Hydrocarbon Inclusion Characteristics in the Cambrian-Ordovician Carbonates of the TS2 Well: Implication for Deep Hydrocarbon Exploration in the Tahe Oilfield,Tarim Basin,Northwest China

Going deep has been the strategy for the sustainable development of the Tahe Oilfield.Following the TS1 well in block 1,which revealed excellent combinations of hydrocarbon generation,migration and accumulation in the deeper parts of the Tarim Basin,the TS2 well was drilled to learn more about the prospectivity in the deeper parts of the main blocks of the Tahe Oilfield.Seventeen core samples were collected to perform fluid inclusion studies,including petrography,fluorescence microspectrometry,and microthermometry.The results show that the deeper parts of the Tahe Oilfield have a good hydrocarbon potential.The Cambrian source rocks can supply sufficient oil for not only the Cambrian reservoirs,but also for the Lower Ordovician reservoirs.The CambrianOrdovician carbonates reservoirs experienced at least three oil charging events and one late gas charging event.Oil accumulations formed in the early stage of basin evolution were likely destroyed in the late stage with deep burial,tectonic movements,or invasion of hydrothermal fluids.Therefore,the deep hydrocarbon exploration of the Tahe Oilfield,even the whole Tarim Basin,should focus on gas accumulations,although oil accumulations,especially in Cambrian reservoirs,cannot be neglected.     

气相色谱法测试土壤中分段石油烃的标准化定量方法初探

目前土壤样品中分段石油烃的分析方法中石油烃包括的碳原子数范围和采用的校准物质不统一,造成不同实验室的量值不具有可比性。为保证不同实验室之间结果的可比性,本文尝试建立一种石油烃相邻碳原子数标准化定量方法。该方法主要包括:(1)规定了石油烃包括的碳原子数范围为气相色谱峰中正己烷和正四十碳烷之间所有的烃(含正己烷);(2)总石油烃(TPH)分为挥发性石油烃(VPH)和半挥发性石油烃(SPH),分别选取碳原子数为6～10的5个正构烷烃作为VPH校准物质,选取碳原子数为10～40的31个正构烷烃作为SPH校准物质。采用平均响应因子法或一次线性回归法,建立校准物质的峰面积-浓度的校准关系;(3)采用相邻峰标准化校准方法,逐一定量所有的目标色谱峰;(4)计算正构烷烃含量、总石油烃含量和任意分段的石油烃含量。该方法为环境样品中石油烃分析方法的标准化建设提供了数据基础。     

New high-resolution 2D seismic imaging of fluid escape structures in the Makran subduction zone,Arabian Sea

Seabed fluid escape is active in the Makran subduction zone, Arabian Sea. Based on the new high-resolution 2D seismic data, acoustic blanking zones and seafloor mounds are identified. Acoustic blanking zones include three kinds of geometries: Bell-shaped, vertically columnar and tilted zones. The bell-shaped blanking zone is characterized by weak and discontinuous reflections in the interior and up-bending reflections on the top, interpreted as gas chimneys. Vertically columnar blanking zone is interpreted as side-imaged gas chimneys associated with focused fluid flow and topped by a seafloor anomaly expressed as a localized reflection discontinuity, which may together serve as a vent structure. Tilted acoustic blanking zone could be induced by accretionary thrust activity and rapid sedimentation surrounding slope. Seafloor mounds occur at the sites of bell-shaped acoustic blanking zone and may be associated with the material intrusion. Bottom simulating refectors (BSRs) are widely distributed and exhibit a series of characteristics including diminished amplitude, low continuity as well as local shoaling overlapping with these acoustic blanking zones. The large amount of gases dissociated from the gas hydrates migrated upwards and then arrived at the near-seafloor sediments, followed by the formation of the gas hydrates and hence the seafloor mound.     

