25th International Meeting on Organic Geochemistry IMOG 2011

P-082
Geochemical assessment of oil migration in the Upper Shuaiba
of the Lekhwair High in NW of Block 6, Oman
Mohammed Al Ghammari 1 , Paul Taylor 2 , Gordon Coy 1
1 Petroleum Development of Oman, Muscat, Oman, 2 Shell, Houston, United States of America
(corresponding author:Mohd.MRK.Ghammari@pdo.co.om)
The Upper Shuaiba oil play in the Northwestern
corner of Block 6 (PDO concession) has been central
to PDO‘s exploration strategy for a number of years.
With the expansion of the play away from the
sweetspot of the Lekhwair high an improved
understanding of hydrocarbon migration into the area
was required for improved prospect risking and
ranking.
The majority of oil discoveries in the North western
part of block 6 (PDO concession) occur on or around
the Lekhwair High, where two major oil families have
been identified. They are the Precambrian-Cambrian
Huqf and Jurassic Tuwaiq oil families. The Tuwaiq oil
is believed to have migrated laterally from Tuwaiq
source rocks in the western UAE, whereas the deeper
Huqf charge is thought to come from the Fahud Basin
by migrating up and along N-S trending regional faults
and through extensional fractures on the foreland
bulge. It is believed that after vertical migration of the
Huqf charge it migrated laterally below regional Nahr
Umr seal into Upper Shuaiba reservoirs making them
a very attractive exploration target.
The two oil families form a SE/E-NW/W mixing trend
where the pure Tuwaiq oils are restricted to the
Northwestern and western part of the Lekhwair High,
whereas pure Huqf oils occur to the SE and East of
the high. Gas compositions in the area show mixing
characteristic of a Huqf gas with an isotopically
heavier gas charge.
Well results to the southeast of the Lekhwhair high,
on a proposed Huqf migration path were variable.
Well A successfully tested oil in the uppermost part of
Upper Shuaiba, whereas adjacent wells, which were
also believed to be on the Huqf migration pathway
were dry. In order to explain these dry holes, a charge
shadow model for the Huqf was proposed.
The aim of this study was to help understand the well
results by delineating the Huqf migration pathway in
the area to the southeast of the Lekhwair High, and
proves or disproves a Huqf charge shadow in this
area. The study consists of three parts:
•Oil-oil correlation and understanding of the
distribution of oil types in Lekhwair High
•Fluid inclusions analysis in the dry holes.
•Crusher CSIA analysis of microshows identified
It is found that Well A correlates well with Huqf typical
oil and fits the SE-NW trend of Huqf-Tuwaiq
distribution. The microshows found towards the upper
most part of Upper Shuaiba of Well A and two of the
dry well, Well B and Well C which are located
southwest to Well A correlates well with the gases
found in the area which are a mixture of Huqf and the
isotopically heavier gas charge. This finding is
supported by the presence of oil fluid inclusion and
the carbon isotopes of C1-C8 carbon isotopes (CSIA).
CSIA analysis indicates a gradation from mixed Huqf
and the isotopically heavier charge in the C1-C4
range to predominating Huqf in the C5-C8 range.
This mixing of Huqf and heavier charge elements is
not observed in microshows from the Shuaiba in Well
D, a dryhole in the southernmost part of the area,
which only show the isotopically heavier gas charge.
This suggests that this area did not receive Huqf
charge. This study proposed a wider area for
exploration in the southeastern area of Lekhwair High,
but also proved that the southernmost area (around
well D) of Lekhwair High lacks the typical Huqf
charge.
d13C
-20
-25
-30
-35
-40
-45
Crusher_C1
Crusher_C2
Crusher_C3
Crusher_nC4
Crusher_nC5
C7_NC4
C7_NC5
C7_NC6
C7_NC7
C7_NC8
NC9
NC10
NC11
NC12
NC13
NC14
NC15
NC16
NC17
NC18
NC19
NC20
NC21
NC22
NC23
NC24
NC25
NC26
NC27
NC28
NC29
NC30
Well D
Gradation to Lighter carbon isotopes
(in Well B & Well C microshows)
Well A
Well A (1509-1511)
Well A (1517-1521)
Well A (1545-1560)
Naga-1(1422-1434)
Well B (1446-1458)
Well B (1474-1486)
Well C 1462.7
Well C 1471.6
Well C 1488.23
Well C 1466.72
Well C 1464.65
Well C 1481.06
Well C 1469.02
Well D (1546.6)
Well D (1544.94)
Well D (1544.94)
Well D (1545.64)
Well A
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