Resistivity of reservoir sandstones and organic rich shales on the Barents Shelf:Implications for interpreting CSEM data

Marine controlled source electromagnetic(CSEM)data have been utilized in the past decade during petroleum exploration of the Barents Shelf,particularly for de-risking the highly porous sandstone reservoirs of the Upper Triassic to Middle Jurassic Realgrunnen Subgroup.In this contribution we compare the resistivity response from CSEM data to resistivity from wireline logs in both water-and hydrocarbon-bearing wells.We show that there is a very good match between these types of data,particularly when reservoirs are shallow.CSEM data,however,only provide information on the subsurface resistivity.Careful,geology-driven interpretation of CSEM data is required to maximize the impact on exploration success.This is particularly important when quantifying the relative re-sistivity contribution of high-saturation hydrocarbon-bearing sandstone and that of the overlying cap rock.In the presented case the cap rock comprises predominantly organic rich Upper Jurassic-Early Cretaceous shales of the Hekkingen Formation(i.e.a regional source rock).The resistivity response of the reservoir and its cap rock become merged in CSEM data due to the transverse resistance equivalence principle.As a result of this,it is imperative to understand both the relative contributions from reservoir and cap rock,and the geological sig-nificance of any lateral resistivity variation in each of the units.In this contribution,we quantify the resistivity of organic rich mudstone,i.e.source rock,and reservoir sandstones,using 131 exploration boreholes from the Barents Shelf.The highest resistivity(＞10,000 Ωm)is evident in the hydrocarbon-bearing Realgrunnen Subgroup which is reported from 48 boreholes,43 of which are used for this study.Pay zone resistivity is primarily controlled by reservoir quality(i.e.porosity and shale fraction)and fluid phase(i.e.gas,oil and water saturation).In the investigated wells,the shale dominated Hekkingen Formation exhibits enhanced resistivity compared to the background(i.e.the underlying and overlying stratigraphy),though rarely exceeds 20Ωm.Marine mudstones typically show good correlation between measured organic richness and resistivity/sonic velocity log signatures.We conclude that the resistivity contribution to the CSEM response from hydrocarbon-bearing sandstones out-weighs that of the organic rich cap rocks.     

Compositions and phase relations of calcic amphiboles in epidote- and clinopyroxene-bearing rocks of the amphibolite and lower granulite facies,central Massachusetts,USA

Calcic amphiboles coexisting with epidotegroup minerals (zoisite, clinozoisite, epidote) and/or clinopyroxene±plagioclase±quartz±garnet occur in amphibolites and calc-silicate rocks that underwent amphibolite to lower granulite-facies metamorphism in the Acadian metamorphic high of central Massachusetts, USA. Across the region, peak metamorphic conditions range from about 580° C and 6.2 kbar to 730° C and 6.3 kbar. The coexistence of most Ca-amphiboles with Fe³⁺-rich epidote-group minerals suggests the presence of Fe³⁺ in most of these amphiboles. An empirical Fe³⁺ estimation for the microprobe analyses is based on two constraints: the Na?Ca content of the M4 sites of Ca-saturated, gravimetrically analyzed hornblendes gives the relation: Ca(M4) ^c =-1.479 Na(M4) ^c +2 (c=corrected). The second constraint is the stoichiometric equation Ca(M4)+Na(M4)+FM=15, where FM is the sum of all cations exclusive of Ca, Na, and K. Solving the two equations simultaneously gives: 20.185=0.479 Ca(M4)+1.479 ΣFM. Starting with the uncorrected values of Ca(M4) ^u and ΣFM(M4) ^u (u = uncorrected) of the all ferrous formula, the normalization factor NF for calculating the corrected cations of the ferric formulas is: 20.185/(0.478 Ca(M4) ^u +1.479 ΣFM ^u ). From the deficient oxygen the Fe³⁺ content which is equal to 2(23-ΣOX) can be calculated. Determinations of Fe³⁺ contents of four hornblende separates by Mössbauer spectroscopy are in agreement with the calculated values. The Ca-amphiboles show systematic changes in composition with increasing grade of metamorphism within the amphibolite and lower granulite-facies zones: increasing edenite and tschermakite substitution, increasing Ti content, and increasing Fe²⁺/(Fe²⁺+Mg) ratio. In addition, the coexisting clinopyroxenes are also characterized by an increase in Fe²⁺/(Fe²⁺+Mg) ratio. In quartz-free rocks with coexisting Ca-amphibole and plagioclase there is an increase in the ratio X _Ab/X _Ed, where X _Ab=Na/(Na+Ca) in plagioclase and X _Ed=Na in the amphibole A-site. These chemical changes in mineral composition together with the disappearance of epidote at the transition to granulite-facies metamorphic conditions are attributed to the continuous reaction: albite+epidote+Fe-Mg hornblende→Fe?Mg clinopyroxene+anorthite+(NaAlSi_-1)^Hbl+H₂O.     

Die Verwendung von Mineralen mariner Evaporite als Indikatoren der Luftfeuchtigkeit

Vapor-pressure measurements in the seawater system are used to show how far evaporites can be used as humidity indicators.

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Der Deutschen Forschungsgemeinschaft danken wir für eine Sachbeihilfe. Dr. H. Nielsen, Zentrallabor für Geochemie der Isotope, Göttingen, danken wir für Ratschläge beim Aufbau der Apparatur.     

