Geological Society of London
10.11440060317_si_001.pdf (23.22 MB)

CMS III - A Carboniferous Westphalian channel sand development in the Southern North Sea

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journal contribution
posted on 2020-04-30, 14:15 authored by M. M. COOPER, S. D. W. EASTON, J. J. LYNCH, I. M. FOZDAR
This 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.