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    Palaeostructure and palaeogeography from 3D seismic interpretation; examples from the Permian Basin in Poland
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    Abstract:
    The Permian Basin is the main target of exploration in western Poland. Porous Rotliegendes sandstone and two Zechstein carbonate formations are the most important reservoirs. Every depositional system includes different lithofacies, and interrelations create patterns of trap/reservoir and sealing horizons. Combination traps, with both structural and facial elements involved in their closure, create a comparatively high risk for exploration. Palaeogeographic analysis based on 3D seismic data presents opportunities for improved interpretation leading to a significant reduction of risk in exploration and development drilling. There is no direct information in 3D seismic data, but they allow us to reproduce the palaeogeography and successive stages of structural redevelopment by means of flattened seismic sections and construction of the corresponding maps, i.e. pseudo-palaeogeographical maps.
    Keywords:
    Palaeogeography
    Environmental geology
    Gemology
    Economic geology
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    ABSTRACT Interpretations of commercial marine shallow seismic data are generally limited to a prognosis of lithologies based on sparse ground truth data and regional stratigraphic models and a probability assessment of encountering perceived geohazards. However, an approach based on analyses of available petrophysical data can provide a more robust assessment of shallow marine lithologies and a more confident interpretation of shallow gas and overpressured formations. Generation of well‐ and borehole‐log acoustic impedance curves provides the starting point for these investigations and, although not all of the requisite data may be present in shallow section wireline suites, the Faust and Gardner equations, and other empirically derived relationships, can supply acceptable mathematical approximations. Impedance inversions of reflection seismic data facilitate more confident interpretations of lithological units, especially when combined with additional datasets such as gamma‐ray, resistivity, porosity, and S‐wave sonic, as elastic and extended elastic inversions. Anomalous seismic events interpreted to represent a probability of encountering shallow gas using traditional interpretation methods may be further investigated using amplitude‐versus‐offset cross‐plotting techniques, including fluid factor calculations, and the potential for overpressured gas accumulations or flow sands may be estimated from velocity‐derived pore pressure calculations. Geological and synthetic seismic modelling exercises provide the opportunity to test petrophysical interpretations in the absence of ground truth control data.
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    Lithology
    Wireline
    Economic geology
    Amplitude versus offset
    Environmental geology
    Seismic to simulation
    Igneous petrology
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    S.K. Basha, Anup Kumar, J.K. Borgohain, Ranjit Shaw, Mukesh Gupta and Surender Singh explain how the search for heavy oil in the Baghewala area, western India was progressed using rock physics modelling and simultaneous inversion.
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    In the Romanian East Carpathians overthrust relations between the Tarcau, the Marginal folds and the Subcarpathian nappes and the Moldavian and Moesian platforms have been deduced from seismic profiles and confirmed by wells. The down steps of the platform, under the nappes, have created many faulted blocks. South of the Trotus Valley, the Pralea-Focsani Depression has developed on the platform basement. Between the Slanic and Dambovita valleys, in the Mio-Pliocene zone, the Subcarpathian nappe, the diapir folds and the Oligocene deep structure have been delineated on seismic profiles. The presence of all the conditions for oil generation and entrapment encourages new investment in geological and geophysical exploration.
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    The Permian Basin is the main target of exploration in western Poland. Porous Rotliegendes sandstone and two Zechstein carbonate formations are the most important reservoirs. Every depositional system includes different lithofacies, and interrelations create patterns of trap/reservoir and sealing horizons. Combination traps, with both structural and facial elements involved in their closure, create a comparatively high risk for exploration. Palaeogeographic analysis based on 3D seismic data presents opportunities for improved interpretation leading to a significant reduction of risk in exploration and development drilling. There is no direct information in 3D seismic data, but they allow us to reproduce the palaeogeography and successive stages of structural redevelopment by means of flattened seismic sections and construction of the corresponding maps, i.e. pseudo-palaeogeographical maps.
    Palaeogeography
    Environmental geology
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    Economic geology
    Tarim basin
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    The East African margin has a complex structure due to multiple phases of rifting with different stretching directions. The main phase of rifting leading to Indian Ocean opening lasted from the Late Pliensbachian to the Bajocian ( c. 183 – 170 Ma). This occurred during impingement of the Bouvet hotspot which weakened the lithosphere sufficiently to allow continental break-up. Thick salt and marine shales were deposited during the Toarcian in the Majunga, Ambilobe and Mandawa basins and the onshore Ogaden Basin; marking the onset of the Indian Ocean marine incursion, when good quality oil-prone source rocks were deposited at this time. The recent giant gas discoveries in Tanzania and Mozambique are believed to be sourced from overmature Jurassic or, possibly, deeper Permian age Karoo shales. The margin from the Lamu Basin in the north to the Zambesi Delta in the south is covered by thick Tertiary and Cretaceous sediment derived from the East African rift shoulders, and Lower Jurassic source rocks are predicted to be in the gas window along most of the margin. However, the margins in South Africa, south Mozambique, northern Somalia and Madagascar are less deeply buried, and have better oil potential. The large Tsimimo and Bemolanga tar sand deposits and the recent announcement of an oil rim in the Inhasorro Field indicate that there are good oil-prone source rocks in the Karoo rifts and in the Albian Domo shales; and the search for oil continues with companies exploring in areas where Jurassic source rocks may be less deeply buried, and/or potential Albian–Turonian-aged source rocks are sufficiently buried to generate oil. Supplementary material: Figures S1–S3 are available at: https://doi.org/10.6084/m9.figshare.c.3894931
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