Changes

Deep-water marine reservoirs have been increasingly found since the 1970s, particularly as a result of an increase in offshore drilling activity. Many of these are Tertiary in age, although large reservoirs of Jurassic and Cretaceous age have also been found, particularly in the North Sea.

Deep-water marine reservoirs have been increasingly found since the 1970s, particularly as a result of an increase in offshore drilling activity. Many of these are Tertiary in age, although large reservoirs of Jurassic and Cretaceous age have also been found, particularly in the North Sea.

The term deep water has been used in two different ways. It applies in a geological context to deep-water systems that have been transported by gravity flow processes in a marine setting.<ref name=WeimerandSlatt>Weimer, P., and R. M. Slatt, 2004, Petroleum systems of deep-water settings: SEG/EAGE (Society of Exploration Geophysicists/European Association of Geoscientists and Engineers) Distinguished Instructor Series 7, 465 p.</ref> Deep water is also defined as present-day sea depths in excess of 500 m (1640 ft) deep.

The term deep water has been used in two different ways. It applies in a geological context to deep-water systems that have been transported by [[gravity]] flow processes in a marine setting.<ref name=WeimerandSlatt>Weimer, P., and R. M. Slatt, 2004, Petroleum systems of deep-water settings: SEG/EAGE (Society of Exploration Geophysicists/European Association of Geoscientists and Engineers) Distinguished Instructor Series 7, 465 p.</ref> Deep water is also defined as present-day sea depths in excess of 500 m (1640 ft) deep.

Since 1984 there has been an intensive effort in exploring for reservoirs located in present-day deep water with numerous prolific discoveries.<ref>Pettingill, H. S., and P. Weimer, 2001, Global deep-water exploration: Past, present and future frontiers, in R. H. Fillon, N. C. Rosen, P. Weimer, A. Lowrie, H. W. Pettingill, R. L. Phair, H. H. Roberts, and B. Van Hoorn, eds., Petroleum systems of deep-water basins: Global and Gulf of Mexico experience: GCS-SEPM Foundation, p. 1–22.</ref> Deep-water exploration in the Gulf of Mexico, Brazil, and west Africa is targeting and finding a large number of hydrocarbon pools in deep-water marine-sand systems. Only about 20% of these reservoirs had been developed to 2004.<ref name=WeimerandSlatt />

Since 1984 there has been an intensive effort in exploring for reservoirs located in present-day deep water with numerous prolific discoveries.<ref>Pettingill, H. S., and P. Weimer, 2001, Global deep-water exploration: Past, present and future frontiers, in R. H. Fillon, N. C. Rosen, P. Weimer, A. Lowrie, H. W. Pettingill, R. L. Phair, H. H. Roberts, and B. Van Hoorn, eds., Petroleum systems of deep-water basins: Global and Gulf of Mexico experience: GCS-SEPM Foundation, p. 1–22.</ref> Deep-water exploration in the [[Gulf of Mexico]], Brazil, and west Africa is targeting and finding a large number of hydrocarbon pools in deep-water marine-sand systems. Only about 20% of these reservoirs had been developed to 2004.<ref name=WeimerandSlatt />

==Deep-water marine reservoirs can be prolific reservoirs==

==Deep-water marine reservoirs can be prolific reservoirs==

| Widespread amalgamation of channel-fill sandstones in channelized systems || Creates laterally and vertically connected high-volume reservoirs ||  

| Widespread amalgamation of channel-fill sandstones in channelized systems || Creates laterally and vertically connected high-volume reservoirs ||  

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| Shale drapes or late-stage channel-fill shales common in channel-fill sandstones || || Reduces vertical and lateral connectivity between individual channel-fill sandstones

| Shale drapes or late-stage channel-fill shales common in channel-fill sandstones || || Reduces vertical and [[lateral]] connectivity between individual channel-fill sandstones

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| Preferential water ingress along channel axes || || Banked oil may form along channel margins

| Preferential water ingress along channel axes || || Banked oil may form along channel margins

| Levee sediments in channel-levee complexes are thin bedded but can show reservoir connectivity across a large area || Levee sediments can be a production target in their own right

| Levee sediments in channel-levee complexes are thin bedded but can show reservoir connectivity across a large area || Levee sediments can be a production target in their own right

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| Laterally extensive mudstones commonly form permeability barriers to vertical flow || Encourages edge-water drive and can suppress early water production || Creates hydraulic units; water overrun is common

| Laterally extensive [[mudstones]] commonly form permeability barriers to vertical flow || Encourages edge-water drive and can suppress early water production || Creates hydraulic units; water overrun is common

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| Fill and spill geometries || || Potential to create bypassed oil volumes in cellar oil accumulations

| Fill and spill geometries || || Potential to create bypassed oil volumes in cellar oil accumulations

==Production from sheet complexes==

==Production from sheet complexes==

[[File:M91FG112.JPG|thumb|300px|{{figure number|4}}Formation tester data taken in wells that have been drilled postproduction provide invaluable data on how the reservoir splits up into hydraulic units showing different pressures. This example is from the Magnus field in the UK North Sea (from Morris et al).<ref>Morris, P. H., S. N. J. Payne, and D. P. J. Richards, 1999, Micropalaeontological biostratigraphy of the Magnus Sandstone Member (Kimmeridgian to early Volgian), Magnus field, UK North Sea, in R. W. Jones and M. D. Simmons, eds., Biostratigraphy in production and development geology: Geological Society (London) Special Publication 152, p. 55–73.</ref> Reprinted with permission from, and &copy by, the Geological Society. GR = Gamma Ray; RFTtrade = Repeat Formation Tester; UKCF = Upper Kimmeridge Clay Formation.]]

[[File:M91FG112.JPG|thumb|300px|{{figure number|4}}Formation tester data taken in wells that have been drilled postproduction provide invaluable data on how the reservoir splits up into hydraulic units showing different pressures. This example is from the Magnus field in the UK North Sea (from Morris et al).<ref>Morris, P. H., S. N. J. Payne, and D. P. J. Richards, 1999, Micropalaeontological biostratigraphy of the Magnus Sandstone Member (Kimmeridgian to early Volgian), Magnus field, UK North Sea, in R. W. Jones and M. D. Simmons, eds., Biostratigraphy in production and development geology: Geological Society (London) Special Publication 152, p. 55–73.</ref> Reprinted with permission from, and &copy; by, the Geological Society. GR = Gamma Ray; RFTtrade = Repeat Formation Tester; UKCF = Upper Kimmeridge Clay Formation.]]

Sheet sandstones form excellent reservoirs. Their characteristics include simple tabular geometries, good lateral continuity, and few erosional features.<ref name=WeimerandSlatt /> A large volume of deep-water sheet sandstones can be produced by a single production well. Width-to-thickness ratios are large, more than 500:1 for sheet complexes compared to a range of 10:1 to 300:1 for channels.<ref name=WeimerandSlatt /> Vertical connectivity can be variable depending on the amount of interbedded shales or the degree of sand-on-sand amalgamation.

Sheet sandstones form excellent reservoirs. Their characteristics include simple tabular geometries, good lateral continuity, and few erosional features.<ref name=WeimerandSlatt /> A large volume of deep-water sheet sandstones can be produced by a single production well. Width-to-thickness ratios are large, more than 500:1 for sheet complexes compared to a range of 10:1 to 300:1 for channels.<ref name=WeimerandSlatt /> Vertical connectivity can be variable depending on the amount of interbedded shales or the degree of sand-on-sand amalgamation.

==References==

==References==

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