At the end of the Palaeozoic Era, most species on Earth disappeared completely and the global sed... more At the end of the Palaeozoic Era, most species on Earth disappeared completely and the global sedimentary environment and biology changed dramatically. The Permian–Triassic boundary (PTB) was studied in three sections of the middle Upper Yangtze Platform, SW China: Xingwen well and Zhijin and Shangsi sections. These sections are characterized by carbonate-platform, toe-of-slope and basin facies, respectively. Detailed analysis of 100 closely spaced thin-sections revealed a total of 24 microfacies and 11 microfacies associations based on the dominant carbonate grain size and the skeletal material (type and proportion). Six bioassemblages are documented for the first time, spanning c. 1 Ma across the boundary succession, including normal, resurrected and miniaturized Permian biota, and cyanobacteria-dominated, survival post-crisis and neonatal Triassic biota. The Xingwen well indicated sedimentary evolution from a rimmed carbonate platform to a homoclinal carbonate ramp, as well as a ...
Geological Society, London, Special Publications, 2016
Petroleum exploration and production in the region of the Niger Delta to date has mainly focused ... more Petroleum exploration and production in the region of the Niger Delta to date has mainly focused on the onshore, deltaic and offshore deep-water Miocene successions. Although Miocene turbidites have been the principal deep-water target, deeper-lying Oligocene sandstones are now being considered for exploration. This study targets an area beneath the Niger Basin slope at a present-day water depth of 800–1500 m. Within this study area, the Miocene to Recent sands above a burial depth of 3600 m show very good reservoir quality with porosities as high as 35% and permeabilities in the Darcy range. The aim of this study is to predict the reservoir quality and properties of the Oligocene sandstones below 3800 m using basin modelling to predict conditions where quartz cementation will take place and quartz cementation models to predict the amount of cementation and hence the potential porosity loss. Modelling results show that the Oligocene sandstones have been exposed to conditions favoura...
In simulations of CO2 storage in saline aquifers, it is often assumed that there is a sharp bound... more In simulations of CO2 storage in saline aquifers, it is often assumed that there is a sharp boundary between the aquifer and the caprock. However, this is not always the case. In many cases there is a gradual transition between sand-rich facies in the aquifer and mud-rich facies in the caprock. Moreover, some simulations assume a smooth interface, whereas typically the surface is irregular, due to sedimentological and stratigraphic effects or structural deformation. We have conducted a range of numerical simulations on a variety of heterogeneous aquifer/caprock models to investigate the impact of the different types of aquifer/caprock interfaces. Firstly, the nature of the interface can influence estimates of storage capacity. A transition zone between the aquifer and the caprock leads to uncertainty in the effective aquifer volume. Secondly, the aquifer/caprock interface can affect the security of CO2 storage. A transition zone can increase the security by providing partial baffles to hinder CO2 migration towards the caprock. Rugosity at the aquifer/caprock interface, may assist or hinder structural trapping. Small domes may provide extra storage volume. On the other hand, topographical highs may provide pathways for rapid migration of CO2 from the injector.
At the end of the Palaeozoic Era, most species on Earth disappeared completely and the global sed... more At the end of the Palaeozoic Era, most species on Earth disappeared completely and the global sedimentary environment and biology changed dramatically. The Permian–Triassic boundary (PTB) was studied in three sections of the middle Upper Yangtze Platform, SW China: Xingwen well and Zhijin and Shangsi sections. These sections are characterized by carbonate-platform, toe-of-slope and basin facies, respectively. Detailed analysis of 100 closely spaced thin-sections revealed a total of 24 microfacies and 11 microfacies associations based on the dominant carbonate grain size and the skeletal material (type and proportion). Six bioassemblages are documented for the first time, spanning c. 1 Ma across the boundary succession, including normal, resurrected and miniaturized Permian biota, and cyanobacteria-dominated, survival post-crisis and neonatal Triassic biota. The Xingwen well indicated sedimentary evolution from a rimmed carbonate platform to a homoclinal carbonate ramp, as well as a ...
Geological Society, London, Special Publications, 2016
Petroleum exploration and production in the region of the Niger Delta to date has mainly focused ... more Petroleum exploration and production in the region of the Niger Delta to date has mainly focused on the onshore, deltaic and offshore deep-water Miocene successions. Although Miocene turbidites have been the principal deep-water target, deeper-lying Oligocene sandstones are now being considered for exploration. This study targets an area beneath the Niger Basin slope at a present-day water depth of 800–1500 m. Within this study area, the Miocene to Recent sands above a burial depth of 3600 m show very good reservoir quality with porosities as high as 35% and permeabilities in the Darcy range. The aim of this study is to predict the reservoir quality and properties of the Oligocene sandstones below 3800 m using basin modelling to predict conditions where quartz cementation will take place and quartz cementation models to predict the amount of cementation and hence the potential porosity loss. Modelling results show that the Oligocene sandstones have been exposed to conditions favoura...
In simulations of CO2 storage in saline aquifers, it is often assumed that there is a sharp bound... more In simulations of CO2 storage in saline aquifers, it is often assumed that there is a sharp boundary between the aquifer and the caprock. However, this is not always the case. In many cases there is a gradual transition between sand-rich facies in the aquifer and mud-rich facies in the caprock. Moreover, some simulations assume a smooth interface, whereas typically the surface is irregular, due to sedimentological and stratigraphic effects or structural deformation. We have conducted a range of numerical simulations on a variety of heterogeneous aquifer/caprock models to investigate the impact of the different types of aquifer/caprock interfaces. Firstly, the nature of the interface can influence estimates of storage capacity. A transition zone between the aquifer and the caprock leads to uncertainty in the effective aquifer volume. Secondly, the aquifer/caprock interface can affect the security of CO2 storage. A transition zone can increase the security by providing partial baffles to hinder CO2 migration towards the caprock. Rugosity at the aquifer/caprock interface, may assist or hinder structural trapping. Small domes may provide extra storage volume. On the other hand, topographical highs may provide pathways for rapid migration of CO2 from the injector.
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Papers by Dorrik Stow