The microstructural analysis of muds and mudrocks requires very high-resolution measurement. Recent advances in electron microscopy have contributed significantly to the improved characterisation of mudrock microstruc...The microstructural analysis of muds and mudrocks requires very high-resolution measurement. Recent advances in electron microscopy have contributed significantly to the improved characterisation of mudrock microstructures and their consequent petrophysical properties. However, imaging through electron microscopy is limited to small areas of coverage such that upscaling of these properties is a great challenge. In this paper, we develop a new methodology for multiple large-area imaging using scanning electron microscopy through automated acquisition and stitching from polished thin-sections and ion-milled samples. The process is fast, efficient and minimises user-input and bias. It can provide reliable, quantifiable data on sediment grain size, grain orientation, pore size and porosity. Limitations include the time involved for individual runs and manual segmentation, the large amount of computer memory required, and instrument resolution at the nano-scale. This method is applied to selected samples of Quaternary muddy sediments from the Iberian margin at IODP Site 1385. The section comprises finegrained(very fine clayey silts), mixed-composition, biogenic-terrigenous hemipelagites, with a pronounced but non-regular colour cyclicity. There is a multi-tiered and diverse trace fossil assemblage of the deep-water Zoophycos ichnofacies. The sediment microstructures show small-scale heterogeneity in all properties, and an overall random fabric with secondary preferred grain-alignment. These results on the fabric differ, in part, from previous studies of hemipelagic muds. Further work is underway on their comparison with other deep-water sediment facies.展开更多
The central aim of this paper is to address the role of unconformities in affecting reservoir quality.Do they facilitate diagenesis that leads to either enhanced or reduced porosity through dissolution or cementation?...The central aim of this paper is to address the role of unconformities in affecting reservoir quality.Do they facilitate diagenesis that leads to either enhanced or reduced porosity through dissolution or cementation?Or,do they have little effect?We have investigated the Late Triassic Skagerrak sandstone reservoir underlying the Mid-Cimmerian Unconformity in the Kittiwake Field,central North Sea.There is strong evidence for the development of secondary porosity through the dissolution of unstable silicate minerals,primarily feldspars.This includes the presence of oversized pores,partial dissolution of framework grains,and complete dissolution of grains leaving remnant grain margins and partially filled cores.This dissolution as a late-stage event is demonstrated by the complete lack of compaction effects on the secondary pores and diagenetic products despite present burial depths in excess of 3000 m.These observations,coupled with an absence of systematic trends linked to the unconformity surface in respects of reservoir porosity,feldspar amount and dissolution,and kaolinization,lead to the conclusion that there has been no effect of the Mid-Cimmerian Unconformity on reservoir quality in the Kittiwake Field.There is no evidence for leaching or cementation linked to meteoric water influx either shortly after deposition or following the uplift and exposure,which led to development of the Mid-Cimmerian Unconformity.Instead,we propose that the late-stage dissolution of feldspar and generation of secondary porosity are most likely related to the influx of organic acids and carbon dioxide generated either from thermogenic maturation of the source rock or from biodegradation of oil within the reservoir near the oil-water contact(OWC)transition zone.展开更多
基金the sponsorship received from Petroleum Technology Development Fund, Nigeria
文摘The microstructural analysis of muds and mudrocks requires very high-resolution measurement. Recent advances in electron microscopy have contributed significantly to the improved characterisation of mudrock microstructures and their consequent petrophysical properties. However, imaging through electron microscopy is limited to small areas of coverage such that upscaling of these properties is a great challenge. In this paper, we develop a new methodology for multiple large-area imaging using scanning electron microscopy through automated acquisition and stitching from polished thin-sections and ion-milled samples. The process is fast, efficient and minimises user-input and bias. It can provide reliable, quantifiable data on sediment grain size, grain orientation, pore size and porosity. Limitations include the time involved for individual runs and manual segmentation, the large amount of computer memory required, and instrument resolution at the nano-scale. This method is applied to selected samples of Quaternary muddy sediments from the Iberian margin at IODP Site 1385. The section comprises finegrained(very fine clayey silts), mixed-composition, biogenic-terrigenous hemipelagites, with a pronounced but non-regular colour cyclicity. There is a multi-tiered and diverse trace fossil assemblage of the deep-water Zoophycos ichnofacies. The sediment microstructures show small-scale heterogeneity in all properties, and an overall random fabric with secondary preferred grain-alignment. These results on the fabric differ, in part, from previous studies of hemipelagic muds. Further work is underway on their comparison with other deep-water sediment facies.
文摘The central aim of this paper is to address the role of unconformities in affecting reservoir quality.Do they facilitate diagenesis that leads to either enhanced or reduced porosity through dissolution or cementation?Or,do they have little effect?We have investigated the Late Triassic Skagerrak sandstone reservoir underlying the Mid-Cimmerian Unconformity in the Kittiwake Field,central North Sea.There is strong evidence for the development of secondary porosity through the dissolution of unstable silicate minerals,primarily feldspars.This includes the presence of oversized pores,partial dissolution of framework grains,and complete dissolution of grains leaving remnant grain margins and partially filled cores.This dissolution as a late-stage event is demonstrated by the complete lack of compaction effects on the secondary pores and diagenetic products despite present burial depths in excess of 3000 m.These observations,coupled with an absence of systematic trends linked to the unconformity surface in respects of reservoir porosity,feldspar amount and dissolution,and kaolinization,lead to the conclusion that there has been no effect of the Mid-Cimmerian Unconformity on reservoir quality in the Kittiwake Field.There is no evidence for leaching or cementation linked to meteoric water influx either shortly after deposition or following the uplift and exposure,which led to development of the Mid-Cimmerian Unconformity.Instead,we propose that the late-stage dissolution of feldspar and generation of secondary porosity are most likely related to the influx of organic acids and carbon dioxide generated either from thermogenic maturation of the source rock or from biodegradation of oil within the reservoir near the oil-water contact(OWC)transition zone.
