Carbon and oxygen isotopic composition of car- bonate cements of different phases in terrigenous siliciclastic reservoirs and significance for their origin： A case study from sandstones of the Triassic Yanchang Formation, southwestern Ordos Basin, China     

Qi Wang  Xizhun Zhuo  Guojun Chen  Xiaoyan Li 《中国地球化学学报》2008,27(3):249-256

Early carbonate cements in the Yanchang Formation sandstones are composed mainly of calcite with relatively heavier carbon isotope （their δ^18O values range from -0.3‰- -0.1‰） and lighter oxygen isotope （their δ^18O values range from -22.1‰- -19.5‰）. Generally, they are closely related to the direct precipitation of oversaturated calcium carbonate from alkaline lake water. This kind of cementation plays an important role in enhancing the anti-compaction ability of sandstones, preserving intragranular volume and providing the mass basis for later disso- lution caused by acidic fluid flow to produce secondary porosity. Ferriferous calcites are characterized by relatively light carbon isotope with δ^13C values ranging from -8.02‰ to -3.23‰, and lighter oxygen isotope with δ^18O values ranging from -22.9‰ to -19.7‰, which is obviously related to the decarboxylation of organic matter during the late period of early diagenesis to the early period of late diagenesis. As the mid-late diagenetic products, ferriferous cal- cites in the study area are considered as the characteristic authigenic minerals for indicating large-scaled hydrocarbon influx and migration within the clastic reservoir. The late ankerite is relatively heavy in carbon isotope with δ^13C values ranging from -1.92‰ to -0.84‰, and shows a wide range of variations in oxygen isotopic composition, with δ^18O values ranging from -20.5‰ to -12.6‰. They are believed to have nothing to do with decarboxylation, but the previously formed marine carbonate rock fragments may serve as the chief carbon source for their precipitation, and the alkaline diagenetic environment at the mid-late stage would promote this process.  相似文献   

Research Advances and Exploration Significance of Large-area Accumulation of Low and Medium Abundance Lithologic Reservoirs   总被引：1，自引：1，他引：0  

ZHAO Wenzhi  WANG Zecheng  WANG Hongjun  CHEN Mengjin 《《地质学报》英文版》2008,82(3):463-476

In recent years, a series of large low and medium abundance oil and gas fields are discovered through exploration activities onshore China, which are commonly characterized by low porosity-permeability reservoirs, low oil/gas column height, multiple thin hydrocarbon layers, and distribution in overlapping and connection, and so on. The advantageous conditions for large-area accumulation of low-medium abundance hydrocarbon reservoirs include： （1） large （fan） delta sandbodies are developed in the hinterland of large flow-uncontrolled lake basins and they are alternated with source rocks extensively in a structure like ＂sandwiches＂; （2） effective hydrocarbon source kitchens are extensively distributed, offering maximum contact chances with various sandbodies and hydrocarbon source rocks; （3） oil and gas columns are low in height, hydrocarbon layers are mainly of normal-low pressure, and requirements for seal rock are low; （4） reservoirs have strong inheterogeneity and gas reservoirs are badly connected; （5） the hydrocarbon desorption and expulsion under uplifting and unloading environments cause widely distributed hydrocarbon source rocks of coal measures to form large-area reservoirs; （6） deep basin areas and synclinal areas possess reservoir-forming dynamics. The areas with great exploration potential include the Paleozoic and Mesozoic in the Ordos Basin, the Xujiahe Formation in Dachuanzhong in the Sichuan basin, deep basin areas in the Songliao basin etc. The core techniques of improving exploration efficiency consist of the sweetspot prediction technique that focuses on fine characterization of reservoirs, the hydrocarbon layer protecting and high-speed drilling technique, and the rework technique for enhancing productivity.  相似文献   

The characteristics and sources of natural gases from Ordovician weathered crust reservoirs in the Central Gas Field in the Ordos Basin   总被引：2，自引：2，他引：0  

Xianqing Li  Guoyi Hu  Jian Li  Dujie Hou  Peng Dong  Zhihong Song  Yunfeng Yang 《中国地球化学学报》2008,27(2):109-120

