The geophysical identification, characteristics, and petroliferous significance of sublacustrine fan deposits in the second member of Dongying Formation in Liaozhong Depression, Bohai Bay Basin

Large sublacustrine fan deposits have been identified within the lacustrine successions of the second member of the Palaeogene Dongying Formation in the Liaozhong Depression. In this study, by using comprehensive and detailed analyses of the borehole lithology, limited cores, wireline logs, and seismic facies, 4 types of sublacustrine fan deposits were identified and characterized. Then, an integrated depositional model was established based on the above investigations. The result indicates that the geophysical characteristics of the different sublacustrine fan deposits differed from each other, in terms of their internal configuration and external geometry of seismic reflections, and stacking patterns of wireline logs, and stratigraphic position in the vertical successions. Subsequently, the model was established according to the comprehensive analysis of the geophysical characteristics and stratigraphic position. The discussion of developing conditions and hydrocarbon discoveries within different types of sublacustrine fan deposits provided robust insights regarding how to locate and evaluate reservoirs in such deposits. Furthermore, the results of this study may potentially assist in achieving a new understanding of how to identify sublacustrine fan deposits in similar lacustrine basins and may also assist in making further decisions regarding the terms of hydrocarbon migration and accumulation.

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Sea level rising faster now than during 1990s, new study shows

Global mean sea level is rising 25 percent faster now than it did during the late 20th century largely due to increased melting of the Greenland Ice Sheet, a new study shows. Satellites first started measuring sea level rise in 1993. The new study revisits how well these measurements agree with independently observed changes in the various components contributing to sea level rise.

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Diagenesis of tight oil sand reservoirs: Upper Triassic tight sandstones of Yanchang Formation in Ordos Basin, China

Upper Triassic sandstones in the Ordos Basin, northern‐central China, comprise tight oil reservoirs. Using a combination of thin sections, SEM, BSE, EDS, XRD, and fluid inclusion analyses, 24 core samples from 13 wells were collected to study the petrology, paragenesis, and diagenetic processes and implications for reservoir quality. Quartz cement usually occurs as overgrowths or euhedral quartz. Extensive dissolution and albitization of K‐feldspar can be observed. Five types of carbonate cements, ferrocalcite, ankerite, dolomite, calcite, and siderite, occur during different diagenetic stages. Two main types of illite and 5 main habits of chlorite are observed in this study. Kaolinite mainly occurs as booklets and vermicular aggregates. Diagenetic illite, chlorite, biotite, mixed‐layer illite/smectite (I/S), and other minor minerals are also observed. The diagenetic processes include compaction, alteration of volcanic materials and mica, clay mineral transformation, cementation (silica, aluminosilicate, and carbonate), and dissolution of feldspars and rock fragments. Compaction was a significant porosity‐reducing agent, and the presence of carbonate cement exerts a dominant impact on the reduction of porosity. Quartz cement and authigenic clays are less important; however, it is worth mentioning that pore‐lining clays are conducive to porosity preservation. In this study, most of the porosity variation is caused by a combination of compaction, carbonate cements, quartz cement, and authigenic clays. This study gives insights into diagenetic alterations within tight sandstones and has implications for reservoir quality prediction in similar settings.

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Strong earthquake widely filmed in Chile

A swarm of magnitude ~5-6 earthquakes offshore Chile on April 23 was punctuated two days later by a much larger M6.9 earthquake yesterday evening. While nobody could have specifically predicted the size and timing of this earthquake, it is a terribly unsurprising event, occurring as it did in the midst of this swarm of heightened seismic activity, and in the highly seismically hazardous region of coastal Chile. As has been pointed out …

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Mineralogical compositions and elemental enrichment of shales in lacustrine rift basin: a case study in the Cenozoic Lunpola Basin, central Tibet

The Lunpola Basin in central Tibet is a Cenozoic lacustrine rift basin with widespread organic‐rich shale and oil shale depositions. Forty‐nine samples were collected from the Lunpola section to evaluate the controlling factors of trace‐element enrichment and mineralogical composition in the lacustrine rift basin. Minerals identified in the Lunpola section include abundant quartz, calcite, and clay minerals; minor quantities of feldspar, dolomite, siderite, and mirabilite; and trace amounts of aragonite, magnesite, salt, pyrite, hematite, zeolite, barite, amphibole, gypsum, anhydrite, anatase, galena, sphalerite, apatite, chromite, zircon, and monazite. The Lunpola shale and oil shale are enriched in trace elements B, Cr, Ni, Mo, and U, in comparison to the upper continental crust. Three processes were probably responsible for the geochemical anomalies found in the Lunpola Basin, including the detrital material input, lake water, and hydrothermal activities. Mineralogical and geochemical data show that the lake water is the dominant influences on the elevated trace element concentrations in the shale and oil shale. The depletion or enrichment of trace elements in sediments from the lacustrine rift basin is governed by general processes (e.g. anoxic environment). Additionally, hydrothermal fluids also cause remobilization of some trace elements in the Lunpola lacustrine rift basin. Copyright © 2017 John Wiley & Sons, Ltd.

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