Geoscience Reference
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19694
19943
11100
20643
20893
21093
11125
W
E
2/1-4
2/1-3
11095
11115
11120
-40
Shoreface sst
3.0
Erosion
Turbidite sst?
-20
3.5
4.0
+0
4.5
2.5 km
+20
ms TWT
5.0
Fig. 12.
West-East structural cross-section over Gyda Field. The location of an area of interpod crestal erosion has been
added to this figure based on the correlation shown in Fig. 14. The location of this section is indicated on Figs 1 and 8.
Case Study 2: The Gyda Field:
Type C - Interpod setting
The sandstones of the Gyda Field (Fig. 5) are
dominated by shoreface (S4) to lower shoreface
(S3) facies and are of late Kimmeridgian age,
i.e. relatively young compared to other shallow
marine sandstones of the Central North Sea.
Nonetheless, their sedimentary characteristics are
much the same as elsewhere. Studies by Aase
et al
.
(1996) have shown the occurrence of
Rhaxella
sponge spicules in certain layers, as high-lighted
by the localised occurrence of secondary porosity
development resulting from sponge spicule disso-
lution (Fig. 13). The spicule-rich zone belongs
predominantly to the retrogradational part of the
shoreface progradational-retrogradational cycles
and is useful for sequence stratigraphic correlation.
Evidence for uplift, erosion and redeposition of
the Gyda Sandstone comes from the integration
of well correlations with seismic data (Fig. 13).
Erosion of the upper parts of the J66 Sequence
can be identified by extrapolating the spicule
zone identified by Aase
et al
. (1996) using the
characteristic low porosity signature on neutron-
density logs across the field towards the 2/1-4
and 2/1-3 wells where this zone is interpreted to
be progressively eroded (Fig. 14). This erosion
surface on the eastern part of the Gyda Field
(Fig. 12) suggests that the Gyda interpod structure
was tilted and uplifted by salt movement post-J71
TEMFS.
The Gyda Field forms part of the Ula Trend, a
petroleum province located on the eastern margin
of the Central Graben (Spencer
et al
., 1986; Brown
et al
, 1992; Bjørnseth & Gluyas, 1995; Fig. 1). Fields
within this trend include the Ula Field, which has
produced more than 500 MMboe and the Gyda
Field which has produced more than 300 MMboe
(Norwegian Petroleum Directorate figures).
The Gyda Field is located in an area of the basin
where thick deposits of Zechstein salt were devel-
oped. In this area, late Jurassic rifting took place
through the reactivation of older Permian faults.
The Ula-Gyda fault zone is defined by deep
Rotliegend faulting and marks the easternmost
boundary of the Jurassic graben. West of this zone,
Triassic pods were rotated forming terraces that
step down into the graben (Bjørnseth & Gluyas,
1995). These terraces contain the Gyda Field devel-
oped over a thick (~1000 m) Zechstein salt layer as
an interpod structure (Fig. 12). The characteristic
features of this Type C interpod setting are the
development of Jurassic sandstones over a former
salt high which deflated by salt dissolution or salt
withdrawal during the late Jurassic, thereby pro-
viding accommodation space for deposition of the
Middle Jurassic Bryne Formation and the overly-
ing Gyda Sandstone.
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