The Upper Devonian Buchan Formation in the Central North Sea is a typical terrestrial deposit and predominantly comprises fine to medium-grained sandstones with occasional conglomerates and mudstones. The Buchan Forma...The Upper Devonian Buchan Formation in the Central North Sea is a typical terrestrial deposit and predominantly comprises fine to medium-grained sandstones with occasional conglomerates and mudstones. The Buchan Formation has been previously described as being made up mostly of braided fluvial sandstones;however, this study confirms the presence and significance of aeolian sandstones within this fluvial-dominated sequence. Facies architecture is investigated through analogue outcrop study, well log curves and numerical facies modelling, and the results show contrasting differences between fluvial and aeolian facies. The fluvial facies is composed of multiple superimposed and sand-dominated fining-upward cycles in the vertical direction, and laterally an individual cycle has a large width/thickness ratio but is smaller than the field scale. However, the high channel deposition proportion (CDP, average value = 72%) in fluvial-dominated intervals means that it is likely all the sand bodies are interconnected. Aeolian facies comprise superimposed dune and interdune depositions and can be laterally correlated over considerable distances (over 1 km). Although the aeolian sandstones are volumetrically minor (approx. 30%) within the whole Buchan Formation, they have very high porosity and permeability (14.1% - 28%, 27 - 5290 mD) and therefore are excellent potential reservoirs. The fluvial sandstones are significantly cemented by quartz overgrowth and dolomite and by comparison with the aeolian sandstones are poor reservoirs. Aeolian sandstones can be differentiated from fluvial sandstones using several features: pin-stripe lamentation, good sorting, high visible porosity, friable nature and lack of muddy or conglomeratic contents;these characteristics allow aeolian sandstones can be tentatively recognized by low gamma ray values, high sonic transit time and low density in uncored wells. The thin, laterally correlatable and permeable aeolian sandstones within the Buchan Formation are effective reservoirs and could form important exploration targets when the Devonian is targeted elsewhere in the North Sea.展开更多
The Upper Devonian Buchan Formation reservoirs in the UK Central North Sea are litharenite/sublitharenite and were deposited in fluvial-aeolian settings. The grain-coating clays in the aeolian sandstones have effectiv...The Upper Devonian Buchan Formation reservoirs in the UK Central North Sea are litharenite/sublitharenite and were deposited in fluvial-aeolian settings. The grain-coating clays in the aeolian sandstones have effectively inhibited quartz overgrowth. Hence, the reduction of reservoir quality is mainly due to mechanical compaction and early dolomite pre- cipitation in both fluvial and aeolian sandstones; quartz overgrowth and kaolinite illitization in fluvial sandstones; and limited smectite illitization in aeolian sandstones. The carbon/oxygen stable isotopes of dolomite cements suggest a predominantly marine carbon source and precipitation temperatures between 25 and 58 ~C indicating a shallow burial depth during dolomite precipitation. The temperatures and the dolomite distribution indicate that the cements originated from the overlying Upper Permian Zechstein carbonates. Extensive quartz overgrowths formed at 80 and 120 ~C in the late and deep diagenetic burial history. The most probable silica source was from feldspar kaolinitization and pressure dissolution of quartz grains. Through detailed petrography and geochemical analyses, the burial-paragenesis-thermal history of the Buchan Formation has been constructed. Similar diagenetic processes are likely to have occurred in the Buchan Formation in other parts of the Central and Northern North Sea. This study may allow new petroleum plays to be considered in areas previously thought to have poor hydrocarbon potential.展开更多
In 1996,my interests as a passionate gardener and photo-based artist,that both dated from the 1970s,collided when I made the connection that plants are actually a form of photography;(photography from the Greek-meanin...In 1996,my interests as a passionate gardener and photo-based artist,that both dated from the 1970s,collided when I made the connection that plants are actually a form of photography;(photography from the Greek-meaning light drawing).Both photography and plants use the magical,mysterious ingredient that is LIGHT and the essential force that drives life on the planet.In fact,the largest photosensitive emulsion we know of is the planet earth.I draw inspiration and endless fascination from the awareness that the earth rotates in space and orbits the sun at a precise distance for the sun’s radiation to affect the elegant process of photosynthesis through the myriad of plants that have evolved and grow on the planet.The earth is a three dimensional living photograph.The atmosphere and biosphere are also key factors that mediate the harshness of radiation bombarding the earth and nurture life on the planet that we know and depend upon.The process is an amazing thing and something we should revere and protect.Imagine the earth as a basket ball,wrapped in the thinnest paper you could find.The thickness of this delicate paper is equivalent to the atmosphere,and the depth of the paper’s texture is thicker than the tallest trees,even thicker than the tallest high rise buildings!Image sequences from NASSA shows how vegetation grows,dies back,changes colour with the seasons,how the“photographic image”that is our planet alters.Increasingly human intervention plays a larger role in transforming the image of the globe we inhabit.Imagine foliated land as a photo-sensor(like in a digital camera).展开更多