The Central Gas Field is a famous large-sized gas field in the Ordos Basin of China. However, identification of main gas sources of the Ordovician reservoirs in this gas field remains puzzling. On the basis of a lot of geochemical data and geological research on natural gases, the characteristics and sources of natural gases from Ordovician weathered crust reservoirs in the Central Gas Field in the Ordos Basin were studied. The results indicated that natural gases from Ordovician weathered crust reservoirs in the Central Gas Field in the Ordos Basin have similar chemical and isotopic compositions to highly mature and over-mature dry gases. Both coal-derived gases and oil-type gases coexist in the Central Gas Field in the Ordos Basin. The former was derived mainly from Carboniferous-Permian coal measures and the latter from Lower Paleozoic marine carbonates. It is suggested that coal-derived gases occur in the eastern part of the Central Gas Field while oil-type gases may be produced mainly in the northern, western and southern parts of the Central Gas Field in the Ordos Basin.  相似文献   

Application of Spectral Decomposition to Detection of Fracture-Cavity Carbonate Reservoir Beds in the Tahe Oiifieid, Tarim Basin, NW China     

Liu Xiaoping  Yang Xiaolan  Zhang Yazhong  Han Long 《《地质学报》英文版》2008,82(3):530-536

Ordovician fracture-cavity carbonate reservoir beds are the major type of producing formations in the Tahe oilfield, Tarim Basin. The seismic responses of these beds clearly changes depending on the different distance of the fracture-cavity reservoir bed from the top of the section. The seismic reflection becomes weak or is absent when the fracture-cavity reservoir beds are less than 20 ms below the top Ordovician. The effect on top Ordovician reflection became weaker with deeper burial of fracture-cavity reservoir beds but the developed deep fracture-cavity reservoir beds caused stronger reflection in the interior of the Ordovician. This interior reflection can be divided into strong long-axis, irregular and bead string reflections, and was present 80 ms below the top Ordovician. Aimed at understanding reflection characteristics, the spectral decomposition technique, which uses frequency to ＂tune-in＂ bed thickness, was used to predict Ordovician fracture-cavity carbonate formations in the Tahe oilfield. Through finely adjusting the processing parameters of spectral decomposition, it was found that the slice at 30 Hz of the tuned data cube can best represent reservoir bed development. Two large N-S-trending strong reflection belts in the mid-western part of the study area along wells TK440- TK427-TK417B and in the eastern part along wells TK404-TK409 were observed distinctly on the 30 Hz slice and 4-D time-frequency data cube carving. A small N-S trending reflection belt in the southern part along wells T403-TK446B was also clearly identified. The predicted reservoir bed development area coincides with the fracture-cavities connection area confirmed by drilling pressure testing results. Deep karst cavities occur basically in three reservoir bed-development belts identified by the Ordovician interior strong reflection. Spectral decomposition proved to be a useful technique in identifying fracture-cavity reservoir beds.  相似文献   

下庄矿田湖子地区铀矿找矿方向探讨   总被引：2，自引：0，他引：2       下载免费PDF全文

邱列  毛孟才  王建雄 《地质找矿论丛》2008,23(1):11-15,26

湖子地区位于NNE向诸广-新兴铀成矿带与近EW向大东山-漳州大断裂复合部位,是华南早、晚两期铀成矿热液活动叠加区、放射性高场区,既有"硅化带大脉"型铀矿产出,又有"交点"型铀矿存在,找矿前景良好.文章在论述下庄矿田铀成矿地质环境、铀成矿特征及铀矿定位条件基础上,分析了湖子地区铀成矿条件与找矿前景,指出该区今后铀矿找矿方向是:① 6009号硅化断裂带,在其北段找硅化带大脉型铀矿,在其南段找"交点"型铀矿;②新桥-下庄硅化断裂带和6009号带之间成矿部位,寻找硅化带型和"交点"型铀矿;③NW向、近EW向辉绿岩脉与NNE向、NE向构造交汇部位(交点),寻找"交点"型铀矿.  相似文献   

中伊朗盆地Garmsar区块Qom组沉积微相及储层特征研究   总被引：1，自引：1，他引：0  

徐国盛  马若龙  张长俊  秦润森 《物探化探计算技术》2008,30(6)

