Tectonic control on sedimentation, erosion and redeposition of Upper Jurassic sandstones, Central Graben, North Sea - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 501

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SW NE

30/13-4

Erosion

Tu rbidite sst

Bryne Fm

Triassic

Shoreface sst

Salt

Rotliegend

15 km

ms TWT

Fig. 22. Uplift of shoreface sandstone on the Joanne Horst to the west of the 30/13-4 well giving the potential for reworking
of previously deposited shoreface sandstones (yellow) and subsequent re-deposition as Freshney Member turbidites
(orange). The location of this section is indicated on Figs 1 and 8.

helped provide a rigid grain framework. During
burial, the development of increasingly high over-
pressure within the reservoir helped to minimize
further compactional effects, as indicated by the
general absence of significant pressure solution
effects at grain contacts. Compaction tends to be
higher in the muddier reservoir facies where sec-
ondary porosity predominates.
The most significant controls on primary poros-
ity within these dominantly fine-grained sand-
stones have been summarised by Lasocki et al .,
1999 as follows: (1) disseminated clay which
occludes porosity (up to 37% clay content) and is
related to shoreface proximal-distal trends and the
role of bioturbating organisms which re-distribute
the clay; (2) carbonate cementation as concre-
tions, which are locally abundant, localised as

overgrowths on winnowed shell beds (e.g. well
22/30c-13) and composed mainly of dolomite and
ankerite (Hendry et al ., 2000a/b; Burns et al .,
2005); (3) mesoquartz cementation and (4) late
pyrobitumen formation that occludes around 2%
of the porosity.
In addition, a variety of factors influence
secondary porosity development including: (1)
secondary porosity creation through dissolution
of sponge spicules and associated microquartz
coating of pore spaces (Walgenwitz & Wonham,
2003); (2) feldspar dissolution (Wilkinson et al .,
1997; 2006) and (3) minor carbonate (shell debris)
dissolution. The role hydrocarbon charging his-
tory played in inhibiting quartz cementation and
the preservation of porosity is debatable (Osborne
& Swarbrick, 1997; Wilkinson et al ., 2006; Taylor