Nanogeology in China: A review

Nanogeology is a subject that is a combination of geology and nanoscale science, and it has been a frontier field in recent years. It is also a new subject with the features of intersectionality and multidisciplinary. Digging deeper into geological problems and nanoscale phenomena helps better revealing the more essential mechanisms and processes in geological science, which is also an evitable path in the development of geology. In this paper, we elaborate the concept, feature and main subdisciplines, and summarize three stages of nanogeology development from preliminary research in the 1990s to subject formation in China. After summarizing the researchers’ achievements in this field, we illustrate some primary research progresses of nanogeology in China as eight subdisciplines. On the basis of the above content, we propose the development prospect of nanogeology in China. There are many geologic problems with scientific values and economic benefits, such as research of geologic fundamental problems, resource exploration and development, mechanism study and prediction of geological activities (disasters), mechanism research and management of environmental pollution and others. Nanogeology has a great potential in China to solve all of these problems. As a result, the theories and methods of nanogeology will become enriching and advanced. It offers important theoretical basis and technological methods to deal with major issues concerning the national economy and the people’s livelihoods, such as the prediction of geological activities, as well as resource distribution and its exploration and utilization.     

绿色能源,世纪工程--西气东输工程

西气东输工程是国家实施西部大开发战略的重要举措.在鄂尔多斯盆地和塔里木盆地进行的大规模天然气勘探工作表明,可以为西气东输工程准备较为充分的天然气可采储量.同时,根据对河南、安徽、江苏、浙江和上海等五省市天然气需求的预测,天然气需求市场的形势良好.西气东输工程是中国境内第一条达到国际标准的大口径、高压力、长距离输气管道.通过技术攻关和高新技术的应用,西气东输工程从管材及制管、焊接、内涂敷、压缩机增压系统优化、自动化控制到流量计量和焊接的无损检测技术等方面都取得了突破性进展.西气东输工程跨越多个自然环境区和地质构造区带,在工程可行性研究中就环境保护和地质灾害的预防做了大量的研究工作,提出了一系列的保护和预防措施.     

内蒙古中、上元古界地层的找金远景

内蒙古自治区境内,中、上元古界地层发育,其中所赋存的金属、非金属、贵金属矿产甚多。最近在中元古界朱拉扎嘎毛道组变质粉砂岩中所发现的微细浸染型金矿,是我局在元古界地层中寻找新类型金矿的一个突破,具有十分重要的意义。     

Large-scale depositional characteristics of the Ulleung Basin and its impact on electrical resistivity and Archie-parameters for gas hydrate saturation estimates

Gas hydrate saturation estimates were obtained from an Archie-analysis of the Logging-While-Drilling (LWD) electrical resistivity logs under consideration of the regional geological framework of sediment deposition in the Ulleung Basin, East Sea, of Korea. Porosity was determined from the LWD bulk density log and core-derived values of grain density. In situ measurements of pore-fluid salinity as well as formation temperature define a background trend for pore-fluid resistivity at each drill site. The LWD data were used to define sets of empirical Archie-constants for different depth-intervals of the logged borehole at all sites drilled during the second Ulleung Basin Gas Hydrate Drilling Expedition (UBGH2). A clustering of data with distinctly different trend-lines is evident in the cross-plot of porosity and formation factor for all sites drilled during UBGH2. The reason for the clustering is related to the difference between hemipelagic sediments (mostly covering the top ∼100 mbsf) and mass-transport deposits (MTD) and/or the occurrence of biogenic opal. For sites located in the north-eastern portion of the Ulleung Basin a set of individual Archie-parameters for a shallow depth interval (hemipelagic) and a deeper MTD zone was achieved. The deeper zone shows typically higher resistivities for the same range of porosities seen in the upper zone, reflecting a shift in sediment properties. The presence of large amounts of biogenic opal (up to and often over 50% as defined by XRD data) was especially observed at Sites UBGH2-2_1 and UBGH2-2_2 (as well as UBGH1-9 from a previous drilling expedition in 2007). The boundary between these two zones can also easily be identified in gamma-ray logs, which also show unusually low readings in the opal-rich interval. Only by incorporating different Archie-parameters for the different zones a reasonable estimate of gas hydrate saturation was achieved that also matches results from other techniques such as pore-fluid freshening, velocity-based calculations, and pressure-core degassing experiments. Seismically, individual boundaries between zones were determined using a grid of regional 2D seismic data. Zoning from the Archie-analysis for sites in the south-western portion of the Ulleung Basin was also observed, but at these sites it is linked to individually stacked MTDs only and does not reflect a mineralogical occurrence of biogenic opal or hemipelagic sedimentation. The individual MTD events represent differently compacted material often associated with a strong decrease in porosity (and increase in density), warranting a separate set of empirical Archie-parameters.     