伊朗Garmsar区块Qom组形成于碳酸盐岩台地沉积环境,岩性以生物屑灰岩、含砂生物屑灰岩、泥晶灰岩为主,是典型的裂缝~孔隙型储层。利用区内野外实测剖面资料和露头岩样测试资料,对Qom组沉积相进行标识及类型划分,并对Qom组沉积微相及其平面展布特征进行分析,指出了该区域开阔台地相~高能红藻滩微相和局限台地相~泻湖夹台内滩微相是研究区储层发育的有利部位。F段中部的粒内溶孔较为发育,而溶缝主要出现在C1、C3亚段,整个Qom组构造微裂缝不甚发育。但储层孔渗条件比较差,属于中~低孔、低渗~特低渗储层,且存在严重的不均一性。为此,从沉积相与储层特征角度研究认为,中伊朗盆地Garmsar区块Qom组油气勘探存在一定的风险。  相似文献   

潜水面对储层压力的作用机制   总被引：5，自引：0，他引：5  

许浩  汤达祯  张君峰  尹微 《煤田地质与勘探》2008,36(5)

潜水面与地表不一致会使储层压力产生异常,给煤层气勘探开发造成影响。从异常压力的成因机理入手,应用理论分析与实例解剖相结合的方法,通过不同系统中潜水面对储层压力的作用机制研究,分析了开放系统中区域潜水面变化所引起的储层压力变化规律,反映了盆地水动力场作用下的储层压力系统的动态演化过程,指出潜水面变化是储层异常压力形成的重要机制。  相似文献   

三峡水库建设前后10年库区景观空间格局动态变化研究——以重庆开县为例   总被引：2，自引：1，他引：1  

邵怀勇  仙巍  杨武年  周万村 《测绘科学》2008,33(6):176-178

在遥感和地理信息系统技术的支持下,以1992年和2002年TM图像为基础,采用斑块密度、斑块平均面积、景观形状指数、景观分离度指数、景观多样性指数、景观优势度指数、景观相对聚集度指数深入而全面地研究了三峡工程建设前后十年重庆开县景观空间格局的动态变化,本研究的开展旨在为库区生态环境保护提供科学依据。研究结果表明,十年间研究区景观空间格局发生了明显变化,草地、未利用地、旱地、果园和水田面积净减,森林、建设用地、灌木林和水域面积增加,退耕还林已初见成效。  相似文献   

曲流点坝内部剩余油形成与分布规律物理模拟   总被引：7，自引：0，他引：7  

闫百泉  马世忠  王龙  张全恒 《地学前缘》2008,15(1):65-70

建立了曲流点坝物理模型,模拟地下曲流点坝储层进行驱替实验。观察注入剂的运动规律,同时,在模型上布置了测量电极,以双电极法测量驱替过程中垂向电阻变化,反映注入剂波及高度的变化规律。分析了侧积泥岩夹层的建筑结构对注入剂在点坝砂体中的流动规律,以及对剩余油的形成分布的影响。通过实验研究证实,在曲流点坝内部,侧积泥岩夹层对注入剂具有强烈的遮挡作用,受其影响形成侧积体差异型剩余油、重力型剩余油以及压力异常型剩余油三种类型剩余油,主要分布在点坝的中上部。在实际生产中,利用水平井钻遇点坝上部进行开采是主要的手段。  相似文献   

渤南洼陷沙四上段非均质性储层“二步建模”方法及应用     

张守鹏 《地学前缘》2008,15(1):202-208

渤南洼陷沙四上段油气储层非均质性明显,砂层薄且与泥质间层分布,储层分布规律和空间叠置关系复杂。储层主要受深水盐湖、扇三角洲、滑塌浊积扇、近岸浊积扇、远岸浊积扇五类沉积相控制。利用先进的GridStrat建模软件,采用特殊的"二步建模"处理方法,根据不同沉积相的储层参数分布规律,进行井间插值或随机模拟,建立了沉积相、岩性、孔隙度、渗透率和产能系数模型。沉积相模型显示出扇三角洲及浊积扇是砂体分布的主体,且分布范围广;岩性模型显示出不同岩类的分布受沉积相带、构造位置及不同物源控制。孔、渗模型显示沉积相带和岩性是决定储层孔隙度与渗透率发育程度的主控因素。孔隙度决定了储油气空间的数量,渗透率决定了储层产能系数的大小。产能系数模型显示出产能潜力区为浊积扇和扇三角洲的叠合分布区。研究结论对油田开发部署起到积极指导作用。  相似文献