婆罗洲地质构造特征及其对南海南部盆地的影响

南海南部曾母、文莱—沙巴盆地油气资源丰富,已发现一大批油气田及含油气构造。曾母盆地南部与文莱—沙巴盆地油气的生成、运移和聚集与婆罗洲地块息息相关。婆罗洲地块地质特征复杂,自古新世开始,古南海逐渐消失,与婆罗洲地块发生碰撞,中新世开始隆升造山。在这种地质背景下,婆罗洲拉让河和巴兰河为曾母盆地南部与文莱—沙巴盆地的主要物源,发育三角洲相、滨浅海相、浊积扇相、浅海相砂岩储层;同时,压扭型构造发育,不仅形成断块与背斜型油气藏,同时具有良好的油气运移条件。     

塔东地区上奥陶统层序地层特征

通过大量的地震、钻井、录井、测井等资料分析,针对塔里木东部地区(简称塔东地区)上奥陶统进行了层序地层和沉积学方面的研究,结果表明,塔东地区上奥陶统可识别出1个二级层序、3个三级层序,自下而上分别是层序SQ1、SQ2和SQ3。层序SQ1识别出TST体系域,为一套深水盆地沉积,发育深水盆地、浊流沉积;层序SQ2可三分为LST、TST和HST体系域,LST体系域发育海退背景下的陆架边缘三角洲沉积,TST体系域为快速水进期,发育海相泥岩沉积,HST发育高水位滨岸沉积;SQ3发育浅海沉积,主要为三角洲—滨岸沉积体系。地层层序发育和沉积相分布受控于构造运动、沉积物源供给和相对海平面升降3个因素。3套层序的划分明确了塔东地区上奥陶统潜在的源岩层、储层和盖层的分布,其中层序SQ1为有利的烃源岩层、SQ2陆架边缘三角洲是潜在的有利储层,SQ3发育的滨岸砂岩为已经证实的油气藏。     

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.     

中国东部海域活动构造定量研究若干问题探讨

晚更新世以来的活动构造与现代地质灾害密切相关,目前针对陆域活动构造的定量研究成果卓著,而在海域方面研究薄弱。本文综述了国内外有关海域活动构造的研究进展,提出了目前国内海域活动构造定量研究存在的主要问题。在研究实践的基础上,阐述了海域活动构造的主要研究方法、其定量研究的关键问题及解决方案,重点总结了海域活动构造区地震危险性定量评价的研究方案,并进一步探讨了海域活动构造自身因素的危险性定量评价的研究思路。     

Spatiotemporal variation and mechanisms of temperature inversion in the Bay of Bengal and the eastern equatorial Indian Ocean

In the northern Bay of Bengal, the existence of intense temperature inversion during winter is a widely accepted phenomenon. However, occurrences of temperature inversion during other seasons and the spatial distribution within and adjacent to the Bay of Bengal are not well understood. In this study, a higher resolution spatiotemporal variation of temperature inversion and its mechanisms are examined with mixed layer heat and salt budget analysis utilizing long-term Argo（2004 to 2020） and RAMA（2...     

Structural-stratigraphic control on the Umitaka Spur gas hydrates of Joetsu Basin in the eastern margin of Japan Sea

Integrated geological, geochemical, and geophysical exploration since 2004 has identified massive accumulation of gas hydrate associated with active methane seeps on the Umitaka Spur, located in the Joetsu Basin on the eastern margin of Japan Sea. Umitaka Spur is an asymmetric anticline formed along an incipient subduction zone that extends throughout the western side of the Japanese island-arc system. Seismic surveys recognized chimney structures that seem strongly controlled by a complex anticlinal axial fault system, and exhibit high seismic amplitudes with apparent pull-up structures, probably due to massive and dense accumulation of gas hydrate. Bottom simulating reflectors are widely developed, in particular within gas chimneys and in the gently dipping eastern flank of the anticline, where debris can store gas hydrates that may represent a potential natural gas resource. The axial fault system, the shape of the anticline, and the carrier beds induce thermogenic gas migration to the top of the structure, and supply gas to the gas hydrate stability zone. Gas reaching the seafloor produces strong seepages and giant plumes in the sea water column.     

