| 1. |
- El-Ghali, M. A. K., et al.
(författare)
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Distribution of carbonate cements within depositional facies and sequence stratigraphic framework of shoreface and deltaic arenites, Lower Miocene, the Gulf of Suez rift, Egypt
- 2013
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Ingår i: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172 .- 1873-4073. ; 45, s. 267-280
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Tidskriftsartikel (refereegranskat)abstract
- This study aims to unravel the spatial and temporal distribution of diagenetic alterations of the Mheiherrat Member, the Rudeis Formation (lower Miocene) of the Gulf of Suez rift, Egypt within depositional fades and sequence stratigraphy. The Mheiherrat member is represented by shoreface calcarenites and hybrid arenites (transgressive and highstand systems tracts; TST and HST; respectively) and deltaic rudites and coarse-grained calcarenites and hybrid arenites (lowstand systems tracts; LST). Petrographic, stable O- and C-isotopes, mineral chemical and geochemical analyses have revealed that the arenites are pervasively cemented by eogenetic carbonates and, to small extent, by zeolite and pyrite as well as by telogenetic palygorskite. The shoreface TST and HST calcarenites and hybrid arenites were dominantly cemented by microcrystalline grain-rimming and inter- and intragranular pore-filling calcite (delta O-13(V-PDB) = -3.6 parts per thousand to -0.3 parts per thousand and delta C-13(V-PDB) = -2.3 parts per thousand to -0.7 parts per thousand) and rhombic dolomite (delta C-13(V-PDB) = -3.9 parts per thousand to +0.9 parts per thousand and delta C-13(V-PDB) = -2.5 parts per thousand to -0.7 parts per thousand). These cements are interpreted to be formed by marine to brackish waters with delta O-13(V-SMOW) -1.2 parts per thousand to +3.2 parts per thousand, at temperature of 20-55 degrees C. The deltaic LST coarse-grained calcarenites and hybrid arenites were dominantly cemented by coarse-crystalline, inter- and intragranular pore-filling calcite (delta O-13(V-PDB) -4.4 parts per thousand to -2.3% and delta C-13(V-PDB) = -2.8 parts per thousand. to -1.3 parts per thousand.), which are interpreted to have precipitated from pore waters with delta O-13(V-SWOM) +3.5 parts per thousand. to +5.5 parts per thousand, at temperatures of greater than 55 degrees C. Such pervasive cementation by carbonates is attributed to the occurrence of abundant intrabasinal carbonate grains. The carbonate cement texture is suggested to be controlled by changes in pore-water chemistry owing to transgression and regression events. This case study revealed that better understanding of factors controlling the extent and textural habits of carbonate cements can be achieved when it is linked with depositional facies and sequence stratigraphy.
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| 2. |
- Höök, Mikael, 1982-, et al.
(författare)
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Development of oil formation theories and their importance for peak oil
- 2010
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Ingår i: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172 .- 1873-4073. ; 27:9, s. 1995-2004
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Tidskriftsartikel (refereegranskat)abstract
- This paper reviews the historical development of both biogenic and non-biogenic petroleum formation. It also examines the recent claim that the so-called “abiotic” oil formation theory undermines the concept of “peak oil,” i.e. the notion that world oil production is destined to reach a maximum that will be followed by an irreversible decline. We show that peak oil is first and foremost a matter of production flows. Consequently, the mechanism of oil formation does not strongly affect depletion. We would need to revise the theory beyond peak oil only for the extreme — and unlikely — hypothesis of abiotic petroleum formation.
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| 3. |
- Khalifa, Muftah, et al.