Curvature Wavefront Sensor For Solar Adaptive Optics

Active or adaptive optics often require the ability to characterize wavefront aberrations using natural extended sources. The task becomes especially challenging when dealing with widely extended sources such as the solar granulation. We propose a new approach based on the processing of oppositely defocused images. This method, which is a generalization of a technique known as curvature sensing, derives the wavefront curvature from the difference between two oppositely defocused images and determines the second momenta of the point spread function. The proposed method measures the wavefront aberration from the images themselves, requires little computational resources, is fast enough to be used in a real-time adaptive optics system and is particularly adapted to random patterns such as solar granulation or spot penumbras whose morphology evolves during the observation. We envision the application of the method to real-time seeing compensation in solar astronomical telescopes, and to the correction of optical system aberrations in remote sensing instrumentation. This effort is directed towards building a curvature sensor for the real-time applications.     

Growth and grazing rate dynamics of major phytoplankton groups in an oligotrophic coastal site

There has been more attention to phytoplankton dynamics in nutrient-rich waters than in oligotrophic ones thus requiring the need to study the dynamics and responses in oligotrophic waters. Accordingly, phytoplankton community in Blanes Bay was overall dominated by Prymnesiophyceae, remarkably constant throughout the year (31 ± 13% Total chlorophyll a, Tchl a) and Bacillariophyta with a more episodic appearance (20 ± 23% Tchl a). Prasinophyceae and Synechococcus contribution became substantial in winter (Prasinophyceae = 30% Tchl a) and summer (Synechococcus = 35% Tchl a). Phytoplankton growth and grazing mortality rates for major groups were estimated by dilution experiments in combination with high pressure liquid chromatography and flow cytometry carried out monthly over two years. Growth rates of total phytoplankton (range = 0.30–1.91 d⁻¹) were significantly higher in spring and summer (μ > 1.3 d⁻¹) than in autumn and winter (μ ∼ 0.65 d⁻¹) and showed a weak dependence on temperature but a significant positive correlation with day length. Microzooplankton grazing (range = 0.03–1.4 d⁻¹) was closely coupled to phytoplankton growth. Grazing represented the main process for loss of phytoplankton, removing 60 ± 34% (±SD) of daily primary production and 70 ± 48% of Tchl a stock. Chla synthesis was highest during the Bacillarophyceae-dominated spring bloom (Chl a_synt = 2.3 ± 1.6 μg Chl a L⁻¹ d⁻¹) and lowest during the following post-bloom conditions dominated by Prymnesiophyceae (Chl a_synt = 0.23 ± 0.08 μg Chl a L⁻¹ d⁻¹). This variability was smoothed when expressed in carbon equivalents mainly due to the opposite dynamics of C:chl a (range = 11–135) and chl a concentration (range = 0.07–2.0 μg chl a L⁻¹). Bacillariophyta and Synechococcus contribution to C fluxes was higher than to biomass because of their fast-growth rate. The opposite was true for Prymnesiophyceae.     

Polyfluorinated compounds in waste water treatment plant effluents and surface waters along the River Elbe, Germany

Polyfluorinated compounds (PFCs) were investigated in waste water treatment plant (WWTP) effluents and surface waters of the River Elbe from samples collected in 2007. Concentrations of various PFCs, including C₄–C₈ perfluorinated sulfonates (PFSAs), C₆ and C₈ perfluorinated sulfinates, 6:2 fluorotelomer sulfonate, C₅–C₁₃ perfluorinated carboxylic acids (PFCAs), C₄ and C₈ perfluoroalkyl sulfonamides and 6:2, 8:2 and 10:2 unsaturated fluorotelomercarboxylic acids were quantified. ∑PFC concentrations of the river water ranged from 7.6 to 26.4 ng L⁻¹, whereas ∑PFC concentrations of WWTP effluents were approximately 5–10 times higher (30.5–266.3 ng L⁻¹), indicating that WWTPs are potential sources of PFCs in the marine environment. PFC patterns of different WWTP effluents varied depending on the origin of the waste water, whereas the profile of PFC composition in the river water was relatively constant. In both kinds of water samples, perfluorooctanoic acid (PFOA) was the major PFC, whereas perfluorobutane sulfonate (PFBS) was the predominant PFSA.     

Alaska as a site for high duty-cycle solar observations

The day/night cycle at a single observatory prevents definitive observations of many aspects of solar activity, convection, and oscillations with timescales near 1 day. Solutions to this problem include multi-site networks, spacecraft observatories, and observations from high-latitude sites during their summer season. We report here on our experience in using Alaska as a high-latitude site for observations of solar oscillations.     

Huminsäuren natürlicher Gewässer

Zusammenfassung Es wird der Humins?uregehalt eines von mehreren Gr?ben entw?sserten Verlandungshochmoors untersucht und eine Methode zur Bestimmung der Humins?uren im Wasser ausgearbeitet. Das Prinzip der Methode besteht darin, dass die Humins?uren mit einem Spezialharz (Wofatit E) von nichthuminoiden Begleitstoffen abgetrennt werden und der Kaliumpermanganatverbrauch (PV) des Untersuchungswassers auf diese Weise in zwei Bestandteile aufgegliedert wird. Der den Humins?uren zugeh?rige Anteil des Kaliumpermanganatverbrauchs (PV₁) entspricht der Differenz aus dem Gesamt-PV und dem PV nichthuminoider Belgeitstoffe (PV?). Durch Multiplikation von PV₁ mit dem Umrechnungsfaktork _HS wird der Humins?uregehalt des Untersuchungswassers in Milligramm Humins?ure pro 1 erhalten. Ergebnisse der im Juni 1962 in der Mathematisch-Naturwissenschaftlichen Fakult?t der Martin-Luther-Universit?t Halle-Wittenberg vorgelegten gleichnamigen Dissertationsarbeit. 1. Mitteilung: Schweiz. Z. Hydrol.25 (1963), 9.