Stress state in the Cuu Long and Nam Con Son basins, offshore Vietnam

The results presented in this paper are the first published estimates of the complete stress tensor in the Cuu Long and Nam Con Son basins, offshore Vietnam. We analysed in situ stress and pore pressure fields in the sedimentary formations using data from petroleum exploration and production wells to evaluate the stress state in these basins. The data were obtained from the seafloor to 4300 m burial depth and include both hydrostatic and overpressured sections. Minimum horizontal stresses were obtained from extended leak-off tests and mini-fracture tests. Maximum horizontal stresses were estimated from drilling-induced fracture parameters and borehole breakout widths in twelve wells using rock properties measured in the laboratory or estimated empirically from wireline logs. Seven data points are located in sediments, and seventeen data points in igneous basement rocks at depths greater than 3000 m.The estimated magnitudes of σ_H are 70-110% of the σ_v magnitudes. Considering the errors in the stress magnitude estimates, their relative magnitudes suggest that a borderline normal/strike-slip stress regime presently exists in normally pressured sequences of the Nam Con Son and Cuu Long basins. Of the twenty-four data points, twenty have effective stress ratios at a critical stress state for faulting on the assumption that there are faults present that are optimally oriented for failure with friction coefficients of ∼0.5. The results suggest that the stress state in these basins is generally critical.     

珠江口盆地东南部揭阳凹陷A区油气地质条件及勘探前景

揭阳凹陷A区位于珠江口盆地东南部与台西南盆地西南部过渡区,属于中—新生代形成的断陷盆地。受制于缺乏基础资料(仅有二维地震),该研究区勘探工作一直未有进展。研究工作中充分利用新采集的三维地震资料,以层序地层学理论为指、结合构造分析与烃源岩压力预测技术,完成区内地层发育、洼陷结构特征、烃源发育以及构造目标、岩性目标发育情况总结,综合分析认为：研究区具备形成石油天然气的基本地质条件,勘探前景评价认为,研究区域具有可观的石油地质储量,是油气藏勘探的重要场所。     

The Paleogene vegetation and petroleum system in the tropics: A biomarker approach

The present study investigates the biomarker signatures of sediments and crude oils to infer the paleovegetation from the two petroleum systems of Assam Basin, eastern India. They are classified as the Paleocene-middle Eocene and the middle Eocene-Oligocene petroleum systems. The sediments are oil and gas prone with an early catagenetic stage of thermal evolution. Here we report tricyclic diterpanes such as rimuane, pimarane, rosane and isopimarane along with tetracyclic diterpanes: ent-beyerane, phyllocladane, kaurane from Paleocene-Eocene coal-bearing sediments and crude oils. These diterpane biomarkers attest dominant contribution from conifers, possibly from Podocarpaceae and Araucariaceae. However, diterpanes are not detected in Oligocene sediments and oils. Crude oils from both Paleocene-Eocene and Oligocene reservoirs and organic rich sediments contain angiosperm biomarkers such oleanane and related triterpanes along with bicadinane, a biomarker specific for the Dipterocarpaceae family of angiosperms. The equatorial position of India during early Paleogene along with the presence of angiosperm signatures including Dipterocarpaceae and gymnosperms reflect the emergence of tropical rainforest elements in eastern India. Absence of diterpenoids in Oligocene samples and difference in angiosperm parameters from Paleocene-Eocene samples suggests a change in source vegetation and organofacies.     

Cenozoic sequence stratigraphy of the Kachchh Basin,India

The Kachchh sedimentary basin in the western continental margin of India is a peri-cratonic rift basin which preserves a nearly complete rock record from Middle Jurassic to Recent, punctuated by several stratigraphic breaks. The Cenozoic sediments exposed in the western part of the Kachchh mainland extend offshore into the present-day continental shelf. The unique feature of the outcropping area is a nearly complete, richly fossiliferous and easily accessible Cenozoic succession. Detailed field mapping and litho-biostratigraphic studies have made it possible to identify the chronostratigraphic units, map them in the field and extend the correlation into the offshore, aided by the development of continuously recognizable key biostratigraphic horizons and time boundaries. Detailed field mapping of key sections integrated with the litho-biostratigraphic information has helped in working out a sequence stratigraphic framework for the Cenozoic succession in the basin. The succession comprises a first-order passive margin sequence. Excellent biostratigraphic control has enabled identification of unconformities of various magnitudes which in turn have helped in mapping 5 second-order and four third-order sequences. Each sequence is discussed with respect to its extent, nature of sequence boundaries, sedimentary fill, key sequence stratigraphic surfaces and depositional setup, to understand the Cenozoic sequence stratigraphic architecture of the basin.