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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
AAPG Bulletin, V.
1Manuscript received January 27, 1997; revised manuscript
received July 2, 1998; final acceptance September 22, 1998.
2T. H. Huxley School of Environment, Earth Science and Engineering,
Imperial College of Science Technology and Medicine, Prince Consort Road,
London SW7 2BP, United Kingdom; e-mail: [email protected]
Block
16/26 are thanked for allowing us to publish seismic data from
the Alba three-dimensional data set. H. D. Johnson, S. Laubach, B. Trudgill,
and P. Yilmaz, and especially Editor N. Hurley, are thanked for constructive
reviews that led to substantial improvements in versions of this paper.
ABSTRACT
The main reservoir in the Alba field is an elongate (12 km long, 1-2
km wide, up to 90 m thick), fine-grained, massive sandstone body that may
have been deposited in a deep-water channel or slope gully. Although depositional
processes likely have been responsible for the dominantly linear sandstone
distribution, the current reservoir geometry is largely controlled by the
location of polygonal faults in the surrounding hemipelagic mudstones.
Sandstones interpreted as injected along faulted margins of the Alba field
indicate that faulting facilitated remobilization and sand injection during
early burial, further modifying the reservoir shape. Unusual, isolated
1-km-wide subcircular mounds to the west of the main field also are attributed
to sand withdrawal and remobilization during early burial.
On a mapped marker horizon in the mudrocks 80-120 m above the reservoir
there is a marked decrease in polygonal fault density compared to areas
away from the reservoir. On a horizon in mudrocks within 5-50 m of the
base of the reservoir there is an increase in horizon disruption due to
small faults directly below the sand body. Changes in polygonal fault density
and pattern thus may indicate the presence of sandstones and may be a useful
exploration tool for explorationists searching for subtle Eocene deep-water
sand bodies that typically are poorly imaged on seismic data in the North
Sea.
Polygonal faults attributed to three-dimensional (3-D) volumetric contraction
of muddy sediments during early burial are widespread within the Eocene-lower
Miocene succession of the United Kingdom central North Sea. The analysis
of a 3-D seismic survey encompassing the Eocene Alba field in the central
North Sea has allowed us to investigate (1) the influence of polygonal
faults in surrounding mudrocks on the geometry of the Alba deep-water sandstone
reservoir and (2) how the presence of the reservoir sandstone influences
the polygonal fault pattern above and below the reservoir.
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