Analysis of 3 D seismic data and well log data from the Rovuma Basin in East Africa reveals the presence of a late Eocene channel-lobe complex on its slope.The first two channels,denoted as channel-1 and channel-2,are...Analysis of 3 D seismic data and well log data from the Rovuma Basin in East Africa reveals the presence of a late Eocene channel-lobe complex on its slope.The first two channels,denoted as channel-1 and channel-2,are initiated within a topographic low on the slope but come to a premature end when they are blocked by a topographic high in the northwest region of the basin.New channels migrate southeastward from channel-1 to channel-6 due to the region’s sufficient sediment supply and stripping caused by bottom currents.The primary factors controlling the development of the channel complex include its initial paleo-topographic of seafloor,the property of gravity flows,the direction of the bottom current,and the stacking and expansion of its levees.The transition zone from channel to lobe can also be clearly identified from seismic sections by its pond-shaped structure.At a certain point,thest systems record a transiton from erosive features to sedimentary features,and record a transition from a confined environment to an open environment.Channels and lobes can be differentiated by their morphologies:thick slump-debris flows are partly developed under channel sand sheets,whereas these slump-debris flows are not very well developed in lobes.Well log responses also record different characteristics between channels and lobes.The interpreted shale volume throughout the main channel records a box-shaped curve,thereby implying that confined channel complexes record high energy currents and abundant sand supply,whereas the interpreted shale volume throughout the lobe records an upward-fining shape curve,thereby indicating the presence of a reduced-energy current in a relatively open environment.Within the Rovuma Basin of East Africa,the average width of the Rovuma shelf is less than 10 km,the width of the slope is only approximately 40 km,and the slope gradient is 2°–4°.Due to this steep slope gradient,the sand-rich top sheet within the channel also likely contributes to the straight feature of the channel system.It is currently unclear whether the bottom current has any effect on its sinuosity.展开更多
The mechanisms causing quality variations and key control factors of submarine-fan reservoirs in the gas field X of the Rovuma Basin,East Africa are analyzed based on core and well-log data in this paper.Depositional ...The mechanisms causing quality variations and key control factors of submarine-fan reservoirs in the gas field X of the Rovuma Basin,East Africa are analyzed based on core and well-log data in this paper.Depositional fabric,lithofacies difference and characteristics of genetic units are the fundamental reasons of reservoir quality variations.In the case of weak cementation,porosity and permeability of submarine-fan reservoirs are controlled by grain sorting and clay content,respectively.Reservoir quality variations for 5 main lithofacies are related to variable depositional fabrics and calcite cementation.Among them,massive medium-coarse sandstones with weak cementation have the highest porosity and permeability,and coarser or finer sandstones have poorer reservoir quality.The existence of bottom current can develop laminated sandstones,improving the pore structure and physical properties greatly.Lithofacies vary among different types,locations and stages of genetic units,and they control the distribution patterns of submarine-fan reservoir quality:the physical properties of channel shaft or lobe main body are better than those of the channel or lobe edge.The sandstone sorting and physical properties are gradually improved from near-source to far-source.When multi-stage sand bodies are superimposed,the sand-mud ratio in the later stage is higher than that in the earlier stage,making the physical properties get better in the later stage.展开更多
基金The China-ASEAN Maritime Cooperation Fund Project under contract No.12120100500017001the National Natural Science Foundation of China under contract Nos 42076219,92055211 and 42006067
文摘Analysis of 3 D seismic data and well log data from the Rovuma Basin in East Africa reveals the presence of a late Eocene channel-lobe complex on its slope.The first two channels,denoted as channel-1 and channel-2,are initiated within a topographic low on the slope but come to a premature end when they are blocked by a topographic high in the northwest region of the basin.New channels migrate southeastward from channel-1 to channel-6 due to the region’s sufficient sediment supply and stripping caused by bottom currents.The primary factors controlling the development of the channel complex include its initial paleo-topographic of seafloor,the property of gravity flows,the direction of the bottom current,and the stacking and expansion of its levees.The transition zone from channel to lobe can also be clearly identified from seismic sections by its pond-shaped structure.At a certain point,thest systems record a transiton from erosive features to sedimentary features,and record a transition from a confined environment to an open environment.Channels and lobes can be differentiated by their morphologies:thick slump-debris flows are partly developed under channel sand sheets,whereas these slump-debris flows are not very well developed in lobes.Well log responses also record different characteristics between channels and lobes.The interpreted shale volume throughout the main channel records a box-shaped curve,thereby implying that confined channel complexes record high energy currents and abundant sand supply,whereas the interpreted shale volume throughout the lobe records an upward-fining shape curve,thereby indicating the presence of a reduced-energy current in a relatively open environment.Within the Rovuma Basin of East Africa,the average width of the Rovuma shelf is less than 10 km,the width of the slope is only approximately 40 km,and the slope gradient is 2°–4°.Due to this steep slope gradient,the sand-rich top sheet within the channel also likely contributes to the straight feature of the channel system.It is currently unclear whether the bottom current has any effect on its sinuosity.
文摘The mechanisms causing quality variations and key control factors of submarine-fan reservoirs in the gas field X of the Rovuma Basin,East Africa are analyzed based on core and well-log data in this paper.Depositional fabric,lithofacies difference and characteristics of genetic units are the fundamental reasons of reservoir quality variations.In the case of weak cementation,porosity and permeability of submarine-fan reservoirs are controlled by grain sorting and clay content,respectively.Reservoir quality variations for 5 main lithofacies are related to variable depositional fabrics and calcite cementation.Among them,massive medium-coarse sandstones with weak cementation have the highest porosity and permeability,and coarser or finer sandstones have poorer reservoir quality.The existence of bottom current can develop laminated sandstones,improving the pore structure and physical properties greatly.Lithofacies vary among different types,locations and stages of genetic units,and they control the distribution patterns of submarine-fan reservoir quality:the physical properties of channel shaft or lobe main body are better than those of the channel or lobe edge.The sandstone sorting and physical properties are gradually improved from near-source to far-source.When multi-stage sand bodies are superimposed,the sand-mud ratio in the later stage is higher than that in the earlier stage,making the physical properties get better in the later stage.
