License P1359

License P1359
23rd Licence Round
Promote Two Year Report
Blocks 49/2c, 3b, 4d
Wintershall Noordzee BV (100%)
December 2007
Synopsis
The current Promote Two Years Report has been written in support of the
relinquishment of the licence following a detailed investigation of its Carboniferous
exploration potential. Because no viable economic prospect could be defined during
the first phase of the Initial Term the operator has chosen not to commit to drill a well
during the second phase of the Initial Term and to relinquish the licence.
After detailed investigation two of the three prospects, Ketex South and Alpha, which
were recognised at the time of the licence application, were discarded as viable
prospects. The volumes of the third prospect, Marjan, are too low to form an
economic viable drilling candidate.
Exploration Activities
Wintershall was awarded Licence P1359 in the 23rd Licensing Round. After the
application was granted in January 2006, the following exploration activities have
been undertaken:
For seismic interpretation the PGS SNS MegaMerge 3D survey was used and key
horizons have been interpreted, such as the base Zechstein, the base Permian
Unconformity (BPU) and the top Early Westphalian B. A regional velocity study was
carried out using data from ca. 150 wells, which resulted in an improved velocity
model:
Interval
Function
Constants
V0 Grid values
North Sea Group
V=V0+k*z
k = 0.37
V0 = 1646 – 1900
Chalk
V=V0+k*z
k = 1.30
V0 = 1549 – 2475
Triassic
V=V0+k*z
k = 0.39
V0 = 2586 – 3176
Zechstein
Wedge Model
d = Vst + c
c = 25
Vs = 4400
Rotliegend
Constant velocity
Vint = 4300m/sec
Carboniferous
Constant velocity
Vint = 4300m/sec
Table 1
Velocity model
A regional Carboniferous reservoir study was carried out, which resulted in a detailed
zonation (Fig. 2). Well data were used to create zonal isopachs. These were
subsequently used to create a detailed subcrop map at the BPU level (Fig 3). This
facilitated the identification of sections with good reservoir quality within BPU
closure and possible stratigraphic trapping configurations.
Promote Two Year Report, Blocks 49/2c, 3b, 4d
Prospectivity Analysis
The BPU horizon is complicated to interpret in the northern Quad 49 blocks in areas
with poor seismic quality. During the present study the horizon has been interpreted in
detail and was converted to depth with the improved velocity model. This affected the
size and outlines of the prospects as presented in the application report (Fig. 4).
In general, the source rock presence, maturity and charge are no major concern in the
license area, since every valid structural test in the Silverpit Basin showed to be gasbearing. The main risks lie in trap effectiveness and reservoir presence. The presence
of the Lower Leman sandstone, as demonstrated by well 49/8-2, causes the
stratigraphic traps to fail as is the case for the Ketex and Alpha prospects.
Additionally, 49/8-2 showed tight gas in the Westphalian C. Although decreased in
size, the remaining prospectivity of the licence lies in the Marjan prospect.
P1359
Figure 1
Location map.
Promote Two Year Report, Blocks 49/2c, 3b, 4d
Figure 2
Carboniferous stratigraphy.
Promote Two Year Report, Blocks 49/2c, 3b, 4d
2°24’00”
2°36’00”
54°00’00”
2°12’00”
Ketex South
53°50’00”
Marjan
Alpha
Subcrop map at Base Permian Unconformity (BPU) (for legend see Fig. 2).
54°00’00”
Figure 3
Ketex South
53°50’00”
Marjan
Alpha
2°12’00”
2°24’00”
Figure 4
2°36’00”
Base Permian Unconformity depth map
Promote Two Year Report, Blocks 49/2c, 3b, 4d
Alpha (Fig. 5)
The Alpha prospect relies on a Westphalian C pinch-out trap with Silverpit top seal
and Westphalian B bottom seal to the east and south. The triangular structure spills at
3650 m along the northwestern edge. The Carboniferous zonation study showed that
the pinch-out of the EWC sands could be drawn slightly further south than originally
mapped. However, the trap will fail with the presence of the Lower Leman sandstone.
Given the close position to well 49/8-2 and 49/9-6z this is very likely. The
stratigraphic trapping mechanism for this prospect is therefore unlikely and thus
reducing the chance of success for the prospect.
BPU depth map
Figure 5
Prospect details Alpha
Marjan (Fig. 6)
A base Silverpit trap with a closing contour of 3860 m forms the Marjan prospect.
The detailed interpretation of the BPU horizon and an adjusted velocity model
resulted in a slightly different prospect outline and a lower vertical closure when
compared to the application report, with 88% of the gross rock volume between 3860
and 3800 meters. Previous problems to close the structure in the southeast corner,
related to the interpretation of a narrow ridge, are still a concern in the new model.
For well 49/2-4z a GWC of 3860 m is given in the end-of-well report, but reevaluation of the data cannot support this interpretation. Most pressure points of 49/24z plot along a water line, with a possible gas point at 3775 m. The gas line through
this point intersects the water line at 3860 m. However, the pressure point on the gas
line shows tight gas and the pressure test was abandoned. The log data of well 49/2-3
Promote Two Year Report, Blocks 49/2c, 3b, 4d
also indicate an isolated gas pocket in a sandstone layer at 3855 m. However, the
pressure points of 49/2-3 all plot along a waterline, and the water saturation values
show that the well is water bearing up to 3820 m. A sample taken from 3835 m
contained only formation water and drilling fluids. The issue was raised previously
that the eastern and western parts of the Marjan prospect may or may not be
connected along a narrow zone separated by a NW-SE trending fault. The model
shows only limited offset along the
BPU depth map
Figure 6
Prospect details Marjan
fault and the throw is insufficient for fault sealing to be likely. This strengthens the
case for an overall WUT level of 3820 m. The two wells drilled in the structure both
show poor quality Westphalian C reservoir. Both wells mainly intersect the lower
shaley part of the LWC. The new model confirms that along the edges of the prospect
the LWC thickens, which brings the more sandy upper part of the LWC into closure,
albeit no significant part will be above 3820 m.
Reserves Summary
A volumetric assessment of the Marjan prospect is presented below. No volumes were
calculated for the Alpha and Ketx South prospects, since these are no longer
considered to be valid prospects.
Marjan
P10
P50
P90
GIIP (Bcm)
Reserves (Bcm)
POS = 25%
2.6
1.6
1.5
0.9
0.9
0.5
Promote Two Year Report, Blocks 49/2c, 3b, 4d
Promote Two Year Report, Blocks 49/2c, 3b, 4d