文摘The Upper Devonian Buchan Formation in the Central North Sea is a typical terrestrial deposit and predominantly comprises fine to medium-grained sandstones with occasional conglomerates and mudstones. The Buchan Formation has been previously described as being made up mostly of braided fluvial sandstones;however, this study confirms the presence and significance of aeolian sandstones within this fluvial-dominated sequence. Facies architecture is investigated through analogue outcrop study, well log curves and numerical facies modelling, and the results show contrasting differences between fluvial and aeolian facies. The fluvial facies is composed of multiple superimposed and sand-dominated fining-upward cycles in the vertical direction, and laterally an individual cycle has a large width/thickness ratio but is smaller than the field scale. However, the high channel deposition proportion (CDP, average value = 72%) in fluvial-dominated intervals means that it is likely all the sand bodies are interconnected. Aeolian facies comprise superimposed dune and interdune depositions and can be laterally correlated over considerable distances (over 1 km). Although the aeolian sandstones are volumetrically minor (approx. 30%) within the whole Buchan Formation, they have very high porosity and permeability (14.1% - 28%, 27 - 5290 mD) and therefore are excellent potential reservoirs. The fluvial sandstones are significantly cemented by quartz overgrowth and dolomite and by comparison with the aeolian sandstones are poor reservoirs. Aeolian sandstones can be differentiated from fluvial sandstones using several features: pin-stripe lamentation, good sorting, high visible porosity, friable nature and lack of muddy or conglomeratic contents;these characteristics allow aeolian sandstones can be tentatively recognized by low gamma ray values, high sonic transit time and low density in uncored wells. The thin, laterally correlatable and permeable aeolian sandstones within the Buchan Formation are effective reservoirs and could form important exploration targets when the Devonian is targeted elsewhere in the North Sea.
基金EnQuest PLC for supporting this research through access to internal data and financial support
文摘The Upper Devonian Buchan Formation reservoirs in the UK Central North Sea are litharenite/sublitharenite and were deposited in fluvial-aeolian settings. The grain-coating clays in the aeolian sandstones have effectively inhibited quartz overgrowth. Hence, the reduction of reservoir quality is mainly due to mechanical compaction and early dolomite pre- cipitation in both fluvial and aeolian sandstones; quartz overgrowth and kaolinite illitization in fluvial sandstones; and limited smectite illitization in aeolian sandstones. The carbon/oxygen stable isotopes of dolomite cements suggest a predominantly marine carbon source and precipitation temperatures between 25 and 58 ~C indicating a shallow burial depth during dolomite precipitation. The temperatures and the dolomite distribution indicate that the cements originated from the overlying Upper Permian Zechstein carbonates. Extensive quartz overgrowths formed at 80 and 120 ~C in the late and deep diagenetic burial history. The most probable silica source was from feldspar kaolinitization and pressure dissolution of quartz grains. Through detailed petrography and geochemical analyses, the burial-paragenesis-thermal history of the Buchan Formation has been constructed. Similar diagenetic processes are likely to have occurred in the Buchan Formation in other parts of the Central and Northern North Sea. This study may allow new petroleum plays to be considered in areas previously thought to have poor hydrocarbon potential.
文摘In 1996,my interests as a passionate gardener and photo-based artist,that both dated from the 1970s,collided when I made the connection that plants are actually a form of photography;(photography from the Greek-meaning light drawing).Both photography and plants use the magical,mysterious ingredient that is LIGHT and the essential force that drives life on the planet.In fact,the largest photosensitive emulsion we know of is the planet earth.I draw inspiration and endless fascination from the awareness that the earth rotates in space and orbits the sun at a precise distance for the sun’s radiation to affect the elegant process of photosynthesis through the myriad of plants that have evolved and grow on the planet.The earth is a three dimensional living photograph.The atmosphere and biosphere are also key factors that mediate the harshness of radiation bombarding the earth and nurture life on the planet that we know and depend upon.The process is an amazing thing and something we should revere and protect.Imagine the earth as a basket ball,wrapped in the thinnest paper you could find.The thickness of this delicate paper is equivalent to the atmosphere,and the depth of the paper’s texture is thicker than the tallest trees,even thicker than the tallest high rise buildings!Image sequences from NASSA shows how vegetation grows,dies back,changes colour with the seasons,how the“photographic image”that is our planet alters.Increasingly human intervention plays a larger role in transforming the image of the globe we inhabit.Imagine foliated land as a photo-sensor(like in a digital camera).