(författare)
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Impact of structural setting on diagenesis of fluvial and tidal sandstones: The Bahi Formation, Upper Cretaceous, NW Sirt Basin, North Central Libya
- 2012
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Ingår i: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172 .- 1873-4073. ; 38:1, s. 211-231
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Tidskriftsartikel (refereegranskat)abstract
- This petrographic, mineral chemical, fluid inclusion, and stable isotopic study shows that the distribution of diagenetic modifications and their influence on reservoir quality and heterogeneity in tidal and fluvial sandstones of the Upper Cretaceous Bahi Sandstones in the rift Sirt Basin, NW Libya varies systematically along a series of closely-spaced, dominantly normal faults between the basin margin and more basinward-located areas. Shallow eogenetic modifications resulting from the percolation of meteoric waters, include infiltration of grain coating clays, kaolinitization of detrital silicates, and cementation by dolomite and K-feldspar overgrowths. Mesogenetic alterations (>70 °C, >2 km) include feldspar albitization, illitization of infiltrated clay and kaolinite, conversion of kaolinite into dickite, and cementation by quartz overgrowths (T h 112 °C-134 °C), barite (T h 145 °C-158 °C) and Fe-carbonates. The restriction of barite and Fe-carbonate cements to the basinward-located sandstones suggests formation by hydrothermal fluids along the faults. Extensive feldspar dissolution and formation of moldic pores in sandstones from the basin margin were probably caused by deep percolation of meteoric waters. Results from this study regarding the structural control on the spatial distribution of diagenetic alterations have implications for constraining the flux of pore fluids and, by extension, reservoir quality in analogous epicratonic rift basins.
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| 4. |
- Kordi, Masoumeh, et al.
(författare)
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Linking diagenesis to sequence stratigraphy in fluvial and shallow marine sandstones : Evidence from the Cambrian-Ordovician lower sandstone unit in southwestern Sinai, Egypt
- 2011
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Ingår i: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172 .- 1873-4073. ; 28:8, s. 1554-1571
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Tidskriftsartikel (refereegranskat)abstract
- By integrating diagenesis and sequence stratigraphy, the distribution of diagenetic alterations and their impact on reservoir quality was investigated within a sequence stratigraphic framework using the fluvial and shallow marine sandstones in the Cambrian-Ordovician succession of southwest Sinai. The pero-graphic and geochemical analysis of the studied sandstone revealed that the eogenetic alterations display fairly systematic spatial and temporal distribution patterns within the lowstand system tract and transgressive system tract, as well as along the sequence stratigraphic surfaces (i.e., sequence boundaries, transgressive surfaces and parasequence boundaries). During relative sea-level fall, percolation of meteoric waters through sandstones of the LST and below sequence and parasequence boundaries resulted in extensive dissolution of detrital grains and formation of kaolinite, authigenic K-feldspar and feldspar overgrowths as well as formation of mechanical infiltrated clays around the detrital grains. During relative sea-level rise, invasion of marine water into the sandstones as a consequence of landward migration of the shoreline, as well as low sedimentation rates encountered in the TST, resulted in the formation of glauconite, apatite and pyrite. Development of pseudomatrix, which was formed by mechanical compaction of mud intraclasts, is mostly abundant along transgressive surfaces and parasequence boundaries of the TST, and is related to the abundance of mud intraclasts in the transgressive lag deposits. The types and extent of eogenetic alterations have an important impact on the distribution of the mesogenetic alterations, including the formation of quartz overgrowths and dickite. Distribution of mesogenetic quartz overgrowths in the sandstones was controlled by the distribution of mechanically infiltrated clays and the presence of eogenetic cement. Sandstones that remained poorly cemented during eodiagenesis and that have thin or discontinuous infiltrated clay rims around the detrital grains were cemented during mesodiagenesis by quartz. The absence of extensive eogenetic cements in the sandstones suggested that the partial deterioration of porosity was mainly due to mechanical compaction. Partial transformation of kaolinite to dickite, which indicates neomorphic change to a better-ordered and more stable crystal structure at the elevated temperatures during mesodiagenesis, is partially a function of distribution of kaolinite during eodiagenesis. The conceptual model developed in this study shows the diagenetic evolutionary pathways in the reservoir sandstones within a sequence stratigraphic context, which in turn provides some insights into the controls on reservoir heterogeneity.
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| 5. |
- Mansurbeg, Howri, et al.
