| 1. |
- Ketzer, João Marcelo
(författare)
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Diagenesis and Sequence Stratigraphy : an integrated approach to constrain evolution of reservoir quality in sandstones
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Diagenesis and sequence stratigraphy have been formally treated as two separate disciplines in sedimentary petrology. This thesis demonstrates that synergy between these two subjects can be used to constrain evolution of reservoir quality in sandstones. Such integrated approach is possible because sequence stratigraphy provides useful information on parameters such as pore water chemistry, residence time of sediments under certain geochemistry conditions, and detrital composition, which ultimately control diagenesis of sandstones. Evidence from five case studies and from literature, enabled the development of a conceptual model for the spatial and temporal distribution of diagenetic alterations and related evolution of reservoir quality in sandstones deposited in paralic environments. Diagenetic alterations that have been constrained within the context of sequence stratigraphy include: (i) formation of kaolinite and intragranular porosity, and mechanical infiltration of clay minerals in sandstones lying at variable depths below sequence boundaries, (ii) formation of pseudomatrix and cementation by calcite, dolomite, and siderite in lag deposits at parasequence boundaries, (iii) cementation by kaolinite, pyrite, and calcite in sandstones lying in the vicinity of parasequence boundaries with coal deposits, (iv) formation of glaucony in condensed interval at parasequence boundaries, transgressive and maximum flooding surfaces, (v) formation of berthierine in fluvial-dominated deltaic deposits of the highstand systems tract, (vi) cementation by calcite in bioclastic sandstones of the transgressive systems tract, and (vii) formation of kaolinite in fluvial deposits of the lowstand systems tract. The distribution of such alterations put important constrains for the pattern of burial diagenesis (e.g., formation of chlorite, illite, quartz), related evolution of reservoir quality in sandstones, and distribution of baffles and barriers for fluid flow in the context of sequence stratigraphy.
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| 2. |
- Khalifa, Muftah
(författare)
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Parameters Controlling Distribution of Diagenetic Alterations within Fluvial and Shallow Marine Sandstone Reservoirs : Evidence from the Libyan Basins
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis demonstrates that geological setting, depositional facies, open system flux of hot basinal brines and descending of shallow waters have a strong impact on the distribution of the diagenetic alterations within continental and paralic/shallow marine sandstones which in turn control the quality and heterogeneities of the reservoirs.Geological setting controls the mineralogical and textural maturity of sandstone, whereas depositional facies control the pore water chemistry (marine, brackish or meteoric), sedimentary texture and sand body geometry. Eogenetic alterations in the fluvial deposits are dominated by precipitation of infiltrated clays, kaolinitization of detrital silicates, whereas the shallow marine deposits are dominated by precipitation of early calcite and kaolinite. Conversely mesogenetic alterations are dominated by clay minerals transformation, quartz overgrowths and Ferroan- carbonates, barite and anhydrite. Flux of hot basinal brines is evidenced by precipitation of mesogenetic minerals that lack of internal sources (e.g. barite, anhydrite and ferroan carbonate cements), which is evidenced by: (1) restricted occurrence of these minerals in downthrown blocks. (2) The high fluid inclusion homogenization temperatures (Th) of quartz overgrowths (Th > 110-139°C), and carbonate cements (T > 80-140°C), which also have light δ18OV-PDB(-17.6‰ to -6.7‰). Flux of hot basinal brines is further evidenced by occurrence of saddle Fe-dolomite along stylolites. Fluid inclusion microthermometry further revealed a dramatic shift in pore- water chemistry from NaCl dominated brines during precipitation of quartz overgrowths to NaCl-CaCl2 dominated brines during cementation by Fe-dolomite. Presence of mixed brine (NaCl+CaCl2) systems in the fluid inclusions suggests flux of descending waters, which have circulated in the overlying carbonate-evaporite successions. The restricted occurrence of oil- filled inclusion to quartz overgrowths and methane to Fe-carbonate cements suggest migration of oil during precipitation by quartz and migration of methane during precipitation by Fe- carbonate cements. The extensive mesogenetic cements in the down thrown blocks is attributed to flux of basinal brines along deep seated faults, i.e. open system diagenesis.Integration of fluid inclusion microthermometry, isotopes, Raman spectrometry and thermal tectonic evolution of basins are essential techniques for unraveling the evolution of basinal fluids, cementation conditions and relative timing of hydrocarbons migration.
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| 3. |
- Shahabi-Ghahfarokhi, Sina
(författare)
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Baltic Sea sediments : Source and sink for metal contamination
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Baltic Sea sediments record spatial and temporal information about metalsand metalloids (hereafter referred to as metals), which could help to understandthe past and present contamination sinks in different basins. In addition, giventhe expanding anoxic zones in the Baltic Sea, the response of metals to artificialreoxygenation is poorly understood. This thesis calculated background valuesfor As, Cd, Co, Cu, Pb, U, and Zn and measured their concentration in sedimentsfrom pre-industrial to recent times. Metal concentration peaks during the1970—1980s and clearly decline till present-day, possibly owing to effectivepollution control measures. Furthermore, anoxic Baltic Proper sedimentssubjected to reoxygenation experiments showed that As, Ba, Co, K, Mn, Rb, U,Sr, and Mo are released to bottom waters, suggesting possible aggravation ofmetal pollution if such mitigation option is applied.During previous coastline transgression (5000 years before CE), rich sulfidicsediments (known as potential acid sulfate soils) were deposited and laterexposed to air by natural processes and/or by artificial drainage systems ofcoastal areas of the present-day Baltic Sea. Oxidation of sulfidic phases resultedin the formation of acid sulfate soils, which are a potential source of metalcontamination to drainage areas. This thesis investigated an area in Kristianstad,southern Sweden, in which metal contamination is sourced from acid sulfatesoils. From the acid sulfate soil site, the dispersion showed enrichment of Fe inthe adjacent wetland in the form of akaganeite/schwertmannite, identified usingX-ray absorption spectroscopy. Furthermore, Be, U, rare-earth elements, and Alwere enriched in the drain sediments. Simultaneously, metals such as Mn, Co,Ni, Zn, and Cd were not or only marginally enriched in the drain sediment. Aremediation experiment to remove metals from the drainage water using spentcoffee-grounds and dissolved humic acid was performed. The spent coffeegroundsefficiently removed Al, Ca, Co, Fe, Mn, Ni, and Zn via adsorption, butfail to remove S from the acid sulfate soil drainage. However, the dissolvedhumic acid removed up to 25% of the S from the drainage.
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