicum assemblage, except for the Core ZKA4, which is barren of foraminifers in this interval. AMS C-14 dates and foraminiferal assemblages both confirm that the transgression-regression sequence in these cores belongs to the "Ammonia transgression" during the Holocene. In addition to documenting the post-glacial sea-level fluctuations, the benthic foraminifers also reflect a warmer climate during the early-middle Holocene. The foraminiferal differences among the three cores can be used to interpret the influence of seawater during the post-glacial sea-level fluctuations. The area in the vicinity of Core ZKA4 was affected by marine water only during the middle Holocene, which was much shorter than the areas of the other cores.