Acoustic impedance is a rock property that, under specific conditions, can be derived from seismic data and can provide important insights into reservoir parameters-such as porosity, lithology, fluid content, etc. Direct measurements of acoustic impedance are available from sonic and density well logs. Seismic inversion, a process of converting seismic data into relative impedance, provides estimates of relative acoustic impedance away from the well locations. Because absolute acoustic impedance can be related to other rock properties, the inverted relative seismic impedance could be used to predict these properties away from the wells if the missing low frequencies could be reliably calculated and compensated for. In chalk, seismic inversion finds its most significant application in porosity prediction. Compared to the well acoustic impedance, inverted relative acoustic impedance has a limited bandwidth, which is restricted on low and high ends of the frequency spectrum. Band-limited impedance (in this article referred to as relative impedance) is a useful seismic attribute for a better qualitative understanding of reservoir properties, and it often can be used for quantitative estimation of other reservoir properties, especially in clastic reservoirs. Since chalk consists of homogeneous lithofacies with clean matrix character with its porosity as the main variable, it is a perfect medium for qualitative prediction of this specific attribute. However, quantitative reservoir characterization in chalk is severely limited by the lack of low-frequency information because the bulk of the strong correlation between impedance and porosity is carried by the low-frequency trend. The missing low-frequency part of the inverted impedance data can be modeled by lateral interpolation of impedance logs between well locations. Conventionally, this interpolation has been driven by distance between the wells, which often leads to artifacts and generation of nongeologic solutions. Distance-based, well-log interpolation can be significantly improved by using seismic velocities to guide the well-log interpolation. Although the use of velocities is a major improvement, it is limited by seismic resolution and accuracy that generally deteriorates with depth. Velocity data only partially provide the missing information in the lowest frequency range. In the present study, event-based validated multivariate interpolation was successfully applied to recover lowfrequency acoustic impedance using well data, velocity data, and seismic attributes. The examples given in this article originate from the Danish sector in the North Sea. Using seismic estimates of interval velocities, layer depths, formation thicknesses, and reflection amplitudes, it was possible to significantly improve the accuracy of the predicted low-frequency response and therefore the porosity estimates as compared to conventional methods. Impedance information in the frequency interval between 0 and somewhat higher than 8 Hz was estimated, achieving an improvement especially ...

Several approaches exist to use trends in 3D seismic data, in the form of seismic attributes, to interpolate sparsely sampled well-log measurements between well locations. Kriging and neural networks are two such approaches. We have applied a method that finds a relation between seismic attributes ͑such as two-way times, interval velocities, reflector rough-ness͒ and rock properties ͑in this case, acoustic impedance͒ from information at well locations. The relation is designed for optimum prediction of acoustic impedances away from well sites, and this is accomplished through a combination of cross validation and the Tikhonov-regularized least-squares method. The method is fast, works well even for highly underdetermined problems, and has general applicability. We apply it to two case studies in which we estimate 3D cubes of low-frequency impedance, which is essential for producing good porosity models. We show that the method is superior to traditional least squares: Numerous blind tests show that estimated low-frequency impedance away from well locations can be determined with an accuracy very close to estimations obtained at well locations.

The northwestern Pacific Ocean is one of the hotspots of species richness and one of the high endemicity areas of the World Ocean. However, large-scale biodiversity patterns of major deep‑sea taxa such as Isopoda and Polychaeta are still poorly studied. The goal of this research is to study the distribution, biodiversity, and community composition of Isopoda and Polychaeta (including Siboglinidae and Echiura) across the northwestern Pacific Ocean and the adjacent Arctic Ocean. The study area was divided into equal-sized hexagonal cells (c. 700,000 km²), ecoregions, 5° latitudinal bands, and 200 m depth intervals as unit of analysis. Our results revealed that the area around the Philippines and the Laptev Sea had the highest isopod and polychaete’s species richness compared to the other geographic regions of our study, with a latitudinal decline of species richness in shallow waters in both taxa. In the deep sea, maximum species richness increased towards the temperate latitudes. Gamma species richness (number of species per 200 m depth interval) also declined with depth. Rarefied species richness of isopods peaked around 5000 m depth. Rarefaction curves demonstrated a great potential for undiscovered richness across 5° latitudinal bands and depth intervals. In shallow waters, polychaetes with a pelagic larval phase had a wider distribution range compared to brooding isopods, but, in the deep sea, isopods had slightly wider distribution ranges compared to polychaetes. These results thus demonstrated that shallow water taxa with pelagic larvae and polychaete species with a wide vertical distribution range could potentially invade higher latitudes, such as species from the Northwest Pacific invading the Arctic Ocean under the rapid climate change and catastrophic reduction of sea ice cover. These changes might dramatically change the benthic communities of the Arctic Ocean and management of such should take an adaptive approach and apply measures that take potential extension and invasion of species into account.

The present paper describes the basis for delineating a significant volume of non-structurally trapped oil within low permeable chalk at the flank of the mature Dan field offshore Denmark. Drilling of extensive long horizontal wells at the flank of the main field, including one that set a world record horizontal section, has resulted in the discovery of a thin high porous (>30%) Maastrichtian chalk unit. The best reservoir zone is developed with consistent high oil saturation in the order of 80–90%, and trapped between lower porosity predominantly water bearing Danian and Maastrichtian Chalk units. Full vertical and lateral pressure continuity is observed between the hydrocarbon and water bearing units on the main field. It was therefore surprising to find the oil in the better of the units extending down flank, and outside the structural closure far beyond what could be predicted from modeling of the saturation profiles observed in the crestal wells. Drilling of three wells with up to 19,600 ft long horizontal sections in the flank area, consistently found the free water level dipping and deepening significantly to the north-west of the field allowing hydrocarbon filling of the units of highest reservoir quality in this area. Drilling of long reach horizontal wells thus provided the data needed for regional mapping of the free water level required as input to fluid modeling. Information on layer thickness and matrix porosity, necessary for volumetric calculations, was provided from well logs and through stochastic forward modeling of seismic acoustic impedance data extracted from a regional 3D survey. Improved understanding of the hydro- and geodynamic induced fluid pattern, combined with seismic mapping and modeling, thus resulted in the identification of significant and yet undrained volumes at the flanks of a mature oil field.

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