Marine hydrocarbon source rocks of the Upper Permian Longtan Formation and their contribution to gas accumulation in the northeastern Sichuan Basin,southwest China

Identification of the main hydrocarbon source rocks of the large Puguang gas field (northeastern Sichuan Basin, southwest China) has been the subject of much discussion in recent years. A key aspect has been the lack of a comprehensive understanding of the development of hydrocarbon source rocks of the Upper Permian Longtan Formation, which had been thought to contain mainly coal seams and thick carbonate layers. In this paper, based on geological data from more than ten wells and outcrops and their related mineralogy and geochemistry, we investigated the depositional environment and main factors controlling organic matter enrichment in the Longtan Formation. We propose a model which combines information on the geological environment and biological changes over time. In the model, organic matter from prolific phytoplankton blooms was deposited in quiescent platform interior sags with rising sea-levels. During the Longtan period, the area from Bazhong to Dazhou was a platform interior sag with relatively deep water and a closed environment, which was controlled by multiple factors including syngenetic fault settling, isolation of submarine uplifts and rising sea-levels leading to water column stratification. Although the bottom water was anoxic, the phytoplankton were able to bloom in the well-lit upper euphotic zone thus giving rise to a set of sapropelic black shales and marlstones containing mostly algal organic matter with minor terrestrial contributions. As a consequence, these rocks have a high hydrocarbon generation potentials and can be classified as high-quality source rocks. The area from Bazhong to Dazhou is a center of hydrocarbon generation, being the main source of reservoired paleo-oils and presently discovered as pyrobitumen in the Puguang gas field. The identification of these source rocks is very important to guide future petroleum exploration in the northeastern Sichuan Basin.     

Seabed morphology and gas venting features in the continental slope region of Krishna–Godavari basin,Bay of Bengal: Implications in gas-hydrate exploration

Increased oil and gas exploration activity has led to a detailed investigation of the continental shelf and adjacent slope regions of Mahanadi, Krishna–Godavari (KG) and Cauvery basins, which are promising petroliferous basins along the eastern continental margin of India. In this paper, we analyze the high resolution sparker, subbottom profiler and multibeam data in KG offshore basin to understand the shallow structures and shallow deposits for gas hydrate exploration. We identified and mapped prominent positive topographic features in the bathymetry data. These mounds show fluid/gas migration features such as acoustic voids, acoustic chimneys, and acoustic turbid layers. It is interesting to note that drilling/coring onboard JOIDES in the vicinity of the mounds show the presence of thick accumulation of subsurface gas hydrate. Further, geological and geochemical study of long sediment cores collected onboard Marion Dufresne in the vicinity of the mounds and sedimentary ridges shows the imprints of paleo-expulsion of methane and sulfidic fluid from the seafloor.     

The thermal structure of the Dvurechenskii mud volcano and its implications for gas hydrate stability and eruption dynamics

The sediment temperature distribution at mud volcanoes provides insights into their activity and into the occurrence of gas hydrates. If ambient pressure and temperature conditions are close to the limits of the gas hydrate stability field, the sediment temperature distribution not only limits the occurrence of gas hydrates, but is itself influenced by heat production and consumption related to the formation and dissociation of gas hydrates. Located in the Sorokin Trough in the northern Black Sea, the Dvurechenskii mud volcano (DMV) was in the focus of detailed investigations during the M72/2 and M73/3a cruises of the German R/V Meteor and the ROV Quest 4000 m in February and March 2007. A large number of in-situ sediment temperature measurements were conducted from the ROV and with a sensor-equipped gravity corer. Gas hydrates were sampled in pressurized cores using a dynamic autoclave piston corer (DAPC). The thermal structure of the DMV suggests a regime of fluid flow at rates decreasing from the summit towards the edges of the mud volcano, accompanied by intermittent mud expulsion at the summit. Modeled gas hydrate dissociation temperatures reveal that the gas hydrates at the DMV are very close to the stability limits. Changes in heat flow due to variable seepage rates probably do not result in changes in sediment temperature but are compensated by gas hydrate dissociation and formation.