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CMS III - A Carboniferous Westphalian channel sand development in the Southern North Sea
journal contribution
posted on 2020-04-30, 14:15 authored by M. M. COOPER, S. D. W. EASTON, J. J. LYNCH, I. M. FOZDARThis core display consists of samples from various parts of the Westphalian
channel sand reservoirs producing as part of the CMS III (Caister-Murdoch
System) development in the Southern North Sea. The project consists of
production from 6 individual accumulations.
The Westphalian CD can be broadly subdivided into three chronostratigraphic
units - from the base, these are the Lower Schooner, the Lower Ketch, and the
Upper Ketch. The Lower Ketch 2 sub-unit contains the best developed reservoir
sands of the Westphalian CD observed in the Boulton B and Hawksley fields.
The sands tend to be blocky in log character, and conglomerate is common,
especially in the more proximal setting around Hawksley.
The Hawksley development well was brought on stream providing a
constrained initial rate of 184 MMSCF and a potentially commercial
accumulation was identified in the overlying Rotliegendes North Leman
Sandstone. The McAdam discovery well 44/17-1 encountered gas in the
Murdoch and overlying Westphalian B sandstones. The Watt discovery well
44/22b-8 encountered a gas sand within the Westphalian B .
Murdoch K is a wedge of Westphalian C/D fluvial sandstones on the
down-thrown side of a major NE-SW trending spoon-shaped Carboniferous
normal fault to the SE of Murdoch, with an initial constrained rate of 204
MMSCF.
Carboniferous diagenesis is strongly influenced by multi-phase weathering
processes. There are repeated episodes of dissolution, quartz cementation
and replacement of feldspars by kaolinite. Early quartz cementation has
inhibited compaction and preserved high primary porosity which is enhanced by
the generation of secondary porosity due to dissolution. Reservoir quality within
the Carboniferous sandstones is principally a result of depositional texture. The
clean, coarse grained, often conglomeratic channel-fill sandstones exhibit the
best permeabilities due to lower cement content and enhanced framework grain
dissolution. The flood-related sandstones (crevasse and sheetflood deposits) show poor
reservoir quality due to their finer grain size and significantly
enhanced ductile content, which has rendered them more susceptible to the
effects of compaction.
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Ketch 2 sub-unitMMSCFNE-SWCMS IIIHawksleySouthern North SeaRotliegendes North Leman SandstoneWestphalian CDWestphalian B sandstonesframework grain dissolutionCarboniferous Westphalian channel sand developmentSEMurdochreservoir qualityWestphalian channel sand reservoirsquartz cementationconglomeratic channel-fill sandstones exhibitGeology