1. Licence Information
Licence Number
P1726
Licence Round
25th (2008)
Licence Type
Traditional
Blocks
43/17a & 43/18a
Licensees
RWE Dea UK SNS Limited (50%, operator)
Dana Petroleum (E&P) Limited (50%)
Work Programme
Drill one well to 3,600 m or to the Top Kinderscoutian,
whichever is shallower, on the Severn prospect.
Drilling of the 43/18a-2Y exploration well fulfilled the licence
commitment.
2. Synopsis
Licence P1726 is located in the northern part of the UK Southern North Sea, approximately
100 km east of Teeside on the east coast of the United Kingdom (Figure 1). The Licence
was awarded to RWE Dea UK (now Dea UK) and Dana Petroleum as part of the UKCS 25th
Licensing Round, with a commitment to drill one well to a depth of 3,600 m or to Top Kinderscoutian, whichever was shallower, on the Severn Prospect. The licence was awarded with
effect from 1st May 2010.
Exploration well 43/18a-2Y was drilled on the Severn prospect in 2013 but was plugged and
abandoned with minor gas shows in the Carboniferous. Following this, at the end of the Initial Term, a partial mandatory relinquishment was made for the licence to enter the Second
Term. DECC agreed to allow the licence partners to retain slightly more than 50% of the
licence while the remaining prospectivity was assessed.
A full technical evaluation was carried out and the licence partners concluded that further
drilling was not warranted. The licence was therefore surrendered, effective 30th April 2015.
3. Regional Setting
P1726 lies in the Silverpit Basin at the far north-west of the Southern Permian Basin. The
Trent field is located approximately 9 km to the south-east and the Browney and Pegasus
discoveries lie approximately 4 km and 12 km to the north, respectively (Figure 1). This part
of the Silverpit Basin has undergone a complex tectonic history including a series of extensional and compressional events as well as Zechstein halokenisis. The dominant pre-salt
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structural trend is NW-SE where pre-Permian extensional faults have been reactivated
through Alpine inversion.
The main reservoir intervals in this part of the Southern North Sea are the Carboniferous
Namurian to Westphalian fluvio-deltaic sands of the Millstone Grit and Caister Formations
(Figure 2) which sub-crop the Base Permian Unconformity. Carboniferous coals and carbonaceous mudstones are mature for gas and represent the primary source rocks in the area.
Regionally, top seal is provided by Permian evaporates, shales of the Rotliegendes Silverpit
Formation as well as intra-Carboniferous shales.
4. Exploration History
Prior to award of P1726, two wells had been drilled on the licence. Well 43/17-1 was drilled
to target the Bunter Sandstone by Amoco in 1969. The well was plugged and abandoned as
a dry hole. In 1989 British Gas drilled exploration well 43/17-2 and tested gas at low rates
from three horizons in the Namurian.
5. Severn Prospect
At the time of application, Severn was identified as the main prospect in the licence area.
The Severn prospect is located on a northwest-southeast trending horst which straddles
blocks 43/17a and 43/18a. Severn was first identified by RWE and Dana in 2003. At the time
however, the licence group only held block 43/18 and decided to relinquish the acreage and
re-apply for blocks 43/17a and 43/18a during the 25th Licence Round in 2008, with a firm
well commitment.
Severn was interpreted to comprise two Namurian to Westphalian sand units: the Trent and
Crawshaw Sandstones (Figure 2). Both units are in production at the nearby Trent field but
had not been tested within P1726. The sands were mapped in a combination trap with dipclosure to the south-east and stratigraphic sub-crop at Base Permian to the north-west within
the Severn Horst (Figure 3). The trap relied on side seal against the Rotliegendes Silverpit
Formation and base seal at Top Kinderscoutian against the gracile marine band and overlying shales.
The Severn prospect was drilled in 2013 by exploration well 43/18a-2 and two sidetracks.
Both the parent well and the first sidetrack, 43/18a-2Z, were plugged and abandoned in the
Triassic for mechanical reasons. The second sidetrack, 43/18a-2Y, reached the Carboniferous. The prognosed Trent and Crawshaw sands were absent and an older Marsdenian to
Kinderscoutian section was penetrated (Figure 2). 43/18a-2Y was plugged and abandoned
with minor gas shows in the Carboniferous.
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6. Remaining Prospectivity
a. Kinderscoutian
43/18a-2Y encountered gas shows in a Kinderscoutian sand approximately 250 feet below Base Permian. There is updip potential where the Kinderscoutian sub-crops the
Base Permian to the northwest of 43/18a-2Y. A small closure has been mapped in block
43/17a (Figure 4). Using a lowest closing contour of 3,150 m, in-place resources are calculated at 24-32-41 bscf (P90-P50-P10) and further exploration is not warranted.
b. Arnsbergian
In the centre of the Severn Horst, up-dip of 43/18a-2Y, a structural closure can be
mapped on which two wells, 43/16-2 and 43/17-2, have tested gas from two separate,
low reservoir quality Arnsbergian sands (Figures 5 and 6). Both wells were drilled on the
flanks of this structure and the central, core area of this closure has not been tested.
Given the tight sands encountered in both existing wells, reservoir quality is considered a
key risk.
43/16-2 - using a lowest closing contour of 3,100 m for the sand tested by this well,
in-place resources are estimated to be 56-87-131 bscf (P90-P50-P10) (Figure 5). In
addition to the key reservoir risk, a large proportion of the structure lies outside of
P1726.
43/17-2 – post-drill mapping of the structure intersected using 43/17-2 suggests that
the aerial closure is small (7.5 km2) (Figure 6). Given the key reservoir risk and low
flow rates achieved when tested, further investigation is not warranted.
c. SW closure within 43/17a
In the far south-west of 43/17a, on trend with the Kilmar field, lies a small (1.4 km 2) closure at Base Permian and Top Arnsbergian. This structure is deemed too small to warrant further investigation (Figure 6).
7. Conclusions
The Severn prospect was tested by exploration well 43/18a-2Y. The target reservoir units
were absent and an older Carboniferous reservoir was encountered. The well was plugged
and abandoned with gas shows. A number of other Carboniferous leads have been identi3
fied. However, these are deemed too small or too high risk to warrant further investigation
and the licensees surrendered the licence.
8. Clearance
RWE Dea UK confirms that the OGA has clearance to publish this report and that all third
party ownership rights (on any contained data and/or interpretations) have been considered
and appropriately cleared for publication purposes.
The seismic line shown in Figure 3 is taken from PGS’s MegaSurvey dataset. PGS ownership of the data is hereby acknowledged.
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9. Figures
Figure 1. Location of licence P1726 and exploration wells 43/18a-2, 2Z and 2Y. The area of P1726
within block 43/18 which was relinquished at the end of the initial licence term is outlined with a black
dashed line. The two 3D seismic datasets used for the pre and post drill interpretation are also shown.
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Figure 2. Namurian – Westphalian stratigraphic column. The target reservoir section at Severn and
the reservoir section penetrated are highlighted.
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Figure 3. Geo-seismic section showing the revised post-drill interpretation at the Severn structure.
Arbitrary seismic line courtesy of PGS.
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Figure 4. Top Kinderscoutian depth map and schematic cross section illustrating possible accumulation up-dip of 43/18a-2Y.
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Figure 5. Top Arnsbergian depth map. 43/16-2 was drilled on the flank on the structure and the core
area (blue shaded area) remains untested.
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Figure 6. Intra-Arnsbergian depth map illustrating the two separate closures penetrated by 43/16-2
and 43/17-2.
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