(författare)
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Meteoric-water diagenesis in late Cretaceous canyon-fill turbidite reservoirs from the Espirito Santo Basin, eastern Brazil
- 2012
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Ingår i: Marine and Petroleum Geology. - : Elsevier BV. - 0264-8172 .- 1873-4073. ; 37:1, s. 7-26
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Tidskriftsartikel (refereegranskat)abstract
- Parameters controlling the diagenetic evolution of passive margin, marine turbidites, which are important targets of hydrocarbon exploration, are poorly constrained in the literature. This study aims to unravel the conditions of diagenesis and its impact on the reservoir quality evolution from late Cretaceous canyon-filling turbiditic sandstones of the onshore portion of Espirito Santo Basin, eastern Brazil. Kaolinization (delta O-18 = +13.3 parts per thousand to +15.2 parts per thousand; delta D = 96.6 parts per thousand to -79.6 parts per thousand) and dissolution of framework silicate grains is attributed to meteoric water incursion during eodiagenesis in response to a considerable fall in relative sea-level. Eogenetic alterations also include cementation by siderite (average delta O-18 = -72 parts per thousand; delta C-13 = +9.3 parts per thousand) and pyrite. Progressive sediment burial (present depths = 1530-2027 m) resulted in the formation of poikilotopic calcite, ferroan dolomite-ankerite (average delta O-18 = -7.9 parts per thousand; delta C-13 = +2.9 parts per thousand), minor amounts of quartz overgrowths and in partial dickitization of kaolinite. Isotopic values of calcite and dolomite-ankerite follow two trends of co-variance of delta C-13 with decreasing delta O-18 and increasing temperature. From a composition closer to marine (approximate to 0 parts per thousand), one trend goes towards positive delta C-13 values (up to +22.4 parts per thousand for calcite; +18.6 parts per thousand for dolomite-ankerite), indicating increasing input of carbonate from methanogenic fermentation. The other trend develops towards negative delta C-13 values (down to -17.2 parts per thousand for calcite; 15 parts per thousand for dolomite-ankerite), suggesting increasing contribution from thermal decarboxylation with increasing temperature and depth. Despite the presence of various cement types, mechanical compaction was more important than cementation in reducing depositional porosity in the onshore Urucutuca sandstones.
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| 6. |
- Heidenreich, Axel, et al.
(författare)
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Early Detection of Prostate Cancer: European Association of Urology Recommendation
- 2013
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Ingår i: European Urology. - : Elsevier BV. - 1873-7560 .- 0302-2838. ; 64:3, s. 347-354
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Tidskriftsartikel (refereegranskat)abstract
- Background: The recommendations and the updated EAU guidelines consider early detection of PCa with the purpose of reducing PCa-related mortality and the development of advanced or metastatic disease. Objective: This paper presents the recommendations of the European Association of Urology (EAU) for early detection of prostate cancer (PCa) in men without evidence of PCa-related symptoms. Evidence acquisition: The working panel conducted a systematic literature review and meta-analysis of prospective and retrospective clinical studies on baseline prostate-specific antigen (PSA) and early detection of PCa and on PCa screening published between 1990 and 2013 using Cochrane Reviews, Embase, and Medline search strategies. Evidence synthesis: The level of evidence and grade of recommendation were analysed according to the principles of evidence-based medicine. The current strategy of the EAU recommends that (1) early detection of PCa reduces PCa-related mortality; (2) early detection of PCa reduces the risk of being diagnosed and developing advanced and metastatic PCa; (3) a baseline serum PSA level should be obtained at 40-45 yr of age; (4) intervals for early detection of PCa should be adapted to the baseline PSA serum concentration; (5) early detection should be offered to men with a life expectancy >= 10 yr; and (6) in the future, multivariable clinical risk-prediction tools need to be integrated into the decision-making process. Conclusions: A baseline serum PSA should be offered to all men 40-45 yr of age to initiate a risk-adapted follow-up approach with the purpose of reducing PCa mortality and the incidence of advanced and metastatic PCa. In the future, the development and application of multivariable risk-prediction tools will be necessary to prevent over diagnosis and over treatment. (C) 2013 European Association of Urology. Published by Elsevier B. V. All rights reserved.
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